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DDDD Basic in 180 Days Book IV - Editor: Ramon F. aeroramon.com Contents

1 Day 1 1 1.1 History of photographic lens ...... 1 1.1.1 Early photographic ...... 1 1.1.2 Meniscus or 'landscape' lens ...... 3 1.1.3 Petzval Portrait lens ...... 3 1.1.4 Overcoming optical aberrations ...... 4 1.1.5 stops ...... 4 1.1.6 ...... 7 1.1.7 Anastigmat lens ...... 8 1.1.8 Cooke Triplet ...... 9 1.1.9 ...... 9 1.1.10 Ernostar and Sonnar ...... 9 1.1.11 Asymmetric double Gauss ...... 11 1.1.12 Anti-reflection coating ...... 12 1.1.13 Retrofocus wide-angle lens ...... 14 1.1.14 ...... 16 1.1.15 Macro lens ...... 16 1.1.16 Supplementary lens ...... 16 1.1.17 ...... 19 1.1.18 Rise of Japanese optical industry ...... 21 1.1.19 Catadioptric “mirror” lens ...... 21 1.1.20 Movable element ...... 22 1.1.21 ...... 22 1.1.22 Improving standards of quality ...... 23 1.1.23 Inexpensive asphere ...... 23 1.1.24 lens ...... 23 1.1.25 Image-stabilized lens ...... 24 1.1.26 Diffractive optic lens ...... 24 1.1.27 Lenses in the digital era ...... 24 1.1.28 References ...... 25 1.1.29 Further reading ...... 34

2 Day 2 48

i ii CONTENTS

2.1 ...... 48 2.1.1 Theory of operation ...... 49 2.1.2 Construction ...... 49 2.1.3 Aperture and ...... 50 2.1.4 Number of elements ...... 51 2.1.5 Lens mounts ...... 51 2.1.6 Types of lens ...... 52 2.1.7 History and technical development of photographic camera lenses ...... 53 2.1.8 Lens ...... 53 2.1.9 See also ...... 54 2.1.10 Notes ...... 54 2.1.11 References ...... 54 2.1.12 External links ...... 55

3 Day 3 59 3.1 ...... 59 3.1.1 Design ...... 59 3.1.2 Types of lenses ...... 62 3.1.3 History ...... 65 3.1.4 See also ...... 67 3.1.5 References ...... 67

4 Day 4 69 4.1 Aperture ...... 69 4.1.1 Application ...... 69 4.1.2 In photography ...... 70 4.1.3 Equivalent aperture range ...... 73 4.1.4 In scanning or sampling ...... 73 4.1.5 See also ...... 74 4.1.6 References ...... 74 4.2 () ...... 80 4.2.1 Iris diaphragms versus other types ...... 81 4.2.2 History ...... 82 4.2.3 See also ...... 84 4.2.4 References ...... 84

5 Day 5 85 5.1 ...... 85 5.1.1 Perspective effects of short or long focal-length lenses ...... 85 5.1.2 'Normal' lenses vary for different formats ...... 85 5.1.3 Typical normal focal lengths for different formats ...... 85 5.1.4 References ...... 87 CONTENTS iii

5.2 Prime lens ...... 87 5.2.1 As alternative to zoom lens ...... 88 5.2.2 Traditional meaning as primary lens ...... 88 5.2.3 Popular focal lengths ...... 89 5.2.4 Specialist lenses ...... 90 5.2.5 References ...... 90 5.2.6 External links ...... 90 5.3 Zoom lens ...... 91 5.3.1 Characteristics ...... 91 5.3.2 History ...... 92 5.3.3 Design ...... 93 5.3.4 Varifocal lens ...... 97 5.3.5 See also ...... 98 5.3.6 References ...... 98 5.3.7 External links ...... 98

6 Day 6 99 6.1 Telephoto lens ...... 99 6.1.1 Construction ...... 99 6.1.2 History ...... 101 6.1.3 See also ...... 103 6.1.4 References ...... 103 6.1.5 External links ...... 104 6.2 ...... 104 6.2.1 Function ...... 105 6.2.2 See also ...... 107 6.2.3 References ...... 107

7 Day 7 108 7.1 Long-focus lens ...... 108 7.1.1 Effects of long-focus lenses ...... 108 7.1.2 as long-focus lenses ...... 110 7.1.3 See also ...... 110 7.1.4 References ...... 110 7.2 Close-up filter ...... 111 7.2.1 See also ...... 114 7.2.2 External links ...... 114 7.3 ...... 114 7.3.1 History ...... 115 7.3.2 Equipment and techniques ...... 115 7.3.3 35 mm equivalent magnification ...... 120 7.3.4 Technical considerations ...... 121 iv CONTENTS

7.3.5 See also ...... 124 7.3.6 References ...... 124 7.3.7 External links ...... 125

8 Day 8 126 8.1 Wide-angle lens ...... 126 8.1.1 ...... 127 8.1.2 Characteristics ...... 127 8.1.3 Wide-angle lenses for ...... 127 8.1.4 considerations ...... 127 8.1.5 Construction ...... 128 8.1.6 See also ...... 128 8.1.7 References ...... 128 8.1.8 Notes ...... 129 8.1.9 External links ...... 129 8.2 Fisheye lens ...... 134 8.2.1 Uses in photography ...... 135 8.2.2 Sample images ...... 139 8.2.3 Other applications ...... 140 8.2.4 Mapping function ...... 141 8.2.5 See also ...... 143 8.2.6 Notes ...... 143 8.2.7 References ...... 143 8.2.8 External links ...... 144

9 Day 9 145 9.1 Optical coating ...... 145 9.1.1 Types of coating ...... 145 9.1.2 Current market and forecast ...... 150 9.1.3 Sources ...... 150 9.1.4 References ...... 150 9.1.5 See also ...... 150 9.1.6 External links ...... 150 9.2 Optical filter ...... 150 9.2.1 Absorptive ...... 152 9.2.2 Dichroic filter ...... 152 9.2.3 Monochromatic ...... 152 9.2.4 Infrared ...... 152 9.2.5 ...... 153 9.2.6 Neutral density ...... 153 9.2.7 Longpass ...... 153 9.2.8 Bandpass ...... 153 CONTENTS v

9.2.9 Shortpass ...... 153 9.2.10 Guided-mode resonance filters ...... 153 9.2.11 Metal mesh filters ...... 154 9.2.12 Polarizer ...... 154 9.2.13 Arc welding ...... 154 9.2.14 See also ...... 154 9.2.15 References ...... 154 9.3 Photographic filter ...... 155 9.3.1 Uses of filters in photography ...... 156 9.3.2 Materials and construction ...... 161 9.3.3 Filter sizes and mountings ...... 161 9.3.4 See also ...... 163 9.3.5 References ...... 163 9.3.6 External links ...... 163

10 Day 10 164 10.1 Optical transfer function ...... 164 10.1.1 Definition and related concepts ...... 164 10.1.2 Examples ...... 165 10.1.3 The three-dimensional optical transfer function ...... 169 10.1.4 Calculation ...... 170 10.1.5 Measurement ...... 172 10.1.6 Factors affecting MTF in typical camera systems ...... 174 10.1.7 Digital inversion of the optical transfer function ...... 175 10.1.8 Limitations ...... 175 10.1.9 See also ...... 175 10.1.10 References ...... 175 10.1.11 External links ...... 176 10.2 Optical resolution ...... 176 10.2.1 Lateral resolution ...... 176 10.2.2 Lens resolution ...... 177 10.2.3 Sensor resolution (spatial) ...... 178 10.2.4 Sensor resolution (temporal) ...... 179 10.2.5 Analog bandwidth effect on resolution ...... 179 10.2.6 System resolution ...... 180 10.2.7 Ocular resolution ...... 180 10.2.8 Atmospheric resolution ...... 180 10.2.9 Measuring optical resolution ...... 181 10.2.10 See also ...... 184 10.2.11 References ...... 184 10.2.12 External links ...... 185 10.3 1951 USAF resolution test chart ...... 185 vi CONTENTS

10.3.1 Pattern format ...... 185 10.3.2 Images ...... 185 10.3.3 See also ...... 187 10.3.4 References ...... 187 10.3.5 External links ...... 187

11 Text and image sources, contributors, and licenses 188 11.1 Text ...... 188 11.2 Images ...... 191 11.3 Content license ...... 198 Chapter 1

Day 1

1.1 History of photographic lens design

Cutaway drawing of an early photographic lens design, the Petzval Portrait

The invention of the camera in the early 19th century led to an array of lens designs intended for photography. The problems of photographic lens design, creating a lens for a task that would cover a large, flat image plane, were well known even before the invention of photography[1] due to the development of lenses to work with the focal plane of the .

1.1.1 Early photographic camera lenses

The early photographic experiments of Thomas Wedgwood, Nicéphore Niépce, Henry Fox Talbot, and Louis Da- guerre all used simple single-element convex lenses.[2] These lenses were found lacking. Simple lenses could not focus an image over a large flat film plane (Field curvature) and suffered from other optical aberrations. Their severe longitudinal meant the light the photographers were seeing (generally yellow light) and the light

1 2 CHAPTER 1. DAY 1

Biconvex (or double convex) lens with aperture stop in front of it to which the early photographic mediums were sensitive not converge to the same point, making it difficult to focus.

Reversed

Charles Chevalier's Paris optical firm produced lenses for both Niépce and Daguerre for their experiments in pho- tography. In 1829, Chevalier created an achromatic lens (a two-element lens made from and flint glass) to cut down on chromatic aberration for Daguerre’s experiments. Chevalier reversed the lens (originally designed as a ) to produce a much flatter image plane and modified the achromat to bring the blue end of the spectrum to a sharper focus. Reversing the lens caused severe so a narrow aperture stop was 1.1. HISTORY OF PHOTOGRAPHIC LENS DESIGN 3 necessary in front of the lens. On 22 June 1839, Daguerre contracted Alphonse Giroux (France) to manufacture his apparatus. The Giroux Le Daguerreotype camera used an almost 16-inch (40 cm) focal length reversed achromatic lens with a f/16 stop in front of it made by Chevalier to take 6½×8½ inch (about 16.5×21.5 cm) images.[3][4]

1.1.2 Meniscus or 'landscape' lens

In 1804 William Hyde Wollaston invented a positive meniscus lens for eyeglasses. In 1812 Wollaston adapted it as a lens for the camera obscura[5] by mounting it with the concave side facing outward with an aperture stop in front of it, making the lens reasonably sharp over a wide field. Niépce began using Wollaston Meniscus in 1828.[6][7] Daguerre used this lens in his experiments, but since it was a single-element lens that lacked any chromatic aberration control it was impossible to focus accurately with the blue-sensitive media in the daguerreotype process.[8] By the end of 1839, Chevalier had created an achromatic version of the meniscus that combined field flattening and chromatic aberration control.[9][10] The lens had the reverse concave flint glass side facing the subject and an f/16 aperture stop at its radius of curvature, making it reasonably sharp over a wide field of about 50°.[11] Reversing the lens did increase chromatic aberration, but this fault could be lessened by adjusting the achromat to bring at the blue end of the spectrum into focus to match the blue-sensitive nature of the photographic emulsion.[12] This design was copied by other lens makers. Because of its large flat field over a wide angle of view and its “slow” f/16 aperture (requiring twenty to thirty minutes for outdoor daguerreotype exposures), this lens came to be known as the “French landscape lens” or simply the “landscape lens”.

1.1.3 Petzval Portrait lens

Petzval Portrait lens

Because the Achromat Landscape lens was quite slow, the French Society for the Encouragement of Industry offered an international prize in 1840 for a faster one. Joseph Petzval (of modern Slovakia) was a mathematics professor with no optical physics experience, but, with the aid of several human computers of the Austro-Hungarian army, he took up the challenge of producing a lens fast enough for a daguerreotype portrait. 4 CHAPTER 1. DAY 1

He came up with the Petzval Portrait (modern Austria) in 1840, a four-element lens consisting of a front-cemented achromat and a rear air-spaced achromat that, at f/3.6, was the first wide-aperture portrait lens. It was appropriate for one- to two-minute shaded outdoors daguerreotype exposures. With the faster collodion (wet plate) process developed in the 1850s, a camera equipped with this lens could take one- to two-minute indoor portraits. Because of national chauvinism, the Petzval did not win the prize, despite being far superior to all other entries.[13] A 150mm Petzval lens was fitted to a conical metal Voigtländer camera taking circular in 1841. The Voigtländer-Petzval was the first camera and lens specifically designed to take , instead of being simply a modified artist’s camera obscura.[14][15][16] The Petzval Portrait was the dominant portrait lens for nearly a century. It had what would now be considered severe field curvature and astigmatism, but It was centrally sharp (about a 20° field of view, or 10° for critical applications), and it quickly drifted out of focus to a soft outer field, producing a pleasant halo effect around the subject. The Petzval Portrait remains popular as a projection lens where the narrow angles involved mean the field curvature is not significant.[17] The Portrait was illegally copied by every lens maker, and Petzval had a nasty falling out with Peter Voigtländer over unpaid royalties and died an embittered old man.[18] Although the Portrait was the first mathematically computed lens formula,[19] trial and error would continue to dominate photographic lens design for another half century, despite well-established physical mathematics dating from 1856 (by Ludwig von Seidel [modern Germany], working for Hugo Adolph Steinheil [modern Germany]), to the detriment of lens improvement.[20]

1.1.4 Overcoming optical aberrations

The Achromat Landscape was also afflicted with rectilinear – straight lines were imaged as curved. This distortion was a pressing problem as was an important photography subject early on.[21] In addition, photographs of exotic places (especially in stereoscope form[22]) were a popular means to see the world from the comfort of one’s home – the picture postcard is a mid-19th century invention.[23] The distortion got progressively worse as the field of view increased, which meant the Achromat Landscape could not be used as a wide-angle lens. The first successful wide-angle lens was the Harrison & Schnitzer Globe (USA) of 1862,[24] although with a f/16 maximum aperture (f/30 was more realistic). The lens had a 92° maximum field of view, although 80° was more realistic. Charles Harrison and Joseph Schnitzer’s Globe had a symmetric four-element formula; the name refers to the consideration that if the two outer surfaces were continued and then joined, they would form a sphere.[25][26] Symmetry was discovered in the 1850s to automatically correct the distortion, , and transverse chromatic distortions.[27][28][29][30] There are also decentration aberrations arising from manufacturing errors. A real lens will not produce images of expected quality if it is not constructed to or cannot stay in specification.[31] There are additional optical phenomena that can degrade image quality but are not considered aberrations. For example, the oblique cos4θ light falloff, sometimes called natural ,[32][33] and lateral magnification and perspective distortions seen in wide angle lenses are really geometric effects of projecting three-dimensional objects down into two-dimensional images, not physical defects.[34] The Globe’s symmetric formula directly influenced the design of the Dallmeyer Rapid-Rectilinear (UK) and Stein- heil Aplanat (modern Germany). By coincidence, John Dallmeyer's Rapid-Rectilinear and Adolph Steinheil’s Aplanat had virtually identical symmetric four-element formulae, arrived at almost simultaneously in 1866, all of which cor- rected most optical aberrations, except for spherical and field curvature, to f/8. The breakthrough was to use glass of maximum difference but equal dispersion in each achromat. The Rapid-Rectilinear and Aplanat lenses were scalable over many focal lengths and fields of view for all contemporaneous media, and they were the standard moderate-aperture, general-purpose lenses for more than half a century.[35][36] The Landscape, the Portrait, the Globe, and the Rapid-Rectilinear/Aplanat constituted the nineteenth-century pho- tographer’s entire lens arsenal.[37]

1.1.5 Aperture stops

Main article: Aperture

It was known in the 1500s that an aperture stop would improve lens image quality.[38] It would be discovered that this was because a center stop that blocks peripheral light limits the transverse aberrations (coma, astigmatism, field curvature, distortion, and lateral chromatic) unless the stop is so small that diffraction becomes dominant.[39] Even 1.1. HISTORY OF PHOTOGRAPHIC LENS DESIGN 5

Harrison & Schnitzer Globe

today, most lenses produce their best images at their middle , at a compromise between transverse aberrations and diffraction.[40] Therefore, even the Meniscus had a permanent stop. Nevertheless, the earliest lenses did not have adjustable stops: their small working apertures and the lack of sensitivity of the daguerreotype process meant that times were measured in many minutes. Photographers did not want to limit the light passing through the lens and lengthen the exposure time. When the increased sensitivity wet collodion process was perfected in 1851, exposure times were shortened dramatically and adjustable stops became practical.[41] The earliest selectable stops were the Waterhouse stops of 1858, named for John Waterhouse. These were sets of accessory brass plates with sized holes, mounted through a slot in the side of the lens structure.[42][43] Around 1880, photographers realized that aperture size affected depth of field.[44] Aperture control gained more significance, and adjustable stops became a standard lens feature. The iris diaphragm made its appearance as an adjustable lens stop in the 1880s, andi t became the standard adjustable stop about 1900. The iris diaphragm had been common in early nineteenth century obscura, and Niépce used one in at least one of his experimental cameras.[45] However, the specific type of iris used in modern lenses was invented in 1858 by Charles Harrison and Joseph Schnitzer.[46] Harrison and Schnitzer’s iris diaphragm was capable of rapid open and close cycles, an absolute necessity for lenses with camera auto-aperture control.[47] The modern lens aperture markings of f-numbers in geometric sequence of f/1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, 6 CHAPTER 1. DAY 1

Dallmeyer Rapid-Rectilinear and Steinheil Aplanat

45, 64, 90, etc. was standardized in 1949. Previously, this British system competed with the Continental (German) sequence of f/1.1, 1.6, 2.2, 3.2, 4.5, 6.3, 9, 12.5, 18, 25, 36, 50, 71, 100 ratios. In addition, the Uniform System (U.S., invented UK) sequence of 1, 2, 4, 8, 16, 32, 64, 128, etc. (where U.S. 1 = f/4, U.S. 2 = f/5.6, U.S. 4 = f/8, etc.), was favored by Eastman early in the twentieth century.[48][49][50] 1.1. HISTORY OF PHOTOGRAPHIC LENS DESIGN 7

1.1.6 Telephoto lens

Main article: Telephoto lens A single-element camera lens is as long as its focal length; for example, 500 mm-focal-length lens requires 500 mm

Dallmeyer and Miethe telephotos

Busch Bis-Telar from the lens to the image plane. A telephoto lens is made physically shorter than its nominal focal length by pairing 8 CHAPTER 1. DAY 1 a front positive imaging cell with a rear magnifying cell. The powerful front group over-refracts the image, the rear restores the focal plane, thereby greatly shortening the back-focus length.[51] Originally, accessory negative cells were sold to attach to the rear of a regular lens. The Barlow lens, a negative achromat magnifier invented by Peter Barlow in 1833, is still sold to increase the magnification of amateur telescopes.[52] The teleconverter is the modern photographic equivalent.[53][54] In 1891, Thomas Dallmeyer and Adolph Miethe simultaneously attempted to patent new lens designs with nearly identical formulae – complete photographic telephoto lenses consisting of a front achromat doublet and rear achromat triplet. Primacy was never established and no patent was ever granted for the first telephoto lens.[55] The front and rear cells of early telephotos were unmatched and the rear cell also magnified any aberrations, as well as the image, of the imaging cell. The cell spacing was also tunable, because that could be used to adjust the effective focal length, but that only worsened aberration problems. The first telephoto lens optically corrected and fixed as a system was the f/8 Busch Bis-Telar (Germany) of 1905.[56]

1.1.7 Anastigmat lens

Zeiss Protar

The photographic lens leapt forward in 1890 with the Zeiss Protar (Germany).[57] Paul Rudolph's Protar was the first successful anastigmat (highly corrected [for the era] for all aberrations, including properly for astigmatism) lens. It was scalable from f/4.5 portrait to f/18 super wide angle. The Protar was originally called the Anastigmat, but that descriptive term quickly became generic and the lens was given a fanciful name in 1900.[58] The Protar is considered the first “modern” lens, because it had an asymmetric formula allowed by the new design 1.1. HISTORY OF PHOTOGRAPHIC LENS DESIGN 9

freedom opened up by newly available barium oxide, crown optical glasses.[59] These glasses were invented by Ernst Abbe, a physicist, and Otto Schott, a chemist, (both Germany) in 1884, working for Carl Zeiss' Jena Glass Works. Schott glasses have higher refractive index than soda-lime crown glass without higher dispersion. The Protar’s front achromat used older glass, but the rear achromat used high index glass.[60] Virtually all good quality photographic lenses since circa 1930 are anastigmat corrected. (The primary exceptions are deliberately “soft-focus” portrait lenses.) Today’s photographic lens state-of-the-art is apochromatic correction, which is, very roughly, twice as strict as anastigmatic.[61] However, such lenses require correcting for higher ordered aberrations than the original seven[62] with rare earth (lanthanum oxide) or fluorite (calcium fluoride) glasses of very high refractive index and/or very low disper- sion of mid-twentieth century invention.[63][64][65] The first apochromatic lens for consumer cameras was the Leitz APO-Telyt-R 180mm f/3.4 (1975, West Germany) for Leicaflex series (1964, West Germany) 35mm SLRs.[66] Most professional telephoto lenses since the early 1980s are apochromatic.[67][68] Note, better-than- lenses are available for scientific/military/industrial work.[69]

1.1.8 Cooke Triplet

Main article: Cooke triplet The quintessential twentieth century photographic lens was the 1893 Taylor, Taylor & Hobson Cooke Triplet.[70] Dennis Taylor's (UK, not related to the Taylors of T, T & H) Cooke Triplet was a deceptively simple looking asym- metric three element anastigmat formula created by reexamining lens design from first principles to take maximum advantage of the advances in new Schott optical glasses. The elements were all of such strong power that they were highly sensitive to misalignment and required tight manufacturing tolerances for the era.[71] The Cooke Triplet became the standard “economy” lens of the twentieth century. For example, the Argus Cintar 50mm f/3.5 for the Argus C3 (1937, USA), probably the best-selling rangefinder camera of all time, used a Cooke triplet.[72] The Triplet was adequate for contact prints from roll film cameras and small enlargements from 35mm “miniature” format cameras, but not for big ones. The films of the first half of the twentieth century did not have much resolving power either, so that was not necessarily a problem.

1.1.9 Tessar

Main article: Tessar Paul Rudolph developed the Tessar from dissatisfaction with the performance of his earlier Protar,[73] although it also resembles the Cooke triplet. The Tessar was originally an f/6.3 lens. It was refined to f/2.8 by 1930, although f/3.5 was the realistic limit for best image quality.[74] The Tessar was the standard high-quality, moderate-aperture, normal-perspective lens of the twentieth century. The Kodak Anastigmat Special 100mm f/3.5 on the Kodak Super Six-20 (1938, USA), the first autoexposure still camera, was a Tessar,[75] as was the D. 2.8 cm f/3.5 on the (1959, Japan), the original Pen half frame camera;[76] the Schneider S-Xenar 40mm f/3.5 on the late version of the Rollei 35 (1974, West Germany/Singapore);[77][78] and the AF D 45mm f/2.8P Special Edition for the FM3A (2001, Japan), the last manual focus 35mm SLR released by a major maker.[79] It was fitting that the Zeiss Stiftung’s last camera, the Zeiss Ikon S 312, had a Zeiss Tessar 40mm f/2.8 (1972, West Germany).[80] It is often incorrectly stated that the Leitz Elmar 50mm f/3.5 fixed to the Leica A (1925, Germany), Leitz’s first camera, was a Tessar.[81] However, at the time the Leica was introduced the 50mm f/3.5 Kino Tessar had only been designed to cover the cine format of 18x24mm, which was insufficient for the new 24x36mm format of the Leica, and Leitz had to develop a new lens to provide adequate full frame coverage. It was only when Zeiss Ikon were designing the in response to the success of the Leica that a 50mm Tessar which could cover the 24x36mm format was designed. The Elmar was based on a modified Cooke Triplet with a different computation to the Tessar and with the stop in the first air .[82]

1.1.10 Ernostar and Sonnar

Main article: With anastigmat image quality achieved, attention next turned to increasing aperture size to allow photography in 10 CHAPTER 1. DAY 1

Taylor, Taylor & Hobson Cooke Triplet

lower light or with faster speeds. The first common very wide aperture lens suitable for candid available light photography was the Ernemann Ernostar (Germany) of 1923.[83] 's formula was originally a 10 cm f/2 lens, but he improved it to 10.5 cm and 85mm f/1.8 in 1924.[84] The Ernostar was also a Cooke Triplet derivative; it has an extra front positive element or group.[85] Mounted on the Ernemann Ermanox (1923, Germany) camera and in the hands of Erich Salomon, the Ernostar pioneered modern . French Premier Aristide Briand once said: “There are just three things necessary for an international conference: a few Foreign Secretaries, a table and Salomon.”[86] Note, American photojournalists favored flash use into the 1950s (see Arthur Fellig [Weegee]). Bertele continued Ernostar development under the more famous Sonnar name after Ernemann was absorbed by Zeiss in 1926. He reached f/1.5 in 1932 with the Zeiss Sonnar 50mm f/1.5[87][88] for the Contax I 35mm rangefinder camera (1932, Germany).[89] The Sonnar was (and is) also popular as a telephoto lens design – the Sonnar is always at least slightly telephoto 1.1. HISTORY OF PHOTOGRAPHIC LENS DESIGN 11

Zeiss Tessar because of its powerful front positive elements. The Zeiss Olympia Sonnar 180mm f/2.8 for the Contax II (both 1936, Germany) is a classic, if not mythic, example.[90]

1.1.11 Asymmetric double Gauss

Main article: Double-Gauss lens

In 1817 Carl Friedrich Gauss improved the Fraunhofer telescope objective by adding a meniscus lens to its single convex and concave lens design. Alvan Clark further refined the design in 1888 by taking two of these lenses and placing them back to back. The lens was named in honour of Gauss. The current design can be traced back to 1895, when Paul Rudolph of Carl Zeiss Jena used cemented doublets as the central lenses to correct for chromatic aberration. Later the design was developed with additional glasses to give high-performance lenses of wide aperture. The main 12 CHAPTER 1. DAY 1

Ernemann Ernostar 10.5cm f/1.8 development was due to Taylor Hobson in the 1920s, resulting in the f/2.0 Opic and later the Speed Panchro designs, which were licensed to various other manufacturers. The design forms the basis for many camera lenses in use today, especially the wide-aperture standard lenses used on 35 mm and other small-format cameras. It can offer good results up to f/1.4 with a wide field of view, and has sometimes been made at f/1.0. The design is presently used in inexpensive-but-high-quality fast lenses such as the Canon EF 50mm f/1.8 and Nikon 50 mm f/1.8D AF Nikkor. It is also used as the basis for faster designs, with elements added, such as a seventh element as in both Canon[91] and Nikon’s 50 mm f/1.4 offerings[92] or an aspherical seventh element in Canon’s 50 mm f/1.2.[93] The design appears in other applications where a simple fast normal lens is required (~53° diagonal) such as in projectors.

1.1.12 Anti-reflection coating

Surface reflection was a major limiting factor in nineteenth century lens design. With a four to eight percent (or more) reflective light loss at every glass-air interface dimming the light transmission plus the reflected light scattering everywhere producing flare, a lens would not be of practical use with more than six or eight losses. This, in turn, limited the number of elements a could use to control aberrations.[94] Some lenses were marked by T-stops (transmission stops) instead of f-stops to indicate the light losses.[95] T-stops were “true” or effective aperture stops and were common for motion picture lenses,[96] so that a cinematographer could ensure that consistent exposures were made by all the different lenses used to make a movie. This was less important for still cameras and only one still lens line was ever marked in T-stops: for the Bell & Howell Foton 35mm rangefinder camera. Bell & Howell was normally a cinematographic equipment maker. The Foton’s standard lens was the Taylor, Taylor & Hobson Cooke Amotal Anastigmat 2 inch f/2 (T/2.2) (1948; camera USA; lens UK, a Double Gauss).[97] The quarter stop difference between f/2 and T/2.2 is a 16% loss. 1.1. HISTORY OF PHOTOGRAPHIC LENS DESIGN 13

Zeiss Sonnar 50mm f/1.5

Development of the Double Gauss

It was noticed by Dennis Taylor in 1896 that some lenses with glass tarnished by age counterintuitively produced brighter images. Investigation revealed that the oxidation layer suppressed surface reflections by destructive interference.[98][99] Lenses with glass elements artificially “single-coated” by vacuum deposition of a very thin layer (approximately 130- 140 nanometers[100]) of magnesium or calcium fluoride to suppress surface reflections[101] were invented by Alexander Smakula working for Zeiss in 1935[102][103] and first sold in 1939.[104] Antireflection coating could cut reflection by two-thirds.[105] In 1941, the (USA) 35mm RF was introduced with the first complete antireflection coated lens line for a consumer camera: the Kodak 35mm f/3.3, 50mm f/3.5, 50mm f/1.9, 90mm f/3.5, 135mm f/3.8 and 153mm f/4.5.[106] World War II interrupted all consumer camera production and coated lenses did not appear in large numbers until the late 1940s. They became standard for high quality cameras by the early 1950s. 14 CHAPTER 1. DAY 1

The availability of antireflection coating permitted the Double Gauss to rise to dominance over the Sonnar. The Sonnar had more popularity before World War II because, before antireflection coating, the Sonnar’s three cell with six air-glass surfaces versus the Double Gauss’s four and eight made it less vulnerable to flare.[107] Its telephoto effect also made the lens shorter, an important factor for the Leica and Contax 35mm RFs designed to be compact. As maximum aperture continued to increase, the Double Gauss’s greater symmetry promised easier aberration cor- rection. This was especially important for SLRs because, without the parallax error of RFs, they also began offering much closer focusing distances (typically a half meter instead a whole meter).[108] The Double Gauss became the preferred normal lens design in the 1950s with the availability of antireflection coating and new generation extra high refractive index rare earth optical glasses.[109] Coating lenses with up to a dozen or more different layers of chemicals to suppress reflections across the visual spectrum (instead of at only one compromise wavelength) were a logical progression. Asahi Optical’s SMC Takumar lenses (1971, Japan) were the first all multicoated (Super-Multi-Coated) lenses for consumer cameras (M42 screw mount Asahi SLRs).[110] Modern highly corrected zoom lenses with fifteen, twenty or more elements would not be possible without multicoating.[111][112] The transmission efficiency of a modern multicoated lens surface is about 99.7% or better.[113] Antireflection coating does not relieve the need for a (a conical tube slipped, clipped, screwed or bayoneted onto the front of a lens to block non-image forming rays from entering the lens) because flare can also result from strong stray light reflecting off of other inadequately blacked internal lens and camera components.[114][115][116]

1.1.13 Retrofocus wide-angle lens

Main article: Angénieux retrofocus Regular wide angle lenses (meaning lenses with focal length much shorter than the format diagonal and producing a

Angénieux Retrofocus 35mm f/2.5 wide field of view) need to be mounted close to the film. However, SLR cameras require that lenses be mounted far 1.1. HISTORY OF PHOTOGRAPHIC LENS DESIGN 15

Zeiss Biogon 21mm f/4.5

enough in front of the film to provide space for the movement of the mirror (the “mirror box”); about 40 mm for a 35mm SLR compared to less than 10 mm in non-SLR 35mm cameras. This prompted the development of wide field of view lenses with more complex retrofocus optical designs. These use very large negative front elements to force back-focus distances long enough to ensure clearance.[117][118] In 1950, the Angénieux Retrofocus Type R1 35mm f/2.5 (France) was the first retrofocus wide angle lens for 35mm SLRs (Exaktas).[119] Except for the front element, Pierre Angénieux' R1 was a five element Tessar. Note, “retrofocus” was an Angénieux trademark before losing exclusive status. The original generic term was “inverted” or “reversed telephoto.” A telephoto lens has a front positive cell and rear negative cell;[120] retrofocus lenses have the negative cell in front and positive cell to the rear.[121] The first inverted telephoto imaging lens was the Taylor, Taylor & Hobson 35mm f/2 (1931, UK) developed to provide back-focus space for the beamsplitter prism used by the full- via three negatives Technicolor motion picture camera.[122] Other early members of the Angénieux Retrofocus line included the 28mm f/3.5 Type R11 of 1953 and the 24mm f/3.5 Type R51 of 1957.[123] Retrofocus lenses are extremely asymmetric with their large front elements and therefore very difficult to correct for distortion by traditional means. On the upside, the large negative element also limits the oblique cos4θ light falloff of regular wide-angle lenses.[124][125][126] Retrofocus design also influenced non-retrofocus lenses. For example, Ludwig Bertele’s 21mm f/4.5,[127] released in 1954 for the Contax IIA (1950, West Germany) 35mm RF, and its evolution, the Zeiss Hologon 15mm f/8[128] of 1969, fixed to the Zeiss Ikon Hologon Ultrawide (West Germany), were roughly symmetrical designs. However, each half can visualized as retrofocus. The Biogon and Hologon designs take advantage of the large neg- 16 CHAPTER 1. DAY 1 ative elements to limit the light falloff of regular wide angle lenses.[129][130] With a 110° field of view, the Hologon would otherwise have had a 3¼ stop corner light falloff, which is wider than the exposure latitude of contemporaneous films. Nonetheless, the Hologon had a standard accessory radially graduated 2 stop neutral density filter to ensure completely even exposure. The distance from the Hologon’s rear element to the film was only 4.5 mm.[131] Many normal perspective lenses for today’s digital SLRs are retrofocus, because their smaller-than-35mm-film-frame image sensors require much shorter focal lengths to maintain equivalent fields of view, but the continued use of 35mm SLR lens mounts require long back-focus distances.

1.1.14 Fisheye lens

Main article: Fisheye lens A fisheye lens is a special type of ultra-wide angle retrofocus lens with little or no attempt to correct for rectilinear distortion. Most fisheyes produce a circular image with a 180° field of view. The term fisheye comes from the supposition that a fish looking up at the sky would see in the same way.[132] The first fisheye lens was the Beck Hill Sky (or Cloud; UK) lens of 1923. Robin Hill intended it to be pointed straight up to take 360° azimuth barrel distorted hemispheric sky images for scientific cloud cover studies.[133] It used a bulging negative meniscus to compress the 180° field to 60° before passing the light through a stop to a moderate wide angle lens.[134] The Sky was 21mm f/8 producing 63mm diameter images.[135] Pairs were used at 500 meter spacing producing stereoscopes for the British Meteorological Office.[136] Note, it is impossible to have 180° rectilinear coverage because of light falloff. 120° (12mm focal length for the 35mm film format) is about the practical limit for retrofocus designs; 90° (21mm focal length) for non-retrofocus lenses.[137]

1.1.15 Macro lens

Main article: Macro photography

Strictly speaking, macrophotography is technical photography with actual image size ranging from near life-size (1:1 image-to-object ratio) to about ten or twenty times life-size (10 or 20:1 ratio, at which photomicrography begins). “Macro” lenses were originally regular formula lenses optimized for close object distances, mounted on a long exten- sion tube or bellows accessory to provide the necessary close focusing, but preventing focusing on distant objects.[138] However, the Kilfitt Makro-Kilar 4 cm f/3.5 (West Germany/Liechtenstein) of 1955 for Exakta 35mm SLRs changed the everyday meaning of macro lens.[139] It was the first lens to provide continuous close focusing. Ver- sion D of Heinz Kilfitt's (West Germany) Makro-Kilar focused from infinity to 1:1 ratio (life-size) at two inches; version E, to 1:2 ratio (half life-size) at four inches.[140] The Makro-Kilar was a Tessar mounted in an extra long draw triple helical. SLR cameras were best for macro lenses because SLRs do not suffer from viewfinder parallax error at very close focus distances.[141] Designing close-up lenses is not really that hard – an image size that is close to object size increases symmetry. The Goerz Apo-Artar (Germany/USA) photoengraving process lens was apochromatic in 1904,[142] although ultra-tight quality control helped.[143] It is getting a sharp image continuously from infinity to close-up that is hard – before the Makro-Kilar, lenses generally did not continuously focus to closer than 1:10 ratio. Most SLR lens lines continue to include moderate aperture macro lenses optimized for high magnification.[144] However, their focal lengths tend to be longer than the Makro-Kilar to allow more working distance.[145] “Macro zoom” lenses began appearing in the 1970s, but traditionalists object to calling most of them macro because they stray too far from the technical definition – they usually do not focus closer than 1:4 ratio with relatively poor image quality.[146][147]

1.1.16 Supplementary lens

A supplementary lens is an accessory lens clipped, screwed or bayoneted to the front of a main lens that alters the lens’ effective focal length. If it is a positive (converging) only supplement, it will shorten the focal length and reset the infinity focus of the lens to the focal length of the supplementary lens. These so-called close-up lenses are often 1.1. HISTORY OF PHOTOGRAPHIC LENS DESIGN 17

Beck Hill Sky

uncorrected single element menisci, but are a cheap way to provide close focusing for an otherwise limited focus range lens.[148][149] An afocal attachment is a more sophisticated supplementary lens. It is a so-called Galilean telescope accessory mounted to the front of a lens that alters the lens’ effective focal length without moving the focal plane. There are two types: the telephoto and the wide angle. The telephoto type is a front positive plus rear negative cell combination 18 CHAPTER 1. DAY 1

Zeiss Tele-Mutar and Wide-Angle-Mutar

that increases the image size; the wide angle has a front negative and rear positive arrangement to reduce the image size. Both have cell separation equal to cell focal length difference to maintain the focal plane.[150][151] Since afocal attachments are not an integral part of the main lens’ formula, they degrade image quality and are not appropriate for critical applications.[152] However, they have been available for amateur motion picture, video and still cameras since the 1950s.[153] Before the zoom lens, afocal attachments were a way to provide a cheap sort of 1.1. HISTORY OF PHOTOGRAPHIC LENS DESIGN 19

interchangeable lens system to an otherwise fixed lens camera. In the zoom lens era, they are a cheap way to extend the reach of a zoom. Some afocal attachments, such as the Zeiss Tele-Mutar 1.5× and Wide-Angle-Mutar 0.7× (1963, West Germany) for various fixed lens Franke and Heidecke Rolleiflex 120 roll film twin-lens reflex cameras, were of higher quality and price, but still not equal to true interchangeable lenses in image quality. The very bulky Mutars could change a Rolleiflex 3.5E/C’s Heidosmat 75mm f/2.8 and Zeiss Planar 75mm f/3.5 (1956, West Germany) viewing and imaging lenses into 115mm and 52mm equivalents.[154][155] Afocal attachments are still available for digital point-and-shoot cameras.[156][157] The IIIc and IIc (USA/West Germany) collapsable lens 35mm rangefinder cameras of 1954 took the supplementary lens idea to the extreme with their interchangeable lens “components.” This system allowed swap- ping the front cell component of their standard Schneider Retina-Xenon C 50mm f/2 lenses (a Double Gauss) for Schneider Retina-Longar-Xenon 80mm f/4 long-focus and Schneider Retina-Curtar-Xenon 35mm f/5.6 wide-angle components.[158][159] Component lens design is tightly constrained by the need to reuse the rear cell and the lenses are extremely bulky, range limited and complex compared with fully interchangeable lenses,[160] but the Retina’s interlens Synchro-Compur leaf shutter restricted lens options.

1.1.17 Zoom lens

Main article: Zoom lens The zoom lens evolved from the focal length compression elements found in telephoto lens. Varying the spacing between a telephoto’s front positive and rear negative cells changes the lens’ magnification. However, this will upset focus and aberration optimization, and introduce pincushion distortion. A real zoom lens needs a compensating cell to push the focal plane back to the appropriate place and took decades of development to become practical. The earliest zooms came out between 1929 and 1932 for professional motion picture cameras and were called “Traveling,” “Vario” and “Varo” lenses.[161] The first zoom lens for still cameras was the Voigtländer-Zoomar 36-82mm f/2.8 (USA/West Germany) of 1959,[162] for Voigtländer Bessamatic series (1959, West Germany) 35mm leaf shutter SLRs.[163] It was designed by Zoomar in the United States and manufactured by Kilfitt in West Germany for Voigtländer.[164] The Zoomar 36-82 was very large and heavy for the focal length[165] – 95mm filter size.[166] Frank Back (Germany/USA) was the early champion of zoom lenses and his Zoomars would hurl far into the future the lance of zoom lens development and popularity, starting with his original Zoomar 17-53mm f/2.9 (1946, USA)[167] for 16mm motion picture cameras.[168] The image quality of early zoom lenses could be very poor – the Zoomar’s has been described as “pretty rotten.”[169]

Development

Most early zoom lenses produced mediocre, or even poor, images. They were adequate for low resolution require- ments such television and amateur movie cameras, but usually not still photography. For example, Nippon Kogaku always apologetically acknowledged that Takashi Higuchi's Zoom-Nikkor Auto 43-86mm f/3.5, the first popular zoom lens, did not meet its normal image quality standards.[170] However, efforts to improve them were ongoing. In 1974, the Ponder & Best (Opcon/Kino) Vivitar Series 1 70-210mm f/3.5 Macro Focusing Zoom (USA/Japan) was widely hailed as the first professional- quality very close focusing “macro” zoom lens for 35mm SLRs. Ellis Betensky's (USA) Opcon Associates perfected the Series 1’s fifteen element/ten group/four cell formula by calculations on the latest digital computers.[171] Freed from the drudgery of hand computation in the 1960s, designs of such variety and quality only dreamt of by earlier generations of optical engineers became possible.[172][173] Modern computer created zoom designs may be so complex that they have no resemblance to any of the classical human created designs. The optical zooming action of the Series 1 was different from most earlier zooms such as the Zoomar. The Zoomar was an “optically compensated” zoom. Its zooming cell and focal plane compensating cell were fixed together and moved together with a stationary cell in between.[174] The Series 1 was a “mechanically compensated” zoom. Its zooming cell was mechanically cammed with a focal plane compensating cell and moved at different rates.[175] The tradeoff for greater optical design freedom was this increase in mechanical complexity. The external controls of the Series 1 were also mechanically more complex than the Zoomar. Most early zooms had separate twist control rings to vary the focus and focal length – a “two touch” zoom. The Series 1 used a single control 20 CHAPTER 1. DAY 1

ring: twist to focus, push-pull to zoom – a “one touch” zoom. For a short time, about 1980-1985, one-touch zooms were the dominant type, because of their ease of handling. However, the arrival of interchangeable lens autofocus cameras in 1985 with the Maxxum 7000 (Japan; called Alpha 7000 in Japan, 7000 AF in Europe) necessarily forced the decoupling of focusing and zooming controls and two touch zooms made an instant comeback. In 1977, zoom lenses had advanced far enough that the Fuji Fujinon-Z 43-75mm f/3.5-4.5 (Japan) became the first zoom lens to be sold as the primary lens for an interchangeable lens camera, the Fujica AZ-1 (1977, Japan) 35mm SLR, instead of a prime.[176] Small quick “supernormal” zooms of around 35-70mm focal length became popular 50mm substitutes in Japan by 1980.[177] However, they never gained much of a foothold in the United States,[178] although 70-210mm telephoto zooms were very popular as second lenses. The first auto-everything 35mm point-and-shoot camera with built-in zoom lens, the camera type that dominated the 1990s, was the Asahi Optical Pentax IQZoom (1987, Japan) with Pentax Zoom 35-70mm f/3.5-6.7 Tele-Macro.[179] The next landmark zoom was the Sigma 21-35mm f/3.5-4 (Japan) of 1981. It was the first super-wide angle zoom lens for still cameras (most 35mm SLRs). Previously, combining the complexities of rectilinear super-wide an- gle lenses, retrofocus lenses and zoom lenses seemed impossible. The Sigma’s all-moving eleven element/seven group/three cell formula was a triumph of computer-aided design and multicoating.[180] Along with optical complexity, the mechanical complexity of the Sigma, with three cells moving at differing rates, required the latest in manufacturing technology. Super-wide angle zoom lenses are even more complicated for most of today’s digital SLRs, because the usually smaller-than-35mm-film-frame image sensors require much shorter focal lengths to maintain equivalent fields of view, but the continued use of 35mm SLR lens mounts require the same large back-focus distances. Japanese zoom interchangeable lens production surpassed that of prime lenses in 1982.[181]

Widespread use

The need for one lens able to do everything, or at least as much as possible, was an influence on lens design in the last quarter century. The Kino Precision Kiron 28-210mm f/4-5.6 (Japan) of 1985 was the first very large ratio focal length zoom lens for still cameras (most 35mm SLRs). The fourteen element/eleven group Kiron was first 35mm SLR zoom lens to extend from standard wide angle to long telephoto (sometimes referred to as "superzoom"),[182] able to replace 28, 35, 50, 85, 105, 135 and 200mm prime lenses, albeit restricted to a small variable maximum aperture to keep size, weight and cost within reason (129×75 mm, 840 g, 72mm filter, US$359 list).[183][184][185] Early 35mm SLR zooms focal length ratios rarely exceeded 3 to 1, because of unacceptable image quality issues. However, zoom versatility, despite increasing optical complexity and stricter manufacturing tolerances, continued to increase. Despite their many image quality compromises, convenient wide range zoom lenses (sometimes with ratios over 10 to 1 and four or five independently moving cells) became common on amateur level 35mm SLRs by the late 1990s. They remain a standard lens on today’s amateur digital SLRs,[186] attaining up to 19X.[187] Wide range “superzooms” also sell by the millions on digital point-and-shoots.[188] The desire for an all-in-one lens is hardly a new phenomenon. Convertible lenses, still used by film photographers (insofar as large format photography is used), consisting of two cells that could be used individually or screwed together, giving three-lenses-in-one,[189] date back to at least the Zeiss Convertible Protar (Germany) of 1894.[190] Convenience of a different sort was the major feature of the Tokina SZ-X 70-210mm f/4-5.6 SD (Japan) of 1985. It was the first ultra-compact zoom (85×66 mm, 445 g, 52mm filter); half the size of most earlier 70-210 zooms[191] (the third generation Vivitar Series 1 70-210mm f/2.8-4 [1984, USA/Japan] was 139×70 mm, 860 g, 62mm filter).[192] Like the Kiron 28-210mm, the twelve element/eight group/three cell Tokina had a small variable maximum aperture, but added low dispersion glass and a new bidirectional nonlinear zooming action, to bring size and weight down to an absolute minimum.[193] Small aperture 35mm format lenses were made practical by the availability of snapshot quality, high sensitivity ISO 400 color films in the 1980s (and ISO 800 in the 1990s), as well as cameras with built-in flash units. During the 1990s, point-and-shoot cameras with compact small aperture zooms were the dominant camera type. Compact variable aperture zoom (some wide range, some not) lenses remain a standard lens on today’s digital point-and-shoot cameras. At about this time the image quality of zooms was noticed to be equalled that of primes.[194] 1.1. HISTORY OF PHOTOGRAPHIC LENS DESIGN 21

Note, many of today’s wide range zoom lenses are not “parfocal"; that is, not true zooms. They are “varifocal” – the focus point shifts with the focal length – but are easier to design and manufacture. The focus shift usually goes unnoticed as they are mounted on autofocus cameras that will automatically refocus.[195]

1.1.18 Rise of Japanese optical industry

Japanese photographic lens production dates from 1931 with the Konishiroku (Konica) Hexar 10.5 cm f/4.5[196] for the Konishiroku Tropical Lily small plate camera. However, the Japanese advanced quickly and were able to man- ufacture very high quality lenses by 1950[197] – LIFE magazine photographer David Douglas Duncan's “discovery” of Nikkor lenses is an oft-told tale.[198][199][200] In 1954, the Japan Camera Industry Association (JCIA) began promoting the development of a high quality photo- graphic industry to increase exports as part of Japan’s post-World War II economic recovery. To that end, the Japan Machine Design Center (JMDC) and Japan Camera Inspection Institute (JCII) banned the slavish copying of designs and the export of low quality photographic equipment, enforced by a testing program before issuance of shipping permits.[201][202] By the end of the 1950s, the Japanese were seriously challenging the Germans. For example, the Nippon Kogaku Nikkor-P Auto 10.5 cm f/2.5 of 1959, for the Nikon F 35mm SLR (1959), is reputed to be one of the best portrait lenses ever made, with superb sharpness and bokeh. It originated as the Nikkor-P 10.5 cm f/2.5 (1954) for the Nikon S series 35mm RF, was optically upgraded in 1971 and available until 2006.[203] In 1963, the Tokyo Kogaku RE Auto-Topcor 5.8 cm f/1.4 came out along with the Topcon RE Super/Super D (1963) 35mm SLR. The Topcor is reputed to be one of the best normal lenses ever made.[204] The Nikkor and the Topcor were sure signs of the Japanese optical industry eclipsing the Germans’. Topcon in particular was highly avant-garde in producing two ultra-fast lenses by 1960 - the R-Topcor 300 F2.8 (1958) and the R-Topcor 135 F2 (1960). The former was not eclipsed until 1976. Germany had been the optical leader for a century, but the Germans turned very conservative after World War II; failing to achieve unity of purpose, innovate or respond to market conditions.[205][206] Japanese camera production surpassed West German output in 1962.[207] Early Japanese lenses were not novel designs: the Hexar was a Tessar; the Nikkor was a Sonnar; the Topcor was a Double Gauss. They began breaking new ground around 1960: the Nippon Kogaku Auto-Nikkor 8.5–25 cm f/4-4.5 (1959), for the Nikon F, was the first telephoto zoom lens for 35mm still cameras (and second zoom after the Zoomar),[208] the Canon 50mm f/0.95 (1961), for the Canon 7 35mm RF, with its superwide aperture, was the first Japanese lens a photographer might lust after,[209][210] and the Nippon Kogaku Zoom-Nikkor Auto 43-86mm f/3.5 (1963), originally fixed on the Nikkorex Zoom 35mm SLR, later released for the Nikon F, was the first popular zoom lens, despite mediocre image quality.[211][212] German lenses disappear from this history at this point. After ailing throughout the 1960s, such famous German nameplates as Kilfitt, Leitz, Meyer, Schneider, Steinheil, Voigtländer and Zeiss went bankrupt, were sold off, con- tracted production to East Asia or became boutique in the 1970s.[213][214] Names for design types also disap- pear at this point. Apparently the Japanese are not fans of lens names, they use only brand names and feature codes for their lens lines.[215] The JDMC/JCII testing program, having fulfilled its goals, ended in 1989 and its gold “PASSED” sticker passed into history.[216] The JCIA/JCII morphed into the Camera & Imaging Products Association (CIPA) in 2002.[217]

1.1.19 Catadioptric “mirror” lens

Main article: Catadioptric photographic lenses (or "CAT" for short) combine many historical inventions such as the Catadioptric Mangin mirror (1874), (1931), and the (1941) along with Laurent Cassegrain’s Cassegrain telescope (1672). The Cassegrain system folds the light path and the convex secondary acts as a telephoto element, making the focal length even longer than the folded system and extending the light cone to a focal point well behind the primary mirror so it can reach the film plane of the attached camera. The Catadioptric system, where a spherical reflector is combined with a lens with the opposite spherical aberration, corrects the common optical errors of a reflector such as the Cassegrain system, making it suitable for devices that need a large aberration free focal plane (cameras). The first general purpose photographic catadioptric lens was Dmitri Maksutov 1944 MTO (Maksutov Tele-Objectiv) 500mm f/8 Maksutov–Cassegrain configuration, adapted from his 1941 Maksutov telescope.[218] Designs followed 22 CHAPTER 1. DAY 1 using other optical configurations including Schmidt configuration and solid catadioptric designs (made from a single glass cylinder with a maksutov or aspheric form polished into the front face and the back spherical surface silvered to make the “mirror”). In 1979 was able to produce a very compact light weight catadioptric by using rear surface silvered mirrors, a “Mangin mirror” configuration that saved on mass by having the aberration corrected by the light passing through the mirror itself.[219] The catadioptric camera lens’ heyday was the 1960s and 1970s, before apochromatic refractive telephoto lenses. CATs of 500mm focal length were common; some were as short as 250mm, such as the Minolta RF Rokkor-X 250mm f/5.6 (Japan) of 1979 (a Mangin mirror CAT roughly the size of a 50mm f/1.4 lens).[220] The CAT is the only reasonable solution for 1000+ mm lenses. Dedicated photographic mirror lenses fell out of favor in the 1980s for various reasons. However, commercial reflector astronomical Maksutov–Cassegrain and Schmidt–Cassegrain telescopes with 14 to 20 inch (or even larger) diameter primary mirrors are available. With an accessory camera adapter, they are 4000mm f/11 to f/8 equivalent.[221][222]

1.1.20 Movable element prime lens

The complex internal movements of zoom were also adapted to prime lens designs. Traditionally, prime lenses for rigid cameras were focused closer by physically shifting the entire lens toward the object in a helical or rack and pinion mount. (Cameras with bellows expanded the bellows to shift the lens forward.) However, element spacing for best aberration correction may be different for near versus far objects. Therefore, some prime lenses of this era began using “floating elements” – zoom-like differential cell movement in nested helicals for better close-up performance.[223] For example, retrofocus wide angle lenses tend to have excessive spherical aberration[224] and astigmatism at close focusing distances and so the Nippon Kogaku Nikkor-N Auto 24mm f/2.8 (Japan) of 1967 for Nikon 35mm SLRs had a Close Range Correction system with a rear three element cell that moved separately from the main lens to maintain good wide aperture image quality to a close focus distance of 30 cm/1 ft.[225] Other prime lenses began using “internal focusing,” such as Kiyoshi Hayashi's Nippon Kogaku Nikkor 200mm f/2 ED IF (Japan) of 1977. Focusing by moving only a few internal elements, instead of the entire lens, ensured the lens’ weight balance would not be upset during focusing.[226][227] Internal focusing was originally popular in heavyweight, wide-aperture telephoto lenses for professional press, sports and wildlife photographers, because it made their handling easier. IF gained all-around significance in the autofocus era, because moving a few internal elements instead of the entire lens for focusing conserved limited battery power and eased the strain on the focusing motor.[228] Note, floating elements and internal focusing produces a zooming effect and the effective focal length of an FE or IF lens at closest focusing distance can be one-third shorter than the marked focal length.[229]

1.1.21 Bokeh

Bokeh is the subjective quality of the out-of-focus or blurry part of the image. Traditionally, time consuming hand computation limited lens to correcting aberrations for the in-focus image only, with little consideration given to the out-of-focus image. Therefore, approaching and outside the specified or depth-of- field, aberrations built up in the out-of-focus image differently in different lens design families. Differences in the out-of-focus image can influence the perception of overall image quality. There is no precise definition of bokeh and no objective tests for it – as with all aesthetic judgments. However, symmetrical optical formulae such as the Rapid-Rectilinear/Aplanat and the Double Gauss are usually considered pleasing, while asymmetric retrofocus wide angle and telephoto lenses are often thought harsh.[230] The unique “donut” bokeh produced by mirror lenses because of the optical pathway obstruction of the secondary mirror is especially polarizing.[231][232] In the 1970s, as increasing powerful computers proliferated, the Japanese optical houses began to spare computing cycles to study the out-of-focus image.[233] An early result of these explorations was the Minolta Varisoft Rokkor-X 85mm f/2.8 (Japan) of 1978 for Minolta 35mm SLRs. It used floating elements to allow the photographer to delib- erately under-correct the spherical aberration of the lens system and render unsharp specular highlights as smoothly fuzzy blobs without affecting focus or other aberrations.[234] Bokeh is now a normal lens design parameter for very high quality lenses. However, bokeh is virtually irrelevant 1.1. HISTORY OF PHOTOGRAPHIC LENS DESIGN 23

for the tens of millions of very small sensor digital point-and-shoot cameras sold every year. Their very short focal length and small aperture lenses have enormous depth-of-field – almost nothing is out of focus. Since wide aperture lenses are rare today, most contemporary photographers confuse bokeh with shallow depth-of-field, having never seen either. Many are even unaware of their existence.

1.1.22 Improving standards of quality

Lenses have improved over time. On average, lenses are sharper today than they were in the past.[235] Image format sizes have been steadily shrinking over the last two centuries, while standard print sizes have stayed about the same. Today’s lenses have higher resolving power than lenses of past eras to maintain an equal level of print quality with the required higher level of enlargement. For example: the human eye can resolve about five lines per millimeter at distance of one foot (about 30 cm). Therefore, a lens must produce a minimum resolution of forty lines per millimeter on a 24×36 mm 35mm film negative if it to provide a linear enlargement of eight times to an 8×10 inch (about 20×25 cm) print and still appear sharp when viewed at one foot.[236] Optical engineers make use of more exact lens formulae. In the nineteenth century, opticians dug to the level of the Seidel aberrations, called mathematically the third-order aberrations, to reach basic anastigmatic correction. Opticians needed to calculate for the fifth-order aberrations by the mid-twentieth century to produce a high-quality lens.[237] Today’s lenses require seventh order aberration solutions.[238] The best photographic lenses of yesteryear were of high image quality (twice the minimum resolution mentioned above) and it may not be possible to conclusively demonstrate the superiority of the best of today’s lens without comparing 20×30 inch (about 50×75 cm) enlargements of exactly the same scene side by side.[239][240]

1.1.23 Inexpensive asphere

Main article: Typical lens elements have spherically curved surfaces. However, this causes off-axis light to be focused closer to the lens than axial rays (spherical aberration); especially severe in wide angle or wide aperture lenses. This can be pre- vented by using elements with convoluted aspheric curves. Although this was theoretically proven by René Descartes in 1637,[241] the grinding and polishing of aspheric glass surfaces was extremely difficult and expensive.[242][243] The first camera lens with an inexpensive mass-produced molded glass aspheric element was the unnamed 12.5mm f/2.8 lens built into the Kodak Disc 4000, 6000 and 8000 (USA) cameras in 1982. It was said to be capable of resolving 250 lines per millimeter. The four element lens was a Triplet with an added rear field-flattener. The Kodak Disc cameras contained very sophisticated . They also had a lithium battery, microchip electronics, programmed autoexposure and motorized film wind for US$68 to US$143 list. It was the Disc film format that was unable to record 250 lpm.[244] Kodak began using mass-produced plastic aspheres in viewfinder optics in 1957, and the Kodak Ektramax (USA) Pocket 110 cartridge film camera had a built-in Kodak Ektar 25mm f/1.9 lens (also a four element Triplet) with a molded plastic aspheric element in 1978 for US$87.50 list.[245] Plastic is easy to mold into complex shapes that can include an integral mounting flange.[246] However, glass is superior to plastic for lens making in many respects – its refractive index, temperature stability, mechanical strength and variety is higher.[247]

1.1.24 Autofocus lens

Main article: Autofocus

Since autofocus is primarily an electromechanical feature of the camera, not an optical one of the lens, it did not greatly influence lens design. The only changes wrought by AF were mechanical adaptations: the popularity of “internal focusing”, the switch back to “two touch” zooming and the inclusion of AF motors or driveshafts, gearing and electronic control microchips inside the lens shell.[248] However, for the record: the first autofocus lens for a still camera was the Konishiroku Konica Hexanon 38mm f/2.8[249] built into the Konica C35 AF (1977, Japan) 35mm point-and-shoot; the first autofocus lens for an SLR camera was the unnamed 116mm f/8[250] built into the Polaroid SX-70 Sonar (1978, USA) instant film SLR; the first interchangeable autofocus SLR lens was the Ricoh AF Rikenon 50mm f/2 (1980, Japan, for any Pentax K mount 24 CHAPTER 1. DAY 1

35mm SLR),[251] which had a self-contained passive electronic rangefinder AF system in a bulky top-mounted box; the first dedicated autofocus was the five electrical contact pin Pentax K-F mount on the Asahi Optical Pentax ME F (1981, Japan) 35mm SLR camera with a TTL phase detection AF system for its unique SMC Pentax AF 35mm-70mm f/2.8 Zoom Lens;[252] the first built-in TTL autofocus SLR lens was the Opcon/Komine/Honeywell Vivitar Series 1 200mm f/3.5 (1984, USA/Japan, for most 35mm SLRs),[253] which had a self-contained TTL passive phase detection AF system in an underslung box and the first complete autofocus lens line was the twelve Minolta AF A mount lenses (24mm f/2.8, 28mm f/2.8, 50mm f/1.4, 50mm f/1.7, 50mm f/2.8 Macro, 135mm f/2.8, 300mm f/2.8 APO, 28-85mm f/3.5-4.5, 28-135mm f/4-4.5, 35-70mm f/4, 35-105mm f/3.5-4.5 and 70- 210mm f/4)[254] introduced with the Minolta Maxxum 7000 (1985, Japan) 35mm SLR and its TTL passive phase detection AF system.

1.1.25 Image-stabilized lens

Main article:

In 1994, the unnamed 38-105mm f/4-7.8 lens built into the Nikon Zoom-Touch 105 VR (Japan) 35mm point-and- shoot camera was the first consumer lens with built-in image stabilization.[255] Its Vibration Reduction system could detect and counteract handheld camera/lens unsteadiness, allowing sharp photographs of static subjects at shutter speeds much slower than normally possible without a . Although image stabilization is an electromechanical breakthrough, not optical, it was the biggest new feature of the 1990s. The Canon EF 75-300mm f/4-5.6 IS USM (Japan)[256] of 1995 was the first interchangeable lens with built-in image stabilization (called Image Stabilizer; for Canon EOS 35mm SLRs). Image stabilized lenses were initially very expensive and used mostly by professional photographers.[257] Stabilization surged into the amateur digital SLR market in 2006.[258][259][260][261][262] However, the Konica Minolta Maxxum 7D (Japan) digital SLR introduced the first camera body-based stabilization system in 2004[263] and there is now a great engineering and marketing battle over whether the system should be lens-based (counter-shift lens elements) or camera-based (counter-shift ).[264][265]

1.1.26 Diffractive optic lens

With computer-aided design, aspherics, multicoating, very high /low dispersion glass and unlimited budget, it is now possible to control the monochromatic aberrations to almost any arbitrary limit – subject to the absolute diffraction limit demanded by the laws of physics. However, chromatic aberrations remain resistant to these solutions in many practical applications. In 2001, the Canon EF 400mm f/4 DO IS USM (Japan) was first diffractive optics lens for consumer cameras (for Canon EOS 35mm SLRs).[266] Normally photographic cameras use refractive lenses (with the occasional reflective mirror) as their image forming optical system. The 400 DO lens had a multilayer diffractive element containing concentric circular diffraction gratings to take advantage of diffraction’s opposite color dispersion (compared to re- fraction) to correct chromatic and spherical aberrations with less low dispersion glass, fewer aspheric surfaces and less bulk.[267][268][269] As of 2010, there have been only two expensive professional level diffractive optics lenses for consumer cameras,[270] but if the technology proves useful, prices will drop and its popularity will rise.

1.1.27 Lenses in the digital era

In 2004, the Kodak (Sigma) DSC Pro SLR/c (USA/Japan) digital SLR was loaded with optical performance profiles on 110 lenses so that the on-board computer could correct the lateral chromatic aberration of those lenses, on-the-fly as part of the capture process.[271] Also in 2004, DO Labs DxO Optics Pro (France) computer software modules were introduced, loaded with information on specific cameras and lenses, that could correct distortion, vignetting, blur and lateral chromatic aberration of images in post-production.[272] Lenses have already appeared whose image quality would have been marginal or unacceptable in the film era, but are acceptable in the digital era because the cameras for which they are intended automatically correct their defects. For example, onboard automatic software image correction is a standard feature of 2008’s Micro Four Thirds digital format. Images from the 2009 14-140mm f/4-5.8 G VARIO ASPH. MEGA O.I.S. and the 2010 1.1. HISTORY OF PHOTOGRAPHIC LENS DESIGN 25

Olympus M. Zuiko Digital 14-150mm f/4-5.6 ED lenses (both Japan) have their severe barrel distortion at the wide angle settings automatically reduced by a Panasonic DMC-GH1 and Olympus Pen E-, respectively. The Panasonic 14-140mm lens also has its chromatic aberration corrected. (Olympus has not yet implemented chromatic aberration correction.)[273][274]

1.1.28 References

[1] Rudolf Kingslake, A history of the photographic lens, page 23

[2] Michael R. Peres, Focal encyclopedia of photography: digital imaging, theory and applications, page 55

[3] Todd Gustavson, Camera: A From Daguerreotype to Digital. New York, NY: Sterling Innova- tion/Sterling Publishing Co., Inc., 2009. ISBN 978-1-4027-5656-6. pp 8-9.

[4] Colin Harding, Classic Cameras. Lewes, East Sussex, UK: Photographers’ Institute Press, 2009. ISBN 978-1-86108-529-0. pp 18-19.

[5] Kingslake 1989, pp. 23-26, 307.

[6] Gernsheim 1969, p. 61.

[7] Kingslake 1989, p. 136.

[8] Kingslake 1989, p. 25.

[9] Kingslake 1989, pp. 27-28.

[10] Peres 2007, p. 158.

[11] Michael R. Peres, Focal encyclopedia of photography: digital imaging, theory and applications, page 158

[12] Kingslake 1989, p. 25.

[13] Kingslake 1989, pp. 35-36.

[14] Kingslake 1989, p. 37.

[15] Robert G. Mason and Norman Snyder; editors, The Camera. Life Library of Photography. New York, NY: TIME-LIFE Books, 1970. No ISBN. pp 135, 140-141.

[16] Wade, Short History. pp 18, 20.

[17] Kraszna-Krausz, p 836.

[18] Kingslake 1989, pp. 37, 263, 299.

[19] Peres 2007, p. 159.

[20] Kingslake 1989, pp. 3-4, 289.

[21] Kingslake 1989, pp. 49-50.

[22] George Gilbert, Collecting Photographica: The Images and Equipment of the First Hundred Years of Photography. New York, NY: Hawthorn/Dutton, 1976. ISBN 0-8015-1407-X. pp 90-92.

[23] Mason and Snyder, pp 148-149.

[24] Charles Harrison and Joseph Schnitzer, Lens For Photographic Cameras. United States Patent #35,605: granted 17 June 1862.

[25] Kingslake 1989, pp. 52-53.

[26] Peres 2007, p. 160.

[27] Kingslake 1989, pp. 49-50.

[28] Kraszna-Krausz, pp 3-6, 1029-1030.

[29] Mark D. Licker; publisher, McGraw-Hill Encyclopedia of Science and Technology. 10th Edition. 20 Volumes. New York, NY: McGraw-Hill, 2007. ISBN 0-07-144143-3. Volume 1. Aberration (optics), pp 9-14. Volume 4. Chromatic aberration, pp 126-128. 26 CHAPTER 1. DAY 1

[30] Peres 2007, pp. 174, 716-717.

[31] Cox 1971, pp. 147-150, 198-200.

[32] Norman Goldberg, Camera Technology: The Dark Side of the Lens. San Diego, CA: Academic Press, 1992. ISBN 0-12- 287570-2. pp 255-257.

[33] Lester Lefkowitz, “Lenses: Facts and Fallacies,” pp 75-98. Modern Photography, Volume 47, Number 9; September 1983. ISSN 0026-8240.

[34] Peres 2007, p. 717.

[35] Kingslake 1989, pp. 59-62.

[36] Peres 2007, p. 167.

[37] Kingslake 1989, p. 8.

[38] Kraszna-Krausz, p 453.

[39] Kraszna-Krausz, p 438.

[40] Dan Richards, “Lens Special: Behind The Glass: Lessons from 444 lens tests.” pp 74-79. Popular Photography, Volume 72 Number 2; February 2008. ISSN 1542-0337.

[41] Kingslake, p 10.

[42] Kraszna-Krausz, pp 436-437.

[43] Ray, Photographic Lens. pp 84-85.

[44] Kingslake, p 12.

[45] Kraszna-Krausz, p 136, 454.

[46] Charles Harrison and Joseph Schnitzer, Diaphragm For Photographic Cameras. United States Patent #21,470: granted 7 September 1858.

[47] Kingslake, p 11.

[48] Kingslake, pp 12-13.

[49] Kraszna-Krausz, p 439.

[50] Ray, Photographic Lens. p 83.

[51] Ray, Photographic Lens. pp 166-167.

[52] Kingslake, p 131.

[53] Kingslake, p 191.

[54] Ray, Photographic Lens. pp 196-197.

[55] Kingslake, pp 133-134.

[56] Kingslake, pp 135-137.

[57] Paul Rudolph, Photographic Objective. United States Patent #444,714; granted 13 January 1891.

[58] Kingslake, pp 82-83.

[59] Peres, p 168.

[60] Kraszna-Krausz, p 838.

[61] Anonymous, “Too Hot To Handle,” p 67. Modern Photography, Volume 48, Number 10; October 1984. ISSN 0026-8240.

[62] Sidney F. Ray, Applied Photographic Optics. Third edition. Woburn, MA: Focal Press/Elsevier, 2002. ISBN 0-240-51540- 4. p 82.

[63] Kingslake, p 79.

[64] Ray, Photographic Lens. pp 34-36, 56, 166-167. 1.1. HISTORY OF PHOTOGRAPHIC LENS DESIGN 27

[65] Bennett Sherman, “Techniques Tomorrow: New glasses make the optical scene brighter and clearer. What are they and what are they doing?" pp 10, 14. Modern Photography, Volume 48 Number 8; August 1984. ISSN 0026-8240.

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[67] Bennett Sherman, “Techniques Tomorrow: A quick inside look at what makes those big lenses so big, so expensive, so special.” pp 27, 36. Modern Photography, Volume 48, Number 2; February 1984. ISSN 0026-8240.

[68] Bennett Sherman, “Techniques Tomorrow: Just what goes into the new ED glass tele lenses that makes them bigger, better?" pp 8, 43. Modern Photography, Volume 49, Number 5; May 1985. ISSN 0026-8240.

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[71] Kingslake, pp 103-106.

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[73] Paul Rudolph, Photographic Objective. United States Patent #721,240; granted 24 February 1903.

[74] Kingslake, pp 86-88

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[81] Jason Schneider, “The Camera Collector: You can't beat the system. Leitz knew that over 50 years ago, and proceeded to give us the world’s first 'system 35.'" pp 54-56. Modern Photography, Volume 48 Number 6; June 1984. ISSN 0026-8240.

[82] Die Leica, 1933 No. 6. “Was ist eigentlich “Elmar"?

[83] Ludwig Bertele, Photographic Lens. United States Patent #1,584,271; granted 11 May 1926.

[84] Jason Schneider, “The Camera Collector: The Ermanox Legend, or how a super-fast lens turned a conventional camera into the darling of the press corps.” pp 22, 30-31, 68, 132. Modern Photography, Volume 47 Number 7; July 1983. ISSN 0026-8240.

[85] Kingslake, p 112.

[86] Mason and Snyder, p 164.

[87] Ludwig Bertele, Objective. United States Patent #1,975,678; granted 2 October 1934.

[88] Kingslake, pp 117-118.

[89] Jason Schneider, “The Camera Collector: Zeiss-Ikon’s answer to the Leica was the Contax, a camera praised and damned for its brilliantly complex design.” pp 18, 22-23, 150. Modern Photography, Volume 48, Number 10; October 1984.

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[91] “EF50mm f/1.4 USM”. Canon Camera Museum. Retrieved 2016-10-26. 28 CHAPTER 1. DAY 1

[92] AF Nikkor 50mm f/1.4D

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[94] Cox, pp 215-218.

[95] Cox, p 222.

[96] Kraszna-Krausz, p 440.

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[98] Kingslake, pp 16-17.

[99] Harold Dennis Taylor, A Method of Increasing the Brilliancy of the Images Formed by Lenses. United Kingdom Patent #GB29,561 (1904); granted 23 November 1905.

[100] Horder, pp 74-77.

[101] Kraszna-Krausz, pp 260-261, 835, 842, 851.

[102] Firma Carl Zeiss, Jena, Verfahren zur Erhöhung der Lichtdurchlässigkeit optischer Teile durch Erniedrigung des Brechung- sexponenten an den Grenzflächen dieser optischen Teile. (Method to increase the light transmittance of optical parts through decrease of the refraction exponent at the interfaces of these optical parts.) German Patent #685,767; granted 30 November 1939.

[103] Ray, Photographic Lens. pp 30-31, 74-75.

[104] Anonymous, “Letters: Zeiss lens confusion,” p 98. Popular Photography, Volume 63 Number 1; January 1999. ISSN 0032-4582. “Noncoated Zeiss lenses are pre-1939. Beginning in '39 and continuing postwar, all Zeiss lenses, East and West, were coated.”

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[106] Stephen Gandy, “The 1941 Kodak Ektra,” from http://www.cameraquest.com/ektra.htm retrieved 5 January 2006.

[107] Ray, Photographic Lens. p 152.

[108] Herbert Keppler, “SLR: Perspective, Controlled: What’s your personal focal? Here’s how I found mine.” pp 28, 30, 32. Popular Photography & Imaging, Volume 69 Number 3; March 2005. ISSN 1542-0337.

[109] Ray, Photographic Lens. p 152.

[110] Danilo Cecchi, and Pentax SLR 35mm Cameras: 1952-1989. Susan Chalkley, translator. Hove Collector’s Guide. Hove, Sussex, UK: Hove Foto Books, 1991. ISBN 0-906447-62-3. pp 96-98.

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[113] Anonymous, HOYA Filters: The Difference is Clear: All Filters Are Not Created Equal! Long Beach, CA: THK Photo Products, no publication date, but circa 2009. p 56.

[114] Cox, pp 214-215, 230-231.

[115] Kraszna-Krausz, p 843.

[116] Bennett Sherman, “Techniques Tomorrow: Veiled threats from inside your camera may be lighting up your pictures in the wrong spots.” pp 40-41, 44, 132. Modern Photography, Volume 48, Number 10; October 1984. ISSN 0026-8240.

[117] Kingslake, pp 142-143.

[118] Kraszna-Krausz, pp 1675-1676.

[119] Herbert Keppler, “SLR: Are the sacrifices we make to use an SLR worth it?" pp 27-28, 30, 34. Popular Photography, Volume 64 Number 6; June 2000. ISSN 0032-4582.

[120] Ray, Photographic Lens. pp 166-167.

[121] Ray, Photographic Lens. pp 160-161.

[122] Kraszna-Krausz, p 840. 1.1. HISTORY OF PHOTOGRAPHIC LENS DESIGN 29

[123] Aguila and Rouah, pp 129-130.

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[129] Kingslake, pp 150-152.

[130] Leslie Stroebel and Richard Zakia; editors, The Focal Encyclopedia of Photography. 3rd ed. Stoneham, MA: Focal Press/Butterworth-Heinemann, 1993. ISBN 0-240-80059-1. pp 423, 434-435.

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[133] Robin Hill and R. & J. Beck, Ltd., Improvements in Photographic Lenses. United Kingdom Patent #GB225,398; granted 4 December 1924.

[134] Kraszna-Krausz, p 747.

[135] Stroebel and Zakia, p 432.

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[138] Kraszna-Krausz, p 901.

[139] Bob Schwalberg, “Historical Focus,” p 8. Popular Photography, Volume 95, Number 2; February 1988. ISSN 0032-4582.

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[142] Kingslake, pp 101-102.

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[145] Bob Schwalberg, “History of Macro Lenses,” p 79. Popular Photography, Volume 94 Number 11; November 1987. ISSN ISSN 0032-4582.

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[147] Lefkowitz, p 95.

[148] Kraszna-Krausz, pp 1485, 1488.

[149] Kingslake, p 182.

[150] Cox, pp 290-292.

[151] Ray, Photographic Lens. pp 198-199.

[152] Kraszna-Krausz, p 1488.

[153] Kingslake, pp 182-183.

[154] Kraszna-Krausz, p 846. 30 CHAPTER 1. DAY 1

[155] Jason Schneider, “The Camera Collector: A farewell to the twin-lens Rolleiflex: elegant to the end. It never switched lenses or lowered its patrician standards.” pp 82, 86, 92-93, 136. Modern Photography, Volume 47, Number 11; November 1983. ISSN 0026-8240.

[156] Anonymous, “Canon: Spring/Summer 2010. Digital Camera Full Product Guide: EOS: Powershot.” Lake Success, NY: Canon U.S.A. Inc., 5/2010. pp 49, 51.

[157] Anonymous, “Nikon Digital Product Guide. Fall 2010.” Melville, NY: Nikon Inc., 10/2010. pp 60, 73.

[158] Kingslake, pp 188-199.

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[161] Kingslake, pp 155-156.

[162] Frank G. Back, Reflex Camera Varifocal Lens. United States Patent #2,902,901; granted 8 September 1959.

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[165] Kouichi Oshita, “Japan’s First Compact Zoom Lens with Practical Use: Tale Four: Zoom-NIKKOR Auto 43-86mm f/3.5,” from http://www.nikon.co.jp/main/eng/portfolio/about/history/nikkor/n04_e.htm retrieved 28 February 2006.

[166] Gandy, “Historic Zoomar.”

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[168] Kingslake, p 170.

[169] Jason Schneider, “The Camera Collector: Auto and match-needle exposure, instant-return mirror and diaphragm plus full finder information in an early-60s SLR? Alas, it was too good to be really reliable.” pp 24, 26, 28, 32, 34, 144. Modern Photography, Volume 45 Number 9; September 1981. ISSN 0026-8240.

[170] “Too Hot To Handle."June 1985. p 51.

[171] Herbert Keppler, “Keppler’s SLR Notebook: Good Grief! Three Series 1 70-210 Vivitar Zooms???" pp 35, 74. Modern Photography, Volume 48 Number 8; August 1984. ISSN 0026-8240.

[172] Bennett Sherman, “Techniques Tomorrow: It’s still back to the basics when it comes to computing a lens design.” pp 52-53. Modern Photography, Volume 47 Number 7; July 1983. ISSN 0026-8240.

[173] Bennett Sherman, “Techniques Tomorrow: You still need time, and a computer, to zoom in on the good zoom lens design,” pp 27-28. Modern Photography, Volume 47 Number 8; August 1983. ISSN 0026-8240.

[174] Cox, pp 296, 302-304.

[175] Rinzo Watanabe and Ellis I. Betensky, Zoom Lens Having Close-Up Focusing Mode of Operation. United States Patent #3,817,600; granted 18 June 1974.

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[178] Herbert Keppler, “SLR Notebook: Zoom Lens Choice Not Easy For Me,” pp 44-45. Modern Photography, Volume 48, Number 4; April 1984. ISSN 0026-8240.

[179] Anonymous, “Modern Tests: Pentax IQZoom: First Point-And-Shoot 35 With Built-in Zoom,” pp 54-59, 96. Modern Photography, Volume 51, Number 5; May 1987. ISSN 0026-8240.

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[181] Anonymous, “History of Single-Lens Reflex (SLR) Cameras: Debut of Nikon F3,” from http://www.nikon.co.jp/main/ eng/portfolio/about/history/d-archives/camera/history-f3.htm retrieved 27 June 2005. 1.1. HISTORY OF PHOTOGRAPHIC LENS DESIGN 31

[182] Efthimia Bilissi, Michael Langford, Langford’s Advanced Photography, CRC Press - 2013, page 72

[183] Anonymous, “More What’s New For '85: Kiron stretches zoom range from 28mm to 210mm!!" p 58. Modern Photography, Volume 48 Number 12; December 1984. ISSN 0026-8240.

[184] Anonymous, “Modern Tests: Wide Ranging 28-210 One-Touch Kiron,” pp 52-53, 75. Modern Photography, Volume 50 Number 1; January 1986. ISSN 0026-8240.

[185] Herbert Keppler, “Keppler’s SLR Notebook: Wide to Tele Zooms Keep Sizes Down,” pp 48-49, 90. Modern Photography, Volume 49 Number 6; June 1985. ISSN 0026-8240.

[186] Peter Kolonia, “Not you father’s Superzoom: Once scorned by serious shooters, superzooms are getting serious” pp 90-91. Popular Photography & Imaging, Volume 69 Number 8; August 2005. ISSN 1542-0337.

[187] Mark Goldstein, “Tamron AF 16-300mm F/3.5-6.3 Di II VC PZD Review”, http://www.photographyblog.com/reviews/ tamron_af_16_300mm_f3_5_6_3_di_ii_vc_pzd_review/

[188] Andrew Brandt, et al, “Dawn of the Megazooms: For many photographers, a powerful optical zoom may be more valuable than a mountain of megapixels. These advanced point-and-shoot cameras let you pull in a tight shot from very far away.” pp 101-106. PC World, Volume 26 Number 8; August 2008. ISSN 0737-8939.

[189] Cox, pp 286-288.

[190] Ray, Photographic Lens. pp 150-151.

[191] Anonymous, “Modern Tests: Super Small 70-210 f/4-5.6 Tokina,” pp 57, 64. Modern Photography, Volume 50, Number 4; April 1986. ISSN 0026-8240.

[192] Anonymous, “Modern Tests: Vivitar Series 1 70-210 f/2.8-4 Zoom,” pp 58-59. Modern Photography, Volume 49, Number 3; March 1985. ISSN 0026-8240.

[193] Herbert Keppler, “Keppler’s SLR Notebook: Is Smaller More Loveable In Zooms?" pp 106, 108. Modern Photography, Volume 49 Number 12; December 1985. ISSN 0026-8240.

[194] Herbert Keppler, “Keppler’s SLR Notebook: Super Stretch Zooms: Do You Lose Picture Quality?" pp 34-35, 74. Modern Photography, Volume 50 Number 6; June 1986. ISSN 0026-8240.

[195] Jason Schneider, “How to: Check that Your Zoom Stays in focus,” p 76. Popular Photography, Volume 63 Number 10; October 1999. ISSN 0032-4582.

[196] Peres, p 735.

[197] Jacob Deschin, “Japanese Camera: 35mm Nikon and Lenses Tested by Experts,” p X21. The New York Times; 10 Decem- ber 1950. ISSN 0362-4331.

[198] Kouichi Ohshita, “Legendary Lens: Tale 36: Nikkor P.C 8.5 cm f/2.” from http://imaging.nikon.com/history/nikkor/36/ index.htm retrieved 9 January 2008.

[199] Simon Stafford and Rudi Hillebrand & Hans-Joachim Hauschild, The New Nikon Compendium: Cameras, Lenses & Ac- cessories since 1917. 2004 Updated North American Edition. Asheville, NC: Lark Books, 2003. ISBN 1-57990-592-7. pp 5, 11.

[200] Herbert Keppler, “Inside Straight: Rating Game: Why and how photographers went crazy testing lenses,” pp 36-37. Popular Photography & Imaging, Volume 71 Number 11; November 2007. ISSN 1542-0337.

[201] Herbert Keppler, “Whatever Happened to The Japan Camera Inspection Institute? Until 1989 no one would purchase Japanese photo products unless they carried this seal. But where is JCII now?" pp 32, 217. Popular Photography, Volume 64 Number 3; March 2000. ISSN 0032-4582.

[202] Herbert Keppler, “SLR: Calling the Shots: How the Japanese watchdog group CIPA is winning (and losing) the battle over digital camera power ratings,” pp 30, 32-33. Popular Photography & Imaging, Volume 70 Number 1; January 2006. ISSN 1542-0337.

[203] Haruo Sato, “Best-selling Mid-range Telescopic Lens: Tale Five: AI Nikkor 105 mm f/2.5,” from http://www.nikon.co. jp/main/eng/portfolio/about/history/nikkor/n05_e.htm retrieved 28 February 2006.

[204] Herbert Keppler, “SLR: Good grief, what’s this combo?" p 33. Popular Photography & Imaging, Volume 68 Number 2; February 2004. ISSN 1542-0337. 32 CHAPTER 1. DAY 1

[205] Ivor Matanle, Collecting and Using Classic SLRs. First Paperback Edition. New York, NY: Thames and Hudson, 1997. ISBN 0-500-27901-2. Chapter 5 “How the West Was Lost – the 35mm focal-plane SLRs of post-war Western Europe,” pp 85-109.

[206] Small and Barringer, pp 133-137, 155-160.

[207] Kraszna-Krausz, pp 703, 805.

[208] Stephen Gandy, “Historic Early Zoom: Nikon 8.5 - 25 cm: 1st Japanese Zoom, 1st Tele Zoom,” from http://www. cameraquest.com/nf85250.htm retrieved 8 September 2003.

[209] Bob Shell, Canon Compendium: Handbook of the Canon System. Hove, UK: Hove Books, 1994. ISBN 1-897802-04-8. pp 32, 34, 97-98, 100.

[210] John Wade, “Classic Cameras: The Canon 7 And The 'Dream' Lens: Would You Believe f/0.95?" pp 140-141. Shutterbug, Volume 37 Number 6 Issue 451; April 2008. ISSN 0895-321X.

[211] Anonymous, “Too Hot To Handle.” p 51. Modern Photography, Volume 49, Number 6; June 1985. ISSN 0026-8240.

[212] Oshita, “Japan’s First Compact Zoom”

[213] Matanle, Chapter 5 pp 85-109.

[214] Jason Schneider, “How The Japanese Camera Took Over: Before we ever heard of it, the Japanese camera industry was already perfecting western designs. Then, after World War II, it exploded in a burst of brilliant creativity that shook the world.” pp 56-57, 78, 86. Modern Photography, Volume 48 Number 7; July 1984.

[215] Herbert Keppler, “SLR: Optical Alphabet Soup: Now we stir in the digital hot sauce,” pp 47-48, 50, 52. Popular Photog- raphy & Imaging, Volume 68 Number 11; November 2004. ISSN 1542-0337.

[216] Keppler, “Whatever Happened to the JCII?" pp 32, 217.

[217] Keppler, “Calling the Shots,” pp 30, 32-33.

[218] Herbert Keppler, “SLR: The CAT did it: Want a tiny 500mm supertele for $100 or maybe $69? Read on.” pp 34, 36, 38, 40. Popular Photography & Imaging, Volume 67 Number 8; August 2003 . ISSN 1542-0337.

[219] About adaptall-2.org - the 500mm F/8 Tele-Macro Catadioptric

[220] Anonymous, “Modern Tests: 250mm f/5.6 Minolta Mirror Telephoto,” pp 118, 120. Modern Photography, Volume 44 Number 8; August 1980. ISSN 0026-8240.

[221] Anonymous, Astronomy 2009-2010: Telescopes, Accessories. (Celestron catalogue.) No publication data. pp 27, 29, 41.

[222] Anonymous, Find Your Telescope. Find Yourself. (Meade 2009 catalogue.) No publication data. pp 66, 85.

[223] Ellis I. Betensky, “Handbook of Optics. Volume II. page 16.2.” from http://www.opconassociates.com/book/physics162. htm retrieved 30 June 2010.

[224] Ray, Photographic Lens. p 160.

[225] Kouichi Oshita, “The First Lens equipped with the Close-Range-Correction Mechanism: Tale 14: NIKKOR-N Auto 24 mm f/2.8,” from http://imaging.nikon.com/products/imaging/technology/nikkor/n14_e.htm retrieved 28 February 2006.

[226] Anonymous. “Modern Tests: Two Nikon 200s [f/2 Nikkor ED; f/4 Micro-Nikkor]: Fast Or Close,” pp 102-103. Modern Photography, Volume 45 Number 5; May 1981. ISSN 0026-8240.

[227] Haruo Sato, “Press photographers’ favorite lens that witnessed a number of world records: Tale 31: Ai Nikkor 200 mm f/2S IF-ED,” from http://imaging.nikon.com/products/imaging/technology/nikkor/n31_e.htm retrieved 9 January 2008.

[228] Goldberg, pp 45-46.

[229] Herbert Keppler, “SLR: More strange adventures in focal lengths and apertures that are but aren't.” pp 14-16, 22. Popular Photography, Volume 61 Number 10; October 1997. ISSN 0032-4582.

[230] Jason Schneider, “Bokeh: Splendor In The Glass. There’s an elusive aspect of lens quality that may be as important as sharpness. Do your lenses have it?" pp 60, 62-63. Popular Photography & Imaging, Volume 69 Number 3; March 2005. ISSN 1542-0337.

[231] Keppler, “The CAT did it.” p 36. 1.1. HISTORY OF PHOTOGRAPHIC LENS DESIGN 33

[232] Peter Kolonia, “Lens Test: Long Shot: [Adorama] ProOptic 500mm f/6.3 mirror lens,” p 62. Popular Photography, Volume 73 Number 3; March 2009. ISSN 1542-0337.

[233] Bennett Sherman, “Techniques Tomorrow: The picture may be out of focus, but now someone’s doing something about it,” pp 10, 12, 48. Modern Photography, Volume 47 Number 10; October 1983. ISSN 0026-8240.

[234] Shuji Ogino, et al, Variable Soft Focus Lens System. United States Patent #4,214,814; granted 29 July 1980.

[235] Herbert Keppler, “SLR: How to find your way out of the lens test –or maybe get more entangled in it?" pp 40, 42, 44, 11279. Popular Photography, Volume 66 Number 6; June 2002.

[236] Bennett Sherman, “Techniques Tomorrow: Resolving the dilemma of the resolving power figures used for lenses by MOD- ERN’s test lab,” pp 10, 12, 141. Modern Photography, Volume 47, Number 11; November 1983. ISSN 0026-8240.

[237] Cox, pp 106-107, 110-111, 116, 120, 122-123, 136.

[238] Sidney F. Ray, Applied Photographic Optics. p 82.

[239] Herbert Keppler, “SLR: Can you see the difference in pictures shot with a super-high-quality modern lens and an inexpensive old SLR lens?" pp 26-27. Popular Photography, Volume 65 Number 5; May 2001.

[240] Herbert Keppler, “SLR: Are cameras and lenses better and often cheaper than 'the good old days?' Believe it!" pp 21-22, 89, 111. Popular Photography, Volume 65 Number 7; July 2001.

[241] Watson, pp 91-92, 114.

[242] Kingslake, pp 4, 15-16.

[243] Ray, Photographic Lens. pp 50-51, 110-111.

[244] Anonymous, “Really New: Kodak’s new Disc: snapshot system of the century,” pp 63-65. Modern Photography, Volume 46 Number 4; April 1982. ISSN 0026-8240.

[245] Paul L. Rubin, “Design and use of mass-produced aspheres at Kodak,” pp 1682-1688. Applied Optics, Volume 24 Issue 11; 1 June 1985. ISSN 0003-6935.

[246] Kingslake, p 78.

[247] Licker, Volume 12. Optical materials, pp 442-447.

[248] Goldberg, pp 45-46, 211-217.

[249] Anonymous, “Modern Tests: Konica C35AF: First Auto-Focus Still Camera,” pp 136-139. Modern Photography, Volume 43, Number 4; April 1979. ISSN 0026-8240.

[250] Anonymous, “Annual Guide: 46 Top Cameras: Polaroid Sonar OneStep,” p 145. Modern Photography, Volume 42, Number 12; December 1978. ISSN 0026-8240.

[251] John Wade, The Collector’s Guide to Classic Cameras: 1945-1985. Small Dole, UK: Hove Books, 1999. ISBN 1-897802- 11-0. pp 165-166.

[252] Anonymous, “Modern Tests: Pentax ME-F: 35mm Auto-Focus SLR,” pp 110-117. Modern Photography, Volume 46, Number 5; May 1982. ISSN 0026-8240.

[253] Herbert Keppler, “Keppler’s SLR Notebook: [Vivitar Series 1 200mm f/3.5] Autofocus Through-Lens Tele For 35mm SLRs Focuses Faster, Sharper Than You Can!!" pp 42-43. Modern Photography, Volume 48, Number 10; October 1984. ISSN 0026-8240.

[254] Anonymous, “Modern Tests: Minolta Maxxum [7000]: First 35mm autofocus SLR system,” pp 56-65, 67-68. Modern Photography, Volume 49, Number 8; August 1985. ISSN 0026-8240.

[255] Anonymous, Nikon Full Line Product Guide, Spring/Summer 1994. Melville, NY: Nikon Inc., 1994. Nikon Zoom-Touch 105 VR QD, p 71.

[256] Anonymous, “Test: Canon EF 75-300[mm] f/4-5.6 IS,” pp 76-77, 169. Popular Photography, Volume 60, Number 2; February 1996. ISSN 0032-4582.

[257] Peter Kolonia and Dan Richards, “Canon Image Stabilization VS Nikon Vibration Reduction,” pp 62, 64, 66, 68, 204. Popular Photography, Volume 65 Number 9; September 2001. ISSN 0032-4582.

[258] Anonymous, “Lens Test: Canon 17-85mm f/4-5.6 IS USM EF-S: Stellar Step Up,” pp 64-65. Popular Photography & Imaging, Volume 70 Number 1; January 2006. ISSN 1542-0337. 34 CHAPTER 1. DAY 1

[259] Michael J. McNamara, “Test: Alpha 100 DSLR: Mix Master: Blending a proven DSLR, 10.2MP sensor, and cool technology,” pp 64, 66, 68. Popular Photography & Imaging, Volume 70 Number 9; September 2006.

[260] Michael J. McNamara, “Test: Pentax K100D: Kid Rock: Shoot sharp and stay steady,” pp 64-67. Popular Photography & Imaging, Volume 70 Number 10; October 2006. ISSN 1542-0337.

[261] Julia Silber, “Lens Test: Nikon 18-200mm f/3.5-5.6G DX VR AF-S: Super Superzoom,” p 67. Popular Photography & Imaging, Volume 70 Number 4; April 2006. ISSN 1542-0337.

[262] Julia Silber, “Lens Test: Canon 70-300mm f/4-5.6 IS USM AF: Long and Strong,” p 65. Popular Photography & Imaging, Volume 70 Number 6; June 2006. ISSN 1542-0337.

[263] Herbert Keppler, “First Look: Konica Minolta Maxxum 7D: Anti-Shake Shake-Up: The anti-shake’s in the body!" p 56. Popular Photography & Imaging, Volume 68, Number 10; October 2004. ISSN 1542-0337.

[264] Michael J. McNamara, “Stop the Shake: Lens Vs. Sensor Shift: What’s the Real Difference?" pp 74-75. Popular Photog- raphy & Imaging, Volume 71 Number 10; October 2007. ISSN 1542-0337.

[265] Mike Stensvold, “Image Stabilization: When you can't or won't use a tripod, these technologies steady your hand,” pp 68-70, 72, 74. Outdoor Photographer, Volume 23 Number 2; March 2007. ISSN 0890-5304.

[266] “EF400mm f/4 DO IS USM”. Canon Camera Museum. Retrieved 2016-10-26.

[267] “Lenses: Multi-layer Diffractive Optical Element”. Canon. Retrieved 2016-10-26.

[268] “DO Lens: A Compact, Reduced-Weight Telephoto Lens”. Canon. Retrieved 2016-10-26.

[269] Herbert Keppler, “News: How Canon will cut the weight & size of tele lenses by about one-third.” pp 62-63, 148. Popular Photography, Volume 65 Number 1; January 2001. ISSN 0032-4582.

[270] Anonymous, Canon Technology Highlights: 2008. (Promotional booklet) Tokyo, Japan: Canon Inc., 2008. p 23.

[271] Michael J. McNamara, “Test: Kodak DCS Pro SLR/c: Kodak’s Canon Takes Aim…: But does it hit the Mark II?" pp 52-55. Popular Photography & Imaging, Volume 68 Number 9; September 2004. ISSN 1542-0337.

[272] Debbie Grossman, “Review: DxO Optics Pro: Optical Illusion: Do you really need a pricey DSLR lens? This $127 software says you don't.” pp 66-67. Popular Photography & Imaging, Volume 68 Number 9; September 2004. ISSN 1542-0337.

[273] Lars Rehm & Andy Westlake, “Panasonic Lumix DMC-GH1 Review,” from http://www.dpreview.com/reviews/panasonicdmcgh1/ page17.asp dated July 2009, retrieved 9 September 2010.

[274] Andy Westlake, “Olympus M. Zuiko Digital ED 14-150mm 1:4-5.6 review,” from http://www.dpreview.com/lensreviews/ olympus_m_14-150_4-5p6_o20/page3.asp dated June 2010, retrieved 9 September 2010.

1.1.29 Further reading

• Cox, Arthur (1971). Photographic Optics, a Modern Approach to the Technique of Definition. London: Focal Press. ISBN 0-8174-0665-4.

• Gernsheim, Helmut; Gernsheim, Alison (1969). The History of Photography: From the Camera Obscura to the Beginning of the Modern Era (2nd ed.). New York: McGraw-Hill. OCLC 55185.

• Kingslake, Rudolf (1989). A History of the Photographic Lens. Boston: Academic Press. ISBN 978-0-12- 408640-1. • Peres, Michael R. (2007). The Focal Encyclopedia of Photography: Digital Imaging, Theory and Applications, History, and Science (4th ed.). Boston: Elsevier/Focal Press. ISBN 978-0-240-80740-9. • Ray, Sidney F. (1992). The Photographic Lens (2nd ed.). Oxford: Focal Press. ISBN 0-240-51329-0. 1.1. HISTORY OF PHOTOGRAPHIC LENS DESIGN 35

Schneider Retina-Xenon C system 36 CHAPTER 1. DAY 1

Voigtländer-Zoomar 36-82mm f/2.8 1.1. HISTORY OF PHOTOGRAPHIC LENS DESIGN 37

Vivitar Series 1 70-210mm f/3.5

Fuji Fujinon-Z 43-75mm f/3.5-4.5 38 CHAPTER 1. DAY 1

Sigma 21-35mm f/3.5-4 1.1. HISTORY OF PHOTOGRAPHIC LENS DESIGN 39

Kiron 28-210mm f/4-5.6 (on a Nikon FM2N)

Tokina SZ-X 70-210mm f/4-5.6 SD 40 CHAPTER 1. DAY 1

Nippon Kogaku Nikkor-P Auto 10.5cm f/2.5 1.1. HISTORY OF PHOTOGRAPHIC LENS DESIGN 41

Nippon Kogaku Zoom-Nikkor Auto 43-86mm f/3.5 42 CHAPTER 1. DAY 1

Example of a catadioptric lens that uses rear surfaced mangin mirrors (Minolta RF Rokkor-X 250mm f/5.6) 1.1. HISTORY OF PHOTOGRAPHIC LENS DESIGN 43

Nippon Kogaku Nikkor-N Auto 24mm f/2.8 44 CHAPTER 1. DAY 1

Nippon Kogaku Nikkor 200mm f/2 ED IF

Minolta Varisoft Rokkor-X 85mm f/2.8 1.1. HISTORY OF PHOTOGRAPHIC LENS DESIGN 45

Kodak (Disc) aspheric 12.5mm f/2.8 46 CHAPTER 1. DAY 1

Kodak Ektar 25mm f/1.9 1.1. HISTORY OF PHOTOGRAPHIC LENS DESIGN 47

Canon EF 400mm f/4 DO IS USM Chapter 2

Day 2

2.1 Camera lens

This section is about the optical system. For the organism, see Kamera lens. A camera lens (also known as photographic lens or photographic objective) is an optical lens or assembly of

Different kinds of camera lenses, including wide angle, telephoto and speciality lenses used in conjunction with a camera body and mechanism to make images of objects either on photographic film or on other media capable of storing an image chemically or electronically. There is no major difference in principle between a lens used for a still camera, a , a telescope, a , or other apparatus, but the detailed design and construction are different. A lens might be permanently fixed to a camera, or it might be interchangeable with lenses of different focal lengths, apertures, and other properties. While in principle a simple convex lens will suffice, in practice a compound lens made up of a number of optical lens elements is required to correct (as much as possible) the many optical aberrations that arise. Some aberrations will be present in any lens system. It is the job of the lens designer to balance these and produce a design that is suitable for photographic use and possibly mass production.

48 2.1. CAMERA LENS 49

2.1.1 Theory of operation

Typical rectilinear lenses can be thought of as “improved” pinhole “lenses”. As shown, a pinhole “lens” is simply a small aperture that blocks most rays of light, ideally selecting one ray to the object for each point on the image sensor. Pinhole lenses have a few severe limitations:

• A with a large aperture is blurry because each is essentially the shadow of the aperture stop, so its size is no smaller than the size of the aperture (below left). Here a pixel is the area of the detector exposed to light from a point on the object. • Making the pinhole smaller improves resolution (up to a limit), but reduces the amount of light captured. • At a certain point, shrinking the hole does not improve the resolution because of the diffraction limit. Beyond this limit, making the hole smaller makes the image blurrier as well as darker.

Practical lenses can be thought of as an answer to the question “how can we modify a pinhole lens to admit more light and give a smaller spot size?" A first step is to put a simple convex lens at the pinhole with a focal length equal to the distance to the film plane (assuming the camera will take pictures of distant objects [1]). This allows the pinhole to be opened up significantly (below right) because a thin convex lens bends light rays in proportion to their distance to the axis of the lens, with rays striking the center of the lens passing straight through. The geometry is almost the same as with a simple pinhole lens, but rather than being illuminated by single rays of light, each image point is illuminated by a focused “pencil” of light rays. From the front of the camera, the small hole (the aperture), would be seen. The virtual image of the aperture as seen from the world is known as the lens’s entrance pupil; ideally, all rays of light leaving a point on the object that enter the entrance pupil will be focused to the same point on the image sensor/film (provided the object point is in the field of view). If one were inside the camera, one would see the lens acting as a projector. The virtual image of the aperture from inside the camera is the lens’s exit pupil. In this simple case, the aperture, entrance pupil, and exit pupil are all in the same place because the only optical element is in the plane of the aperture, but in general these three will be in different places. Practical photographic lenses include more lens elements. The additional elements allow lens designers to reduce various aberrations, but the principle of operation remains the same: pencils of rays are collected at the entrance pupil and focused down from the exit pupil onto the image plane.

2.1.2 Construction

Main articles: Photographic lens design and History of photographic lens design A camera lens may be made from a number of elements: from one, as in the Box 's meniscus lens, to over 20 in the more complex zooms. These elements may themselves comprise a group of lenses cemented together. The front element is critical to the performance of the whole assembly. In all modern lenses the surface is coated to reduce abrasion, flare, and surface reflectance, and to adjust . To minimize aberration, the curvature is usually set so that the angle of incidence and the angle of refraction are equal. In a prime lens this is easy, but in a zoom there is always a compromise. The lens usually is focused by adjusting the distance from the lens assembly to the image plane, or by moving elements of the lens assembly. To improve performance, some lenses have a cam system that adjusts the distance between the groups as the lens is focused. Manufacturers call this different things: Nikon calls it CRC (close range correction); Canon calls it a floating system; and and Mamiya call it FLE (floating lens element).[2] Glass is the most common material used to construct lens elements, due to its good optical properties and resistance to scratching. Other materials are also used, such as quartz glass, fluorite,[3][4][5][6] plastics like acrylic (Plexiglass), and even germanium and meteoritic glass.[7] Plastics allow the manufacturing of strongly aspherical lens elements which are difficult or impossible to manufacture in glass, and which simplify or improve lens manufacturing and performance. Plastics are not used for the outermost elements of all but the cheapest lenses as they scratch easily. Molded plastic lenses have been used for the cheapest disposable cameras for many years, and have acquired a bad reputation: manufacturers of quality optics tend to use euphemisms such as “optical resin”. However many modern, high performance (and high priced) lenses from popular manufacturers include molded or hybrid aspherical elements, so it is not true that all lenses with plastic elements are of low photographic quality. The 1951 USAF resolution test chart is one way to measure the resolving power of a lens. The quality of the material, coatings, and build affect the resolution. Lens resolution is ultimately limited by diffraction, and very few photographic lenses approach this resolution. Ones that do are called “diffraction limited” and are usually extremely expensive.[8] 50 CHAPTER 2. DAY 2

The zoom lens assembly of the Canon Elph

Today, most lenses are multi-coated in order to minimize lens flare and other unwanted effects. Some lenses have a UV coating to keep out the ultraviolet light that could taint color. Most modern optical cements for bonding glass elements also block UV light, negating the need for a UV filter. UV photographers must go to great lengths to find lenses with no cement or coatings. A lens will most often have an aperture adjustment mechanism, usually an iris diaphragm, to regulate the amount of light that passes. In early camera models a rotating plate or slider with different sized holes was used. These Waterhouse stops may still be found on modern, specialized lenses. A shutter, to regulate the time during which light may pass, may be incorporated within the lens assembly (for better quality imagery), within the camera, or even, rarely, in front of the lens. Some cameras with leaf shutters in the lens omit the aperture, and the shutter does double duty.

2.1.3 Aperture and focal length

The two fundamental parameters of an optical lens are the focal length and the maximum aperture. The lens’ focal length determines the magnification of the image projected onto the image plane, and the aperture the light intensity of that image. For a given photographic system the focal length determines the angle of view, short focal lengths giving a wider field of view than longer focal length lenses. A wider aperture, identified by a smaller f-number, allows using a faster for the same exposure.[9] The maximum usable aperture of a lens is specified as the focal ratio or f-number, defined as the lens’s focal length divided by the effective aperture (or entrance pupil), a dimensionless number. The lower the f-number, the higher light intensity at the focal plane. Larger apertures (smaller f-numbers) provide a much shallower depth of field than smaller apertures, other conditions being equal. Practical lens assemblies may also contain mechanisms to deal with measuring light, secondary apertures for flare reduction,[10] and mechanisms to hold the aperture open until the instant of exposure to allow SLR cameras to focus with a brighter image with shallower depth of field, theoretically allowing better focus accuracy. Focal lengths are usually specified in millimetres (mm), but older lenses might be marked in centimetres (cm) or inches. For a given film or sensor size, specified by the length of the diagonal, a lens may be classified as a:

• Normal lens: angle of view of the diagonal about 50° and a focal length approximately equal to the image diagonal. • Wide-angle lens: angle of view wider than 60° and focal length shorter than normal. 2.1. CAMERA LENS 51

• Long-focus lens: any lens with a focal length longer than the diagonal measure of the film or sensor.[11] Angle of view is narrower. The most common type of long-focus lens is the telephoto lens, a design that uses special optical configurations to make the lens shorter than its focal length.

A side effect of using lenses of different focal lengths is the different distances from which a subject can be framed, resulting in a different perspective. Photographs can be taken of a person stretching out a hand with a wideangle, a normal lens, and a telephoto, which contain exactly the same image size by changing the distance from the subject. But the perspective will be different. With the wideangle, the hands will be exaggeratedly large relative to the head. As the focal length increases, the emphasis on the outstretched hand decreases. However, if pictures are taken from the same distance, and enlarged and cropped to contain the same view, the pictures will have identical perspective. A moderate long-focus (telephoto) lens is often recommended for portraiture because the perspective corresponding to the longer shooting distance is considered to look more flattering. The widest aperture lens in history of photography is believed to be the Carl Zeiss Planar 50mm f/0.7,[12] which was designed and made specifically for the NASA Apollo lunar program to capture the far side of the moon in 1966. Three of these lenses were purchased by filmmaker Stanley Kubrick in order to film scenes in his movie Barry Lyndon, using candlelight as the sole light source.[13][14][15]

2.1.4 Number of elements

Main article: Photographic lens design

The complexity of a lens — the number of elements and their degree of asphericity — depends upon the angle of view, the maximum aperture, and intended price point, among other variables. An extreme wideangle lens of large aperture must be of very complex construction to correct for optical aberrations, which are worse at the edge of the field and when the edge of a large lens is used for image-forming. A long-focus lens of small aperture can be of very simple construction to attain comparable image quality: a doublet (two elements) will often suffice. Some older cameras were fitted with convertible lenses (German: Satzobjektiv) of normal focal length. The front element could be unscrewed, leaving a lens of twice the focal length, and half the angle of view and half the aperture. The simpler half-lens was of adequate quality for the narrow angle of view and small relative aperture. Obviously the bellows had to extend to twice the normal length. Good-quality lenses with maximum aperture no greater than f/2.8 and fixed, normal, focal length need at least three (triplet) or four elements (the trade name "Tessar" derives from the Greek tessera, meaning “four”). The widest- range zooms often have fifteen or more. The reflection of light at each of the many interfaces between different optical media (air, glass, plastic) seriously degraded the contrast and color saturation of early lenses, particularly zoom lenses, especially where the lens was directly illuminated by a light source. The introduction many years ago of optical coatings, and advances in coating technology over the years, have resulted in major improvements, and modern high-quality zoom lenses give images of quite acceptable contrast, although zoom lenses with many elements will transmit less light than lenses made with fewer elements (all other factors such as aperture, focal length, and coatings being equal).[16]

2.1.5 Lens mounts

Main article: Lens mount

Many single-lens reflex cameras and some rangefinder cameras have detachable lenses. A few other types do as well, notably the Mamiya TLR cameras and mirrorless interchangeable-lens cameras. The lenses attach to the camera using a lens mount, which contains mechanical linkages and often also electrical contacts between the lens and camera body. The lens mount design is an important issue for compatibility between cameras and lenses. There is no universal standard for lens mounts, and each major camera maker typically uses its own proprietary design, incompatible with other makers.[17] A few older manual focus lens mount designs, such as the Leica M39 lens mount for rangefinders, for early SLRs, and the Pentax K mount are found across multiple brands, but this is not common today. A few mount designs, such as the Olympus/Kodak mount for DSLRs, have also been li- censed to other makers.[18] Most large-format cameras take interchangeable lenses as well, which are usually mounted in a lensboard or on the front standard. 52 CHAPTER 2. DAY 2

The most common interchangeable lens mounts on the market today include the Canon EF, EF-S and EF-M autofocus lens mounts, the Nikon F manual and autofocus mounts, the Olympus/Kodak Four Thirds and Olympus/Panasonic Micro Four Thirds digital-only mounts, the Pentax K mount and autofocus variants, the Sony Alpha mount (derived from the Minolta mount) and the Sony E digital-only mount.

2.1.6 Types of lens

“Close-up” or macro

A macro lens used in macro or “close-up” photography (not to be confused with the compositional term close up) is any lens that produces an image on the focal plane (i.e., film or a digital sensor) that is the same size or larger than the subject being imaged. This configuration is generally used to image close-up very small subjects. A macro lens may be of any focal length, the actual focus length being determined by its practical use, considering magnification, the required ratio, access to the subject, and illumination considerations. It can be a special lens corrected optically for close up work or it can be any lens modified (with adapters or spacers) to bring the focal plane “forward” for very close photography. The depth-of-field is very narrow, limiting its usefulness. Lenses are usually stopped down to give a greater depth-of-field.[9][19]

Zoom

Main article: Zoom lens

Some lenses, called zoom lenses, have a focal length that varies as internal elements are moved, typically by rotating the barrel or pressing a button which activates an electric motor. Commonly, the lens may zoom from moderate wide-angle, through normal, to moderate telephoto; or from normal to extreme telephoto. The zoom range is limited by manufacturing constraints; the ideal of a lens of large maximum aperture which will zoom from extreme wideangle to extreme telephoto is not attainable. Zoom lenses are widely used for small-format cameras of all types: still and cine cameras with fixed or interchangeable lenses. Bulk and price limit their use for larger film sizes. Motorized zoom lenses may also have the focus, iris, and other functions motorized.

Special-purpose

• Apochromat (APO) lenses have added correction for chromatic aberration.

• Process lenses have extreme correction for aberrations of geometry (pincushion distortion, barrel distortion) and are generally intended for use at a specific distance.

Process and apochromat lenses are normally of small aperture, and are used for extremely accurate pho- tographs of static objects. Generally their performance is optimized for subjects a few inches from the front of the lens, and suffers outside this narrow range.

• lenses are made to be used with photographic (specialised projectors), rather than cameras.

• Lenses for .

• Fisheye lenses: extreme wide-angle lenses with an angle of view of up to 180 degrees or more, with very noticeable (and intended) distortion.

• Stereoscopic lenses, to produce pairs of photographs which give a 3-dimensional effect when viewed with an appropriate viewer.

• Soft-focus lenses which give a soft, but not out-of-focus, image and have an imperfection-removing effect popular among portrait and photographers.

• Infrared lenses

• Ultraviolet lenses 2.1. CAMERA LENS 53

• Swivel lenses rotate while attached to a camera body to give unique perspectives and camera angles. • Shift lenses and /shift lenses (collectively perspective control lenses) allow special control of perspective on SLR cameras by mimicking movements.

2.1.7 History and technical development of photographic camera lenses

Further information: History of photographic lens design

2.1.8 Lens designs

Main article: Photographic lens design

Some notable photographic optical lens designs are:

• Angenieux retrofocus • Cooke triplet • Double-Gauss • Goerz Dagor • Leitz Elmar • Rapid Rectilinear • Zeiss Sonnar • Zeiss Planar • Zeiss Tessar

Some lens manufacturers (2009):

• Canon • • Dörr Danubia • Leica/Leitz • Nikon • Olympus • Pentax • Rodenstock • Samyang Optics • Schneider Kreuznach • • Sony • Tamron • Tokina • Zeiss 54 CHAPTER 2. DAY 2

2.1.9 See also

• Anti-fogging treatment of optical surfaces

•

• Lens (optics)

• Lens hood

• Lens cover

• Lenses for SLR and DSLR cameras

• Teleconverter

• Teleside converter

• William Taylor (inventor)

• Optical train

2.1.10 Notes

• Kingslake, Rudolf (1989). A History of the Photographic Lens. Boston: Academic Press. ISBN 978-0-12- 408640-1.

• Guy, NK (2012). The Lens: A Practical Guide for the Creative Photographer. Rocky Nook. ISBN 978-1- 933952-97-0.

2.1.11 References

[1] If the object is at a distance, one can assume the light rays will arrive perpendicular to the plane of the lens, and thus converge at the focal point.

[2] “PhotoNotes.org Dictionary - Floating element”. photonotes.org. Retrieved 2014-10-25.

[3] “Ultraviolet Quartz Lenses”. Universe Kogaku. Retrieved 2007-11-05.

[4] “Technical Room - Fluorite / UD / Super UD glass Lenses”. Canon. Retrieved 2007-11-05.

[5] “Lenses: Fluorite, aspherical and UD lenses”. Canon Professional Network. Retrieved 2008-10-04.

[6] Gottermeier, Klaus. “The Macrolens Collection Database”. Retrieved 2007-11-05.

[7] Cavina, Marco (August 25, 2006). “Fuori banda: gli obiettivi per fotografia multispettrale della Asahi Optical Co” (PDF) (in Italian). Retrieved 2007-11-05. Rank Taylor Hobson IRTAL II 100mm f/1.0, an example of specific target for recovery in the IR spectral range of 2000 nm with lenses made of Germanium, transparent these wavelengths extremely high but completely opaque to visible light. ... In the'50s A swarm of iron meteorites impact to states in the Northeast USA; It was pallasiti, or beautiful Aeroliti metal that hard crystalline nuclei, usually Peridot or olivine say that we want (a mixture Isomorphic with nesosilicato iron bivalent and nesosilicato magnesium which must be green, in fact, the iron In the first component, called fayalite, borrowed from the matrix ferrous), but the exceptional of these meteorites Was that the crystal nuclei were fully incorporated transparent and free of impurities as the best glass Optical; Mr.. Wollensak was aware of this curious anomaly, and I think immediately to exploit this “glass” Achieving: purchase a large quantity of these abnormal pallasiti, extracting and testing the crystalline material Transparent; Immediately he realized that it was amorphous quartz and devoid of negative characteristics of Earth’s natural crystalline material (polarization, birifrangenza, etc.). ; Surveys spectrophotometry Evidenziarono that the quartz alien sent well frequencies of ultraviolet deep, beautiful beyond the threshold 320 nm granted by conventional optical glass, providing partial transparency to the fateful threshold of 200nm!

[8] “Understanding Lens Diffraction”. luminous-landscape.com. Retrieved 2014-10-25.

[9] Kingslake 1989,

[10] “Canon EF 20-35mm f/3.5~4.5 USM - Index Page”. mir.com.my. Retrieved 2014-10-25. 2.1. CAMERA LENS 55

[11] Ray, S.F. (2002). Applied Photographic Optics: Lenses and Optical Systems for Photography, , Video, Electronic and Digital Imaging. Focal. p. 294. ISBN 9780240515403. Retrieved 2014-12-12.

[12] “Mutable Conclusions: World’s fastest lens: Zeiss 50mm f/0.7.”. web.archive.org. Archived from the original on March 9, 2009. Retrieved 2014-12-12.

[13] Guy, 2012, p 43.

[14] “Hollywood, NASA, and the chip industry put their trust in Carl Zeiss”. zeiss.com. Retrieved 2014-12-12.

[15] Dr. J. Kämmerer «When is it advisable to improve the quality of camera lenses?» Excerpt from a lecture given during the Optics & Photography Symposium, Les Baux, 1979

[16] Suess, B.J. (2003). Mastering Black-and-White Photography: From Camera to . Allworth Press. ISBN 9781581153064. Retrieved 2014-10-25.

[17] Guy 2012, page 53

[18] Guy 2012, page 266

[19] Lens work, Canon Inc. 1992, Japan

2.1.12 External links

• Photo.net Lens Tutorial

• optical glass 56 CHAPTER 2. DAY 2

Large (top) and small (bottom) apertures on the same lens. 2.1. CAMERA LENS 57

How focal length affects composition: adjusting the camera’s distance from the main subject while changing focal length, the main subject can remain the same size, while the other at a different distance changes size. 58 CHAPTER 2. DAY 2

A tilt/shift lens, set to its maximum degree of tilt relative to the camera body.

Collapsible Leica rangefinder lens Chapter 3

Day 3

3.1 Photographic lens design

For general lens design, see .

The design of photographic lenses for use in still or cine cameras is intended to produce a lens that yields the most acceptable rendition of the subject being photographed within a range of constraints that include cost, weight and materials. For many other optical devices such as telescopes, and theodolite where the visual image is observed but often not recorded the design can often be significantly simpler than is the case in a camera where every image is captured on film or image sensor and can be subject to detailed scrutiny at a later stage. Photographic lenses also include those used in enlargers and projectors.

3.1.1 Design

Design requirements

Main article: Optical lens design

From the perspective of the photographer, the ability of a lens to capture sufficient light so that the camera can operate over a wide range of lighting conditions is important. Designing a lens that reproduces colour accurately is also important as is the production of an evenly lit and sharp image over the whole of the film or sensor plane. For the lens designer, achieving these objectives will also involve ensuring that internal flare, optical aberrations and weight are all reduced to the minimum whilst zoom, focus and aperture functions all operate smoothly and predictably. However, because photographic films and electronic sensors have a finite and measurable resolution, photographic lenses are not always designed for maximum possible resolution since the recording medium would not be able to record the level of detail that the lens could resolve. For this, and many other reasons, camera lenses are unsuited for use as projector or enlarger lenses. The design of a fixed focal length lens (also known as prime lenses) presents fewer challenges than the design of a zoom lens. A high-quality prime lens whose focal length is about equal to the diameter of the film frame or sensor may be constructed from as few as four separate lens elements, often as pairs on either side of the aperture diaphragm. Good examples include the Zeiss Tessar or the Leitz Elmar.

Design constraints To be useful in photography any lens must be able to fit the camera for which it is intended and this will physically limit the size where the bayonet mounting or screw mounting is to be located. Photography is a highly competitive commercial business and both weight and cost constrain the production of lenses. Refractive materials such as glass have physical limitations which limit the performance of lenses. In particular the range of refractive indices available in commercial glasses span a very narrow range. Since it is the refractive index that determines how much the rays of light are bent at each interface and since it is the differences in refractive indices

59 60 CHAPTER 3. DAY 3 in paired plus and minus lenses that constrains the ability to minimise chromatic aberrations, having only a narrow spectrum of indices is a major design constraint.

Lens elements

Elements of a cheap 28mm lens.

Main article: Lens (optics)

Except for the most simple and inexpensive lenses, each complete lens is made up from a number of separate lens elements arranged along a common axis. The use of many lens elements serves to minimise aberrations and to provide a sharp image free from visible imperfections. To do this requires lens elements of different compositions and different shapes. To minimise chromatic aberrations, e. g., in which different wavelengths of light are refracted to different degrees, requires, at a minimum, a doublet of lens elements with a positive element having a high matched with a negative element of lower Abbe number. With this design one can achieve a good degree of convergence of different wavelengths in the visible spectrum. Most lens designs do not attempt to bring infrared wavelengths to the same common focus and it is therefore necessary to manually alter the focus when photographing in infrared light. Other kinds of aberrations like coma or astigmatism can also be minimized by combining different lens elements. Complex photographic lenses can consist of more than 15 lens elements. Most lens elements are made with curved surfaces with a spherical profile. That is, the curved shape would fit on the surface of a sphere. This is partly to do with the history of lens making but also because grinding and manufacturing of spherical surface lenses is relatively simple and cheap. However, spherical surfaces also give rise to lens aberrations and can lead to complicated lens designs of great size. Higher-quality lenses with fewer elements and lower size can be achieved by using aspheric lenses in which the curved surfaces are not spherical, giving more degrees of freedom to correct aberrations.

Lens glass Main article: Refraction

The majority of photographic lenses have the lens elements made from glass although the use of high-quality plastics is becoming more common in high-quality lenses and has been common in inexpensive cameras for some time. The design of photographic lenses is very demanding as designers push the limits of existing materials to make more versatile, better-quality, and lighter lenses. As a consequence many exotic glasses have been used in modern lens manufacturing. Caesium[1] and lanthanum[2] glass lenses are now in use because of their high refractive index and very low dispersion properties. It is also likely that a number of other transition element glasses are in use but 3.1. PHOTOGRAPHIC LENS DESIGN 61 manufacturers often prefer to keep their material specification secret to retain a commercial or performance edge over their rivals.

Focus

Main article: Focus (optics)

Until recent years focusing of a camera lens to achieve a sharp image on the film plane was achieved by means of a very shallow helical thread in the lens mount through which the lens could be rotated moving it closer or further from the film plane. This arrangement, whilst simple to design and construct, has some limitations not least the rotation of the greater part of the lens assembly including the front element. This could be problematical if devices such as polarising filters were in use that require maintaining an accurate vertical orientation irrespective of focus distance. Later developments adopted designs in which internal elements were moved to achieve focus without affecting the outer barrel of the lens or the orientation of the front element. Many modern cameras now use automatic focusing mechanisms which use ultrasonic motors to move internal ele- ments in the lens to achieve optimum focus.

Aperture control

Main article: Aperture

The aperture control, usually a multi-leaf diaphragm, is critical to the performance of a lens. The role of the aperture is to control the amount of light passing through the lens to the film or sensor plane. An aperture placed outside of the lens, as in the case of some Victorian cameras, risks vignetting of the image in which the corners of the image are darker than the centre. A diaphragm too close to the image plane risks the diaphragm itself being recorded as a circular shape or at the very least causing diffraction patterns at small apertures. In most lens designs the aperture is positioned about midway between the front surface of the objective and the image plane. In some zoom lenses it is placed some distance away from the ideal location in order to accommodate the movement of floating lens elements needed to perform the zoom function. Most modern lenses for 35mm format rarely provide a stop smaller than f/22 because of the diffraction effects caused by light passing through a very small aperture. As diffraction is based on aperture width in absolute terms rather than the f-stop ratio, lenses for very small formats common in compact cameras rarely go above f/11 (1/1.8”) or f/8 (1/2.5”), while lenses for medium- and large-format provide f/64 or f/128. Very-large-aperture lenses designed to be useful in very low light conditions with apertures ranging from f/1.2 to f/0.9 are generally restricted to lenses of standard focal length because of the size and weight problems that would be encountered in telephoto lenses and the difficulty of building a very wide aperture wide angle lens with the refractive materials currently available. Very-large-aperture lenses are commonly made for other types of optical instruments such as microscopes but in such cases the diameter of the lens is very small and weight is not an issue. Many very early cameras had diaphragms external to the lens often consisting of a rotating circular plate with a number of holes of increasing size drilled through the plate.[3] Rotating the plate would bring an appropriate sized hole in front of the lens. All modern lenses use a multi-leaf diaphragm so that at the central intersection of the leaves a more or less circular aperture is formed. Either a manual ring, or an electronic motor controls the angle of the diaphragm leaves and thus the size of the opening. The placement of the diaphragm within the lens structure is constrained by the need to achieve even illumination over the whole film plane at all apertures and the requirement to not interfere with the movement of any movable lens element. Typically the diaphragm is situated at about the level of the optical centre of the lens.

Shutter mechanism

Main article: Shutter (photography)

A shutter controls the length of time light is allowed to pass through the lens onto the film plane. For any given light intensity, the more sensitive the film or detector or the wider the aperture the shorter the exposure time need to be 62 CHAPTER 3. DAY 3 to maintain the optimal exposure. In the earliest camera exposures were controlled by moving a rotating plate from in front of the lens and then replacing it. Such a mechanism only works effectively for exposures of several seconds or more and carries a considerable risk of inducing camera shake. By the end of the 19th century spring tensioned shutter mechanisms were in use operated by a lever or by a cable release. Some simple shutters continued to be placed in front of the lens but most were incorporated within the lens mount itself. Such lenses with integral shutter mechanisms developed in the current Compur shutter as used in many non-reflex cameras such as Linhof. These shutters have a number of metal leaves that spring open and then close after a pre-determined interval. The material and design constraints limit the shortest speed to about 0.002 second. Although such shutters cannot yield as short an exposure time as focal-plane shutter they are able to offer flash synchronisation at all speeds. Incorporating a commercial made Compur type shutter required lens designers to accommodate the width of the shut- ter mechanism in the lens mount and provide for the means of triggering the shutter on the lens barrel or transferring this to the camera body by a series of levers as in the Minolta twin-lens cameras. The need to accommodate the shutter mechanism within the lens barrel limited the design of wide-angle lenses and it was not until the widespread use of focal-plane shutters that extreme wide-angle lenses were developed.

3.1.2 Types of lenses

Example of a prime lens - Carl Zeiss Tessar.

The type of lens being designed is significant in setting the key parameters.

• Prime lens - a photographic lens whose focal length is fixed, as opposed to a zoom lens, or that is the primary lens in a combination lens system.

• Zoom lenses - variable focal length lenses. Zoom lenses cover a range of focal lengths by utilising movable elements within the barrel of the lens assembly. In early varifocal lens lenses the focus also shifted as the lens focal length was changed. Varifocal lenses are also used in many modern autofocus cameras as the lenses are cheaper and simpler to construct and the autofocus can take care of the re-focussing requirements. Many mod- ern zoom lenses are now confocal, meaning that the focus is maintained throughout the zoom range. Because of the need to operate over a range of focal lengths and maintain confocality, zoom lenses typically have very many lens elements. More significantly, the front elements of the lens will always be a compromise in terms 3.1. PHOTOGRAPHIC LENS DESIGN 63

of its size, light-gathering capability and the angle of incidence of the incoming rays of light. For all these reasons, the optical performance of zoom lenses tends to be lower than fixed-focal-length lenses.

• Normal lens - a lens with a focal length about equal to the diagonal size of the film or sensor format, or that reproduces perspective that generally looks “normal” to a human observer.

Front Diaphragm element

Cross-section of a typical short-focus wide-angle lens.

• Wide angle lens - a lens that reproduces perspective that generally looks “wider” than a normal lens. The problem posed by the design of wide-angle lenses is to bring to an accurate focus light from a wide area without causing internal flare. Wide-angle lenses therefore tend to have more elements than a normal lens to help refract the light sufficiently and still minimise aberrations whilst adding light-trapping baffles between each lens element.

• Extreme or ultra-wide-angle lens - a wide-angle lens with an angle of view above 90 degrees.[4] Extreme-wide-angle lenses share the same issues as ordinary wide-angle lenses but the focal length of such lenses may be so short that there is insufficient physical space in front of the film or sensor plane to construct a lens. This problem is resolved by constructing the lens as an inverted telephoto, or retrofocus with the front element having a very short focal length, often with a highly exaggerated convex front surface and behind it a strongly negative lens grouping that extends the cone of focused rays so that they can be brought to focus at a reasonable distance.

• Fisheye lens - an extreme wide-angle lens with a strongly convex front element. Spherical aberration is usually pronounced and sometimes enhanced for special effect. Optically designed as a reverse telephoto to enable the lens to fit into a standard mount as the focal length can be less than the distance from lens mount to focal plane.

• Long-focus lens - a lens with a focal length greater than the diagonal of the film frame or sensor. Long focus lenses are relatively simple to design, the challenges being comparable to the design of a prime lens. However, as the focal length increases the length of the lens and the size of the objective increase in size and length 64 CHAPTER 3. DAY 3

Cross-section of a typical retrofocus wide-angle lens.

Cross-section - typical telephoto lens. L1 - Tele positive lens group L2 - Tele negative lens group D - Diaphragm

and weight quickly become significant design issues in retaining utility and practicality for the lens in use. In addition because the light path through the lens is long and glancing, the importance of baffles to control flare increases in importance. • Telephoto lens - an optically compressed version of the long-focus lens. The design of telephoto lenses reduces some of the problems encountered by designers of long-focus lenses. In particular, telephoto lenses are typically much shorter and may be lighter for equivalent focal length and aperture. However telephoto designs increase the number of lens elements and can introduce flare and exacerbate some optical aberrations. • Catadioptric lens - catadioptric lenses are a form of telephoto lens but with a light path that doubles back on itself and with an objective that is a mirror combined with some form aberration correcting lens (a catadioptric system) rather than just a lens. A centrally-placed secondary mirror and usually an additional small lens group bring the light to focus. Such lenses are very lightweight and can easily deliver very long focal lengths but 3.1. PHOTOGRAPHIC LENS DESIGN 65

they can only deliver a fixed aperture and have none of the benefits of being able to stop down the aperture to increase depth of field.

• Anamorphic lenses are used principally in to produce wide-screen films where the projected image has a substantially different ratio of height to width than the image recorded on the film plane. This is achieved by the use of a specialised lens design which compresses the image laterally at the recording stage and the film is then projected through a similar lens in the cinema to recreate the wide-screen effect. Although in some cases the anamorphic effect is achieved by using an anamorphising attachment as a supplementary element on the front of a normal lens, most films shot in anamorphic formats use specially designed anamorphic lenses, such as the Hawk lenses made by Vantage Film or ’s anamorphic lenses. These lenses incorporate one or more aspheric elements in their design.

Enlarger lenses

Lenses used in photographic enlargers are required to focus light passing through a relatively small film area on a larger area of photographic paper or film. Requirements for such lenses include

• the ability to record even illumination over the whole field • to record fine detail present in the film being enlarged • to withstand frequent cycles of heating and cooling as the illumination lamp is turned on and off • to be able to be operated in the dark - usually by means of click stops and some luminous controls

The design of the lens is required to work effectively with light passing from near focus to far focus - exactly the reverse of a camera lens. This demands that internal light baffling within the lens is designed differently and that the individual lens elements are designed to maximize performance for this change of direction of incident light.

Projector lenses

Projector lenses share many of the design constraints as enlarger lenses but with some critical differences. Projector lenses are always used at full aperture and must produce an acceptably illuminated and acceptably sharp image at full aperture. However, because projected images are almost always viewed at some distance, lack of very fine focus and slight unevenness of illumination is often acceptable. Projector lenses have to be very tolerant of prolonged high temper- atures from the projector lamp and frequently have a focal length much longer than the taking lens. This allows the lens to be positioned at a greater distance from the illuminated film and allows an acceptable sized image with the projector some distance from the screen. It also permits the lens to be mounted in a relatively coarsely threaded focusing mount so that the projectionist can quickly correct any focusing errors.

3.1.3 History

Main article: History of photographic lens design The lenses of the very earliest cameras were simple meniscus or simple bi convex lenses. It was not until 1840 that Chevalier in France introduced the achromatic lens formed by cementing a crown glass bi-convex lens to a flint glass plano-concave lens. By 1841 Voigtländer using the design of Joseph Petzval manufactured the first commercially successful two element lens. Carl Zeiss was an entrepreneur who needed a competent designer to take his firm beyond just another optical work- shop. In 1866, the service of Dr Ernst Abbe was enlisted. From then on novel products appeared in rapid succession which brought the Zeiss company to the forefront of optical technology. Abbe was instrumental in the development of the famous Jena optical glass. When he was trying to eliminate astigma- tism from microscopes, he realised that the range of optical glasses available was insufficient. After some calculations, he realised that performance of optical instruments would dramatically improve, if optical glasses of appropriate prop- erties were available. His challenge to glass manufacturers was finally answered by Dr Otto Schott, who established the famous glassworks at Jena from which new types of optical glass began to appear from 1888, and employed by Zeiss and other makers. 66 CHAPTER 3. DAY 3

Diagram of Petzval’s 1841 portrait lens - crown glass shaded pink, flint glass shaded blue

The new Jena optical glass also opened up the possibility of increased performance of photographic lenses. The first use of Jena glass in a photographic lens was by Voigtländer, but as the lens was an old design its performance was not greatly improved. Subsequently the new glasses would demonstrate their value in correcting astigmatism, and in the production of achromatic and apochromatic lenses. Abbé started the design of a photographic lens of symmetrical design with five elements, but went no further. Zeiss’ innovative photographic lens design was due to Dr Paul Rudolph. In 1890, Rudolph designed an asymmetrical lens with a cemented group at each side of the diaphragm, and appropriately named “Anastigmat”. This lens was made in three series: Series III, IV and V, with maximum apertures of f/7.2, f/12.5, and f/18 respectively. In 1891, Series I, II and IIIa appeared with respective maximum apertures of f/4.5, f/6.3, and f/9 and in 1893 came Series IIa of f/8 maximum aperture. These lenses are now better known by the trademark “Protar” which was first used in 1900. At the time, single combination lenses, which occupy one side of the diaphragm only, were still popular. Rudolph designed one with three cemented elements in 1893, with the option of fitting two of them together in a lens barrel as a compound lens, but it was found to be the same as the Dagor by C.P. Goerz, designed by Emil von Hoegh. Rudolph then came up with a single combination with four cemented elements, which can be considered as having all the elements of the Protar stuck together in one piece. Marketed in 1894, it was called the Protarlinse Series VII, the most highly corrected single combination lens with maximum apertures between f/11 and f/12.5, depending on its focal length. 3.1. PHOTOGRAPHIC LENS DESIGN 67

But the important thing about this Protarlinse is that two of these lens units can be mounted in the same lens barrel to form a compound lens of even greater performance and larger aperture, between f/6.3 and f/7.7. In this configuration it was called the Double Protar Series VIIa. An immense range of focal lengths can thus be obtained by the various combination of Protarlinse units. Rudolph also investigated the Double-Gauss concept of a symmetrical design with thin positive meniscii enclosing negative elements. The result was the Planar Series Ia of 1896, with maximum apertures up to f/3.5, one of the fastest lenses of its time. Whilst it was very sharp, it suffered from coma which limited its popularity. However, further developments of this configuration made it the design of choice for high-speed lenses of standard coverage. Probably inspired by the Stigmatic lenses designed by Hugh Aldis for Dallmeyer of London, Rudolph designed a new asymmetrical lens with four thin elements, the Unar Series Ib, with apertures up to f/4.5. Due to its high speed it was used extensively on hand cameras. The most important Zeiss lens by Rudolph was the Tessar, first sold in 1902 in its Series IIb f/6.3 form. It can be said as a combination of the front half of the Unar with the rear half of the Protar. This proved to be a most valuable and flexible design, with tremendous development potential. Its maximum aperture was increased to f/4.7 in 1917, and reached f/2.7 in 1930. It is probable that every lens manufacturer has produced lenses of the Tessar configuration. Rudolph left Zeiss after the First World War, but many other competent designers such as Merté, Wandersleb, etc. kept the firm at the leading edge of photographic lens innovations. One of the most significant designer was the ex-Ernemann man Dr Ludwig Bertele, famed for his Ernostar high-speed lens. With the advent of the Contax by Zeiss-Ikon, the first serious challenge to the Leica in the field of professional 35 mm cameras, both Zeiss-Ikon and Carl Zeiss decided to beat the Leica in every possible way. Bertele’s Sonnar series of lenses designed for the Contax were the match in every respect for the Leica for at least two decades. Other lenses for the Contax included the Biotar, Biogon, Orthometar, and various Tessars and Triotars. The last important Zeiss innovation before the Second World War was the technique of applying anti-reflective coating to lens surfaces invented by Olexander Smakula in 1935.[5] A lens so treated was marked with a red “T”, short for “Transparent”. The technique of applying multiple layers of coating was also described in the original patent writings in 1935.[6] After the partitioning of Germany, a new Carl Zeiss optical company was established in Oberkochen, while the original Zeiss firm in Jena continued to operate. At first both firms produced very similar lines of products, and extensively cooperated in product-sharing, but they drifted apart as time progressed. Jena’s new direction was to concentrate on developing lenses for the 35 mm single-lens reflex camera, and many achievements were made, espe- cially in ultra-wide angle designs. In addition to that, Oberkochen also worked on designing lenses for large format cameras, interchangeable front element lenses such as for the 35 mm single-lens reflex Contaflex, and other types of cameras. Since the beginning of Zeiss as a photographic lens manufacturer, it has had a licensing programme which allows other manufacturers to produce its lenses. Over the years its licensees included Voigtländer, Bausch & Lomb, Ross, Koristka, Krauss, Kodak. etc. In the 1970s, the western operation of Zeiss-Ikon got together with to produce the new Contax cameras, and many of the Zeiss lenses for this camera, among others, were produced by Yashica’s optical arm, Tomioka. Yashica’s owner ended camera production in 2006. Yashica lenses were then made by Cosina, who also manufactured most of the new Zeiss designs for the new Zeiss Ikon coupled rangefinder camera. Another licensee active today is Sony who uses the Zeiss name on lenses on its video and digital still cameras.

3.1.4 See also

• Camera lens

3.1.5 References

[1] http://specialmetals.chemetall.com/basic.jsp;jsessionid=E7EC988ACA791907FC590ED56D5376F8.ffms29?xml=14B7838C4C8EDCFEC1256EFC005FC3B7

[2] http://www.freepatentsonline.com/3615762.html

[3] Wall, E.J. (1890). Dictionary of Photography. London: Hassel, Watson and Viney.

[4] Sidney F. Ray, Applied photographic optics, page 314

[5] History of Camera Lenses from Carl Zeiss - 1935 - Alexander Smakula develops anti-reflection coating 68 CHAPTER 3. DAY 3

[6] Lens coating invented and developed by Alexander Smakula Chapter 4

Day 4

4.1 Aperture

For other uses, see Aperture (disambiguation). In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of rays that come to a focus in the image plane. The aperture determines how collimated the admitted rays are, which is of great importance for the appearance at the image plane.[2] If an aperture is narrow, then highly collimated rays are admitted, resulting in a sharp focus at the image plane. A wide aperture admits uncollimated rays, resulting in a sharp focus only for rays coming from a certain distance. This means that a wide aperture results in an image that is sharp for things at the correct distance. The aperture also determines how many of the incoming rays are actually admitted and thus how much light reaches the image plane (the narrower the aperture, the darker the image for a given exposure time). In the human eye, the pupil is the aperture. An optical system typically has many openings or structures that limit the ray bundles (ray bundles are also known as pencils of light). These structures may be the edge of a lens or mirror, or a ring or other fixture that holds an optical element in place, or may be a special element such as a diaphragm placed in the optical path to limit the light admitted by the system. In general, these structures are called stops, and the aperture stop is the stop that primarily determines the ray cone angle and brightness at the image point. In some contexts, especially in photography and astronomy, aperture refers to the diameter of the aperture stop rather than the physical stop or the opening itself. For example, in a telescope, the aperture stop is typically the edges of the objective lens or mirror (or of the mount that holds it). One then speaks of a telescope as having, for example, a 100-centimeter aperture. Note that the aperture stop is not necessarily the smallest stop in the system. Magnification and demagnification by lenses and other elements can cause a relatively large stop to be the aperture stop for the system. In , the aperture may be given as a linear measure (for example in inches or mm) or as the dimensionless ratio between that measure and the focal length. In other photography, it is usually given as a ratio. Sometimes stops and diaphragms are called apertures, even when they are not the aperture stop of the system. The word aperture is also used in other contexts to indicate a system which blocks off light outside a certain region. In astronomy, for example, a photometric aperture around a star usually corresponds to a circular window around the image of a star within which the light intensity is assumed.[3]

4.1.1 Application

The aperture stop is an important element in most optical designs. Its most obvious feature is that it limits the amount of light that can reach the image/film plane. This can be either unavoidable, as in a telescope where one wants to collect as much light as possible; or deliberate, to prevent saturation of a detector or overexposure of film. In both cases, the size of the aperture stop is constrained by things other than the amount of light admitted; however:

• The size of the stop is one factor that affects depth of field. Smaller stops (larger f numbers) produce a longer depth of field, allowing objects at a wide range of distances to all be in focus at the same time.

69 70 CHAPTER 4. DAY 4

• The stop limits the effect of optical aberrations. If the stop is too large, the image will be distorted. More sophisticated optical system designs can mitigate the effect of aberrations, allowing a larger stop and therefore greater light collecting ability. • The stop determines whether the image will be vignetted. Larger stops can cause the intensity reaching the film or detector to fall off toward the edges of the picture, especially when, for off-axis points, a different stop becomes the aperture stop by virtue of cutting off more light than did the stop that was the aperture stop on the optic axis. • A larger aperture stop requires larger diameter optics, which are heavier and more expensive.

In addition to an aperture stop, a photographic lens may have one or more field stops, which limit the system’s field of view. When the field of view is limited by a field stop in the lens (rather than at the film or sensor) vignetting results; this is only a problem if the resulting field of view is less than was desired. The biological pupil of the eye is its aperture in optics nomenclature; the iris is the diaphragm that serves as the aperture stop. Refraction in the cornea causes the effective aperture (the entrance pupil in optics parlance) to differ slightly from the physical pupil diameter. The entrance pupil is typically about 4 mm in diameter, although it can range from 2 mm (f/8.3) in a brightly lit place to 8 mm (f/2.1) in the dark. In astronomy, the diameter of the aperture stop (called the aperture) is a critical parameter in the design of a telescope. Generally, one would want the aperture to be as large as possible, to collect the maximum amount of light from the distant objects being imaged. The size of the aperture is limited, however, in practice by considerations of cost and weight, as well as prevention of aberrations (as mentioned above). Apertures are also used in laser energy control, close aperture z-scan technique, diffractions/patterns, and beam cleaning.[4] Laser applications include spatial filters, Q-switching, high intensity x-ray control. In light microscopy, the word aperture may be used with reference to either the condenser (changes angle of light onto specimen field), field iris (changes area of illumination) or possibly objective lens (forms primary image). See .

4.1.2 In photography

The aperture stop of a photographic lens can be adjusted to control the amount of light reaching the film or image sensor. In combination with variation of shutter speed, the aperture size will regulate the film’s or image sensor’s degree of exposure to light. Typically, a fast shutter will require a larger aperture to ensure sufficient light exposure, and a slow shutter will require a smaller aperture to avoid excessive exposure. A device called a diaphragm usually serves as the aperture stop, and controls the aperture. The diaphragm functions much like the iris of the eye – it controls the effective diameter of the lens opening. Reducing the aperture size increases the depth of field, which describes the extent to which subject matter lying closer than or farther from the actual plane of focus appears to be in focus. In general, the smaller the aperture (the larger the number), the greater the distance from the plane of focus the subject matter may be while still appearing in focus. The lens aperture is usually specified as an f-number, the ratio of focal length to effective aperture diameter. A lens typically has a set of marked “f-stops” that the f-number can be set to. A lower f-number denotes a greater aperture opening which allows more light to reach the film or image sensor. The photography term “one f-stop” refers to a factor of √2 (approx. 1.41) change in f-number, which in turn corresponds to a factor of 2 change in light intensity. Aperture priority is a semi-automatic shooting mode used in cameras. It permits the photographer to select an aperture setting and let the camera decide the shutter speed and sometimes also ISO sensitivity for the correct exposure. This is also referred to as Aperture Priority Auto Exposure, A mode, AV mode (aperture-value mode), or semi-auto mode.[5] Typical ranges of apertures used in photography are about f/2.8–f/22 or f/2–f/16,[6] covering 6 stops, which may be divided into wide, middle, and narrow of 2 stops each, roughly (using round numbers) f/2–f/4, f/4–f/8, and f/8–f/16 or (for a slower lens) f/2.8–f/5.6, f/5.6–f/11, and f/11–f/22. These are not sharp divisions, and ranges for specific lenses vary.

Maximum and minimum apertures

Further information: 4.1. APERTURE 71

The specifications for a given lens typically include the maximum and minimum aperture sizes, for example, f/1.4– f/22. In this case, f/1.4 is the maximum aperture (the widest opening), and f/22 is the minimum aperture (the smallest opening). The maximum aperture opening tends to be of most interest and is always included when describing a lens. This value is also known as the lens “speed”, as it affects the exposure time. The aperture is proportional to the square root of the light admitted, and thus inversely proportional to the square root of required exposure time, such that an aperture of f/2 allows for exposure times one quarter that of f/4. Lenses with apertures opening f/2.8 or wider are referred to as “fast” lenses, although the specific point has changed over time (for example, in the 1911 Encyclopaedia Britannica aperture openings wider than f/6 were considered fast). The fastest lenses for the common 35 mm film format in general production have apertures of f/1.2 or f/1.4, with more at f/1.8 and f/2.0, and many at f/2.8 or slower; f/1.0 is unusual, though sees some use. When comparing “fast” lenses, the image format used must be considered. Lenses designed for a small format such as half frame or APS-C need to project a much smaller image circle than a lens used for large format photography. Thus the optical elements built into the lens can be far smaller and cheaper. In exceptional circumstances lenses can have even wider apertures with f-numbers smaller than 1.0; see lens speed: fast lenses for a detailed list. For instance, both the current Leica Noctilux-M 50mm ASPH and a 1960s-era Canon 50mm rangefinder lens have a maximum aperture of f/0.95.[7] Cheaper alternatives have appeared in recent years, such as the Cosina Voigtländer 17.5mm f/0.95, 25mm f/0.95 and 42.5mm f/0.95 manual focus lenses for the .[8][9][10] Professional lenses for some movie cameras have f-numbers as small as f/0.75. Stanley Kubrick's film Barry Lyndon has scenes shot by candlelight with a NASA/Zeiss 50mm f/0.7,[11] the fastest lens in film history. Beyond the expense, these lenses have limited application due to the correspondingly shallower depth of field – the scene must either be shallow, shot from a distance, or will be significantly defocused, though this may be the desired effect. Zoom lenses typically have a maximum relative aperture (minimum f-number) of f/2.8 to f/6.3 through their range. High-end lenses will have a constant aperture, such as f/2.8 or f/4, which means that the relative aperture will stay the same throughout the zoom range. A more typical consumer zoom will have a variable maximum relative aperture since it is harder and more expensive to keep the maximum relative aperture proportional to the focal length at long focal lengths; f/3.5 to f/5.6 is an example of a common variable aperture range in a consumer zoom lens. By contrast, the minimum aperture does not depend on the focal length – it is limited by how narrowly the aperture closes, not the lens design – and is instead generally chosen based on practicality: very small apertures have lower sharpness due to diffraction, while the added depth of field is not generally useful, and thus there is generally little benefit in using such apertures. Accordingly, DSLR lens typically have minimum aperture of f/16, f/22, or f/32, while large format may go down to f/64, as reflected in the name of Group f/64. Depth of field is a significant concern in macro photography, however, and there one sees smaller apertures. For example, the Canon MP-E 65mm can have effective aperture (due to magnification) as small as f/96. The pinhole optic for creative lenses has an aperture of just f/177.[12]

• f/32 – small aperture and slow shutter

• f/5.6 – large aperture and fast shutter

• f/22 – small aperture and slower shutter (Exposure time: 1/80) 72 CHAPTER 4. DAY 4

• f/3.5 – large aperture and faster shutter (Exposure time: 1/2500)

• Changing a camera’s aperture in half-stops, beginning with f/256 and ending with f/1

• Changing a camera’s aperture diameter from zero to infinity

Aperture area

The amount of light captured by a lens is proportional to the area of the aperture, equal to:

( ) ( ) D 2 f 2 Area = π = π 2 2N Where the two equivalent forms are related via the f-number N = f / D, with focal length f and aperture diameter D. The focal length value is not required when comparing two lenses of the same focal length; a value of 1 can be used instead, and the other factors can be dropped as well, leaving area proportion to the reciprocal square of the f-number N. If two cameras of different format sizes and focal lengths have the same angle of view, and the same aperture area, they gather the same amount of light from the scene. In that case, the relative focal-plane illuminance, however, would depend only on the f-number N, so it is less in the camera with the larger format, longer focal length, and higher f-number. This assumes both lenses have identical transmissivity.

Aperture control

Most SLR cameras provide automatic aperture control, which allows viewing and metering at the lens’s maximum aperture, but stops the lens down to the working aperture during exposure, and returns the lens to maximum aperture afterward.[13] The first SLR cameras with internal (“through-the-lens” or “TTL”) meters (e.g., the ) required that the lens is stopped down to the working aperture when taking a meter reading. With a small aperture, this darkened the viewfinder, making viewing, focusing, and composition difficult.[14] Subsequent models soon incorporated mechanical coupling between the lens and the camera body, indicating the working aperture to the camera while allowing the lens to be at its maximum aperture for composition and focusing;[13] this feature became known as automatic aperture control or automatic diaphragm control. For some lenses, including a few long telephotos, lenses mounted on bellows, and perspective-control and tilt/shift lenses, the mechanical linkage was impractical,[13] and automatic aperture control was not provided. Many such lenses incorporated a feature known as a “preset” aperture,[13][15] which allows the lens to be set to working aperture and then quickly switched between working aperture and full aperture without looking at the aperture control. A typical operation might be to establish rough composition, set the working aperture for metering, return to full aperture for a final check of focus and composition, and focusing, and finally, return to working aperture just before exposure. 4.1. APERTURE 73

Although slightly easier than stopped-down metering, operation is less convenient than automatic operation. Preset aperture controls have taken several forms; the most common has been the use of essentially two lens aperture rings, with one ring setting the aperture and the other serving as a limit stop when switching to working aperture. Examples of lenses with this type of preset aperture control are the Nikon PC Nikkor 28 mm f/3.5 and the SMC Pentax Shift 6×7 75 mm f/4.5. The Nikon PC Micro-Nikkor 85 mm f/2.8D lens incorporates a mechanical pushbutton that sets working aperture when pressed and restores full aperture when pressed a second time. Canon EF lenses, introduced in 1987,[16] have electromagnetic diaphragms,[17] eliminating the need for a mechanical linkage between the camera and the lens, and allowing automatic aperture control with the Canon TS-E tilt/shift lenses. Nikon PC-E perspective-control lenses,[18] introduced in 2008, also have electromagnetic diaphragms.[19] Automatic aperture control is provided with the newer Nikon digital SLR cameras; with some earlier cameras, the lenses offer preset aperture control by means of a pushbutton that controls the electromagnetic diaphragm.

Optimal aperture

Optimal aperture depends both on optics (the depth of the scene versus diffraction), and on the performance of the lens. Optically, as a lens is stopped down, the defocus blur at the (DOF) limits decreases but diffraction blur increases. The presence of these two opposing factors implies a point at which the combined blur spot is minimized (Gibson 1975, 64); at that point, the f-number is optimal for image sharpness, for this given depth of field[20] – a wider aperture (lower f-number) causes more defocus, while a narrower aperture (higher f-number) causes more diffraction. As a matter of performance, lenses often do not perform optimally when fully opened, and thus generally have better sharpness when stopped down some – note that this is sharpness in the plane of critical focus, setting aside issues of depth of field. Beyond a certain point, there is no further sharpness benefit to , and the diffraction begins to become significant. There is accordingly a sweet spot, generally in the f/4 – f/8 range, depending on lens, where sharpness is optimal, though some lenses are designed to perform optimally when wide open. How significant this varies between lenses, and opinions differ on how much practical impact this has. While optimal aperture can be determined mechanically, how much sharpness is required depends on how the image will be used – if the final image is viewed under normal conditions (e.g., an 8″×10″ image viewed at 10″), it may suffice to determine the f-number using criteria for minimum required sharpness, and there may be no practical benefit from further reducing the size of the blur spot. But this may not be true if the final image is viewed under more demanding conditions, e.g., a very large final image viewed at normal distance, or a portion of an image enlarged to normal size (Hansma 1996). Hansma also suggests that the final-image size may not be known when a photograph is taken, and obtaining the maximum practicable sharpness allows the decision to make a large final image to be made at a later time; see also critical sharpness.

4.1.3 Equivalent aperture range

See also:

In , the 35mm-equivalent aperture range is sometimes considered to be more important than the actual f-number. Equivalent aperture is the f-number adjusted to correspond to the f-number of the same size absolute aperture diameter on a lens with a 35mm equivalent focal length. Smaller equivalent f-numbers are expected to lead to higher image quality based on more total light from the subject, as well as lead to reduced depth of field. For example, a Sony Cyber-shot DSC-RX10 uses a 1” sensor, 24–200 mm with maximum aperture constant along the zoom range; f/2.8 has equivalent aperture range f/7.6, which is a lower equivalent f-number than some other f/2.8 cameras with smaller sensors.[21]

4.1.4 In scanning or sampling

The terms scanning aperture and sampling aperture are often used to refer to the opening through which an image is sampled, or scanned, for example in a Drum scanner, an image sensor, or a television pickup apparatus. The sampling aperture can be a literal optical aperture, that is, a small opening in space, or it can be a time-domain aperture for sampling a signal waveform. 74 CHAPTER 4. DAY 4

For example, film grain is quantified as graininess via a measurement of film density fluctuations as seen through a 0.048 mm sampling aperture.

4.1.5 See also

• Numerical aperture • Antenna aperture • • Diaphragm (optics) • Bokeh • Shallow focus • Deep focus • Entrance pupil • Exit pupil • Lyot stop

4.1.6 References

• Gibson, H. Lou. 1975. Close-Up Photography and Photomacrography. 2nd combined ed. Kodak Publication No. N-16. Rochester, NY: Eastman Kodak Company, Vol II: Photomacrography. ISBN 0-87985-160-0 • Hansma, Paul K. 1996. View Camera Focusing in Practice. Photo Techniques, March/April 1996, 54–57. Available as GIF images on the Large Format page.

[1] Thomas Blount, Glossographia Anglicana Nova: Or, A Dictionary, Interpreting Such Hard Words of whatever Language, as are at present used in the English Tongue, with their Etymologies, Definitions, &c. Also, The Terms of Divinity, Law, Physick, Mathematics, History, Agriculture, Logick, Metaphysicks, Grammar, Poetry, Musick, Heraldry, Architecture, Painting, War, and all other Arts and Sciences are herein explain'd, from the best Modern Authors, as, Sir Isaac Newton, Dr. Harris, Dr. Gregory, Mr. Lock, Mr. Evelyn, Mr. Dryden, Mr. Blunt, &c., London, 1707.

[2] “What is Aperture?". Wicked Sago. Retrieved 3 March 2013.

[3] Nicholas Eaton, Peter W. Draper & Alasdair Allan, Techniques of aperture photometry Archived 11 March 2007 at the Wayback Machine. in PHOTOM -- A Photometry Package, 20 August 2002

[4] Rashidian Vaziri, M R. “Role of the aperture in Z-scan experiments: A parametric study”. Chinese Physics B. 24 (11). doi:10.1088/1674-1056/24/11/114206.

[5] “Aperture and shutter speed in digital cameras”. elite-cameras.com. Archived from the original on 2006-06-20. Retrieved 2006-06-20. (original link no longer works, but page was saved by archive.org)

[6] What is... Aperture?

[7] Gizmodo: “Leica’s $11,000 Noctilux 50mm f/0.95 Lens Is a Nightvision Owl Eye For Your Camera”, September 2008

[8] The Cosina Voigtländer 17.5mm f/0.95 at B&H Photo

[9] The Cosina Voigtländer 25mm f/0.95 at B&H Photo

[10] The Cosina Voigtländer 42.5mm f/0.95 at B&H Photo

[11] Ed DiGiulio (President, Cinema Products Corporation). “Two Special Lenses for Barry Lyndon"

[12] “Pinhole and Photography for SLR Cameras”. Lensbaby Pinhole optic.

[13] Sidney F. Ray. The geometry of image formation. In The Manual of Photography: Photographic and Digital Imaging, 9th ed, pp. 136–137. Ed. Ralph E. Jacobson, Sidney F. Ray, Geoffrey G. Atteridge, and Norman R. Axford. Oxford: Focal Press, 2000. ISBN 0-240-51574-9 4.1. APERTURE 75

[14] Shipman, Carl (1977). SLR Photographers Handbook. Tucson, AZ: HP Books. p. 53. ISBN 0-912656-59-X.

[15] B. “Moose” Peterson. Nikon System Handbook. New York: Images Press, 1997, pp. 42–43. ISBN 0-929667-03-4

[16] Canon Camera Museum. Accessed 12 December 2008.

[17] EF Lens Work III: The Eyes of EOS. Tokyo: Canon Inc., 2003, pp. 190–191.

[18] Nikon USA web site Archived 12 December 2008 at the Wayback Machine.. Accessed 12 December 2008.

[19] Nikon PC-E product comparison brochure Archived 17 December 2008 at the Wayback Machine.(PDF). Accessed 12 December 2008.

[20] http://www.bobatkins.com/photography/technical/diffraction.html

[21] R Butler. “Sony Cyber-shot DSC RX10 First Impressions Review”. Retrieved January 19, 2014.

• This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). "Aperture". Encyclopædia Britannica (11th ed.). Cambridge University Press. 76 CHAPTER 4. DAY 4

A large (f/2.8) and a small (f/16) aperture. 4.1. APERTURE 77

Aperture mechanism of Canon 50mm f/1.8 II lens, with 5 blades. 78 CHAPTER 4. DAY 4

Definitions of Aperture in the 1707 Glossographia Anglicana Nova.[1]

Diagram of decreasing aperture sizes (increasing f-numbers) for “full stop” increments (factor of two aperture area per stop) 4.1. APERTURE 79

The aperture range of a 50mm Minolta lens, f/1.4–f/16 80 CHAPTER 4. DAY 4

4.2 Diaphragm (optics)

A 35 mm lens set to f/8; the diameter of the seven-sided entrance pupil, the virtual image of the opening in the iris diaphragm, is 4.375 mm

In optics, a diaphragm is a thin opaque structure with an opening (aperture) at its center. The role of the diaphragm is to stop the passage of light, except for the light passing through the aperture. Thus it is also called a stop (an aperture stop, if it limits the brightness of light reaching the focal plane, or a field stop or flare stop for other uses of diaphragms in lenses). The diaphragm is placed in the light path of a lens or objective, and the size of the aperture regulates the amount of light that passes through the lens. The centre of the diaphragm’s aperture coincides with the optical axis of the lens system. Most modern cameras use a type of adjustable diaphragm known as an iris diaphragm, and often referred to simply as an iris. See the articles on aperture and f-number for the photographic effect and system of quantification of varying the opening in the diaphragm. 4.2. DIAPHRAGM (OPTICS) 81

Nine-blade iris

4.2.1 Iris diaphragms versus other types

A natural optical system that has a diaphragm and an aperture is the human eye. The iris is the diaphragm, and the opening in the iris of the eye (the pupil) is the aperture. An analogous dev in a photographic lens is called an iris diaphragm. In the early years of photography, a lens could be fitted with one of a set of interchangeable diaphragms , often as brass strips known as Waterhouse stops or Waterhouse diaphragms. The iris diaphragm in most modern still and video cameras is adjusted by movable blades, simulating the iris of the eye. The diaphragm has two to twenty blades (with most lenses today featuring between five and ten blades), depending on price and quality of the device in which it is used. Straight blades result in polygon shape of the diaphragm opening, while curved blades improve the roundness of the iris opening. In a photograph, the number of blades that the iris diaphragm has can be guessed by counting the number of diffraction spikes converging from a light source or bright reflection. For an odd number of blades, there are twice as many spikes as there are blades. In case of an even number of blades, the two spikes per blade will overlap each other, so the number of spikes visible will be the number of blades in the diaphragm used. This is most apparent in pictures taken in the dark with small bright spots, for example night cityscapes. Some cameras, such as the Olympus XA or lenses such as the MC Zenitar-ME1, however, use a two-bladed diaphragm with right-angle blades creating a square aperture. Similarly, out-of-focus points of light (circles of confusion) appear as polygons with the same number of sides as the aperture has blades. If the blurred light is circular, then it can be inferred that the aperture is either round or the image was shot “wide-open” (with the blades recessed into the sides of the lens, allowing the interior edge of the lens barrel to effectively become the iris). 82 CHAPTER 4. DAY 4

Pentacon 2.8/135 lens with 15-blade iris

The shape of the iris opening has a direct relation with the appearance of the blurred out-of-focus areas in an image called bokeh. A rounder opening produces softer and more natural out-of-focus areas. Some lenses utilize specially shaped diaphragms in order to create certain effects. This includes the diffusion discs or sieve aperture of the Rodenstock Tiefenbildner-Imagon, Fuji and Sima soft focus lenses, the sector aperture of Seibold’s Dreamagon, or the circular apodization filter in the Minolta/Sony Smooth Trans Focus or Fujifilm APD lenses. Some modern automatic point-and-shoot cameras do not have a diaphragm at all, and simulate aperture changes by using an automatic ND filter. Unlike a real diaphragm, this has no effect on depth of field. A real diaphragm when more-closed will cause the depth of field to increase (i.e., cause the background and the subject to both appear more in-focus at the same time) and if the diaphragm is opened up again the depth of field will decrease (i.e., the background and foreground will share less and less of the same focal plane).[2]

4.2.2 History

In 1762, Leonhard Euler[3] says with respect to telescopes that, “it is necessary likewise to furnish the inside of the tube with one or more diaphragms, perforated with a small circular aperture, the better to exclude all extraneous light.” 4.2. DIAPHRAGM (OPTICS) 83

A Zeiss rotating diaphragm, 1906.[1] One diaphragm with five apertures.

In 1867, Dr. Désiré van Monckhoven, in one of the earliest books on photographic optics,[4] draws a distinction betweens stops and diaphragms in photography, but not in optics, saying:

“Let us see what takes place when the stop is removed from the lens to a proper distance. In this case the stop becomes a diaphragm. 84 CHAPTER 4. DAY 4

* In optics, stop and diaphragm are synonyms. But in photographic optics they are only so by an un- fortunate confusion of language. The stop reduces the lens to its central aperture; the diaphragm, on the contrary, allows all the segments of the lens to act, but only on the different radiating points placed symmetrically and concentrically in relation to the axis of the lens, or of the system of lenses (of which the axis is, besides, in every case common).”

This distinction was maintained in Wall’s 1889 Dictionary of Photography (see figure), but disappeared after Ernst Abbe's theory of stops unified these concepts. According to Rudolph Kingslake,[5] the inventor of the iris diaphragm is unknown. Others credit Joseph Nicéphore Niépce for this device, around 1820. Mr. J. H. Brown, a member of the Royal Microscopical Society, appears to have invented a popular improved iris diaphragm by 1867.[6] Kingslake has more definite histories for some other diaphragm types, such as M. Noton’s adjustable cat eye diaphragm of two sliding squares in 1856, and the Waterhouse stops of John Waterhouse in 1858.

4.2.3 See also

• Aperture

• f-number • Shutter (photography)

• Leaf shutter • Valbray

• Diffraction spike

4.2.4 References

[1] Louis Derr, Photography for students of physics and chemistry London: The Macmillan Co., 1906

[2] Steven Ascher; Edward Pincus (2007). The Filmmaker’s Handbook: A Comprehensive Guide for the Digital Age. Plume. p. 154. ISBN 978-0-452-28678-8.

[3] Leonhard Euler, “Precautions to be used in the Construction of Telescopes. Necessitiy of blackening the Inside of Tubes. Diaphragms.” 1762, in Letters of Euler on different subjects in physics and philosophy. Addressed to a German princess, Vol. II, Henry Hunter, D.D. (ed.), London, 1802,

[4] Désiré van Monckhoven, Photographic Optics: Including the Description of Lenses and Enlarging Apparatus, English trans- lation, London: Robert Hardwicke, 1867

[5] Rudolf Kingslake, A History of the Photographic Lens, London: Academic Press, 1989

[6] J. Henle, W, Keferstein, and G. Meissner, Bericht über die Fortschritte der Anatomie und Physiologie im Jahre 1867, Liepzip: C. F. Winter’sche Verlagshandlung, 1868. Chapter 5

Day 5

5.1 Normal lens

In photography and cinematography, a normal lens is a lens that reproduces a field of view that appears “natural” to a human observer. However, to find a photographic lens equivalent to the human eye, which has an effective focal length of approximately 17mm,[1] is problematic due to the nature of human binocular vision, being mediated and processed by the cortex, and because of the structure of the human eye which has a concave retina, rather than a flat sensor, with variable sensitivity and resolution across its wider-than-180° horizontal field-of-view. A normal lens then, is one that renders a printed (or otherwise displayed) photograph of a scene that when held at 'normal' viewing distance (usually arms-length) in front of the original scene and viewed with one eye, matches the real-world and the rendered perspective.[2]

5.1.1 Perspective effects of short or long focal-length lenses

Lenses with longer or shorter focal lengths produce an expanded or contracted field of view that appears to distort the perspective when viewed from a normal viewing distance.[3][4] Lenses of shorter focal length are called wide-angle lenses, while longer-focal-length lenses are referred to as long-focus lenses[5] (with the most common of that type being the telephoto lenses). Superimposing a wide-angle image print against the original scene would require holding it closer to the eye, while the telephoto image would need to be placed well into the depth of the photographed scene, or a tiny print to be held at arms-length, to match their perspectives. Such is the extent of distortions of perspective with these lenses that they may not be permitted as legal evidence.[6] The ICP Encyclopaedia of Photography reports that; “Judges will not admit a picture that seems to have been tampered with or that distorts any aspect of the scene” or does not render a normal perspective. “That is, the size relationships of objects in the photograph should be equivalent to what they actually are.”[7]

5.1.2 'Normal' lenses vary for different formats

For still photography, a lens with a focal length about equal to the diagonal size of the film or sensor format is considered to be a normal lens; its angle of view is similar to the angle subtended by a large-enough print viewed at a typical viewing distance equal to the print diagonal;[4] this angle of view is about 43° diagonally. For cinematography, where the image is larger relative to viewing distance, a wider lens with a focal length of roughly a quarter of the film or sensor diagonal is considered 'normal'. The term normal lens can also be used as a synonym for rectilinear lens. This is a completely different use of the term.

5.1.3 Typical normal focal lengths for different formats

85 86 CHAPTER 5. DAY 5

Four “normal” lenses for the 35mm format. 5.2. PRIME LENS 87

Film still

Typical normal lenses for various film formats for photography are: For a 35 mm camera with a diagonal of 43 mm, the most commonly used normal lens is 50 mm, but focal lengths between about 40 and 58 mm are also considered normal. The 50 mm focal length was chosen by Oskar Barnack, the creator of the . Note that the angle of view depends on the as well; a “normal” lens on 35mm does not have the same view as a “normal” lens on 645, for example.

Digital still

In digital photography, the sensor “type” is not the sensor diameter:

(*) refers to TV tube diameters that were standards in the 50s. The normal lens focal length is roughly 2/3 of the TV tube diameter. (**) this is a mathematical calculation because most of the cameras are equipped with zoom lenses.

Cinema

In cinematography, a focal length roughly equivalent to twice the diagonal of the image projected within the camera is considered normal, since movies are typically viewed from a distance of about twice the screen diagonal.[10]

5.1.4 References

[1] Pocock, Gillian & Richards, Christopher D & Richards, Dave A (2013). Human physiology (4th ed). Oxford University Press, Oxford p214

[2] Pirenne, Maurice Henri Leonard (1970). Optics, painting & photography. University Press, Cambridge [England]

[3] Ernst Wildi (2001). Creating World-Class Photography: How Any Photographer Can Create Technically Flawless Pho- tographs. Amherst Media, Inc. p. 44. ISBN 978-1-58428-052-1.

[4] Leslie D. Stroebel (1999). View camera technique (7th ed.). Focal Press. pp. 135–140. ISBN 978-0-240-80345-6.

[5] Bruce Warren, Photography, page 71

[6] Hampton Dillinger (1997) 'Words Are Enough: The Troublesome Use of Photographs, Maps, and Other Images in Supreme Court Opinions’. In Harvard Law Review Vol. 110, No. 8 (Jun., 1997), pp. 1704-1753 The Harvard Law Review Association

[7] International Center of Photography (1984). Encyclopedia of photography (1st ed). Crown Publishers, New York supra note 88, at p.208

[8] The Four Thirds Standard, Four Thirds Consortium, 2008, retrieved 2009-04-17

[9] “No more compromises: the Four Thirds standard”. Olympus Europa. Archived from the original on 2011-09-27.

[10] Anton Wilson, Anton Wilson’s Cinema Workshop, American Cinematographer, 2004 (Page 100) online.

5.2 Prime lens

For ground lenses used in conjunction with secondary lenses, see primary lens. In film and photography, a prime lens is either a photographic lens whose focal length is fixed, as opposed to a zoom lens, or it is the primary lens in a combination lens system. Confusion can sometimes result due to the two meanings of the term if the context does not make the interpretation clear. Alternative terms primary focal length, fixed focal length, and FFL are sometimes used to avoid ambiguity. 88 CHAPTER 5. DAY 5

A 29mm prime lens accompanied by a diagram of its internal lens elements.

5.2.1 As alternative to zoom lens

The term prime has come to be used as the opposite of zoom; that is, a prime lens is a fixed-focal-length, or unifocal lens, while a zoom lens has a variable focal length.[1][2][3] While a prime lens of a given focal length is less versatile than a zoom, it is often of superior optical quality, wider maximum aperture, lighter weight, smaller size. These advantages stem from having fewer moving parts, optical elements optimized for one particular focal length, and a less complicated lens formula which means that they suffer from fewer problems of . The larger maximum aperture (smaller f-number) allows photography in lower light, and a shallower depth of field. A normal lens or “normal prime” is a lens with a focal length about equal to the diagonal size of the film or sensor format, or that reproduces perspective that generally looks “natural” to a human observer under normal viewing conditions.

5.2.2 Traditional meaning as primary lens

An alternative and apparently somewhat older meaning of the term prime lens is the main lens in a combination lens system.[4] When the camera lens is used with some other optical device, such as a close-up lens, teleconverter, or teleside converter, the camera lens itself is properly called the prime lens. Prime is here used in the sense of primary, chief, original, first in order, etc. 5.2. PRIME LENS 89

Prime lenses can have quite large apertures, compared with zoom lenses. These 85mm lenses have maximum apertures of f/1.8 (left) and f/1.2 (right).

Lens manufacturers such as ARRI Media,[5] ISCO Precision Optics,[6] Schneider,[7] Carl Zeiss AG,[8] Canon[9] and others still make variable focal length cine and video lenses regularly catalogued as variable prime lenses. A variable prime is sometimes distinguished from a “true zoom” in that the latter maintains focus as the focal length is varied. This use of the term “prime lens” is an example of a retronym. Early in photography only primary camera lenses were available, and were merely called “lenses” or “objectives”. Later, “auxiliary” lenses were available, which usually fit in front of the front element of the primary, or “prime” lens.

5.2.3 Popular focal lengths

Many lens manufacturers produce or produced prime lenses at or near the following focal lengths: 20 mm, 24 mm, 28 mm, 35 mm, 40 mm, 50 mm, 85 mm, 105 mm, 135 mm, 200 mm, 300 mm, 400 mm, and 600 mm. For these lengths many manufacturers produce two or more lenses with the same focal length but with different maximum apertures to suit the different needs of photographers. Additional focal lengths can be created by using a teleconverter. For 35mm film and full frame digital cameras (in which the image area is 36 by 24 millimeters) prime lenses can be categorized by focal length as follows:

• 14 to 21mm: Ultra-Wide — Because these lenses are usually used at very close subject distances the resulting perspective can provide a dramatic, often extreme image that can be used to selectively distort a scene’s natural proportions.

• 24 to 35mm: Wide — these lenses capture a wider field of view than a standard lens. Because they tend to be used at shorter distances the resulting perspective can show some distortion.

• 50 mm: Standard — with a focal length near the 44mm image diagonal.

• 85 mm: Portrait — A short telephoto lens that allows a longer subject to camera distance, to produce pleasing perspective effects, while maintaining useful image framing.

• 135 mm: Telephoto — these lenses are used by action and sports photographers to capture faraway objects. 90 CHAPTER 5. DAY 5

The Canon EF 50mm f/1.8 II.

• 200 to 500 mm: Super Telephoto — these are specialized, bulky lenses for sports, action, and wildlife pho- tography.

5.2.4 Specialist lenses

Some specialist lenses are only available as prime lenses due to design or cost constraints. Examples of such specialist lenses are: extreme telephoto or wide angle, lenses with tilt and / or shift function, lenses with large apertures and macro lenses.

5.2.5 References

[1] Lenny Lipton (1975). The Super 8 Book. Simon and Schuster. p. 61. ISBN 0-87932-091-5.

[2] A. Arthur Englander and Paul Petzold (1976). Filming for Television. Hastings House.

[3] Gerald Millerson (1993). Effective TV Production. Focal Press. ISBN 0-240-51324-X.

[4] The British Journal of Photography (v.115 ed.). Liverpool Photographic Society. 1967.

[5] “ARRI Variable Prime Lenses”. ARRI Media. Archived from the original on October 20, 2006. Retrieved 2007-11-19.

[6] “Variable Prime System for 35 mm Film” (PDF). ISCO Precision Optics. Archived from the original (PDF) on 2007-10-19. Retrieved 2007-11-19.

[7] “Variable Prime”. Schneider Optics. Retrieved 2007-11-19.

[8] “1998 Scientific & Technical Awards Winners”. Academy of Motion Picture Arts and Sciences. Archived from the original on 2007-08-10. Retrieved 2007-11-19.

[9] “AMPAS Award”. Academy of Motion Picture Arts and Sciences. Archived from the original on 2007-08-23. Retrieved 2007-11-19.

5.2.6 External links

• Photo Dictionary definition • Photography Terms 5.3. ZOOM LENS 91

5.3 Zoom lens

This article is about the camera lens. For the American record label, see Zoom Lens (record label). A zoom lens is a mechanical assembly of lens elements for which the focal length (and thus angle of view) can be

Nikkor 28-200 mm zoom lens, extended to 200 mm at left and collapsed to 28 mm focal length at right varied, as opposed to a fixed focal length (FFL) lens (see prime lens). A true zoom lens, also called a parfocal lens, is one that maintains focus when its focal length changes.[1] A lens that loses focus during zooming is more properly called a varifocal lens. Despite being marketed as zoom lenses, virtually all consumer lenses with variable focal lengths use varifocal design. The convenience of variable focal length comes at the cost of complexity - and some compromises on image quality, weight, dimensions, aperture, autofocus performance, and cost. For example, all zoom lenses suffer from at least slight, if not considerable, loss of image resolution at their maximum aperture, especially at the extremes of their focal length range. This effect is evident in the corners of the image, when displayed in a large format or high resolution. The greater the range of focal length a zoom lens offers, the more exaggerated these compromises must become.[2]

5.3.1 Characteristics

Zoom lenses are often described by the ratio of their longest to shortest focal lengths. For example, a zoom lens with focal lengths ranging from 100 mm to 400 mm may be described as a 4:1 or “4×" zoom. The term superzoom or 92 CHAPTER 5. DAY 5

A photograph taken with a zoom lens, whose focal length was varied during the course of the exposure.

hyperzoom is used to describe photographic zoom lenses with very large focal length factors, typically more than 5× and ranging up to 19× in SLR camera lenses and 83× in amateur digital cameras. This ratio can be as high as 300× in professional television cameras.[3] As of 2009, photographic zoom lenses beyond about 3× cannot generally produce imaging quality on par with prime lenses. Constant fast aperture zooms (usually f/2.8 or f/2.0) are typically restricted to this zoom range. Quality degradation is less perceptible when recording moving images at low resolution, which is why professional video and TV lenses are able to feature high zoom ratios. Digital photography can also accommodate algorithms that compensate for optical flaws, both within in-camera processors and post-production software. Some photographic zoom lenses are long-focus lenses, with focal lengths longer than a normal lens, some are wide- angle lenses (wider than normal), and others cover a range from wide-angle to long-focus. Lenses in the latter group of zoom lenses, sometimes referred to as “normal” zooms, have displaced the fixed focal length lens as the popular one-lens selection on many contemporary cameras. The markings on these lenses usually say W and T for “Wide” and “Telephoto”. Telephoto is designated because the longer focal length supplied by the negative diverging lens is longer than the overall lens assembly (the negative diverging lens acting as the “telephoto group”).[4] Some digital cameras allow cropping and enlarging of a captured image, in order to emulate the effect of a longer focal length zoom lens (narrower angle of view). This is commonly known as digital zoom and produces an image of lower optical resolution than optical zoom. Exactly the same effect can be obtained by using processing software on a computer to crop the digital image and enlarge the cropped area. Many digital cameras have both, combining them by first using the optical, then the digital zoom. Zoom and superzoom lenses are commonly used with still, video, motion picture cameras, projectors, some binoculars, microscopes, telescopes, telescopic sights, and other optical instruments. In addition, the afocal part of a zoom lens can be used as a telescope of variable magnification to make an adjustable beam expander. This can be used, for example, to change the size of a laser beam so that the irradiance of the beam can be varied.

5.3.2 History

Early forms of zoom lenses were used in optical telescopes to provide continuous variation of the magnification of the image, and this was first reported in the proceedings of the Royal Society in 1834. Early patents for telephoto lenses also included movable lens elements which could be adjusted to change the overall focal length of the lens. 5.3. ZOOM LENS 93

Unusual trailed-zoom view of a VLT radio telescope building.[5]

Lenses of this kind are now called varifocal lenses, since when the focal length is changed, the position of the focal plane also moves, requiring refocusing of the lens after each change. The first true zoom lens, which retained near-sharp focus while the effective focal length of the lens assembly was changed, was patented in 1902 by Clile C. Allen (U.S. Patent 696,788). An early use of the zoom lens in cinema can be seen in the opening shot of the movie “It” starring Clara Bow, from 1927. The first industrial production was the Bell and Howell Cooke “Varo” 40–120 mm lens for 35mm movie cameras introduced in 1932. The most impressive early TV Zoom lens was the VAROTAL III from Rank Taylor Hobson from UK built in 1953. The Kilfitt 36–82 mm/2.8 Zoomar introduced in 1959 was the first varifocal lens in regular production for still 35mm photography. The first modern film zoom lens, the Pan-Cinor, was designed around 1950 by Roger Cuvillier, a French engineer working for SOM-Berthiot. It had an optical compensation zoom system. In 1956, Pierre Angénieux introduced the mechanical compensation system, enabling precise focus while zooming, in his 17-68mm lens for 16mm released in 1958. The same year a prototype of the 35mm version of the Angénieux 4x zoom, the 35-140mm was first used by cinematographer Roger Fellous for the production of Julie La Rousse. Angénieux received a 1964 technical award from the academy of motion pictures for the design of the 10 to 1 zoom lenses, including the 12-120mm for 16mm film cameras and the 25-250mm for 35mm film cameras. Since then advances in optical design, particularly the use of computers for optical ray tracing, has made the design and construction of zoom lenses much easier, and they are now used widely in professional and amateur photography.

5.3.3 Design

There are many possible designs for zoom lenses, the most complex ones having upwards of thirty individual lens elements and multiple moving parts. Most, however, follow the same basic design. Generally they consist of a number of individual lenses that may be either fixed or slide axially along the body of the lens. While the magnification of a zoom lens changes, it is necessary to compensate for any movement of the focal plane to keep the focused image sharp. This compensation may be done by mechanical means (moving the complete lens assembly while the magnification of the lens changes) or optically (arranging the position of the focal plane to vary as little as possible while the lens is zoomed). A simple scheme for a zoom lens divides the assembly into two parts: a focusing lens similar to a standard, fixed-focal- length photographic lens, preceded by an afocal zoom system, an arrangement of fixed and movable lens elements that 94 CHAPTER 5. DAY 5

The Voigtländer Zoomar, 36–82 mm f/2.8 5.3. ZOOM LENS 95

Canon AE-1, a 35mm camera with a zoom lens. The advantage of a zoom lens is the flexibility, but the disadvantage is the optical quality. Prime lens have a greater image quality in comparison.

Focussing lens Afocal zoom system

A simple zoom lens system. The three lenses of the are L1, L2, L3 (from left). L1 and L2 can move to the left and right, changing the overall focal length of the system (see image below). does not focus the light, but alters the size of a beam of light travelling through it, and thus the overall magnification of the lens system. In this simple optically compensated zoom lens, the afocal system consists of two positive (converging) lenses of equal focal length (lenses L1 and L3) with a negative (diverging) lens (L2) between them, with an absolute focal length less than half that of the positive lenses. Lens L3 is fixed, but lenses L1 and L2 can be moved axially in a particular non-linear relationship. This movement is usually performed by a complex arrangement of gears and cams in the lens housing, although some modern zoom lenses use computer-controlled servos to perform this positioning.

While the negative lens L2 moves from the front to the back of the lens, the lens L1 moves forward and then backward in a parabolic arc. In doing so, the overall angular magnification of the system varies, changing the effective focal 96 CHAPTER 5. DAY 5

L1 L2 L3

Movement of lenses in an afocal zoom system length of the complete zoom lens. At each of the three points shown, the three-lens system is afocal (neither diverging or converging the light), and hence does not alter the position of the focal plane of the lens. Between these points, the system is not exactly afocal, but the variation in focal plane position can be small enough (about ±0.01 mm in a well-designed lens) not to make a significant change to the sharpness of the image. An important issue in zoom lens design is the correction of optical aberrations (such as chromatic aberration and, in particular, field curvature) across the whole operating range of the lens; this is considerably harder in a zoom lens than a fixed lens, which needs only to correct the aberrations for one focal length. This problem was a major reason for the slow uptake of zoom lenses, with early designs being considerably inferior to contemporary fixed lenses and usable only with a narrow range of f-numbers. Modern optical design techniques have enabled the construction of 5.3. ZOOM LENS 97

Simplified zoom lens in operation

zoom lenses with good aberration correction over widely variable focal lengths and apertures. Whereas lenses used in cinematography and video applications are required to maintain focus while the focal length is changed, there is no such requirement for still photography and for zoom lenses used as projection lenses. Since it is harder to construct a lens that does not change focus with the same image quality as one that does, the latter applications often use lenses that require refocusing once the focal length has changed (and thus strictly speaking are varifocal lenses, not zoom lenses). As most modern still cameras are autofocusing, this is not a problem. Designers of zoom lenses with large zoom ratios often trade one or more aberrations for higher image sharpness. For example, a greater degree of barrel and pincushion distortion is tolerated in lenses that span the focal length range from wide angle to telephoto with a focal ratio of 10× or more than would be acceptable in a fixed focal length lens or a zoom lens with a lower ratio. Although modern have been continually reducing this problem, barrel distortion of greater than one percent is common in these large-ratio lenses. Another price paid is that at the extreme telephoto setting of the lens the effective focal length changes significantly while the lens is focused on closer objects. The apparent focal length can more than halve while the lens is focused from infinity to medium close-up. To a lesser degree, this effect is also seen in fixed focal length lenses that move internal lens elements, rather than the entire lens, to effect changes in magnification.

5.3.4 Varifocal lens

Many so-called “zoom” lenses, particularly in the case of fixed-lens cameras, are actually varifocal lenses, which gives lens designers more flexibility in optical design trade-offs (focal length range, maximal aperture, size, weight, cost) than true parfocal zoom, and which is practical because of autofocus, and because the camera processor can move the lens to compensate for the change in the position of the focal plane while changing magnification (“zooming”), making operation essentially the same as a true parfocal zoom. 98 CHAPTER 5. DAY 5

5.3.5 See also

• Zooming (filmmaking) • Pan tilt zoom camera (PTZ)

• Professional video camera • Tripod (photography)

• View camera

By focal length:

• Prime lens • Superzoom

• Telephoto lens • Wide-angle lens

Focus attributes:

• Parfocal lens

• Varifocal lens

By system:

• List of Canon EF lenses

• Nikon F-mount

• Minolta AF

5.3.6 References

[1] Cavanagh, Roger (2003-05-29). “Parfrocal Lenses”. Archived from the original on 2007-10-07. Retrieved 2007-11-18.

[2] “Tamron 18-270mm f/3.5-6.3 Di II VC LD Lens Review”. Retrieved March 20, 2013.

[3] http://www.letsgodigital.org/en/news/articles/story_1325.html

[4] Business and corporate aviation management: on demand air transportation By John J. Sheehan, page 521

[5] “Funding Opportunities in Chile (Anuncio de Oportunidades)". ESO Announcements. Retrieved 2 May 2014.

• Kingslake, R. (1960), “The development of the zoom lens”. Journal of the SMPTE 69, 534 • Clark, A.D. (1973), Zoom Lenses, Monographs on Applied Optics No. 7. Adam Hildger (London).

• Malacara, Daniel and Malacara, Zacarias (1994), Handbook of Lens Design. Marcel Dekker, Inc. ISBN 0- 8247-9225-4

• "What is Inside a Zoom Lens?", Adaptall-2.com.

5.3.7 External links Chapter 6

Day 6

6.1 Telephoto lens

“Telephoto” redirects here. For the technique for transmitting images, see Wirephoto. In photography and cinematography, a telephoto lens is a specific type of a long-focus lens in which the physical length of the lens is shorter than the focal length.[1] This is achieved by incorporating a special lens group known as a telephoto group that extends the light path to create a long-focus lens in a much shorter overall design. The angle of view and other effects of long-focus lenses are the same for telephoto lenses of the same specified focal length. Long-focal-length lenses are often informally referred to as telephoto lenses although this is technically incorrect: a telephoto lens specifically incorporates the telephoto group.[2] Telephoto lenses are sometimes broken into the further sub-types of medium telephoto: lenses covering between a 30° and 10° field of view (67mm to 206mm in 35mm film format), and super telephoto: lenses covering between 8° through less than 1° field of view (over 300mm in 35mm film format).[3]

6.1.1 Construction

In contrast to a telephoto lens, for any given focal length a simple lens of non-telephoto design is constructed from one lens (which can, to minimize aberrations, consist of several elements to form an achromatic lens). To focus on an object at infinity, the distance from this single lens to focal plane of the camera (where the sensor or film is respectively) has to be adjusted to this focal length. For example, given a focal length of 500 mm, the distance between lens and focal plane is 500 mm. The farther the focal length is increased, the more the physical length of such a simple lens makes it unwieldy. But such simple lenses are not telephoto lenses, no matter how extreme the focal length – they are known as long- focus lenses.[1] While the optical centre of a simple (“non-telephoto”) lens is within the construction, the telephoto lens moves the optical centre in front of the construction. A telephoto lens works by having the outermost (i.e. light gathering) element of a much shorter focal length than the equivalent long-focus lens and then incorporating a second set of elements close to the film or sensor plane that extend the cone of light so that it appears to have come from a lens of much greater focal length. The basic construction of a telephoto lens consists of front lens elements that, as a group, have a positive focus. The focal length of this group is shorter than the effective focal length of the lens. The converging rays from this group are intercepted by the rear lens group, sometimes called the “telephoto group,” which has a negative focus. The simplest telephoto designs could consist of one element in each group, but in practice, more than one element is used in each group to correct for various aberrations. The combination of these two groups produces a lens assembly that is physically shorter than a long-focus lens producing the same image size. This same property is achieved in camera lenses that combine mirrors with lenses. These designs,called catadioptric, 'reflex', or 'mirror' lenses,have a as the primary objective with some form of negative lens in front of the mirror to correct optical aberrations. They also use a curved secondary mirror to relay the image that extends the light cone the same way the negative lens telephoto group does. The mirrors also fold the light path. This makes them much shorter, lighter, and cheaper than an all refractive lens, but at the cost of some optical compromises due to aberrations caused by the central obstruction from the secondary mirror.

99 100 CHAPTER 6. DAY 6

A collection of telephoto lenses

The heaviest non-Catadioptric telephoto lens for civilian use was made by Carl Zeiss and has a focal length of 1700 mm with a maximum aperture of f/4, implying a 425 mm (16.7 in) entrance pupil. It is designed for use with a medium format Hasselblad 203 FE camera and weighs 256 kg (564 lb).[4] 6.1. TELEPHOTO LENS 101

Canon super telephoto lens

A 500 mm lens of a non-telephoto design

Retrofocus lenses

Inverting the telephoto configuration, employing one or more negative lens groups in front of a positive lens group, creates a wide-angle lens with an increased back focal distance. These are called retrofocus lenses or inverted tele- photos, which have greater clearance from the rear element to the film plane than their focal length would permit with a conventional wide-angle lens optical design. This allows for greater clearance for other optical or mechanical parts such as the mirror parts in a single-lens reflex camera. Zoom lenses that are telephotos at one extreme of the zoom range and retrofocus at the other are now common.

6.1.2 History

The concept of the telephoto lens, in reflecting form, was first described by Johannes Kepler in his Dioptrice of 1611,[5] and re-invented by Peter Barlow in 1834.[6] Histories of photography usually credit Thomas Rudolphus Dallmeyer with the invention of the photographic tele- photo lens in 1891, though it was independently invented by others about the same time; some credit his father John Henry Dallmeyer in 1860.[7] 102 CHAPTER 6. DAY 6

A 150–500mm telephoto zoom lens

H'

D

D f ' H'

Diagram of a typical telephoto lens with a large positive lens and a smaller negative telephoto group combined to create a much longer focal length - f.

In 1883 or 1884 New Zealand photographer Alexander McKay discovered he could create a much more manageable long-focus lens by combining a shorter focal length telescope objective lens with negative lenses and other optical parts from opera glasses to modify the light cone. Some of his photographs are preserved in the holdings of the Turnbull Library in Wellington, and two of these can be unequivocally dated as having been taken during May 1886. One of McKay’s photographs shows the Russian warship Vjestnik anchored in Wellington harbour about two and a half kilometres away, with its rigging lines and gun ports clearly visible. The other, taken from the same point, is of a local hotel, the Shepherds Arms, about 100 metres distant from the camera. The masts of the Vjestnik are visible in the background. McKay’s other photographic achievements include photo-micrographs, and a ‘shadow-less technique’ for photographing fossils.[8] McKay presented his work to the Wellington Philosophical Society (the precursor of the Royal Society of New 6.1. TELEPHOTO LENS 103

H'

f ' H'

Diagram of a catadioptric mirrors lens.

D H'

D H' f '

A diagram of light travel through a wide-angle lens showing how focal length can be shorter than the lens.

Zealand) in 1890.[9]

6.1.3 See also

•

•

• Secret photography

• Photographic lens design

• Barlow lens

• Zoom lens

6.1.4 References

[1] R. E. Jacobson, The manual of photography: photographic and digital imaging, page 93

[2] Gregory Hallock Smith, Camera lenses: from to digital, page 207

[3] photographywebsite.co.uk - Lens Types Explained

[4] “Zeiss Apo Sonnar T* 1700 mm F4 lens”. Digital Photography Review. Retrieved 1 October 2006. 104 CHAPTER 6. DAY 6

A Canon F-1, 35mm camera with a telephoto zoom lens.

[5] Edward John Wall and Thomas Bolas (1902). The Dictionary of Photography for the Amateur and Professional Photogra- pher. London: Hazell, Watson, and Viney Ld.

[6] Ray N. Wilson (2004). Reflecting Telescope Optics. Springer. ISBN 978-3-540-40106-3.

[7] New York Times Staff (2004). The New York Times Guide to Essential Knowledge. Macmillan. ISBN 978-0-312-31367-8.

[8] Graham Bishop (2008). The Real McKay: The remarkable life of Alexander McKay, geologist. (1841-1917). Dunedin: Otago University Press. ISBN 978-1-877372-22-3.

[9] Alexander McKay (1891). “On Some Means for increasing the Scale of Photographic Lenses, and the Use of Telescopic Powers in Connection with an Ordinary Camera”. Transactions of the New Zealand Institute. XIII: 461–465.

6.1.5 External links

• Information on Catadioptric mirror lenses • Further clarification: Why Telephoto? • 3 part series on Cheap Super Telephoto Lenses (300-500mm) • Stanford University CS 178 interactive applet showing how a telephoto zoom lens works.

6.2 Teleconverter

A teleconverter (sometimes called tele extender) is a which is mounted between the camera and a photographic lens. Its job is to enlarge the central part of an image obtained by the objective lens. For example, a 2× teleconverter for a 35 mm camera enlarges the central 12×18 mm part of an image to the size of 24×36 mm in the standard 35 mm film format. are typically made in 1.4×, 1.7×, 2× and 3× models, of which 1.4× and 2× are most common. The use of a 2× teleconverter gives the effect of using a lens with twice the focal length. It also decreases the intensity of the light reaching the film by a factor of 4 (an equivalent of doubling the focal ratio) as well as the resolution (by a factor of 2). 6.2. TELECONVERTER 105

A teleconverter attached between a camera and its objective

6.2.1 Function

A teleconverter works similarly to a telephoto group of a proper telephoto lens. It consists of a group of lenses which together act as a single diverging lens. The location of a teleconverter is such that the image produced by the objective is located behind the teleconverter in a distance smaller than its focal length. This image is a virtual object of the teleconverter, which is then focused further away and thus enlarged. For example, when a single negative lens is placed so that the image formed by the objective is located in the midpoint between the lens and its focal point, then the lens produces the image in its focal point and enlarging it two-fold, thereby acting as a 2× teleconverter. When used with somewhat slow lenses they may reduce the effective aperture enough that the camera’s autofocus system will no longer work; depending on the camera system, this may range from f/5.6 to f/8. Dedicated teleconverters only work with a limited number of lenses, usually telephoto lenses made by the same manufacturer, or by a third-party manufacturer to a matching standard. Using a teleconverter with an existing lens is usually less expensive than acquiring a separate, longer telephoto lens, but as the teleconverter is magnifying the existing image circle, it also magnifies any aberrations. The use of a teleconverter also results in a darker image.

• Camera viewfinder with 300mm telephoto lens. 106 CHAPTER 6. DAY 6

An Olympus EC-20 - 2x teleconverter lens attached between a camera.[1] 1 - Camera lens 2 - Teleconverter 3 - Camera body

• Camera viewfinder with 300mm telephoto lens and 2x teleconverter.

• A Leica R series doubler, with the female part of in bayonet mount...

• ...and the male part.

Teleside converter

A different type of teleconverter called a teleside converter[2] can be mounted on the front of the camera’s lens rather than between the primary lens and the camera body. These are popular with users of video cameras and bridge cameras with fixed lenses, as they represent the only way to add more reach to such a camera. They are usually afocal 6.2. TELECONVERTER 107

Teleside converter cross section lenses that do not reduce the brightness of the image, but are more likely to add aberrations to the image, independent of the quality of the main lens.

Versus extension tubes

Teleconverters may be confused with extension tubes, a non-optical component designed to increase magnification (at the expense of reduced focal distance).

6.2.2 See also

• Barlow Lens • Canon Extender EF

• Nikon F-mount teleconverter •

• Convertible lens

6.2.3 References

[1] Olympus EC-20 2x Zuiko Digital TeleConverter Lens

[2] Scientific photography and applied imaging By Sidney F. Ray, page 492 Chapter 7

Day 7

7.1 Long-focus lens

A 500 mm long-focus lens of non-telephoto design

In photography, a long-focus lens is a camera lens which has a focal length that is longer than the diagonal measure of the film or sensor that receives its image.[1][2] It is used to make distant objects appear magnified with magnification increasing as longer focal length lenses are used. A long-focus lens is one of three basic photographic lens types classified by relative focal length, the other two being a normal lens and a wide-angle lens.[3] As with other types of camera lenses, the focal length is usually expressed in a millimeter value written on the lens, for example: a 500 mm lens. The most common type of long-focus lens is the telephoto lens, which incorporate a special lens group known as a telephoto group to make the physical length of the lens shorter than the focal length.[4]

7.1.1 Effects of long-focus lenses

Long-focus lenses are best known for making distant objects appear magnified. This effect is similar to moving closer to the object, but is not the same, since perspective is a function solely of viewing location. Two images taken from the same location, one with a wide angle lens and the other with a long-focus lens, will show identical perspective, in that near and far objects appear the same relative size to each other. Comparing magnification by using a long lens to magnification by moving closer, however, the long-focus-lens shot appears to compress the distance between objects due to the perspective from the more distant location. Long lenses thus give a photographer an alternative to the type of perspective distortion exhibited by shorter focal length lenses where (when the photographer stands closer to the given subject) different portions of a subject in a photograph can appear out of proportion to each other. Long lenses also make it easier to blur the background more, even when the depth of field is the same; photographers will sometimes use this effect to defocus the background in an image to “separate” it from the subject. This background blurring is often referred to as bokeh by photographers.

Still photography

Effect of different focal lengths on photographs taken from the same place:

108 7.1. LONG-FOCUS LENS 109

Sports photographers using long-focus lenses

• 28 mm

• 50 mm

• 70 mm

• 210 mm

The above photos were taken using a 35 mm camera, using lenses of the given focal lengths.

Constant object size

The photographer often moves to keep the same image size on the film for a particular object. Observe in the comparison images below that although the foreground object remains the same size, the background changes size; thus, perspective is dependent on the distance between the photographer and the subject. The longer focus lenses compress the perception of depth, and the shorter focus exaggerate it.[5] This effect is also used for dolly zooms. The perspective of the so-called normal lens, 50 mm focal length for 35 mm film format, is conventionally regarded as a “correct” perspective, though a longer lens is usually preferred for a more pleasing perspective for portraits. 110 CHAPTER 7. DAY 7

• 28 mm

• 50 mm

• 135 mm

7.1.2 Telescopes as long-focus lenses

From the invention of photography in the 19th century, images have been captured using standard optical tele- scopes including telescope objectives adapted as early portrait lenses.[6] Besides being used in an astronomical role in astrophotography, telescopes are adapted as long-focus lenses in , surveillance, machine vision and long-focus microscopy.[7] To use a telescope as a camera lens requires an adapter for the standard 1.25 inch tube eyepiece mount, usually a T-mount adapter, which in turn attaches to an adapter for the system camera's particular lens mount. Controlling exposure is done by exposure time, gain, or filters since telescopes almost always lack diaphragms for aperture ad- justment. The 1.25 inch mount is smaller than many film and sensor formats so they tend to show vignetting around the field edges.[8] Telescopes are normally intended for visual use, so they are not corrected to produce a large flat field like dedicated camera lenses and tend to show optical aberration. Since the late 1990s compact digital cameras have been used in afocal photography, a technique where the camera lens is left attached, taking a picture directly through the telescope’s eyepiece lens itself, also referred to as ".”

7.1.3 See also

• Film format

• Secret photography

• Photographic lens design

7.1.4 References

[1] Sidney F. Ray (2002). Applied photographic optics: lenses and optical systems for photography (3rd ed.). Focal Press. p. 294. ISBN 978-0-240-51540-3.

[2] R. E. Jacobson (2000). The manual of photography: photographic and digital imaging (9th ed.). Focal Press. p. 93. ISBN 978-0-240-51574-8.

[3] Bruce Warren (2001). Photography (2nd ed.). Delmar Thomson (Cengage) Learning. p. 71. ISBN 978-0-7668-1777-7.

[4] Bernard Edward Jones (1911). Cassell’s cyclopaedia of photography (2nd ed.). Ayer Publishing. p. 537. ISBN 978-0- 405-04922-4.

[5] Bill Smith (2001). Designing a Photograph: Visual Techniques for Making Your Photographs Work. Amphoto Books. p. 14. ISBN 0-8174-3778-9. 7.2. CLOSE-UP FILTER 111

[6] Rudolf Kingslake, A history of the photographic lens, page 33

[7] “Long-focus microscope with camera adapter”.

[8] “Astrophotography techniques”.

7.2 Close-up filter

Set of three close-up lenses

In photography, a close-up filter, close-up lens or macro filter is a simple secondary lens used to enable macro photography without requiring a specialised primary lens. They work identically to reading glasses, allowing any primary lens to focus more closely. It is actually more appropriate to use the close-up lens terminology as it is a lens and not a filter, although close-up lenses typically mount on the filter thread of the primary lens, and are manufactured and sold by suppliers of photographic filters. Some manufacturers refer to their close-up lenses as diopters, after the unit of measurement of their optical power. While some single-element close-up lenses produce images with severe aberrations, there are also high-quality close- up lenses composed as achromatic doublets which are capable of producing excellent images, with fairly low loss of sharpness. 112 CHAPTER 7. DAY 7

Typical close-up lens

Close-up lenses are usually specified by their optical power, the reciprocal of the focal length in meters. Several close-up lenses may be used in combination; the optical power of the combination is the sum of the optical powers of the component lenses; a set of lenses of +1, +2, and +4 diopters can be combined to provide a range from +1 to +7 in steps of 1. When you add a close-up lens to a camera which is focusing to infinity, and you don't change the focus adjustment, the focus will move to a distance which is equal to the focal length of the close-up lens. This is the maximal working distance at which you will be able to take a picture with the close-up lens. It suffices to divide 1 by D, the diopter value of the close-up lens, to get this maximal working distance in meters:

Sometimes that distance is also given on the filter in mm. A +3 filter will have a maximal working distance of 0.333 m or 333 mm. The magnification reached in those conditions is the focal distance of the objective lens (f) divided by the focal distance of the close-up lens, i.e. the focal distance of the objective lens, in m, multiplied by the diopter value (D) of the close-up lens:

In the example above, if the lens has a 300 mm focal distance, magnification is equal to 0.3*3 = 0.9. Given the small size of most sensors (about 25 mm for APS C sensors) a 20 mm insect will almost fill the frame at this magnification. Using a zoom lens makes it easy to frame the subject as desired. When you add a close-up lens to a camera which is focusing at the shortest distance at which the objective lens can focus, and you don't change the focus adjustment, the focus will move to a distance which is given by following formula: 7.2. CLOSE-UP FILTER 113

Optical scheme of close-up photography. 1 - Close-up lens. 2 - Camera objective lens (set to infinity). 3 Camera. 4 - Film or CCD plane. y - Object y” - Image

X being the shortest distance at which the objective lens can focus, in m, and D being the Diopter value of the close up filter. This is the minimal working distance at which you will be able to take a picture with the close-up lens. For example, a lens that can focus at 1.5 m combined with a +3 diopter close up lens will give a closest working distance of 1.5/(3*1.5+1)=0.273 m. The magnification reached in those conditions is given by following formula:

MX being the magnification at distance X without the close-up lens. In the example above, the gain of magnification at Xᵢ will be (3*1.5 + 1)= 5.5. It is at this Xᵢ distance that you will get the highest magnification. To use a close up filter it is important to know those maximal and minimal distances, because only if you are within that range it will be possible to take a shot. There is not much of a range between the minimum and maximum values and the difference in magnification is quite moderate also. The close up filters can turn telephoto lenses in macro lenses with a large working distance to prevent scaring small animals and a second advantage is the small size of the background making it easier to isolate the subject from messy surroundings. To use the filters for animals the size of the animal will determine the working distance (small snakes 1 m to 50 cm, lizards 50–25 cm, small butterflies, beetles 25–10 cm), so it is essential to know what will be the favorite subject before screwing on a close up filter. The close up filters are most effective with long focal length objectives and using a zoom lens is very practical to have some flexibility in the magnification. A good technique for sharp focussing is to take a picture at a long focal length first to have optimal sharpness at the essential details and then 114 CHAPTER 7. DAY 7

Photograph taken with a 3 diopter achromatic close-up lens: Pentatomidae-hatchlings underneath a purple beech leave zooming out to have the desired size in the frame.

7.2.1 See also

• Photographic filter#Close-up and split diopter lenses • Deep focus

7.2.2 External links

• Close focus Close-up lenses technique

7.3 Macro photography

Macro photography (or photomacrography[1] or macrography,[2] and sometimes macrophotography[3]), is ex- treme close-up photography, usually of very small subjects and living organisms like insects, in which the size of the subject in the photograph is greater than life size (though macrophotography technically refers to the art of making very large photographs).[2][4] By some definitions, a macro photograph is one in which the size of the subject on the negative or image sensor is life size or greater.[5] However, in other uses it refers to a finished photograph of a subject at greater than life size.[6] The ratio of the subject size on the film plane (or sensor plane) to the actual subject size is known as the reproduction ratio. Likewise, a macro lens is classically a lens capable of reproduction ratios of at least 1:1, although it often refers to any lens with a large reproduction ratio, despite rarely exceeding 1:1.[6][7][8][9] Apart from technical photography and film-based processes, where the size of the image on the negative or image sensor is the subject of discussion, the finished print or on-screen image more commonly lends a photograph its macro 7.3. MACRO PHOTOGRAPHY 115

Photomacrograph of a common yellow dung fly (Scathophaga stercoraria) made using a lens at its maximum 1:1 reproduction ratio, and an 18×24mm image sensor, the on-screen display of the photograph results in a greater than life-size image. status. For example, when producing a 6×4 inch (15×10 cm) print using 35 format (3.6×2.4 cm) film or sensor, a life-size result is possible with a lens having only a 1:4 reproduction ratio.[10][11] Reproduction ratios much greater than 1:1 are considered to be photomicrography, often achieved with digital micro- scope (photomicrography should not be confused with microphotography, the art of making very small photographs, such as for microforms). Due to advances in sensor technology, today’s small-sensor digital cameras can rival the macro capabilities of a DSLR with a “true” macro lens, despite having a lower reproduction ratio, making macro photography more widely accessible at a lower cost.[8][12] In the digital age, a “true” macro photograph can be more practically defined as a photograph with a vertical subject height of 24 mm or less.[13]

7.3.1 History

The term photo-macrograph was proposed in 1899 by W. H. Walmsley for close-up images with less than 10 diameters magnification, to distinguish from true photo-micrographs.[14] One of the earliest pioneers of macro photography was Percy Smith, born in 1880. He was a British nature docu- mentary filmmaker, and was known for his close-up photographs.[15]

7.3.2 Equipment and techniques

“Macro” lenses specifically designed for close-up work, with a long barrel for close focusing and optimized for high reproduction ratios, are one of the most common tools for macro photography. (Unlike most other lens makers, Nikon designates its macro lenses as “Micro” because of their original use in making microform.) Most modern macro lenses can focus continuously to infinity as well and can provide excellent optical quality for normal photography. True macro lenses, such as the Canon MP-E 65 mm f/2.8 or Minolta AF 3x-1x 1.7-2.8 Macro, can achieve higher magnification 116 CHAPTER 7. DAY 7

Headshot of a dragonfly taken with a 100mm macro lens coupled with a 50mm lens in reverse at the end.

Canon MP-E 65 mm macro lens. Small front lens elements are typical of macro lenses. 7.3. MACRO PHOTOGRAPHY 117

Extension tubes for extreme macro use with SLRs. Note the pen placed through the tube to illustrate that it does not contain any lens elements. than life size, enabling photography of the structure of small insect eyes, snowflakes, and other minuscule objects. Others, such as the Infinity Photo-Optical’s TS-160 can achieve magnifications from 0-18x on sensor, focusing from infinity down to 18 mm from the object. Macro lenses of different focal lengths find different uses:

• Continuously-variable focal length – suitable for virtually all macro subjects

• 45–65 mm – product photography, small objects that can be approached closely without causing undesirable influence, and scenes requiring natural background perspective

• 90–105 mm – insects, flowers, and small objects from a comfortable distance

• 150–200 mm – insects and other small animals where additional working distance is required

Extending the distance between the lens and the film or sensor, by inserting either extension tubes or a continuously adjustable bellows, is another equipment option for macro photography. The further the lens is from the film or sensor, the closer the focusing distance, the greater the magnification, and the darker the image given the same aperture. Tubes of various lengths can be stacked, decreasing lens-to-subject distance and increasing magnification. Bellows or tubes eliminate infinity focus. Placing an auxiliary close-up lens (or close-up “filter”) in front of the camera’s lens is another option. Inexpensive screw-in or slip-on attachments provide close focusing. The possible quality is less than that of a dedicated macro lens or extension tubes, with some two-element versions being very good while many inexpensive single element lenses exhibit chromatic aberration and reduced sharpness of the resulting image. This method works with cameras that have fixed lenses, and is commonly used with bridge cameras. These lenses add diopters to the optical power of the lens, decreasing the minimum focusing distance, and allowing the camera to get closer to the subject. They are typically designated by their diopter, and can be stacked (with an additional loss of quality) to achieve the desired magnification. Photographers may employ view camera movements and the Scheimpflug principle to place an object close to the lens in focus, while maintaining selective background focus. This technique requires the use of a view camera or 118 CHAPTER 7. DAY 7

Bellows fitted between an SLR and reversed lens

perspective control lens with the ability to tilt the lens with respect to the film or sensor plane. Lenses such as the Nikon PC-E and Canon TS-E series, the Hartblei Super-Rotator, the Schneider Super Angulon, several Lensbaby models, the Zoerk Multi Focus System, and various tilt-shift adapters for medium format, allow the use of tilt in cameras with fixed lens mounts. Traditional view cameras permit such adjustment as part of their design. Ordinary lenses can be used for macro photography by using a “reversing ring.” This ring attaches to the filter thread on the front of a lens and makes it possible to attach the lens in reverse. Excellent quality results up to 4x life-size magnification are possible. For cameras with all-electronic communications between the lens and the camera body specialty reversing rings are available which preserve these communications. When used with extension tubes or bellows, a highly versatile, true macro (greater than life size) system can be assembled. Since non-macro lenses are optimized for small reproduction ratios, reversing the lens allows it to be used for reciprocally high ratios. Macro photography may also be accomplished by mounting a lens in reverse, in front of a normally mounted lens of greater focal length, using a macro coupler which screws into the front filter threads of both lenses. This method allows most cameras to maintain the full function of electronic and mechanical communication with the normally mounted lens, for features such as open-aperture metering. The magnification ratio is calculated by dividing the focal length of the normally mounted lens by the focal length of the reversed lens (e.g., when an 18 mm lens is reverse mounted on a 300 mm lens the reproduction ratio is 16:1). The use of automatic focus is not advisable if the first lens is not of the internal-focusing type, as the extra weight of the reverse-mounted lens could damage the autofocus mechanism. Working distance is significantly less than the first lens. Increasingly, macro photography is accomplished using compact digital cameras and small-sensor bridge cameras, combined with a high powered zoom lens and (optionally) a close-up diopter lens added to the front of the camera lens. The deep depth of field of these cameras is an advantage for macro work.[12][16] The high pixel density and resolving power of these cameras’ sensors enable them to capture very high levels of detail at a lower reproduction ratio than is needed for film or larger DSLR sensors (often at the cost of greater ). Despite the fact that many of these cameras come with a “macro mode” which does not qualify as true macro, some photographers are using the advantages of small sensor cameras to create macro images that rival or even surpass those from DSLRs.[12] 7.3. MACRO PHOTOGRAPHY 119

Typical close-up lens

Wide-angle lens used as a reversed lens in front of a macro lens

Macro photography techniques

• Optical scheme of close-up macro photography 120 CHAPTER 7. DAY 7

• Reversed-lens macro photography optical scheme

• Optical scheme of macro photography using reversed lens and telephoto lens

• Optical scheme of macro photography using extension tube

Macro photography lenses

[30] [31] [32] [33]

7.3.3 35 mm equivalent magnification

35 mm equivalent magnification, or 35 mm equivalent reproduction ratio, is a measure that indicates the apparent magnification achieved with a small sensor format, or “crop sensor” digital camera compared to a 35 mm-based image enlarged to the same print size.[34][35] The term is useful because many photographers are familiar with the 35 mm film format.[13][36][37][38][39][40] While a “true” macro lens is defined as a lens having a reproduction ratio of 1:1 on the film or sensor plane, with small sensor format digital cameras an actual reproduction ratio of 1:1 is rarely achieved or needed to take macro photographs. What macro photographers often care about more is simply knowing the size of the smallest object that can fill the frame.[8] For example, the 12 megapixel Micro Four Thirds Panasonic Lumix DMC-GH1 camera with a 2x crop sensor only requires a 1:2 reproduction ratio to take a picture with the same subject size, resolution, and apparent magnification as a 12 megapixel “full-frame” Nikon D700 camera, when the images are viewed on screen or printed at the same size. Thus a Four Thirds system macro lens like the Olympus Zuiko Digital 35 mm F3.5 Macro lens with a true maximum image magnification of 1.0x is rated as having a “2.0x 35 mm equivalent magnification”.[41] To calculate 35 mm equivalent reproduction ratio, simply multiply the actual maximum magnification of the lens by the 35 mm conversion factor, or “” of the camera. If the actual magnification and/or crop factor are unknown (such as is the case with many compact or point-and-shoot digital cameras), simply take a photograph of a mm ruler placed vertically in the frame focused at the maximum magnification distance of the lens and measure the height of the frame. Since the object height of a 1.0x magnified 35 mm film image is 24 mm, calculate 35 mm equivalent reproduction ratio and true reproduction ratio by using the following:[42]

(35 mm equivalent reproduction ratio) = 24 / (measured height in mm) 7.3. MACRO PHOTOGRAPHY 121

Nikon AF-S DX Micro 40 mm f/2.8G

(True reproduction ratio) = (35mm equivalent reproduction ratio) / Crop factor.

Since digital compact camera sensor sizes come in a wide diversity of sizes and camera manufacturers rarely publish the macro reproduction ratios for these cameras, a good rule of thumb is that whenever a 24 mm vertical object just fits, or is too tall to fit in the camera viewfinder, you are taking a macro photograph.[13]

7.3.4 Technical considerations 122 CHAPTER 7. DAY 7

35 mm equivalent magnification: The photograph on top was taken with a full-frame (35 mm) sensor digital SLR camera and a 100 mm macro lens at 1:1 magnification. The photograph on the bottom was taken with a Micro Four Thirds (2x crop) sensor camera and a 50 mm macro lens at 1:2 magnification. The subject height in both images is 24 mm. Photographs taken with these two set-ups will be practically indistinguishable at the same print size, lending the photograph on the bottom its 1:1 35 mm equivalent reproduction ratio status.

Depth of field

Limited depth of field is an important consideration in macro photography. Depth of field is extremely small when focusing on close objects. A small aperture (high f-number) is often required to produce acceptable sharpness across 7.3. MACRO PHOTOGRAPHY 123

35 mm equivalent reproduction ratio: the photograph on the left was taken with a Micro Four Thirds (2x crop) sensor camera and a 50 mm macro lens at 1:2 magnification. The photograph on the right was taken with a full-frame (35 mm) sensor digital SLR camera and a 100 mm macro lens at 1:1 magnification. The photographs are practically indistinguishable and therefore equivalent. As the images were taken at slightly different angles, the two images can be viewed as a cross-eyed stereogram.

Shallow depth of field a three-dimensional subject. This requires either a slow shutter speed, brilliant lighting, or a high ISO. Auxiliary lighting (such as from a flash unit), preferably a ring flash is often used (see Lighting section). Like conventional lenses, macro lenses need light, and ideally would provide similar f/# to conventional lenses to provide similar exposure times. Macro lenses also have similar focal lengths, so the entrance pupil diameter is comparable to that of conventional lenses (e.g., a 100 mm f/2.8 lens has a 100 mm/2.8 = 35.7 mm entrance-pupil di- ameter). Because they focus at close subjects, the cone of light from a subject point to the entrance pupil is relatively obtuse (a relatively high subject numerical aperture to use microscopy terms), making the depth of field extraordi- narily small. This makes it essential to focus critically on the most important part of the subject, as elements that are even a millimetre closer or farther from the focal plane might be noticeably blurred. Due to this, the use of a microscope stage is highly recommended for precise focus with large magnification such as photographing skin cells. Alternatively, more shots of the same subject can be made with slightly different focusing lengths and joined 124 CHAPTER 7. DAY 7 afterwards with specialized focus stacking software which picks out the sharpest parts of every image, artificially increasing depth of field.

Lighting

The problem of sufficiently and evenly lighting the subject can be difficult to overcome. Some cameras can focus on subjects so close that they touch the front of the lens. It is difficult to place a light between the camera and a subject that close, making extreme close-up photography impractical. A normal-focal-length macro lens (50 mm on a 35 mm camera) can focus so close that lighting remains difficult. To avoid this problem, many photographers use telephoto macro lenses, typically with focal lengths from about 100 to 200 mm. These are popular as they permit sufficient distance for lighting between the camera and the subject. Ring flashes, with flash tubes arranged in a circle around the front of the lens, can be helpful in lighting at close distances.[43] Ring lights have emerged, using white LEDs to provide a continuous light source for macro photography, however they are not as bright as a ring flash and the white balance is very cool.[44] Good results can also be obtained by using a flash diffuser. Homemade flash diffusers made out of white Styrofoam or plastic attached to a camera’s built-in flash can also yield surprisingly good results by diffusing and softening the light, eliminating specular reflections and providing more even lighting.

7.3.5 See also

• • Photomicroscopy

7.3.6 References

[1] Thomas Clark (2011). Digital Macro and Close-Up Photography For Dummies. John Wiley & Sons. p. 29. ISBN 9781118089200.

[2] Graham Saxby (2010). The Science of Imaging: An Introduction (2nd ed.). CRC Press. p. 269. ISBN 9781439812860.

[3] Webster, Merriam (1996). Collegiate Dictionary, 10th Ed. Merriam-Webster, Inc. p. 698. ISBN 0-87779-711-0.

[4] Michael Freeman (2010). The DSLR Field Guide: The Essential Handbook to Getting the Most from Your Camera. Focal Press. p. 30. ISBN 9780240817200.

[5] Marom, Erez. “Macro photography: Understanding magnification”. Retrieved 20 May 2012.

[6] Photography.com. “Macro Photography”. Archived from the original on 2008-11-06. Retrieved 20 May 2012.

[7] Rockwell, Ken. “Canon 50mm Macro”. Retrieved 20 May 2012.

[8] Cambridge in Colour. “Macro Camera Lenses”.

[9] Long, Ben. “How to take great macro photographs”. Retrieved 20 May 2012.

[10] Olympus. “Macrophotography and your Evolt”. Retrieved 20 May 2012.

[11] Super Tight Stuff. “Incredible Macro Insect Photos”. Retrieved 20 May 2012.

[12] Frank, Bob. “Extreme macro photography”. Retrieved 20 May 2012.

[13] Wattie, John. “Digital Stereo Macro Photography”. Retrieved 20 May 2012.

[14] Walmsley, W. H. (1899). “Photo-micrography for everybody”. The International Annual of Anthony’s Photographic Bul- letin and American Process Year-book. 12: 73–90.

[15] The Story of Macro Photography

[16] Frank, Bob. “Equipment used to create Panasonic FZ30 macro galleries”. Retrieved 23 May 2012.

[17] FUJINON LENS XF60mmF2.4 R Macro | Fujifilm Global

[18] “Schneiderkreuznach TS Macro 90mm” (PDF) (in German). Schneider Kreuznach. Retrieved November 9, 2014. 7.3. MACRO PHOTOGRAPHY 125

[19] “SIGMA Macro 50mm”. Sigma Corporation. Archived from the original on November 9, 2014. Retrieved November 9, 2014.

[20] “SIGMA Macro 70mm”. Sigma Corporation. Retrieved November 9, 2014.

[21] “SIGMA Macro 105mm”. Sigma Corporation. Retrieved November 9, 2014.

[22] “SIGMA Macro 150mm”. Sigma Corporation. Retrieved November 9, 2014.

[23] “SIGMA Macro 180mm”. Sigma Corporation. Retrieved November 9, 2014.

[24] “Tamron Macro 60mm”. Tamron. Retrieved November 9, 2014.

[25] “Tamron Macro 90mm”. Tamron. Retrieved November 9, 2014.

[26] “Tamron Macro 90mm II”. Tamron. Retrieved November 9, 2014.

[27] “Tamron Macro 180mm”. Tamron. Retrieved November 9, 2014.

[28] “Zeiss Macro 50mm”. Carl Zeiss AG. Archived from the original on November 22, 2014. Retrieved November 9, 2014.

[29] “Zeiss Macro 100mm”. Carl Zeiss AG. Archived from the original on October 22, 2014. Retrieved November 9, 2014.

[30] Canon U.S.A. : Consumer & Home Office : EF Lens Lineup

[31] Macro Lenses from Nikon

[32] Pentax U.S.A. : PENTAX Digital Camera Lens Lineup

[33] Macro Lenses | Sony | Sony Store USA

[34] Olympus Imaging Corp. “Olympus Four Thirds Lenses - Macro”. Four-Thirds.org. Olympus Imaging Corp. Retrieved 9 June 2012.

[35] Olympus Imaging Corp. “Panasonic LEICA DG MACRO-ELMARIT 45 mm F2.8”. Four-Thirds.org. Olympus Imaging Corp. Retrieved 9 June 2012.

[36] Digital Photography Review. “Panasonic Leica DG Macro-Elmarit 45 mm F2.8 ASPH OIS Review”. dpreview.com. Digital Photography Review. Retrieved 11 June 2012.

[37] Outdoor Photographer Staff. “Choosing Your Macro”. Outdoor Photographer. Retrieved 11 June 2012.

[38] Pitts, Wes. “Intro To Macro”. Digital Photo Magazine. Retrieved 11 June 2012.

[39] Arva-Toth, Zoltan. “Zuiko Digital ED 50 mm f2 Macro Review”. PhotographyBLOG. Photo 360 Limited. Retrieved 11 June 2012.

[40] Wetpixel: Forums. “Help with reproduction ratio”. Wetpixel.com. Retrieved 11 June 2012.

[41] Olympus Imaging Corp. “OLYMPUS : ZUIKO DIGITAL 35 mm F3.5 Macro”. Four-Thirds.org. Olympus Imaging Corp. Retrieved 9 June 2012.

[42] Wattie, John. “Digital Stereo Macro Photography”. nzphoto.tripod.com. Retrieved 9 June 2012.

[43] Basco, Greg. “No, I'm not a Dentist: The Joy of Ring Flash Photography”. photomigrations.com. Retrieved 21 June 2012.

[44] diyphotography.net. “Introduction To LED Lighting”. diyphotography.net. Retrieved 21 June 2012.

44. http://www.kenrockwell.com/nikon/55af.htm

7.3.7 External links

• Macro Photography Tutorial

• Inexpensive Macro Photography DSLR with Manual Focus Lens

• Use of Microscope Stage for Microphotography Chapter 8

Day 8

8.1 Wide-angle lens

One of Canon’s most-popular wide-angle lenses – 17-40 mm f/4 L retrofocus zoom lens.

In photography and cinematography, a wide-angle lens refers to a lens whose focal length is substantially smaller than the focal length of a normal lens for a given film plane. This type of lens allows more of the scene to be included in the photograph, which is useful in architectural, interior and where the photographer may not be able to move farther from the scene to photograph it. Another use is where the photographer wishes to emphasise the difference in size or distance between objects in the foreground and the background; nearby objects appear very large and objects at a moderate distance appear small and far away. This exaggeration of relative size can be used to make foreground objects more prominent and striking, while cap- turing expansive backgrounds.[1] A wide angle lens is also one that projects a substantially larger image circle than would be typical for a standard design lens of the same focal length. This large image circle enables either large tilt & shift movements with a view

126 8.1. WIDE-ANGLE LENS 127

camera, or a wide field of view. By convention, in still photography, the normal lens for a particular format has a focal length approximately equal to the length of the diagonal of the image frame or digital photosensor. In cinematography, a lens of roughly twice the diagonal is considered “normal”.[2]

8.1.1 Angle of view

A lens is considered wide-angle when it covers the angle of view between 64° and 84° which in return translates to 35–24mm lens in 35mm film format.

8.1.2 Characteristics

Longer lenses magnify the subject more, apparently compressing distance and (when focused on the foreground) blurring the background because of their shallower depth of field. Wider lenses tend to magnify distance between objects while allowing greater depth of field. Another result of using a wide-angle lens is a greater apparent perspective distortion when the camera is not aligned perpendicularly to the subject: parallel lines converge at the same rate as with a normal lens, but converge more due to the wider total field. For example, buildings appear to be falling backwards much more severely when the camera is pointed upward from ground level than they would if photographed with a normal lens at the same distance from the subject, because more of the subject building is visible in the wide-angle shot. Because different lenses generally require a different camera–subject distance to preserve the size of a subject, chang- ing the angle of view can indirectly distort perspective, changing the apparent relative size of the subject and fore- ground.

8.1.3 Wide-angle lenses for 35 mm format

For a full-frame 35 mm camera with a 36 mm by 24 mm format, the diagonal measures 43.3 mm and by custom, the normal lens adopted by most manufacturers is 50 mm. Also by custom, a lens of focal length 35 mm or less is considered wide-angle. Ultra wide angle lenses have a focal length shorter than the short side of the film or sensor. In 35 mm, an ultra wide-angle lens has a focal length shorter than 24 mm. Common wide-angle for a full-frame 35 mm camera are 35, 28, 24, 21, 20, 18 and 14 mm, the latter four being ultra-wide. Many of the lenses in this range will produce a more or less rectilinear image at the film plane, though some degree of barrel distortion is not uncommon here. Ultra wide-angle lenses that do not produce a rectilinear image (i.e., exhibit barrel distortion) are called fisheye lenses. Common focal lengths for these in a 35 mm camera are 6 to 8 mm (which produce a circular image). Lenses with focal lengths of 8 to 16 mm may be either rectilinear or fisheye designs. Wide-angle lenses come in both fixed-focal-length and zoom varieties. For 35 mm cameras, lenses producing recti- linear images can be found at focal lengths as short as 8 mm, including zoom lenses with ranges of 2:1 that begin at 12 mm.

8.1.4 Digital camera considerations

Main article: Crop factor As of 2015, many interchangeable-lens digital cameras have image sensors that are smaller than the film format of full-frame 35 mm cameras.[lower-alpha 1] For the most part, the dimensions of these image sensors are similar to the APS-C image frame size, i.e., approximately 24 mm x 16 mm. Therefore, the angle of view for any given focal- length lens will be narrower than it would be in a full-frame camera because the smaller sensor “sees” less of the image projected by the lens. The camera manufacturers provide a crop factor (sometimes called a field-of-view factor or a focal-length multiplier) to show how much smaller the sensor is than a full 35 mm film frame. For example, one common factor is 1.5 (Nikon DX format and some others), although many cameras have crop factors of 1.6 (most Canon DSLRs), 1.7 (the early Sigma DSLRs) and 2 (the Four Thirds and Micro Four Thirds cameras). The 1.5 128 CHAPTER 8. DAY 8

indicates that the angle of view of a lens on the camera is the same as that of a 1.5 times longer focal length on a 35 mm full-frame camera, which explains why the crop factor is also known as a focal-length multiplier. As example, a 28 mm lens on the DSLR (given a crop factor of 1.5) would produce the angle of view of a 42 mm lens on a full-frame camera. So, to determine the focal length of a lens for a digital camera that will give the equivalent angle of view as one on a full-frame camera, the full-frame lens focal length must be divided by the crop factor. For example, to get the equivalent angle of view of a 30 mm lens on a full-frame 35 mm camera, from a digital camera with a 1.5 crop factor, one would use a 20 mm lens. Lens manufacturers have responded by making wide-angle lenses of much shorter focal lengths for these cameras. In doing this, they limit the diameter of the image projected to slightly more than the diagonal measurement of the photosensor. This gives the designers more flexibility in providing the optical corrections necessary to economically produce high-quality images at these short focal lengths, especially when the lenses are zoom lenses. Examples are 10 mm minimum focal length zoom lenses from several manufacturers. At 10 mm, these lenses provide the angle of view of a 15 mm lens on a full-frame camera when the crop factor is 1.5.

8.1.5 Construction

There are two varieties of wide-angle lens: short-focus lenses and retrofocus lenses. Short-focus lenses are generally made up of multiple glass elements whose shapes are more or less symmetrical in front of and behind the diaphragm. As the focal length decreases, the distance of the rear element of the lens from the film plane or digital sensor also decreases. This makes short-focus wide-angle lenses undesirable for single-lens reflex cameras unless they are used with the reflex mirrors locked up. On large format view cameras and rangefinder cameras, short-focus lenses are widely used because they give less distortion than the retrofocus design and there is no need for a long back focal distance. The retrofocus lens solves this proximity problem through an asymmetrical design that allows the rear element to be further away from the film plane than its effective focal length would suggest. (See Angénieux retrofocus.) For example, it is not uncommon for the rear element of a retrofocus lens of 18 mm to be more than 25 mm from the film plane. This makes it possible to design wide-angle lenses for single-lens reflex cameras. The axial adjustment range for focusing Ultra wide angle lenses and some Wide-angle lenses in large format cameras is usually very small. Some manufacturers (e.g. Linhof) have offered special focusing lens mounts, so-called 'wide- angle focusing devices’ for their cameras that allow the lens to be focused precisely without moving the entire front standard.

8.1.6 See also

• Anamorphic lens

• Image stitching

• Long focus lens

•

• Photographic lens design

• Scioptric ball

• Telephoto lens

• Panomorph

8.1.7 References

[1] “Using wide angle lenses”. Cambridge in Colour. Retrieved 27 December 2011.

[2] Anton Wilson, Anton Wilson’s Cinema Workshop, American Cinematographer, 2004 (Page 100) ISBN 0-935578-26-9 8.1. WIDE-ANGLE LENS 129

8.1.8 Notes

[1] The few exceptions include the Canon EOS-1D X, EOS 5DS/5DS R, EOS 5D Mark III and EOS 6D; Nikon’s D4S, Df, D810, D750 and D610; and Sony’s α99 and α7 family. Discontinued full-frame cameras include the Canon EOS-1Ds, Canon EOS-1Ds Mark II, Canon EOS-1Ds Mark III, EOS 5D, EOS 5D Mark II, , Nikon D3, , Nikon D700, Nikon D600, Contax N Digital, Sony Alpha 900, Sony Alpha 850, Kodak DCS Pro SLR/c and Kodak DCS Pro SLR/n.

8.1.9 External links

• Media related to Wide-angle lenses at Wikimedia Commons 130 CHAPTER 8. DAY 8

How focal length affects photograph composition. Three images depict the same two objects, kept in the same positions. By changing focal length and adjusting the camera’s distance from the pink bottle, it remains the same size in the image, while the blue bottle’s size appears to dramatically change. Also note that at small focal lengths, more of the scene is included. 8.1. WIDE-ANGLE LENS 131

50mm full-frame (24 x 36 mm) full-frame (24 x 36 mm) APS-C (18x24 mm)

APS-C (18x24 mm)

1.6 x 50 = 80 ≠ 70mm APS-C (18x24 mm) full-frame (24 x 36 mm) APS-C (18x24 mm)

full-frame (24 x 36 mm) ≅

Field of view in APS-sized digital cameras is the same as that of a longer lens, increased by crop factor, on a full-frame 35 mm format camera. 132 CHAPTER 8. DAY 8

Front Diaphragm element

Cross-section of a typical short-focus wide-angle lens.

Cross-section of a typical retrofocus wide-angle lens. 8.1. WIDE-ANGLE LENS 133

D H'

D H' f '

Effective focal length is measured from the sensor to where the light cone going to the sensor is the same size as the lens front opening. 134 CHAPTER 8. DAY 8

8.2 Fisheye lens

A fisheye converter lens on a

A fisheye lens is an ultra wide-angle lens that produces strong visual distortion intended to create a wide panoramic or hemispherical image.[1][2] Fisheye lenses achieve extremely wide angles of view by forgoing producing images with straight lines of perspective (rectilinear images), opting instead for a special mapping (for example: equisolid angle), which gives images a characteristic convex non-rectilinear appearance. The term fisheye was coined in 1906 by American physicist and inventor Robert W. Wood based on how a fish would see an ultrawide hemispherical view from beneath the water (a phenomenon known as Snell’s window).[2][3] Their first practical use was in the 1920s for use in meteorology[4][5] to study cloud formation giving them the name “whole-sky lenses”. The angle of view of a fisheye lens is usually between 100 and 180 degrees[1] while the focal lengths depend on the film format they are designed for. Mass-produced fisheye lenses for photography first appeared in the early 1960s[6] and are generally used for their unique, distorted appearance. For the popular 35 mm film format, typical focal lengths of fisheye lenses are between 8 mm and 10 mm for circular images, and 15–16 mm for full-frame images. For digital cameras using smaller 1 1 electronic imagers such as 6.4 mm ( ⁄4 in) and 8.5 mm ( ⁄3 in) format CCD or CMOS sensors, the focal length of “miniature” fisheye lenses can be as short as 1 to 2 mm. These types of lenses also have other applications such as re-projecting images filmed through a fisheye lens, or created via computer generated graphics, onto hemispherical screens. Fisheye lenses are also used for scientific photography such as recording of aurora and meteors, and to study plant canopy geometry and to calculate near-ground solar radiation. They are also used as peephole door viewers to give the user a wide field of view. 8.2. FISHEYE LENS 135

8.2.1 Uses in photography

In a circular fisheye lens, the image circle is inscribed in the film or sensor area; in a full-frame fisheye lens the image circle is circumscribed around the film or sensor area. Further, different fisheye lenses distort images differently, and the manner of distortion is referred to as their mapping function. A common type for consumer use is equisolid angle. Although there are digital fisheye effects available both in-camera and as computer software they can't extend the angle of view of the original images to the very large one of a true fisheye lens.

Circular fisheye

ESO's VLT image taken with a circular fisheye lens.

The first types of fisheye lenses to be developed were “circular fisheye” — lenses which took in a 180° hemisphere and projected this as a circle within the film frame. Some circular fisheyes were available in orthographic projection models for scientific applications. These have a 180° vertical angle of view, and the horizontal and diagonal angle of view are also 180°. Most circular fisheye lenses cover a smaller image circle than rectilinear lenses, so the corners of the frame will be completely dark.

Full-frame fisheye

As fisheye lenses gained popularity in general photography, camera companies began manufacturing fisheye lenses that enlarged the image circle to cover the entire rectangular frame, called a “full-frame fisheye”.[7] The picture angle produced by these lenses only measures 180 degrees when measured from corner to corner: these have a 180° diagonal angle of view, while the horizontal and vertical angles of view will be smaller; for an equisolid angle-type 15 mm full-frame fisheye, the horizontal FOV will be 147°, and the vertical FOV will be 94°.[8] 136 CHAPTER 8. DAY 8

An example of full-frame fisheye used in a closed space (Nikkor 10.5mm)

The first full-frame fisheye lens to be mass-produced was a 16 mm lens made by Nikon in the early 1970s. Digital cameras with APS-C sized sensors require a 10.5 mm lens (or, for Canon APS-C cameras, a 10 mm lens) to get the same effect as a 16 mm lens on a camera with full-frame sensor.[9]

Focal length

Sigma currently makes a 4.5mm fisheye lens that captures a 180-degree field of view on a crop body.[10] Sunex also makes a 5.6mm fisheye lens that captures a circular 185-degree field of view on a 1.5x Nikon and 1.6x Canon DSLR cameras. Nikon produced a 6 mm circular fisheye lens that was initially designed for an expedition to Antarctica. It featured a 220-degree field of view, designed to capture the entire sky and surrounding ground when pointed straight up. This lens is no longer manufactured by Nikon,[11] and is used nowadays to produce interactive virtual-reality images such as QuickTime VR and IPIX. Because of its very wide field of view, it is very large and cumbersome—weighing 5.2 kilograms (11 lb), having a diameter of 236 millimetres (9.3 in), a length of 171 millimetres (6.7 in) and an angle of view of 220 degrees. It dwarfs a regular 35 mm SLR camera[12] and has its own tripod mounting point, a feature normally seen in large long-focus or telephoto lenses to reduce strain on the lens mount because the lens is heavier than the camera. The lens is extremely rare,[13] however, there a new developments by the Japanese manufacturer Entaniya for the Micro Four Thirds standard, which offer an angle of view of 250 degrees with lenses that have a focal length of 2.3 millimetres (0.091 in) to 3.6 millimetres (0.14 in), a lens speed of f/2.8 to f/4.0, a weight of 1.6 kilograms (3.5 lb), a diameter of 120 millimetres (4.7 in) and a length below 100 millimetres (3.9 in).[14] An 8 mm fisheye lens, also made by Nikon, has proven useful for scientific purposes because of its equidistant (equiangular) projection, in which distance along the radius of the circular image is proportional to zenith angle. The fastest commercially available fisheye lens with autofocus is the Olympus M.Zuiko Digital ED 8 mm f/1.8 Fisheye Pro for system cameras of the Micro Four Thirds system. In this camera system there are also fisheye lenses with a field 8.2. FISHEYE LENS 137

Fisheye-Nikkor 6mm f/2.8 mounted on a Nikon F2 in the Nikon Museum.

Fisheye lenses for APS-C cameras

• Nikon AF DX Fisheye-Nikkor 10.5mm f/2.8G ED • Pentax DA 10-17mm lens (F3.5-4.5) / Tokina AF 10-17mm f/3.5-4.5 AT-X DX • Samyang 8mm f3.5 fisheye. Notable for its stereographic projection • Samyang 8mm f2.8 fisheye. For various mirrorless cameras. Notable for its stereographic projection • Sigma 10mm F2.8 EX DC Fisheye HSM lens • Sigma 4.5 mm f/2.8 EX DC Circular Fisheye HSM for APS-C sensors

Fisheye lenses for 35 mm cameras

Circular fisheye

• Peleng 8 mm f/3.5 • Sigma 8 mm f/4.0 EX DG 138 CHAPTER 8. DAY 8

A Peleng 8mm circular fisheye lens.

• Sigma 8 mm f/3.5 EX DG - replaces the Sigma 8 mm f/4.0 EX DG

Full-frame fisheye

• Canon EF 15 mm f/2.8 (discontinued)

• Canon Fisheye FD 15 mm f/2.8 (old lens, does not work on EF mount)

• Minolta AF 16 mm f/2.8 Fisheye lens

• Sigma 15 mm f/2.8 EX DG Diagonal Fisheye

• Fisheye-Nikkor AF 16mm f/2.8 D

• Samyang 12 mm f/2.8 ED AS NCS Diagonal Fish-eye

Zoom fisheye

• Canon EF 8–15mm f/4L Fisheye USM – lens can be used as both a full-frame fisheye and a circular fisheye on a 35 mm full-frame film or DSLR such as the canon 5d (Mark I – III) cameras, it can only be used as a cropped circular or as a full-frame fisheye on EOS DSLRs with APS-C/H size sensors (a zoom lock is included).

• Tokina AT-X 10–17mm f3.4-4.5 AF DX – a fisheye zoom lens designed for APS-C sensor cameras. It’s also sold as a NH version that comes without integrated lens hood, then the fisheye lens is usable on full frame cameras. The lens is also sold under Pentax brand.

• Pentax SMC Pentax-F Fish-Eye 1:3.5–4.5 17–28mm – lens was born for full-frame film cameras, to take the place of the 16mm f/2.8 in the AF era. It starts from a 17mm full-frame fisheye and reaches the end of the excursion as an overdistorted 28mm. Was intended as a “special effect” lens and never had big sales.[15] 8.2. FISHEYE LENS 139

Miniature fisheye lenses

Miniature digital cameras, especially when used as security cameras, often tend to have such lenses for similar reasons. Miniature fisheye lenses are designed for small-format CCD/CMOS imagers commonly used in consumer and security cameras.[16][17] Popular format sizes are 1/4” (active area 3.6mmx2.7mm), 1/3” (active area 4.8mmx3.6mm) and 1/2” (active area 6.6mmx4.8mm). Depending on the imager active area, the same lens can form a circular image on one imager (e.g. 1/2”), and a full frame on the other (e.g. 1/4”).

8.2.2 Sample images

• An image of the Louvre museum entry taken with the 7.5 mm f/5.6 cir- cular fisheye Nikkor lens

• Fisheye used to capture entire Wells Cathedral Chapter House room

• Canon 8–15mm zoom at 8mm of BMW M3 140 CHAPTER 8. DAY 8

• Image shot with a 16mm full-frame fisheye lens before and after remap- ping to rectilinear perspective.[n 1]

8.2.3 Other applications

The Curves of ESO’s Headquarters through a fish-eye lens.[18]

• Many planetariums now use fisheye projection lenses to project the night sky or other digital content onto the interior of a dome.

• Flight simulators and visual combat simulators use fisheye projection lenses in order to create an immersive environment for pilots, air traffic controllers, or military personnel to train in.

• Similarly, the IMAX Dome (previously 'OMNIMAX') motion-picture format involves photography through a circular fisheye lens, and projection through the same onto a hemispherical screen.

• Scientists and resource managers (e.g., biologists, foresters, and meteorologists) use fisheye lenses for hemispherical 8.2. FISHEYE LENS 141

photography to calculate plant canopy indices and near-ground solar radiation. Applications include evaluation of forest health, characterization of monarch butterfly winter roosting sites, and management of vineyards.

• Astronomers use fisheye lenses to capture cloud cover and light pollution data.

• Photographers and videographers use fisheye lenses so they can get the camera as close as possible for action shots whilst also capturing context, for example in skateboarding to focus on the board and still retain an image of the skater.

• The first music video to be shot completely with fisheye lens was for the Beastie Boys song "Hold It Now, Hit It" in 1987.

• In Computer Graphics, circular fisheye images can be used to create environment maps from the physical world. One complete 180-degree wide angle fisheye image will fit to half of cubic mapping space using the proper algorithm. Environment maps can be used to render 3D objects and virtual panoramic scenes.

8.2.4 Mapping function

The mapping of a sideways object leads to a picture position displacement from the image center. The manner of this conversion is the mapping function. The distance of a point from the image center 'r' is dependent on the focal length of the optical system 'f', and the angle from the optical axis 'θ', where 'θ' is in radians.

In the following images the test object "cylindrical tunnel" has • been "photographed" from tunnel center to the left-wall-diirection. Original tunnel to be photographed, with camera looking from in- side center to left wall.

Normal (non-fisheye) lens

• gnomonical Gnomonical

• gnomonical, 40° right Gnomonical, 40° right pan 142 CHAPTER 8. DAY 8

• Gnomonical/Rectilinear (perspective): r = f tan(θ) . Works like the pinhole camera. Straight lines remain straight (distortion free). θ has to be smaller than 90°. The aperture angle is gaged symmetrically to the optical axis and has to be smaller than 180°. Large aperture angles are difficult to design and lead to high prices.

Fisheye lens

Fisheye lenses can have many different mapping functions:[19]

• Stereographic

• Equidistant

• Equisolid angle

• Orthographic

• Stereographic (conform): r = 2f tan(θ/2) . Maintains angles. This mapping would be ideal for photographers because it doesn't compress marginal objects as much. Samyang is the only manufacturer to produce this kind of fisheye lens, but it is available under different brand names. This mapping is easily implemented by software. • Equidistant (linear scaled): r = f · θ . Maintains angular distances. Practical for angle measurement (e.g., star maps). PanoTools uses this type of mapping. 8.2. FISHEYE LENS 143

• Equisolid angle (equal area): r = 2f sin(θ/2) . Maintains surface relations. Every pixel subtends an equal solid angle, or an equal area on the unit sphere. Looks like a mirror image on a ball, best special effect (unsophisticated distances), suitable for area comparison (clouds grade determination). This type is popular but it compresses marginal objects. The prices of these lenses are high, but not extreme. • Orthographic: r = f sin(θ) . Maintains planar illuminance. Looks like an orb with the surroundings lying on < max. 180° aperture angle. • Other mapping functions (for example Panomorph Lenses) are also possible for enhancing the off-axis resolu- tion of fisheye lenses.

With appropriate software, the curvilinear images produced by a fisheye lens can be remapped to a conventional rectilinear projection. Although this entails some loss of detail at the edges of the frame, the technique can produce an image with a field of view greater than that of a conventional rectilinear lens. This is particularly useful for creating panoramic images. All types of fisheye lenses bend straight lines. Aperture angles of 180° or more are possible only with large amounts of barrel distortion.

8.2.5 See also

• Azimuthal equidistant projection • Little planet effect • Stereographic projection

8.2.6 Notes

[1] Camera: a 35mm-format digital SLR, editing tool: Panorama Tools

8.2.7 References

[1] Henry Horenstein (2005-04-20). Photography: A Basic Manual. p. 55. ISBN 9780316373050.

[2] Rudolf Kingslake (1989-10-28). A history of the photographic lens. p. 145. ISBN 9780124086401.

[3] “Philosophical Magazine”.

[4] David Brooks (1982). Lenses and lens accessories: a photographer’s guide. p. 29. ISBN 9780930764340.

[5] Hill, R. 1924. A lens for whole sky photographs. Quarterly Journal of the Royal Meteorological Society 50:227-235.

[6] “The New Nikon Compendium”.

[7] “The Magic of Digital Nature Photography”. ( ) · size frame [8] The formula is FOV = 4 arcsin 4·length focal which comes from inverting the mapping function; Dyxum, Gustavo Orensztajn

[9] “Cameras from Nikon - DSLR and Digital Cameras, Lenses, & More”.

[10] 4.5mm F2.8 EX DC Circular Fisheye HSM

[11] “Additional Information on Fisheye-Nikkor 6mm f/2.8 lens”. Malaysian Internet Resources. Retrieved 2008-11-11.

[12] “Additional Information on Fisheye-Nikkor 6mm f/2.8 lens: Late 70s”. Malaysian Internet Resources. Retrieved 2008- 11-11.

[13] Laurent, Olivier Laurent (23 April 2012). “Rare extreme wide-angle Nikkor lens goes on sale”. British Journal of Photog- raphy. Retrieved 24 April 2012.

[14] Entaniya Fisheye 250 MFT - Micro Four Thirds system lens - 250° Fisheye Lens, entapano.com, retrieved on 15 November 2016 144 CHAPTER 8. DAY 8

[15] “TheFishList - Pentax DA 10-17 -".

[16] 190 Degree FOV Miniature Fisheye Lens

[17] Miniature fisheye lenses

[18] “The Curves of ESO’s Headquarters”. ESO Picture of the Week. Retrieved 26 February 2014.

[19] “Samyang 8 mm f/3.5 Aspherical IF MC Fish-eye review - Introduction - Lenstip.com”.

8.2.8 External links

• Fisheye projection theory

• A list of fisheye lenses • Overview of fish-eye distortion effects

• Various fisheye projections Chapter 9

Day 9

9.1 Optical coating

Optically coated mirrors and lenses.

An optical coating is one or more thin layers of material deposited on an optical component such as a lens or mirror, which alters the way in which the optic reflects and transmits light. One type of optical coating is an antireflection coating, which reduces unwanted reflections from surfaces, and is commonly used on spectacle and photographic lenses. Another type is the high-reflector coating which can be used to produce mirrors which reflect greater than 99.99% of the light which falls on them. More complex optical coatings exhibit high reflection over some range of wavelengths, and anti-reflection over another range, allowing the production of dichroic thin-film optical filters.

9.1.1 Types of coating

The simplest optical coatings are thin layers of metals, such as aluminium, which are deposited on glass substrates to make mirror surfaces, a process known as silvering. The metal used determines the reflection characteristics of the mirror; aluminium is the cheapest and most common coating, and yields a reflectivity of around 88%−92% over the visible spectrum. More expensive is silver, which has a reflectivity of 95%−99% even into the far infrared, but

145 146 CHAPTER 9. DAY 9

Reflectance vs. wavelength curves for aluminium (Al), silver (Ag), and gold (Au) metal mirrors at normal incidence

suffers from decreasing reflectivity (<90%) in the blue and ultraviolet spectral regions. Most expensive is gold, which gives excellent (98%−99%) reflectivity throughout the infrared, but limited reflectivity at wavelengths shorter than 550 nm, resulting in the typical gold colour. By controlling the thickness and density of metal coatings, it is possible to decrease the reflectivity and increase the transmission of the surface, resulting in a half-silvered mirror. These are sometimes used as "one-way mirrors". The other major type of optical coating is the dielectric coating (i.e. using materials with a different refractive index to the substrate). These are constructed from thin layers of materials such as magnesium fluoride, calcium fluoride, and various metal oxides, which are deposited onto the optical substrate. By careful choice of the exact composition, thickness, and number of these layers, it is possible to tailor the reflectivity and transmitivity of the coating to produce almost any desired characteristic. Reflection coefficients of surfaces can be reduced to less than 0.2%, producing an antireflection (AR) coating. Conversely, the reflectivity can be increased to greater than 99.99%, producing a high- reflector (HR) coating. The level of reflectivity can also be tuned to any particular value, for instance to produce a mirror that reflects 90% and transmits 10% of the light that falls on it, over some range of wavelengths. Such mirrors are often used as beamsplitters, and as output couplers in lasers. Alternatively, the coating can be designed such that the mirror reflects light only in a narrow band of wavelengths, producing an optical filter. The versatility of dielectric coatings leads to their use in many scientific optical instruments (such as lasers, optical microscopes, refracting telescopes, and interferometers) as well as consumer devices such as binoculars, spectacles, and photographic lenses. Dielectric layers are sometimes applied over top of metal films, either to provide a protective layer (as in silicon dioxide over aluminium), or to enhance the reflectivity of the metal film. Metal and dielectric combinations are also used to make advanced coatings that cannot be made any other way. One example is the so-called "perfect mirror", which exhibits high (but not perfect) reflection, with unusually low sensitivity to wavelength, angle, and polarization.[1] 9.1. OPTICAL COATING 147

Antireflection coatings

Main article: Anti-reflective coating Antireflection coatings are used to reduce reflection from surfaces. Whenever a ray of light moves from one medium

Comparison of uncoated glasses (top) and glasses with an anti-reflective coating (bottom). to another (such as when light enters a sheet of glass after travelling through air), some portion of the light is reflected 148 CHAPTER 9. DAY 9 from the surface (known as the interface) between the two media. A number of different effects are used to reduce reflection. The simplest is to use a thin layer of material at the interface, with an index of refraction between those of the two media. The reflection is minimized when

√ n1 = n0nS where n1 is the index of the thin layer, and n0 and nS are the indices of the two media. The optimum refractive indices for multiple coating layers at angles of incidence other than 0° is given by Moreno et al. (2005).[2] Such coatings can reduce the reflection for ordinary glass from about 4% per surface to around 2%. These were the first type of antireflection coating known, having been discovered by Lord Rayleigh in 1886. He found that old, slightly tarnished pieces of glass transmitted more light than new, clean pieces due to this effect. Practical antireflection coatings rely on an intermediate layer not only for its direct reduction of reflection coefficient, but also use the interference effect of a thin layer. If the layer’s thickness is controlled precisely such that it is exactly one-quarter of the wavelength of the light (a quarter-wave coating), the reflections from the front and back sides of the thin layer will destructively interfere and cancel each other.

Interference in a quarter-wave antireflection coating

In practice, the performance of a simple one-layer interference coating is limited by the fact that the reflections only exactly cancel for one wavelength of light at one angle, and by difficulties finding suitable materials. For ordinary glass 9.1. OPTICAL COATING 149

(n≈1.5), the optimum coating index is n≈1.23. Few useful substances have the required refractive index. Magnesium fluoride (MgF2) is often used, since it is hard-wearing and can be easily applied to substrates using physical vapour deposition, even though its index is higher than desirable (n=1.38). With such coatings, reflection as low as 1% can be achieved on common glass, and better results can be obtained on higher index media. Further reduction is possible by using multiple coating layers, designed such that reflections from the surfaces undergo maximum destructive interference. By using two or more layers, broadband antireflection coatings which cover the visible range (400-700 nm) with maximum reflectivities of less than 0.5% are commonly achievable. Reflection in narrower wavelength bands can be as low as 0.1%. Alternatively, a series of layers with small differences in refractive index can be used to create a broadband antireflective coating by means of a refractive index gradient.

High-reflection coatings

See also: Dielectric mirror

High-reflection (HR) coatings work the opposite way to antireflection coatings. The general idea is usually based on the periodic layer system composed from two materials, one with a high index, such as zinc sulfide (n=2.32) or titanium dioxide (n=2.4) and low index material, such as magnesium fluoride (n=1.38) or silicon dioxide (n=1.49). This periodic system significantly enhances the reflectivity of the surface in the certain wavelength range called band-stop, whose width is determined by the ratio of the two used indices only (for quarter-wave system), while the maximum reflectivity is increasing nearly up to 100% with a number of layers in the stack. The thicknesses of the layers are generally quarter-wave (then they yield to the broadest high reflection band in compare to the non-quarter-wave systems composed from the same materials), this time designed such that reflected beams constructively interfere with one another to maximize reflection and minimize transmission. The best of these coatings built-up from deposited dielectric lossless materials on the perfect smooth surfaces can reach reflectivities greater than 99.999% (over a fairly narrow range of wavelengths). Common HR coatings can achieve 99.9% reflectivity over a broad wavelength range (tens of nanometers in the visible spectrum range). As for AR coatings, HR coatings are affected by the incidence angle of the light. When used away from normal incidence, the reflective range shifts to shorter wavelengths, and becomes polarization dependent. This effect can be exploited to produce coatings that polarize a light beam. By manipulating the exact thickness and composition of the layers in the reflective stack, the reflection characteristics can be tuned to a particular application, and may incorporate both high-reflective and anti-reflective wavelength regions. The coating can be designed as a long- or short-pass filter, a bandpass or notch filter, or a mirror with a specific reflectivity (useful in lasers). For example, the dichroic prism assembly used in some cameras requires two dielectric coatings, one long-wavelength pass filter reflecting light below 500 nm (to separate the blue component of the light), and one short-pass filter to reflect red light, above 600 nm wavelength. The remaining transmitted light is the green component.

Extreme ultraviolet coatings In the EUV portion of the spectrum (wavelengths shorter than about 30 nm) nearly all materials absorb strongly, making it difficult to focus or otherwise manipulate light in this wavelength range. Telescopes such as TRACE or EIT that form images with EUV light use multilayer mirrors that are constructed of hundreds of alternating layers of a high-mass metal such as molybdenum or tungsten, and a low-mass spacer such as silicon, vacuum deposited onto a substrate such as glass. Each layer pair is designed to have a thickness equal to half the wavelength of light to be reflected. Constructive interference between scattered light from each layer causes the mirror to reflect EUV light of the desired wavelength as would a normal metal mirror in visible light. Using multilayer optics it is possible to reflect up to 70% of incident EUV light (at a particular wavelength chosen when the mirror is constructed).

Transparent conductive coatings

Transparent conductive coatings are used in applications where it is important that the coating conduct electricity or dissipate static charge. Conductive coatings are used to protect the aperture from electromagnetic Interference, while dissipative coatings are used to prevent the build-up of static electricity. Transparent conductive coatings are also used extensively to provide electrodes in situations where light is required to pass, for example in flat panel display technologies and in many photoelectrochemical experiments. A common substance used in transparent conductive coatings is indium tin oxide (ITO). ITO is not very optically transparent, however. The layers must be thin to provide 150 CHAPTER 9. DAY 9 substantial transparency, particularly at the blue end of the spectrum. Using ITO, sheet resistances of 20 to 10,000 ohms per square can be achieved. An ITO coating may be combined with an antireflective coating to further improve transmittance. Other TCOs (Transparent Conductive Oxides) include AZO (Aluminium doped Zinc Oxide), which offers much better UV transmission than ITO. A special class of transparent conductive coatings applies to infrared films for theater-air military optics where IR transparent windows need to have (Radar) stealth (Stealth technology) properties. These are known as RAITs (Radar Attenuating / Infrared Transmitting) and include materials such as boron doped DLC (Diamond-like carbon).

9.1.2 Current market and forecast

Estimated at US$6.5 billion in 2013, the global demand of optical coatings is forecast to grow 6.5% annually over the next years. The largest application market of optical coatings is electronics and semiconductor combined, while the fastest growing one is fiber optics & telecommunication combined.[3]

9.1.3 Sources

• Hecht, Eugene. Chapter 9, Optics, 2nd ed. (1990), Addison Wesley. ISBN 0-201-11609-X.

• I. Moreno, et al., “Thin-film spatial filters,” Optics Letters 30, 914-916 (2005)

• C. Clark, et al., “Two-color Mach 3 IR coating for TAMD systems”, Proc. SPIE Vol. 4375, p. 307-314 (2001)

9.1.4 References

[1] “MIT researchers create a 'perfect mirror'". MIT press release. 1998-11-26. Retrieved 2007-01-17.

[2] "Thin-film spatial filters,” (PDF). Retrieved 2007-05-30.

[3] “Market Report: Global Optical Coatings Market”. Acmite Market Intelligence. External link in |publisher= (help)

9.1.5 See also

• List of telescope parts and construction

9.1.6 External links

• Browser-based thin film design and optimization software

• Java demonstration of anti-reflection coating

• Browser-based numerical calculator of single-layer thin film reflectivity

• - Melles Griot Technical Guide

9.2 Optical filter

Optical filters are devices that selectively transmit light of different wavelengths, usually implemented as plane glass or plastic devices in the optical path which are either dyed in the bulk or have interference coatings. The optical properties of filters are completely described by their frequency response, which specifies how the magnitude and phase of each frequency component of an incoming signal is modified by the filter.[1] Filters mostly belong to one of two categories. The simplest, physically, is the absorptive filter; then there are interference or dichroic filters. Optical filters selectively transmit light in a particular range of wavelengths, that is, colours, while blocking the re- mainder. They can usually pass long wavelengths only (longpass), short wavelengths only (shortpass), or a band of wavelengths, blocking both longer and shorter wavelengths (bandpass). The passband may be narrower or wider; the 9.2. OPTICAL FILTER 151

Coloured and Neutral Density filters

Stacked cases of Cokin filters. transition or cutoff between maximal and minimal transmission can be sharp or gradual. There are filters with more complex transmission characteristic, for example with two peaks rather than a single band;[2] these are more usually older designs traditionally used for photography; filters with more regular characteristics are used for scientific and technical work. Optical filters are commonly used in photography (where some special effect filters are occasionally used as well as 152 CHAPTER 9. DAY 9 absorptive filters), in many optical instruments, and to colour stage lighting. In astronomy optical filters are used to restrict light passed to the spectral band of interest, e.g., to study infrared radiation without visible light which would affect film or sensors and overwhelm the desired infrared. Optical filters are also essential in fluorescence applications such as fluorescence microscopy and fluorescence spectroscopy. Photographic filters are a particular case of optical filters, and much of the material here applies. Photographic filters do not need the accurately controlled optical properties and precisely defined transmission curves of filters designed for scientific work, and sell in larger quantities at correspondingly lower prices than many laboratory filters. Some photographic effect filters, such as star effect filters, are not relevant to scientific work.

9.2.1 Absorptive

Absorptive filters are usually made from glass to which various inorganic or organic compounds have been added. These compounds absorb some wavelengths of light while transmitting others. The compounds can also be added to plastic (often polycarbonate or acrylic) to produce gel filters, which are lighter and cheaper than glass-based filters.

9.2.2 Dichroic filter

Alternately, dichroic filters (also called “reflective” or “thin film” or “interference” filters) can be made by coating a glass substrate with a series of optical coatings. Dichroic filters usually reflect the unwanted portion of the light and transmit the remainder. Dichroic filters use the principle of interference. Their layers form a sequential series of reflective cavities that resonate with the desired wavelengths. Other wavelengths destructively cancel or reflect as the peaks and troughs of the waves overlap. Dichroic filters are particularly suited for precise scientific work, since their exact colour range can be controlled by the thickness and sequence of the coatings. They are usually much more expensive and delicate than absorption filters. They can be used in devices such as the dichroic prism of a camera to separate a beam of light into different coloured components. The basic scientific instrument of this type is a Fabry–Pérot interferometer. It uses two mirrors to establish a res- onating cavity. It passes wavelengths that are a multiple of the cavity’s resonance frequency. Etalons are another variation: transparent cubes or fibers whose polished ends form mirrors tuned to resonate with specific wavelengths. These are often used to separate channels in telecommunications networks that use wavelength division multiplexing on long-haul optic fibers.

9.2.3 Monochromatic

Monochromatic filters only allow a narrow range of wavelengths (essentially a single colour) to pass.

9.2.4 Infrared

The term “infrared filter” can be ambiguous, as it may be applied to filters to pass infrared (blocking other wavelengths) or to block infrared (only). Infrared-passing filters are used to block visible light but pass infrared; they are used, for example, in infrared pho- tography. Infrared cut-off filters are designed to block or reflect infrared wavelengths but pass visible light. Mid-infrared filters are often used as heat-absorbing filters in devices with bright incandescent light bulbs (such as slide and overhead projectors) to prevent unwanted heating due to infrared radiation. There are also filters which are used in solid state video cameras to block IR due to the high sensitivity of many camera sensors to unwanted near-infrared light. 9.2. OPTICAL FILTER 153

9.2.5 Ultraviolet

Ultraviolet (UV) filters block ultraviolet radiation, but let visible light through. Because photographic film and digital sensors are sensitive to ultraviolet (which is abundant in skylight) but the human eye is not, such light would, if not filtered out, make photographs look different from the scene visible to people, for example making images of distant mountains appear unnaturally hazy. An ultraviolet-blocking filter renders images closer to the visual appearance of the scene. As with infrared filters there is a potential ambiguity between UV-blocking and UV-passing filters; the latter are much less common, and more usually known explicitly as UV pass filters and UV bandpass filters.[3]

9.2.6 Neutral density

Neutral density (ND) filters have a constant attenuation across the range of visible wavelengths, and are used to reduce the intensity of light by reflecting or absorbing a portion of it. They are specified by the optical density (OD) of the filter, which is the negative of the common logarithm of the transmission coefficient. They are useful for making photographic exposures longer. A practical example is making a waterfall look blurry when it is photographed in bright light. Alternatively, the photographer might want to use a larger aperture (so as to limit the depth of field); adding an ND filter permits this. ND filters can be reflective (in which case they look like partially reflective mirrors) or absorptive (appearing grey or black).

9.2.7 Longpass

A longpass (LP) Filter is an optical interference or coloured glass filter that attenuates shorter wavelengths and trans- mits (passes) longer wavelengths over the active range of the target spectrum (ultraviolet, visible, or infrared). Long- pass filters, which can have a very sharp slope (referred to as edge filters), are described by the cut-on wavelength at 50 percent of peak transmission. In fluorescence microscopy, longpass filters are frequently utilized in dichroic mirrors and barrier (emission) filters. Use of the older term 'low pass’ to describe longpass filters has become un- common; filters are usually described in terms of wavelength rather than frequency, and a "low pass filter", without qualification, would be understood to be an electronic filter.

9.2.8 Bandpass

Bandpass filters only transmit a certain wavelength band, and block others. The width of such a filter is expressed in the wavelength range it lets through and can be anything from much less than an Ångström to a few hundred nanometers. Such a filter can be made by combining an LP- and an SP filter. Examples of bandpass filters are the Lyot filter and the Fabry-Pérot interferometer. Both of these filters can also be made tunable, such that the central wavelength can be chosen by the user. Bandpass filters are often used in astronomy when one wants to observe a certain process with specific associated spectral lines. The Dutch Open Telescope[4] and Swedish Solar Telescope[5] are examples where Lyot and Fabry-Pérot filters are being used.

9.2.9 Shortpass

A shortpass (SP) Filter is an optical interference or coloured glass filter that attenuates longer wavelengths and trans- mits (passes) shorter wavelengths over the active range of the target spectrum (usually the ultraviolet and visible region). In fluorescence microscopy, shortpass filters are frequently employed in dichromatic mirrors and excitation filters.

9.2.10 Guided-mode resonance filters

A relatively new class of filters introduced around 1990. These filters are normally filters in reflection, that is they are notch filters in transmission. They consist in their most basic form of a substrate waveguide and a subwavelength grating or 2D hole array. Such filters are normally transparent, but when a leaky guided mode of the waveguide is excited they become highly reflective (a record of over 99% experimentally) for a particular polarization, angular 154 CHAPTER 9. DAY 9

orientations, and wavelength range. The parameters of the filters are designed by proper choice of the grating pa- rameters. The advantage of such filters are the few layers needed for ultra-narrow bandwidth filters (in contrast to dichroic filters), and the potential decoupling between spectral bandwidth and angular tolerance when more than 1 mode is excited.

9.2.11 Metal mesh filters

Filters for sub-millimeter and near infrared wavelengths in astronomy are metal mesh grids that are stacked together to form LP, BP, and SP filters for these wavelengths.

9.2.12 Polarizer

Another kind of optical filter is a polarizer or polarization filter, which blocks or transmits light according to its polarization. They are often made of materials such as Polaroid and are used for sunglasses and photography. Re- flections, especially from water and wet road surfaces, are partially polarized, and polarized sunglasses will block some of this reflected light, allowing an angler to better view below the surface of the water and better vision for a driver. Light from a clear blue sky is also polarized, and adjustable filters are used in colour photography to darken the appearance of the sky without introducing colours to other objects, and in both colour and black-and-white pho- tography to control specular reflections from objects and water. Much older than g.m.r.f (just above) these first (and some still) use fine mesh integrated in the lens. Polarized filters are also used to view certain types of stereograms, so that each eye will see a distinct image from a single source.

9.2.13 Arc welding

An arc source puts out visible light that may be harmful to human eyes. Therefore, optical filters on welding helmets must meet ANSI Z87:1 (a safety glasses specification) in order to protect human vision. Some examples of filters that would provide this kind of filtering would be earth elements embedded or coated on glass, but practically speaking it is not possible to do perfect filtering. A perfect filter would remove particular waves and leave plenty of light so a worker can see what he/she is working on.

9.2.14 See also

• Filter (photography)

• Filter (signal processing)

• Filter fluorometer

• Lyot filter

• Dichroic filter

• Dichroic prism

• Atomic line filter

• Warm filter

• Metal mesh optical filters

9.2.15 References

[1] Transmission curves of many filters for monochrome photography, Schneider, p.1 Optical Filter Design and Analysis: A Signal Processing Approach, Christi K. Madsen, Jian H. Zhao, Copyright © 1999 John Wiley & Sons, Inc., ISBNs: 0-471-18373-3 (Hardback); 0-471-21375-6 (Electronic) 9.3. 155

[2] Transmission curves of many filters for monochrome photography, Schneider. See Redhancer 491 for a very complex curve with many peaks

[3] Datasheets on UV pass and bandpass filters

[4] Rutten, Rob. “DOT tomography”. Dutch Open Telescope website. Retrieved 24 May 2011.

[5] Löfdahl, Mats. “SST CRISP images”. SST website. Retrieved 24 May 2011.

9.3 Photographic filter

Four photographic filters. Clockwise, from top-left, an infrared hot mirror filter, a polarising filter, and a UV filter. The larger filter is a polariser for Cokin-style filter mounts.

In photography and videography, a filter is a camera accessory consisting of an optical filter that can be inserted into the optical path. The filter can be of a square or oblong shape and mounted in a holder accessory, or, more commonly, a glass or plastic disk in a metal or plastic ring frame, which can be screwed into the front of or clipped onto the camera lens. Filters modify the images recorded. Sometimes they are used to make only subtle changes to images; other times the image would simply not be possible without them. In monochrome photography coloured filters affect the relative brightness of different colours; red lipstick may be rendered as anything from almost white to almost black with 156 CHAPTER 9. DAY 9 different filters. Others change the colour balance of images, so that photographs under incandescent lighting show colours as they are perceived, rather than with a reddish tinge. There are filters that distort the image in a desired way, diffusing an otherwise sharp image, adding a starry effect, etc. Linear and circular polarising filters reduce oblique reflections from non-metallic surfaces. Many filters absorb part of the light available, necessitating longer exposure. As the filter is in the optical path, any imperfections—non-flat or non-parallel surfaces, reflections (minimised by optical coating), scratches, dirt—affect the image. There is no universal standard naming system for filters. The Wratten numbers adopted in the early twentieth century by Kodak, then a dominant force in film photography, are used by several manufacturers. Colour correction filters are often identified by a code of the form CC50Y—CC for colour correction, 50 for the strength of the filter, Y for yellow. Optical filters are used in various areas of science, including in particular astronomy; they are essentially the same as photographic filters, but in practice often need far more accurately controlled optical properties and precisely defined transmission curves than filters exclusively for photographic use. Photographic filters sell in larger quantities at correspondingly lower prices than many laboratory filters. The article on optical filters has material relevant to photographic filters. In digital photography the majority of filters used with film cameras have been rendered redundant by digital filters applied either in-camera or during post processing. Exceptions include the ultraviolet (UV) filter typically used to protect the front surface of the lens, the neutral density (ND) filter, the polarising filter and the infra red (IR) filter. The neutral density filter permits effects requiring wide apertures or long exposures to be applied to brightly lit scenes, while the graduated neutral density filter is useful in situations where the scene’s dynamic range exceeds the capability of the sensor. Not using optical filters in front of the lens has the advantage of avoiding the reduction of image quality caused by the presence of an extra optical element in the light path and may be necessary to avoid vignetting when using wide-angle lenses.[1][2]

9.3.1 Uses of filters in photography

Filters in photography can be classified according to their use:

• Clear and ultraviolet

• Color correction

• Color conversion (or light balance)

• Color separation, also called color subtraction

• Contrast enhancement

• Infrared

• Neutral density, including the graduated neutral density filter and solar filter

• Polarizing

• Special effects of various kinds, including

• Graduated color, called color grads • Cross screen and star diffractors • Diffusion and contrast reduction • Spot • Close-up or macro diopters, and split diopters or split focus 9.3. PHOTOGRAPHIC FILTER 157

Clear and ultraviolet

Main article: UV filter

Clear filters, also known as window glass filters or optical flats, are transparent and (ideally) perform no filtering of incoming light. The only use of a clear filter is to protect the front of a lens. UV filters are used to block invisible ultraviolet light, to which most photographic sensors and film are at least slightly sensitive. The UV is typically recorded as if it were blue light, so this non-human UV sensitivity can result in an unwanted exaggeration of the bluish tint of atmospheric haze or, even more unnaturally, of subjects in open shade lit by the ultraviolet-rich sky. Normally, the glass or plastic of a camera lens is practically opaque to short-wavelength UV, but transparent to long- wavelength (near-visible) UV. A UV filter passes all or nearly all of the visible spectrum but blocks virtually all ultraviolet radiation. (Most spectral manipulation filters are named for the radiation they pass; green and infrared filters pass their named colors, but a UV filter blocks UV.) It can be left on the lens for nearly all shots: UV filters are often used mainly for lens protection in the same way as clear filters. A strong UV filter, such as a Haze-2A or UV17, cuts off some visible light in the violet part of the spectrum, and has a pale yellow color; these strong filters are more effective at cutting haze,[3][4] and can reduce purple fringing in digital cameras.[5] Strong UV filters are also sometimes used for warming color photos taken in shade with daylight-type film.

An extreme case: a Nikon D700 with a smashed filter which may have saved the Nikkor lens beneath. Usually, all that can reasonably be expected is protection from scratches, nicks and airborne contaminants.

While in certain cases, such as harsh environments, a protection filter may be necessary, there are also downsides to this practice. Arguments for the use of protection filters include:

• If the lens is dropped, the filter may well suffer scratches or breakage instead of the front lens element. 158 CHAPTER 9. DAY 9

• The filter can be cleaned frequently without damage to the lens surface or coatings; a filter scratched by cleaning is much less expensive to replace than a lens. • If there is blowing sand the filter will protect the front of the lens from abrasion and nicks. • A few lenses, such as some of Canon’s L series lenses, require the use of a filter to complete their weather sealing.[6][7][8]

Arguments against their use include:[9]

• Adding another element may degrade image quality if its surfaces are less than perfectly flat and parallel. Filters from reputable makers are very unlikely to cause any problems, but some “bargain” products are optically inferior. • The two additional reflections at air-glass interfaces inevitably result in some light loss—at least four percent at each interface, if the surfaces are uncoated; they also increase the potential for lens flare problems.[10] • Low-quality filters may cause problems with autofocus. • A filter may be incompatible with the use of a lens hood, since not all filters have the required threading for a screw-in hood or will allow a clip-on hood to be attached. Adding a lens hood on top of one or more filters may space the hood away from the lens enough to cause some vignetting.

There is a wide variation in the spectral UV blocking by filters described as ultraviolet.[11]

Color conversion

Appropriate color conversion filters are used to compensate for the effects of lighting not balanced for the film stock’s rated (usually 3200 K for professional tungstens and 5500 K for daylight): e.g., the 80A blue filter used with film for daylight use corrects the perceived orange/reddish cast of incandescent photographic photoflood lighting (for which the usual photographic term is "tungsten lighting"), and significantly improves the stronger cast produced by lower-temperature household incandescent lighting, while the 85B will correct the bluish cast of daylight photographs on tungsten film. Color correction filters are identified by non-standardised numbers which vary from manufacturer to manufacturer. The need for these filters has been greatly reduced by the widespread adoption of digital photography, since color balance may be corrected with camera settings as the image is captured, or by software manipulation afterwards.

The 80A filter, mainly used to correct for the excessive redness of tungsten lighting, can also be used to oversaturate scenes that already have blue. The photo on the left was shot with a polarizer, while the one on the right was shot with a polarizer and an 80A filter.

Color conversion filters (LB filters) must be distinguished from color correction filters (CC filters), which filter out a particular color cast f.e. caused by Schwarzschild effect etc. 9.3. PHOTOGRAPHIC FILTER 159

Color subtraction

Color subtraction filters work by absorbing certain colors of light, letting the remaining colors through. They can be used to demonstrate the primary colors that make up an image. They are perhaps most frequently used in the printing industry for color separations, and again, use has diminished as digital solutions have become more advanced and abundant.

Contrast enhancement

Colored filters are commonly used in black and white photography to alter the effect of different colors in the scene, changing contrast recorded in black and white of the different colours. For example, a yellow or, more dramatically, orange or red, filter will enhance the contrast between clouds and sky by darkening the blue sky. A deep green filter will also darken the sky, and additionally lighten green foliage, making it stand out against the sky. A blue filter mimics the effect of older orthochromatic film, or even older film sensitive only to blue light, rendering blue as light and red and green as dark, showing blue skies as overcast with no contrast between sky and clouds, darkening blond hair, making blue eyes nearly white and red lips nearly black. Diffusion filters reduce contrast in addition to softening resolution.

Effects of using a polarizer and a red filter in black-and-white photography

Polarizer

Main article: Polarizing filter (photography)

A polarizing filter, used for both color and black-and-white photography, is colourless and does not affect colour balance, but filters out light with a particular direction of polarisation. This reduces oblique reflections from non- metallic surfaces, can darken the sky in colour photography (in monochrome photography colour filters are more effective), and can saturate the image more by eliminating unwanted reflections. Linear polarising filters, while effective, can interfere with metering and auto-focus mechanisms when mirrors or beam-splitters are in the light path, as in the digital single lens reflex camera; a circular polarizer is also effective, and does not affect metering or auto-focus.[12] 160 CHAPTER 9. DAY 9

Neutral density

A neutral density filter (ND filter) is a filter of uniform density which attenuates light of all colors equally. It is used to allow a longer exposure (to create blur) or larger aperture (for selective focus) than otherwise required for correct exposure in the prevailing light conditions, without changing the tonal balance of the photograph. A graduated neutral density filter is a neutral density filter with different attenuation at different points, typically clear in one half shading into a higher density in the other. It can be used, for example, to photograph a scene with part in deep shadow and part brightly lit, where otherwise either the shadows would have no detail or the highlights would be burnt out.

Cross screen

A cross screen filter, also known as a star filter, creates a star pattern, in which lines radiate outward from bright objects. The star pattern is generated by a very fine diffraction grating embedded in the filter, or sometimes by the use of prisms in the filter. The number of stars varies by the construction of the filter, as does the number of points each star has.

Diffusion

The bottom left image has a diffusion filter applied to the original image (shown in the top left). The top right is a cross screen effect.

A diffusion filter (also called a softening filter) softens subjects and generates a dreamy haze (see photon diffusion). This is most often used for portraits. It also has the effect of reducing contrast, and the filters are designed, labeled, sold, and used for that purpose too. There are many ways of accomplishing this effect, and thus filters from different manufacturers vary significantly. The two primary approaches are to use some form of grid or netting in the filter, or to use something which is transparent but not optically sharp. Both effects can be achieved in software, which can in principle provide a very precise degree of control of the level of effect, however the “look” may be noticeably different. If there is too much contrast in a scene, the dynamic range of the digital image sensor or film may be exceeded, which post-processing cannot compensate for, so contrast reduction at the time of image capture may be called for. 9.3. PHOTOGRAPHIC FILTER 161

Close-up and split diopter lenses

Main article: Close-up filter

While these are not technically filters but accessory lenses, they are sold by filter manufacturers as part of their product lines, using the same holders and attachment systems. A close-up lens is a single or two-element converging lens used for close-up and macro photography, and works in the same way as spectacles used for reading. The insertion of a converging lens in front of the taking lens reduces the focal length of the combination. Close-up lenses are usually specified by their optical power, the reciprocal of the focal length in meters. Several close-up lenses may be used in combination; the optical power of the combination is the sum of the optical powers of the component lenses; a set of lenses of +1, +2, and +4 diopters can be combined to provide a range from +1 to +7 in steps of one. A split diopter has just a semicircular half of a close-up lens in a normal filter holder. It can be used to photograph a close object and a much more distant background, with everything in sharp focus; with any non-split lens the depth of field would be far too shallow.

9.3.2 Materials and construction

Photo filters are commonly made from glass, resin plastics similar to those used for eyeglasses (such as CR-39), polyester and polycarbonate; sometimes acetate is used. Historically, filters were often made from gelatin, and color gels. While some filters are still described as gelatin or gel filters, they are no longer actually made from gelatin but from one of the plastics mentioned above. Sometimes the filter is dyed in the mass, in other cases the filter is a thin sheet of material sandwiched between two pieces of clear glass or plastic. Certain kinds of filters use other materials inside a glass sandwich; for example, polarizers often use various special films, netting filters have nylon netting, and so forth. The rings on screw-on filters are often made of aluminum, though in more expensive filters brass is used. Aluminum filter rings are much lighter in weight, but can “bind” to the aluminum lens threads they are screwed in to, requiring the use of a filter wrench to get the filter off of the lens. Aluminum also dents or deforms more easily. High quality filters are multi-coated,[13] with multiple-layer optical coatings to reduce reflections. Uncoated filters can reflect up to 12% of the light,[14] single-coated filter can reduce this considerably, and multi-coated filters can allow up to 99.8% of the light to pass through (0.2% unwanted reflection); the loss of light is not important, but part of the light is reflected inside the camera, producing flare and reducing the contrast of the image. Manufacturers brand their high-end multi-coated filters with different labels, for example:

• B+W: MRC (Multi Resistant Coating), MRC nano (99.5% transmission, for XS-Pro series)[15]

• Hoya: HMC (Hoya Multi Coating), HD (8-layer coating, 99.35% transmission)[16]

• Heliopan: SH-PMC (8-layer coating, 99.8% transmission)[17]

9.3.3 Filter sizes and mountings

Manufacturers of lenses and filters have standardized on several different sets of sizes over the years.

Threaded round filters

The most common standard filter sizes for circular filters include 30.5 mm, 37 mm, 40.5 mm, 43 mm, 46 mm, 49 mm, 52 mm, 55 mm, 58 mm, 62 mm, 67 mm, 72 mm, 77 mm, 82 mm, 86 mm, 95 mm, 112 mm and 127 mm. Other filter sizes within this range may be hard to find since the filter size may be non-standard or may be rarely used on camera lenses. The specified diameter of the filter in millimeters indicates the diameter of the male threads on the filter housing. The thread pitch is 0.5 mm, 0.75 mm or 1.0 mm, depending on the ring size. A few sizes (e.g. 30.5 mm) come in more than one pitch. 162 CHAPTER 9. DAY 9

The filter diameter for a particular lens is commonly identified on the lens face by the ⌀ symbol. For example, a lens marking may indicate: “⌀55mm” or “55⌀” meaning it would accept a 55mm filter or lens hood.

Square filters

For square filters, 2” × 2”, 3” × 3” and 4” × 4” were historically very common and are still made by some manufac- turers. 100 mm × 100 mm is very close to 4” × 4”, allowing use of many of the same holders, and is one of the more popular sizes currently (2006) in use; it is virtually a standard in the motion picture industry. 75 mm x 75 mm is very close to 3” × 3” and while less common today, was much in vogue in the 1990s. The French manufacturer Cokin makes a wide range of filters and holders in three sizes which is collectively known as the Cokin System. “A” (amateur) size is 67 mm wide, “P” (professional) size is 84 mm wide, and “X Pro” is 130 mm wide. Many other manufacturers make filters to fit Cokin holders. Cokin also makes a filter holder for 100 mm filters, which they call the “Z” size. Most of Cokin’s filters are made of optical resins such as CR-39. A few round filter elements may be attached to the square/rectangular filter holders, usually polarizers and gradient filters which both need to be rotated and are more expensive to manufacture. Cokin formerly (1980s through mid-1990s) had competition from Hoya’s Hoyarex system (75 mm x 75 mm filters mostly made from resin) and also a range made by Ambico, but both have withdrawn from the market. A small (84 mm) “system” range is still made (as of 2012) by Formatt Hitech.[18] In general, square (and sometimes rectangular) filters from one system could be used in another system’s holders if the size was correct, but each made a different system of filter holder which could not be used together. Lee, Tiffen, Formatt Hitech and Singh Ray also make square / rectangular filters in the 100 × 100 and Cokin “P” sizes. Gel filters are very common in square form, rarely being used in circular form. These are thin flexible sheets of gelatin or plastic which must be held in rigid frames to prevent them from sagging. Gels are made not only for use as photo filters, but also in a wide range of colors for use in lighting applications, particularly for theatrical lighting. Gel holders are available from all of the square “system” makers, but are additionally provided by many camera manufacturers, by manufacturers of gel filters, and by makers of expensive professional camera accessories (particularly those manufacturers which target the movie and television camera markets. Square filter systems often have lens shades available to attach to the filter holders.

Rectangular filters

Graduated filters of a given width (67 mm, 84 mm, 100 mm, etc.) are often made oblong, rather than square, in order to allow the position of the gradation to be moved up or down in the picture. This allows, for example, the red part of a sunset filter to be placed at the horizon. These are used with the “system” holders described above.

Bayonet round filters

Certain manufacturers, most notably Rollei and Hasselblad, have created their own systems of bayonet mount for filters. Each design comes in several sizes, such as Bay I through Bay VIII for Rollei, and Bay 50 through Bay 104 for Hasselblad.

Series filters

Starting in the 1930s, filters were also made in a sizing system known as a series mount. The filters themselves were round pieces of glass (or occasionally other materials) with no threads. Very early filters had no rims around the glass, but the more common later production filters had the glass mounted in metal rims. To mount the filters on a camera, the filter was placed between two rings; the mount ring either screwed into the lens threads or was slipped over the lens barrel and the retaining ring screws into the mounting ring to hold the filter in place. The series designations are generally written as Roman numerals, I to IX, though there are a few sizes not written that way, such as Series 4.5 and Series 5.5. Most Series filter sizes are now obsolete, production having ceased by the late 1970s. However, Series 9 became a standard of the motion picture industry and Series 9 filters are still produced and sold today, particularly for professional motion picture cinematography.[19] 9.3. PHOTOGRAPHIC FILTER 163

9.3.4 See also

• Color gel • List of photographic equipment makers

• Optical filter

9.3.5 References

[1] Seth Barton (January 9, 2014). “Sony FDR-AX100 review - Hands on with first consumer 4K ”.

[2] “CAMERA LENS FILTERS”. Retrieved January 17, 2014.

[3] Joseph Meehan (1998). The Photographer’s Guide to Using Filters. Watson-Guptill. ISBN 0-8174-5452-7.

[4] Tiffen Inc. “Protection & UV Absorbing Filters”. Retrieved 2011-04-12.

[5] Gary Nugent. “Photoshop Technique: Remove Purple Fringing”. Retrieved 2011-04-12.

[6] Canon Inc. “Canon EF 16-35mm f/2.8L II USM Instruction Manual” (PDF). Canon Inc. p. ENG-1. Retrieved 2013-01- 04. Since the front element of this lens moves when zooming, you need to attach a Canon PROTECT filter sold separately for adequate dust- and water-resistant performance. Without a filter, the lens is not dust or water resistant.

[7] Canon Inc. “Canon EF 17-40mm f/4L USM Instruction Manual” (PDF). Canon Inc. p. ENG-1. Retrieved 2013-01-04. Since the front element of this lens moves when focusing (zooming), you need to attach a Canon PROTECT filter sold separately for adequate dust- and water-resistant performance. Without a filter, the lens is not dust or water-resistant.

[8] Canon Inc. “Canon EF 50mm f/1.2L USM Instruction Manual” (PDF). Canon Inc. p. ENG-1. Retrieved 2013-01-04. Since the front element of this lens moves when focusing, you need to attach a Canon PROTECT filter sold separately for adequate dust- and water-resistant performance. Without a filter, the lens is not dust or water resistant.

[9] Thom Hogan. “Filters by Thom Hogan”. Retrieved 2011-04-12.

[10] Paul van Walree. “Filter Flare”. Retrieved 2011-04-12.

[11] Bob Atkins. “UV or not UV?". Retrieved 2007-07-26.

[12] Reichmann, Michael. “Polarizers”. Retrieved 2011-08-19.

[13] Dr. Ching-Kuang Shene. “Coated or Non-Coated?". Retrieved 2011-04-12.

[14] Lenstip.com. “UV filters test - Tiffen 72mm UV”. Retrieved 2011-04-12.

[15] Schneider Optics. “New B+W XS-Pro Digital Filters”. Retrieved 2011-04-12.

[16] HOYA FILTERS. “filter catalog” (PDF). Retrieved 2011-04-12.

[17] Heliopan Lichtfilter. “filter catalog” (PDF). Retrieved 2011-04-12.

[18] Formatt Hitech. “Format Hitech Still Filters”. Retrieved 2012-09-30.

[19] filmtools.com, online catalog retrieved 2011-08-13

9.3.6 External links

• Photography Filters • UV filters test - Description of the results and summary - Lenstip.com

• Polarizing filters test - Results and summary - Lenstip.com • Analysis of Camera Filters | Camera Filters.biz Chapter 10

Day 10

10.1 Optical transfer function

The optical transfer function (OTF) of an optical system such as a camera, microscope, human eye, or projector specifies how different spatial frequencies are handled by the system. It is used by optical engineers to describe how the optics project light from the object or scene onto a photographic film, detector array, retina, screen, or simply the next item in the optical transmission chain. A variant, the modulation transfer function (MTF), neglects phase effects, but is equivalent to the OTF in many situations. Either transfer function specifies the response to a periodic sine-wave pattern passing through the lens system, as a function of its spatial frequency or period, and its orientation. Formally, the OTF is defined as the Fourier transform of the point spread function (PSF, that is, the impulse response of the optics, the image of a point source). As a Fourier transform, the OTF is complex-valued; but it will be real-valued in the common case of a PSF that is symmetric about its center. The MTF is defined as the real magnitude (absolute value) of the complex OTF.

10.1.1 Definition and related concepts

Since the optical transfer function[1] (OTF) is defined as the Fourier transform of the point-spread function (PSF), it is generally speaking a complex valued function of spatial frequency. The projection of a specific periodic pattern is represented by a complex number with absolute value and complex argument proportional to the relative contrast and translation of the projected projection, respectively. Often the contrast reduction is of most interest and the pattern translation can be ignored. The relative contrast is given by the absolute value of the optical transfer function, a function commonly referred to as the modulation transfer function (MTF). On the other hand, when also the pattern translation is important, the complex argument of the optical transfer function can be depicted as a second real-valued function, commonly referred to as the phase transfer function (PhTF). The complex-valued optical transfer function can be seen as a combination of these two real-valued functions:

OTF(ν) = MTF(ν)ei PhTF(ν) where

MTF(ν) = |OTF(ν)| , PhTF(ν) = arg(OTF(ν)), and arg(·) represents the complex argument function, while ν is the spatial frequency of the periodic pattern. In general ν is a vector with a spatial frequency for each dimension, i.e. it indicates also the direction of the periodic pattern. The impulse response of a well-focused optical system is a three-dimensional intensity distribution with a maximum at the focal plane, and could thus be measured by recording a stack of images while displacing the detector axially.

164 10.1. OPTICAL TRANSFER FUNCTION 165

0.8

0.6

0.4

MTF [a.u.] 0.2

0

(a) 0 100 200 300 400 500 (b) 10µm (c) 10µm spatial frequency [cycles / mm]

0.8

0.6

0.4

MTF [a.u.] 0.2

0

(d) 0 100 200 300 400 500 (e) 10µm (f) 10µm spatial frequency [cycles / mm]

Illustration of the optical transfer function and its relation to image quality. The optical transfer function of a well-focused (a), and an out-of-focus optical imaging system without aberrations (d). As the optical transfer function of these systems is real and non-negative, the optical transfer function is equal to the modulation transfer function by definition. Images of a point source and spoke target are shown in (b,e) and (c,f), respectively.

By consequence, the three-dimensional optical transfer function can be defined as the three-dimensional Fourier transform of the impulse response. Although typically only a one-dimensional, or sometimes a two-dimensional section is used, the three-dimensional optical transfer function can improve the understanding of microscopes such as the structured illumination microscope. True to the definition of transfer function, OTF(0) = MTF(0) should indicate the fraction of light that was detected from the point source object. However, typically the contrast relative to the total amount of detected light is most important. It is thus common practice to normalize the optical transfer function to the detected intensity, hence MTF(0) ≡ 1 . Generally, the optical transfer function depends on factors such as the spectrum and polarization of the emitted light and the position of the point source. E.g. the image contrast and resolution are typically optimal at the center of the image, and deteriorate toward the edges of the field-of-view. When significant variation occurs, the optical transfer function may be calculated for a set of representative positions or colors. Sometimes it is more practical to define the transfer functions based on a binary black-white stripe pattern. The transfer function for an equal-width black-white periodic pattern is referred to as the contrast transfer function (CTF).[2]

10.1.2 Examples

The OTF of an ideal lens system

A perfect lens system will provide a high contrast projection without shifting the periodic pattern, hence the optical transfer function is identical to the modulation transfer function. Typically the contrast will reduce gradually towards zero at a point defined by the resolution of the optics. For example, a perfect, non-aberrated, f/4 optical imaging system used, at the visible wavelength of 500 nm, would have the optical transfer function depicted in the right hand figure. 166 CHAPTER 10. DAY 10

1 1

0.8 0.8

0.6 0.6 0.4 0.4

OTF [a.u.] 0.2

Irradiance [a.u.] 0.2 0

0 (a) 10µm -20 -15 -10 -5 0 5 10 15 20 0 100 200 300 400 500 (b) x [µm] (c) spatial frequency [line pairs / mm] 1 π 3π/4 1 0.8 π/2 0.5 0.6 π/4

0 0.4 0 2D MTF [a.u]

sp. freq. y -π/4 MTF [a.u.] [cycles/mm]250 0.2 PhTF [rad] -π/2 0 250 0 -3π/4 -250 0 -250 -π sp. freq. x [cycles/mm] 0 100 200 300 400 500 0 100 200 300 400 500 (d) (e) spatial frequency [line pairs / mm] (f) spatial frequency [line pairs / mm]

Various closely related characterizations of an optical system exhibiting coma, a typical aberration that occurs off-axis. (a) The point-spread function (PSF) is the image of a point source. (b) The image of a line is referred to as the line-spread function, in this case a vertical line. The line-spread function is directly proportional to the vertical integration of the point-spread image. The optical- transfer function (OTF) is defined as the Fourier transform of the point-spread function and is thus generally a two-dimensional complex function. Typically only a one-dimensional slice is shown (c), corresponding to the Fourier transform of the line-spread function. The thick green line indicates the real part of the function, and the thin red line the imaginary part. Often only the absolute value of the complex function is shown, this allows of the two-dimensional function (d); however, more commonly only the one-dimensional function is shown (e). The latter is typically normalized at the spatial frequency zero and referred to as the modulation transfer function (MTF). For completeness, the complex argument is sometimes provided as the phase transfer function (PhTF), shown in panel (f).

0.8

0.6

0.4 MTF [a.u.] 0.2

0

0 100 200 300 400 500 spatial frequency [line pairs / mm] The one-dimensional optical transfer function of a diffraction limited imaging system is identical to its modulation transfer function.

50µm Spoke target imaged by a diffraction limited imaging system. Transfer function and example image of an ideal, optical-aberration-free (diffraction-limited) imaging system.

It can be read from the plot that the contrast gradually reduces and reaches zero at the spatial frequency of 500 cycles per millimeter, in other words the optical resolution of the image projection is 1/500th of a millimeter, or 2 micrometer. Correspondingly, for this particular imaging device, the spokes become more and more blurred towards the center until they merge into a gray, unresolved, disc. Note that sometimes the optical transfer function is given in units of the object or sample space, observation angle, film width, or normalized to the theoretical maximum. 10.1. OPTICAL TRANSFER FUNCTION 167

Conversion between the two is typically a matter of a multiplication or division. E.g. a microscope typically magnifies everything 10 to 100-fold, and a reflex camera will generally demagnify objects at a distance of 5 meter by a factor of 100 to 200. The resolution of a digital imaging device is not only limited by the optics, but also by the number of , more in particular by their separation distance. As explained by the Nyquist-Shannon sampling theorem, to match the optical resolution of the given example, the pixels of each color channel should be separated by 1 micrometer, half the period of 500 cycles per millimeter. A higher number of pixels on the same sensor size will not allow the resolution of finer detail. On the other hand, when the pixel spacing is larger than 1 micrometer, the resolution will be limited by the separation between pixels; moreover, aliasing may lead to a further reduction of the image fidelity.

OTF of an imperfect lens system

An imperfect, aberrated imaging system could possess the optical transfer function depicted in the following figure. 1

0.8

0.6

0.4

0.2OTF [a.u.]

0

0 100 200 300 400 500 spatial frequency [line pairs / mm] The real part of the optical transfer function of an aberrated, imperfect imaging system.

0.8

0.6

0.4

0.2MTF [a.u.]

0

0 100 200 300 400 500 spatial frequency [line pairs / mm] The modulation transfer function of an aberrated, imperfect, imaging system.

10µm The image of a spoke target as imaged by an aberrated optical system. Transfer function and example image of an f/4 optical imaging system at 500 nm with spherical aberration with standard Zernike coefficient of 0.25.

As the ideal lens system, the contrast reaches zero at the spatial frequency of 500 cycles per millimeter. However, at lower spatial frequencies the contrast is considerably lower than that of the perfect system in the previous example. In fact, the contrast becomes zero on several occasions even for spatial frequencies lower than 500 cycles per millimeter. This explains the gray circular bands in the spoke image shown in the above figure. In between the gray bands, the spokes appear to invert from black to white and vice versa, this is referred to as contrast inversion, directly related to the sign reversal in the real part of the optical transfer function, and represents itself as a shift by half a period for some periodic patterns. While it could be argued that the resolution of both the ideal and the imperfect system is 2 μm, or 500 LP/mm, it is clear that the images of the latter example are less sharp. A definition of resolution that is more in line with 168 CHAPTER 10. DAY 10 the perceived quality would instead use the spatial frequency at which the first zero occurs, 10 μm, or 100 LP/mm. Definitions of resolution, even for perfect imaging systems, vary widely. A more complete, unambiguous picture is provided by the optical transfer function.

The OTF of an optical system with a non-rotational symmetric aberration

1

0.5

0 2D OTF [a.u]

sp. freq. y [cycles/mm]250 0 250 -250 0 -250 10µm 10µm (a) (b) sp. freq. x [cycles/mm](c)

When viewed through an optical system with trefoil aberration, the image of a point object will look as a three-pointed star (a). As the point-spread function is not rotational symmetric, only a two-dimensional optical transfer function can describe it well (b). The height of the surface plot indicates the absolute value and the hue indicates the complex argument of the function. A spoke target imaged by such an imaging device is shown by the simulation in (c).

Optical systems, and in particular optical aberrations are not always rotationally symmetric. Periodic patterns that have a different orientation can thus be imaged with different contrast even if their periodicity is the same. Optical transfer function or modulation transfer functions are thus generally two-dimensional functions. The following figures shows the two-dimensional equivalent of the ideal and the imperfect system discussed earlier, next to an optical system with coma, a non-rotational-symmetric aberration. Optical transfer functions are not always real-valued. Period patterns can be shifted by any amount, depending on the aberration in the system. This is generally the case with non-rotational-symmetric aberrations. The hue of the colors of the surface plots in the above figure indicate phase. It can be seen that, while for the rotational symmetric aberrations the phase is either 0 or π and thus the transfer function is real valued, for the non-rotational symmetric aberration the transfer function has an imaginary component and the phase varies continuously.

Practical example – high-definition video system

While optical resolution, as commonly used with reference to camera systems, describes only the number of pixels in an image, and hence the potential to show fine detail, the transfer function describes the ability of adjacent pixels to change from black to white in response to patterns of varying spatial frequency, and hence the actual capability to show fine detail, whether with full or reduced contrast. An image reproduced with an optical transfer function that 'rolls off' at high spatial frequencies will appear 'blurred' in everyday language. Taking the example of a current high definition (HD) video system, with 1920 by 1080 pixels, the Nyquist theorem states that it should be possible, in a perfect system, to resolve fully (with true black to white transitions) a total of 1920 black and white alternating lines combined, otherwise referred to as a spatial frequency of 1920/2=960 line pairs per picture width, or 960 cycles per picture width, (definitions in terms of cycles per unit angle or per mm are also possible but generally less clear when dealing with cameras and more appropriate to telescopes etc.). In practice, this is far from the case, and spatial frequencies that approach the Nyquist rate will generally be reproduced with decreasing amplitude, so that fine detail, though it can be seen, is greatly reduced in contrast. This gives rise to the interesting observation that, for example, a standard definition television picture derived from a film scanner that uses oversampling, as described later, may appear sharper than a high definition picture shot on a camera with a poor modulation transfer function. The two pictures show an interesting difference that is often missed, the former having full contrast on detail up to a certain point but then no really fine detail, while the latter does contain finer detail, but with such reduced contrast as to appear inferior overall. 10.1. OPTICAL TRANSFER FUNCTION 169

10.1.3 The three-dimensional optical transfer function

The three-dimensional point spread functions (a,c) and corresponding modulation transfer functions (b,d) of a wide-field microscope (a,b) and confocal microscope (c,d). In both cases the numerical aperture of the objective is 1.49 and the refractive index of the medium 1.52. The wavelength of the emitted light is assumed to be 600 nm and, in case of the confocal microscope, that of the excitation light 500 nm with circular polarization. A section is cut to visualize the internal intensity distribution. The colors as shown on the logarithmic color scale indicate the irradiance (a,c) and spectral density (b,d) normalized to the maximum value.

Although one typically thinks of an image as planar, or two-dimensional, the imaging system will produce a three- dimensional intensity distribution in image space that in principle can be measured. e.g. a two-dimensional sensor could be translated to capture a three-dimensional intensity distribution. The image of a point source is also a three dimensional (3D) intensity distribution which can be represented by a 3D point-spread function. As an example, the figure on the right shows the 3D point-spread function in object space of a wide-field microscope (a) alongside that of a confocal microscope (c). Although the same microscope objective with a numerical aperture of 1.49 is used, it is clear that the confocal point spread function is more compact both in the lateral dimensions (x,y) and the axial dimension (z). One could rightly conclude that the resolution of a confocal microscope is superior to that of a wide-field microscope in all three dimensions. A three-dimensional optical transfer function can be calculated as the three-dimensional Fourier transform of the 3D point-spread function. Its color-coded magnitude is plotted in panels (b) and (d), corresponding to the point- spread functions shown in panels (a) and (c), respectively. The transfer function of the wide-field microscope has a support that is half of that of the confocal microscope in all three-dimensions, confirming the previously noted lower resolution of the wide-field microscope. Note that along the z-axis, for x=y=0, the transfer function is zero everywhere except at the origin. This missing cone is a well-known problem that prevents optical sectioning using a wide-field microscope.[3] The two-dimensional optical transfer function at the focal plane can be calculated by integration of the 3D optical transfer function along the z-axis. Although the 3D transfer function of the wide-field microscope (b) is zero on the 170 CHAPTER 10. DAY 10

z-axis for z≠0; its integral, the 2D optical transfer, reaching a maximum at x=y=0. This is only possible because the 3D optical transfer function diverges at the origin x=y=z=0. The function values along the z-axis of the 3D optical transfer function correspond to the Dirac delta function.

10.1.4 Calculation

Most optical design software has functionality to compute the optical or modulation transfer function of a lens design. Ideal systems such as in the examples here are readily calculated numerically using software such as Julia, GNU Octave or Matlab, and in some specific cases even analytically. The optical transfer function can be calculated following two approaches:[4]

1. as the Fourier transform of the incoherent point spread function, or

2. as the auto-correlation of the pupil function of the optical system

Mathematically both approaches are equivalent. Numeric calculations are typically most efficiently done via the Fourier transform; however, analytic calculation may be more tractable using the auto-correlation approach.

Example

Ideal lens system with circular aperture

Auto-correlation of the pupil function Since the optical transfer function is the Fourier transform of the point spread function, and the point spread function is the square absolute of the inverse Fourier transformed pupil function, the optical transfer function can also be calculated directly from the pupil function. From the convolution theorem it can be seen that the optical transfer function is in fact the auto-correlation of the pupil function.[4] The pupil function of an ideal optical system with a circular aperture is a disk of unit radius. The optical transfer function of such a system can thus be calculated geometrically from the intersecting area between two identical disks at a distance of 2ν , where ν is the spatial frequency normalized to the highest transmitted frequency.[1] In general the optical transfer function is normalized to a maximum value of one for ν = 0 , so the resulting area should be divided by π . The intersecting area can be calculated as the sum of that of two identical circular segments: θ/2 − sin(θ)/2 , where θ is the circle segment angle. By substituting |ν| = cos(θ/2) , and using the equalities sin(θ)/2√ = sin(θ/2) cos(θ/2) and 1 = ν2 + sin(arccos(|ν|))2 , the equation for the area can be rewritten as arccos(|ν|) − |ν| 1 − ν2 . Hence the normalized optical transfer function is given by: ( √ ) 2 | | − | | − 2 OTF(ν) = π arccos( ν ) ν 1 ν . A more detailed discussion can be found in [4] and.[1]:152–153

Numerical evaluation

The one-dimensional optical transfer function can be calculated as the discrete Fourier transform of the line spread function. This data is graphed against the spatial frequency data. In this case, a sixth order polynomial is fitted to the MTF vs. spatial frequency curve to show the trend. The 50% cutoff frequency is determined to yield the corresponding spatial frequency. Thus, the approximate position of best focus of the unit under test is determined from this data. The Fourier transform of the line spread function (LSF) can not be determined analytically by the following equations:

∫ MTF = F [LSF] MTF = f(x)e−i2π xs dx

Therefore, the Fourier Transform is numerically approximated using the discrete Fourier transform DFT .[5] 10.1. OPTICAL TRANSFER FUNCTION 171

The MTF data versus spatial frequency is normalized by fitting a sixth order polynomial to it, making a smooth curve. The 50% cut-off frequency is determined and the corresponding spatial frequency is found, yielding the approximate position of best focus.

N∑−1 −ik 2π n MTF = DFT [LSF] = Yk = yne N k ∈ [0,N − 1] n=0 where

th • Yk = the k value of the MTF • N = number of data points • n = index • k = kth term of the LSF data

th • yn = n pixel position √ • i = −1 eia = cos(a)  i sin(a) − [ ( ) ( )] N∑1 2π 2π MTF = DFT [LSF] = Y = y cos k n − i sin k n k ∈ [0,N − 1] k n N N n=0 The MTF is then plotted against spatial frequency and all relevant data concerning this test can be determined from that graph.

The vectorial transfer function

At high numerical apertures such as those found in microscopy, it is important to consider the vectorial nature of the fields that carry light. By decomposing the waves in three independent components corresponding to the Cartesian axes, a point spread function can be calculated for each component and combined into a vectorial point spread function. Similarly, a vectorial optical transfer function can be determined as shown in [6] and .[7] 172 CHAPTER 10. DAY 10

10.1.5 Measurement

The optical transfer function is not only useful for the design of optical system, it is also valuable to characterize manufactured systems.

Starting from the point spread function

The optical transfer function is defined as the Fourier transform of the impulse-response of the optical system, also called the point spread function. The optical transfer function is thus readily obtained by first acquiring the image of a point source, and applying the two-dimensional discrete Fourier transform to the sampled image. Such a point-source can, for example, be a bright light behind a screen with a pin hole, a fluorescent or metallic microsphere, or simply a dot painted on a screen. Calculation of the optical transfer function via the point spread function is versatile as it can fully characterize optics with spatial varying and chromatic aberrations by repeating the procedure for various positions and wavelength spectra of the point source.

Using extended test objects for spatially invariant optics

When the aberrations can be assumed to be spatially invariant, alternative patterns can be used to determine the optical transfer function such as lines and edges. The corresponding transfer functions are referred to as the line-spread function and the edge-spread function, respectively. Such extended objects illuminate more pixels in the image, and can improve the measurement accuracy due to the larger signal-to-noise ratio. The optical transfer function is in this case calculated as the two-dimensional discrete Fourier transform of the image and divided by that of the extended object. Typically either a line or a black-white edge is used.

The line-spread function The two-dimensional Fourier transform of a line through the origin, is a line orthogonal to it and through the origin. The divisor is thus zero for all but a single dimension, by consequence, the optical transfer function can only be determined for a single dimension using a single line-spread function (LSF). If necessary, the two-dimensional optical transfer function can be determined by repeating the measurement with lines at various angles. The line spread function can be found using two different methods. It can be found directly from an ideal line approximation provided by a slit test target or it can be derived from the edge spread function, discussed in the next sub section.

The edge-spread function The two-dimensional Fourier transform of an edge is also only non-zero on a single line, orthogonal to the edge. This function is sometimes referred to as the edge spread function (ESF).[8][9] How- ever, the values on this line are inversely proportional to the distance from the origin. Although the measurement images obtained with this technique illuminate a large area of the camera, this mainly benefits the accuracy at low spatial frequencies. As with the line spread function, each measurement only determines a single axes of the optical transfer function, repeated measurements are thus necessary if the optical system cannot be assumed to be rotational symmetric. As shown in the right hand figure, an operator defines a box area encompassing the edge of a knife-edge test target image back-illuminated by a blackbody. The box area is defined to be approximately 10% of the total frame area. The image pixel data is translated into a two-dimensional array (pixel intensity and pixel position). The amplitude (pixel intensity) of each line within the array is normalized and averaged. This yields the edge spread function.

√ ∑ − ∑ − X − µ n 1(x − µ )2 n 1 x ESF = σ = i=0 i µ = i=0 i σ n n where

• ESF = the output array of normalized pixel intensity data • X = the input array of pixel intensity data

th • xi = the i element of X 10.1. OPTICAL TRANSFER FUNCTION 173

In evaluating the ESF, an operator defines a box area equivalent to 10% of the total frame area of a knife-edge test target back- illuminated by a blackbody. The area is defined to encompass the edge of the target image.

• µ = the average value of the pixel intensity data • σ = the standard deviation of the pixel intensity data • n = number of pixels used in average

The line spread function is identical to the first derivative of the edge spread function,[10] which is differentiated using numerical methods. In case it is more practical to measure the edge spread function, one can determine the line spread function as follows:

d LSF = ESF(x) dx Typically the ESF is only known at discrete points, so the LSF is numerically approximated using the finite difference:

d ∆ESF LSF = ESF(x) ≈ dx ∆x ESF − ESF − LSF ≈ i+1 i 1 2(xi+1 − xi) where:

• i = the index i = 1, 2, . . . , n − 1

th th • xi = i position of the i pixel th • ESFi = ESF of the i pixel 174 CHAPTER 10. DAY 10

Using a grid of black and white lines Although 'sharpness’ is often judged on grid patterns of alternate black and white lines, it should strictly be measured using a sine-wave variation from black to white (a blurred version of the usual pattern). Where a square wave pattern is used (simple black and white lines) not only is there more risk of aliasing, but account must be taken of the fact that the fundamental component of a square wave is higher than the amplitude of the square wave itself (the harmonic components reduce the peak amplitude). A square wave test chart will therefore show optimistic results (better resolution of high spatial frequencies than is actually achieved). The square wave result is sometimes referred to as the 'contrast transfer function' (CTF).

10.1.6 Factors affecting MTF in typical camera systems

In practice, many factors result in considerable blurring of a reproduced image, such that patterns with spatial fre- quency just below the Nyquist rate may not even be visible, and the finest patterns that can appear 'washed out' as shades of grey, not black and white. A major factor is usually the impossibility of making the perfect 'brick wall' optical filter (often realized as a 'phase plate' or a lens with specific blurring properties in digital cameras and video ). Such a filter is necessary to reduce aliasing by eliminating spatial frequencies above the Nyquist rate of the display.

Oversampling and downconversion to maintain the optical transfer function

The only way in practice to approach the theoretical sharpness possible in a digital imaging system such as a camera is to use more pixels in the camera sensor than samples in the final image, and 'downconvert' or 'interpolate' using special digital processing which cuts off high frequencies above the Nyquist rate to avoid aliasing whilst maintaining a reasonably flat MTF up to that frequency. This approach was first taken in the 1970s when flying spot scanners, and later CCD line scanners, were developed which sampled more pixels than were needed and then downconverted, which is why movies have always looked sharper on television than other material shot with a video camera. The only theoretically correct way to interpolate or downconvert is by use of a steep low-pass spatial filter, realized by convolution with a two-dimensional sin(x)/x weighting function which requires powerful processing. In practice, various mathematical approximations to this are used to reduce the processing requirement. These approximations are now implemented widely in video editing systems and in image processing programs such as Photoshop. Just as standard definition video with a high contrast MTF is only possible with oversampling, so HD television with full theoretical sharpness is only possible by starting with a camera that has a significantly higher resolution, followed by digitally filtering. With movies now being shot in 4k and even 8k video for the cinema, we can expect to see the best pictures on HDTV only from movies or material shot at the higher standard. However much we raise the number of pixels used in cameras, this will always remain true in absence of a perfect optical spatial filter. Similarly, a 5- megapixel image obtained from a 5-megapixel still camera can never be sharper than a 5-megapixel image obtained after down-conversion from an equal quality 10-megapixel still camera. Because of the problem of maintaining a high contrast MTF, broadcasters like the BBC did for a long time consider maintaining standard definition television, but improving its quality by shooting and viewing with many more pixels (though as previously mentioned, such a system, though impressive, does ultimately lack the very fine detail which, though attenuated, enhances the effect of true HD viewing). Another factor in digital cameras and camcorders is lens resolution. A lens may be said to 'resolve' 1920 horizontal lines, but this does not mean that it does so with full modulation from black to white. The 'Modulation Transfer Function' (just a term for the magnitude of the optical transfer function with phase ignored) gives the true measure of lens performance, and is represented by a graph of amplitude against spatial frequency. Lens aperture diffraction also limits MTF. Whilst reducing the aperture of a lens usually reduces aberrations and hence improves the flatness of the MTF, there is an optimum aperture for any lens and image sensor size beyond which smaller apertures reduce resolution because of diffraction, which spreads light across the image sensor. This was hardly a problem in the days of plate cameras and even 35mm film, but has become an insurmountable limitation with the very small format sensors used in digital cameras and especially video cameras. First generation HD con- sumer camcorders used 1/4 inch sensors, for which apertures smaller than about f4 begin to limit resolution. Even professional video cameras mostly use 2/3 inch sensors, prohibiting the use of apertures around f16 that would have been considered normal for film formats. Certain cameras (such as the Pentax K10D) feature an “MTF autoexpo- sure” mode, where the choice of aperture is optimized for maximum sharpness. Typically this means somewhere in the middle of the aperture range.[11] 10.1. OPTICAL TRANSFER FUNCTION 175

Trend to large-format DSLRs and improved MTF potential

There has recently been a shift towards the use of large image format digital single lens reflex cameras driven by the need for low-light sensitivity and narrow depth of field effects. This has led to such cameras becoming preferred by some film and television program makers over even professional HD video cameras, because of their 'filmic' potential. In theory, the use of cameras with 16- and 21-megapixel sensors offers the possibility of almost perfect sharpness by downconversion within the camera, with digital filtering to eliminate aliasing. In practice, such cameras currently fail in this respect, and they do not have the processing power to do what is required. The Canon EOS 5D Mark II is believed to use only every third line, and hence suffers bad aliasing, as its optical filter is optimized for stills use. The Panasonic Lumix DMC-GH2 may do some processing across pixels, producing very sharp images, but with some aliasing. Nevertheless, such cameras produce very impressive results, and appear to be leading the way in video production towards large-format downconversion with digital filtering becoming the standard approach to the realization of a flat MTF with true freedom from aliasing.

10.1.7 Digital inversion of the optical transfer function

Due to optical effects the contrast may be sub-optimal and approaches zero before the Nyquist frequency of the display is reached. The optical contrast reduction can be partially reversed by digitally amplifying spatial frequencies selectively before display or further processing. Although more advanced digital image restoration procedures exist, the Wiener deconvolution algorithm is often used for its and efficiency. Since this technique multiplies the spatial spectral components of the image, it also amplifies noise and errors due to e.g. aliasing. It is therefore only effective on good quality recordings with a sufficiently high signal-to-noise ratio.

10.1.8 Limitations

In general, the point spread function, the image of a point source also depends on factors such as the wavelength (color), and field angle (lateral point source position). When such variation is sufficiently gradual, the optical system could be characterized by a set of optical transfer functions. However, when the image of the point source changes abruptly upon lateral translation, the optical transfer function does not describe the optical system accurately.

10.1.9 See also

• Transfer function

• Signal transfer function

• Optical resolution

• Signal to noise ratio (image processing)

• Strehl ratio

• Wavefront coding

• Bokeh

• Minimum resolvable contrast

• Minimum resolvable temperature difference

• correction

10.1.10 References

[1] Williams, Charles S. (2002). Introduction to the Optical Transfer Function. SPIE - The International Society for Optical Engineering. ISBN 0-8194-4336-0.

[2] “Contrast Transfer Function”. Retrieved 16 November 2013. 176 CHAPTER 10. DAY 10

[3] Macias-Garza, F.; Bovik, A.; Diller, K.; Aggarwal, S.; Aggarwal, J. (1988). “The missing cone problem and low-pass distortion in optical serial sectioning microscopy”. 2: 890–893.

[4] Goodman, Joseph (2005). Introduction to Fourier Optics (3rd ed, ed.). Roberts & Co Publishers. ISBN 0-9747077-2-4.

[5] Chapra, S.C.; Canale, R.P. (2006). Numerical Methods for Engineers (5th ed.). New York, New York: McGraw-Hill

[6] Sheppard, C.J.R.; Larkin, K. (1997). “Vectorial pupil functions and vectorial transfer functions” (PDF). OPTIK-STUTTGART. 107: 79–87.

[7] Arnison, M. R.; Sheppard, C. J. R. (2002). “A 3D vectorial optical transfer function suitable for arbitrary pupil functions”. Optics Communications. 211: 53. Bibcode:2002OptCo.211...53A. doi:10.1016/S0030-4018(02)01857-6.

[8] Holst, G.C. (1998). Testing and Evaluation of Infrared Imaging Systems (2nd ed.). Florida:JCD Publishing, Washington: SPIE.

[9] Electro Optical Industries, Inc.(2005). EO TestLab Methodology. In Education/Ref. http://www.electro-optical.com/ html/toplevel/educationref.asp.

[10] Mazzetta, J.A.; Scopatz, S.D. (2007). Automated Testing of Ultraviolet, Visible, and Infrared Sensors Using Shared Optics. Infrared Imaging Systems: Design Analysis, Modeling, and Testing XVIII,Vol. 6543, pp. 654313-1 654313-14

[11] B2BVideoSource.com: Camera Terminology

10.1.11 External links

• “Modulation transfer function”, by Glenn D. Boreman on SPIE Optipedia. • “How to Measure MTF and other Properties of Lenses”, by Optikos Corporation.

10.2 Optical resolution

This article is about optical resolution in optics. For the method of separating enantiomers in chemistry, see Chiral resolution.

Optical resolution describes the ability of an imaging system to resolve detail in the object that is being imaged. An imaging system may have many individual components including a lens and recording and display components. Each of these contributes to the optical resolution of the system, as will the environment in which the imaging is done.

10.2.1 Lateral resolution

Resolution depends on the distance between two distinguishable radiating points. The sections below describe the theoretical estimates of resolution, but the real values may differ. The results below are based on mathematical models of Airy discs, which assumes an adequate level of contrast. In low-contrast systems, the resolution may be much lower than predicted by the theory outlined below. Real optical systems are complex and practical difficulties often increase the distance between distinguishable point sources. The resolution of a system is based on the minimum distance r at which the points can be distinguished as individuals. Several standards are used to determine, quantitatively, whether or not the points can be distinguished. One of the methods specifies that, on the line between the center of one point and the next, the contrast between the maximum and minimum intensity be at least 26% lower than the maximum. This corresponds to the overlap of one on the first dark ring in the other. This standard for separation is also known as the Rayleigh criterion. In symbols, the distance is defined as follows:[1]

1.22λ 0.61λ r = = 2n sin θ NA where 10.2. OPTICAL RESOLUTION 177

r is the minimum distance between resolvable points, in the same units as λ is specified λ is the wavelength of light, emission wavelength, in the case of fluorescence, n is the index of refraction of the media surrounding the radiating points, θ is the half angle of the pencil of light that enters the objective, and NA is the numerical aperture

This formula is suitable for confocal microscopy, but is also used in traditional microscopy. In confocal laser-scanned microscopes, the full-width half half-maximum (FWHM) of the point spread function is often used to avoid the diffi- culty of measuring the Airy disc.[2] This, combined with the rastered illumination pattern, results in better resolution, but it is still proportional to the Rayleigh-based formula given above.

0.4λ r = NA Also common in the microscopy literature is a formula for resolution that treats the above-mentioned concerns about contrast differently.[3] The resolution predicted by this formula is proportional to the Rayleigh-based formula, differing by about 20%. For estimating theoretical resolution, it may be adequate.

λ λ r = = 2n sin θ 2NA When a condenser is used to illuminate the sample, the shape of the pencil of light emanating from the condenser must also be included.[4]

1.22λ r = NAobj + NAcond

In a properly configured microscope, NAobj + NAcond = 2NAobj . The above estimates of resolution are specific to the case in which two identical very small samples that radiate incoherently in all directions. Other considerations must be taken into account if the sources radiate at different levels of intensity, are coherent, large, or radiate in non-uniform patterns.

10.2.2 Lens resolution

The ability of a lens to resolve detail is usually determined by the quality of the lens but is ultimately limited by diffraction. Light coming from a point in the object diffracts through the lens aperture such that it forms a diffraction pattern in the image which has a central spot and surrounding bright rings, separated by dark nulls; this pattern is known as an Airy pattern, and the central bright lobe as an Airy disk. The angular radius of the Airy disk (measured from the center to the first null) is given by:

Two adjacent points in the object give rise to two diffraction patterns. If the angular separation of the two points is significantly less than the Airy disk angular radius, then the two points cannot be resolved in the image, but if their angular separation is much greater than this, distinct images of the two points are formed and they can therefore be resolved. Rayleigh defined the somewhat arbitrary "Rayleigh criterion" that two points whose angular separation is equal to the Airy disk radius to first null can be considered to be resolved. It can be seen that the greater the diameter of the lens or its aperture, the greater the resolution. Astronomical telescopes have increasingly large lenses so they can 'see' ever finer detail in the stars. Only the very highest quality lenses have diffraction limited resolution, however, and normally the quality of the lens limits its ability to resolve detail. This ability is expressed by the Optical Transfer Function which describes the spatial (angular) variation of the light signal as a function of spatial (angular) frequency. When the image is projected onto a flat plane, such as photographic film or a solid state detector, spatial frequency is the preferred domain, but when 178 CHAPTER 10. DAY 10

the image is referred to the lens alone, angular frequency is preferred. OTF may be broken down into the magnitude and phase components as follows:

OTF(ξ, η) = MTF(ξ, η) · PTF(ξ, η) where

MTF(ξ, η) = |OTF(ξ, η)| PTF(ξ, η) = e−i2·π·λ(ξ,η) (ξ, η) The OTF accounts for aberration, which the limiting frequency expression above does not. The magnitude is known as the Modulation Transfer Function (MTF) and the phase portion is known as the Phase Transfer Function (PTF). In imaging systems, the phase component is typically not captured by the sensor. Thus, the important measure with respect to imaging systems is the MTF. Phase is critically important to adaptive optics and holographic systems.

10.2.3 Sensor resolution (spatial)

Some optical sensors are designed to detect spatial differences in electromagnetic energy. These include photographic film, solid-state devices (CCD, CMOS detectors, and infrared detectors like PtSi and InSb), tube detectors (vidicon, plumbicon, and photomultiplier tubes used in night-vision devices), scanning detectors (mainly used for IR), pyroelectric detectors, and microbolometer detectors. The ability of such a detector to resolve those differences depends mostly on the size of the detecting elements. Spatial resolution is typically expressed in line pairs per millimeter (lppmm), lines (of resolution, mostly for analog video), contrast vs. cycles/mm, or MTF (the modulus of OTF). The MTF may be found by taking the two-dimensional Fourier transform of the spatial sampling function. Smaller pixels result in wider MTF curves and thus better detection of higher frequency energy. This is analogous to taking the Fourier transform of a signal sampling function; as in that case, the dominant factor is the sampling period, which is analogous to the size of the picture element (pixel). Other factors include pixel noise, pixel cross-talk, substrate penetration, and fill factor. A common problem among non-technicians is the use of the number of pixels on the detector to describe the resolu- tion. If all sensors were the same size, this would be acceptable. Since they are not, the use of the number of pixels can be misleading. For example, a 2-megapixel camera of 20-micrometre-square pixels will have worse resolution than a 1-megapixel camera with 8-micrometre pixels, all else being equal. For resolution measurement, film manufacturers typically publish a plot of Response (%) vs. Spatial Frequency (cycles per millimeter). The plot is derived experimentally. Solid state sensor and camera manufacturers normally publish specifications from which the user may derive a theoretical MTF according to the procedure outlined below. A few may also publish MTF curves, while others (especially intensifier manufacturers) will publish the response (%) at the Nyquist frequency, or, alternatively, publish the frequency at which the response is 50%. To find a theoretical MTF curve for a sensor, it is necessary to know three characteristics of the sensor: the active sensing area, the area comprising the sensing area and the interconnection and support structures (“real estate”), and the total number of those areas (the pixel count). The total pixel count is almost always given. Sometimes the overall sensor dimensions are given, from which the real estate area can be calculated. Whether the real estate area is given or derived, if the active pixel area is not given, it may be derived from the real estate area and the fill factor, where fill factor is the ratio of the active area to the dedicated real estate area.

a · b FF = c · d where 10.2. OPTICAL RESOLUTION 179

• the active area of the pixel has dimensions a×b • the pixel real estate has dimensions c×d

In Gaskill’s notation, the sensing area is a 2D comb(x, y) function of the distance between pixels (the pitch), convolved with a 2D rect(x, y) function of the active area of the pixel, bounded by a 2D rect(x, y) function of the overall sensor dimension. The Fourier transform of this is a comb(ξ, η) function governed by the distance between pixels, convolved with a sinc(ξ, η) function governed by the number of pixels, and multiplied by the sinc(ξ, η) function corresponding to the active area. That last function serves as an overall envelope to the MTF function; so long as the number of pixels is much greater than one (1), then the active area size dominates the MTF. Sampling function:

[ ( ) ( )] ( ) x y x y x y S(x, y) = comb , ∗ rect , · rect , c d a b M · c N · d where the sensor has M×N pixels

10.2.4 Sensor resolution (temporal)

An imaging system running at 24 frames per second is essentially a discrete sampling system that samples a 2D area. The same limitations described by Nyquist apply to this system as to any signal sampling system. All sensors have a characteristic time response. Film is limited at both the short resolution and the long resolution extremes by reciprocity breakdown. These are typically held to be anything longer than 1 second and shorter than 1/10,000 second. Furthermore, film requires a mechanical system to advance it through the exposure mechanism, or a moving optical system to expose it. These limit the speed at which successive frames may be exposed. CCD and CMOS are the modern preferences for video sensors. CCD is speed-limited by the rate at which the charge can be moved from one site to another. CMOS has the advantage of having individually addressable cells, and this has led to its advantage in the high speed photography industry. Vidicons, Plumbicons, and image intensifiers have specific applications. The speed at which they can be sampled depends upon the decay rate of the phosphor used. For example, the P46 phosphor has a decay time of less than 2 microseconds, while the P43 decay time is on the order of 2-3 milliseconds. The P43 is therefore unusable at frame rates above 1000 frames per second (frame/s). See External links for links to phosphor information. Pyroelectric detectors respond to changes in temperature. Therefore, a static scene will not be detected, so they require choppers. They also have a decay time, so the pyroelectric system temporal response will be a bandpass, while the other detectors discussed will be a lowpass. If objects within the scene are in motion relative to the imaging system, the resulting motion blur will result in lower spatial resolution. Short integration times will minimize the blur, but integration times are limited by sensor sensitivity. Furthermore, motion between frames in motion pictures will impact digital movie compression schemes (e.g. MPEG-1, MPEG-2). Finally, there are sampling schemes that require real or apparent motion inside the camera (scanning mirrors, rolling shutters) that may result in incorrect rendering of image motion. Therefore, sensor sensitivity and other time-related factors will have a direct impact on spatial resolution.

10.2.5 Analog bandwidth effect on resolution

The spatial resolution of digital systems (e.g. HDTV and VGA) are fixed independently of the analog bandwidth because each pixel is digitized, transmitted, and stored as a discrete value. Digital cameras, recorders, and displays must be selected so that the resolution is identical from camera to display. However, in analog systems, the resolution of the camera, recorder, cabling, amplifiers, transmitters, receivers, and display may all be independent and the overall system resolution is governed by the bandwidth of the lowest performing component. In analog systems, each horizontal line is transmitted as a high-frequency analog signal. Each picture element (pixel) is therefore converted to an analog electrical value (voltage), and changes in values between pixels therefore become changes in voltage. The transmission standards require that the sampling be done in a fixed time (outlined below), so 180 CHAPTER 10. DAY 10 more pixels per line becomes a requirement for more voltage changes per unit time, i.e. higher frequency. Since such signals are typically band-limited by cables, amplifiers, recorders, transmitters, and receivers, the band-limitation on the analog signal acts as an effective low-pass filter on the spatial resolution. The difference in resolutions between VHS (240 discernible lines per scanline), Betamax (280 lines), and the newer ED Beta format (500 lines) is explained primarily by the difference in the recording bandwidth. In the NTSC transmission standard, each field contains 262.5 lines, and 59.94 fields are transmitted every second. Each line must therefore take 63 microseconds, 10.7 of which are for reset to the next line. Thus, the retrace rate is 15.734 kHz. For the picture to appear to have approximately the same horizontal and vertical resolution (see Kell factor), it should be able to display 228 cycles per line, requiring a bandwidth of 4.28 MHz. If the line (sensor) width is known, this may be converted directly into cycles per millimeter, the unit of spatial resolution. B/G/I/K television system signals (usually used with PAL colour encoding) transmit frames less often (50 Hz), but the frame contains more lines and is wider, so bandwidth requirements are similar. Note that a “discernible line” forms one half of a cycle (a cycle requires a dark and a light line), so “228 cycles” and “456 lines” are equivalent measures.

10.2.6 System resolution

There are two methods by which to determine system resolution. The first is to perform a series of two dimensional convolutions, first with the image and the lens, then the result of that procedure with the sensor, and so on through all of the components of the system. This is computationally expensive, and must be performed anew for each object to be imaged. The other method is to transform each of the components of the system into the spatial frequency domain, and then to multiply the 2-D results. A system response may be determined without reference to an object. Although this method is considerably more difficult to comprehend conceptually, it becomes easier to use computationally, especially when different design iterations or imaged objects are to be tested. The transformation to be used is the Fourier transform.

10.2.7 Ocular resolution

The human eye is a limiting feature of many systems, when the goal of the system is to present data to humans for processing. For example, in a security or air traffic control function, the display and work station must be constructed so that average humans can detect problems and direct corrective measures. Other examples are when a human is using eyes to carry out a critical task such as flying (piloting by visual reference), driving a vehicle, and so forth. The best visual acuity of the human eye at its optical centre (the fovea) is less than 1 arc minute per line pair, reducing rapidly away from the fovea. The human brain requires more than just a line pair to understand what the eye is imaging. Johnson’s criteria defines the number of line pairs of ocular resolution, or sensor resolution, needed to recognize or identify an item.

10.2.8 Atmospheric resolution

Systems looking through long atmospheric paths may be limited by turbulence. A key measure of the quality of atmospheric turbulence is the seeing diameter, also known as Fried’s seeing diameter. A path which is temporally coherent is known as an isoplanatic patch. Large apertures may suffer from aperture averaging, the result of several paths being integrated into one image. Turbulence scales with wavelength at approximately a 6/5 power. Thus, seeing is better at infrared wavelengths than at visible wavelengths. Short exposures suffer from turbulence less than longer exposures due to the “inner” and “outer” scale turbulence; short is considered to be much less than 10 ms for visible imaging (typically, anything less than 2 ms). Inner scale turbulence arises due to the eddies in the turbulent flow, while outer scale turbulence arises from large air mass flow. These masses typically move slowly, and so are reduced by decreasing the integration period. 10.2. OPTICAL RESOLUTION 181

A system limited only by the quality of the optics is said to be diffraction-limited. However, since atmospheric turbulence is normally the limiting factor for visible systems looking through long atmospheric paths, most systems are turbulence-limited. Corrections can be made by using adaptive optics or post-processing techniques.

5/3 1/3 −3.44·(λfν/r0) ·[1−b·(λfν/D) ] MTFs(ν) = e

where

ν is the spatial frequency λ is the wavelength f is the focal length D is the aperture diameter b is a constant (1 for far-field propagation)

and r0 is Fried’s seeing diameter

10.2.9 Measuring optical resolution

A variety of measurement systems are available, and use may depend upon the system being tested. Typical test charts for Contrast Transfer Function (CTF) consist of repeated bar patterns (see Discussion below). The limiting resolution is measured by determining the smallest group of bars, both vertically and horizontally, for which the correct number of bars can be seen. By calculating the contrast between the black and white areas at several different frequencies, however, points of the CTF can be determined with the contrast equation. − contrast = Cmax Cmin Cmax+Cmin where

Cmax

Cmin When the system can no longer resolve the bars, the black and white areas have the same value, so Contrast = 0. At very low spatial frequencies, Cₐₓ = 1 and Cᵢ = 0 so Modulation = 1. Some modulation may be seen above the limiting resolution; these may be aliased and phase-reversed. When using other methods, including the interferogram, sinusoid, and the edge in the ISO 12233 target, it is possible to compute the entire MTF curve. The response to the edge is similar to a step response, and the Fourier Transform of the first difference of the step response yields the MTF.

Interferogram

An interferogram created between two coherent light sources may be used for at least two resolution-related purposes. The first is to determine the quality of a lens system (see LUPI), and the second is to project a pattern onto a sensor (especially photographic film) to measure resolution.

NBS 1010a/ ISO #2 target

This 5 bar resolution test chart is often used for evaluation of microfilm systems and scanners. It is convenient for a 1:1 range (typically covering 1-18 cycles/mm) and is marked directly in cycles/mm. Details can be found in ISO-3334.

USAF 1951 target

The USAF 1951 resolution test target consists of a pattern of 3 bar targets. Often found covering a range of 0.25 to 228 cycles/mm. Each group consists of six elements. The group is designated by a group number (−2, −1, 0, 1, 2, 182 CHAPTER 10. DAY 10

SilverFast Resolution Target USAF 1951 for determining a scanner’s optimum resolution

etc.) which is the power to which 2 should be raised to obtain the spatial frequency of the first element (e.g., group −2 is 0.25 line pairs per millimeter). Each element is the 6th root of 2 smaller than the preceding element in the group (e.g. element 1 is 2^0, element 2 is 2^(−1/6), element 3 is 2(−1/3), etc.). By reading off the group and element number of the first element which cannot be resolved, the limiting resolution may be determined by inspection. The complex numbering system and use of a look-up chart can be avoided by use of an improved but not standardized layout chart, which labels the bars and spaces directly in cycles/mm using OCR-A extended font.

group+ element−1 Resolution = 2 6

NBS 1952 target

The NBS 1952 target is a 3 bar pattern (long bars). The spatial frequency is printed alongside each triple bar set, so the limiting resolution may be determined by inspection. This frequency is normally only as marked after the chart has been reduced in size (typically 25 times). The original application called for placing the chart at a distance 26 times the focal length of the imaging lens used. The bars above and to the left are in sequence, separated by approximately the square root of two (12, 17, 24, etc.), while the bars below and to the left have the same separation but a different starting point (14, 20, 28, etc.) 10.2. OPTICAL RESOLUTION 183

EIA 1956 video resolution target

200 200

300 300

400 400 500 500 600 200 200 600

150 150

200 400 0

500 350 9 300 600

700 8 400 800 200 200 200 300

400 7 400 800 500 600 700

6 600 500 700 400 800 5 400 300 200 200 800 400 200 700 4

600 300 3 300 500 2 200 200 10 9 8 400 200 4 3 2 300 300

400 400 500 500 600 600

150 200 200 150

EIA RESOLUTION CHART 1956

EIA 1956 video resolution target

The EIA 1956 resolution target was specifically designed to be used with television systems. The gradually expand- ing lines near the center are marked with periodic indications of the corresponding spatial frequency. The limiting resolution may be determined by inspection. The most important measure is the limiting horizontal resolution, since the vertical resolution is typically determined by the applicable video standard (I/B/G/K/NTSC/NTSC-J).

IEEE Std 208-1995 target

The IEEE 208-1995 resolution target is similar to the EIA target. Resolution is measured in horizontal and vertical TV lines.

ISO 12233 target

The ISO 12233 target was developed for digital camera applications, since modern digital camera spatial resolution may exceed the limitations of the older targets. It includes several knife-edge targets for the purpose of computing MTF by Fourier transform. They are offset from the vertical by 5 degrees so that the edges will be sampled in many different phases, which allow estimation of the spatial frequency response beyond the Nyquist frequency of the sampling.

Random test patterns

The idea is analogous to the use of a white noise pattern in acoustics to determine system frequency response. 184 CHAPTER 10. DAY 10

Monotonically increasing sinusoid patterns

The interferogram used to measure film resolution can be synthesized on personal computers and used to generate a pattern for measuring optical resolution. See especially Kodak MTF curves.

Multiburst

A multiburst signal is an electronic waveform used to test analog transmission, recording, and display systems. The test pattern consists of several short periods of specific frequencies. The contrast of each may be measured by inspection and recorded, giving a plot of attenuation vs. frequency. The NTSC3.58 multiburst pattern consists of 500 kHz, 1 MHz, 2 MHz, 3 MHz, and 3.58 MHz blocks. 3.58 MHz is important because it is the chrominance frequency for NTSC video.

Discussion

It should be noted whenever using a bar target that the resulting measure is the contrast transfer function (CTF) and not the MTF. The difference arises from the subharmonics of the square waves and can be easily computed.

10.2.10 See also

• Angular resolution • Image resolution, in computing • Minimum resolvable contrast • Siemens star, a pattern used for resolution testing • Square meters per pixel • Superlens • Superresolution

10.2.11 References

[1] http://www.olympusconfocal.com/theory/resolutionintro.html

[2] http://www.olympusconfocal.com/theory/resolutionintro.html

[3] http://www.microscopyu.com/articles/optics/objectiveproperties.html

[4] http://micro.magnet.fsu.edu/primer/anatomy/numaperture.html

• Gaskill, Jack D. (1978), Linear Systems, Fourier Transforms, and Optics, Wiley-Interscience. ISBN 0-471- 29288-5 • Goodman, Joseph W. (2004), Introduction to Fourier Optics (Third Edition), Roberts & Company Publishers. ISBN 0-9747077-2-4 • Fried, David L. (1966), “Optical resolution through a randomly inhomogeneous medium for very long and very short exposures.”, J. Opt. Soc. Amer. 56:1372-9 • Robin, Michael, and Poulin, Michael (2000), Digital Television Fundamentals (2nd edition), McGraw-Hill Professional. ISBN 0-07-135581-2 • Smith, Warren J. (2000), Modern Optical Engineering (Third Edition), McGraw-Hill Professional. ISBN 0-07- 136360-2 • Accetta, J. S. and Shumaker, D. L. (1993), The Infrared and Electro-optical Systems Handbook, SPIE/ERIM. ISBN 0-8194-1072-1 10.3. 1951 USAF RESOLUTION TEST CHART 185

• Roggemann, Michael and Welsh, Byron (1996), Imaging Through Turbulence, CRC Press. ISBN 0-8493- 3787-9

• Tatarski, V. I. (1961), Wave Propagation in a Turbulent Medium, McGraw-Hill, NY

10.2.12 External links

• Norman Koren’s website - includes several downloadable test patterns

• UC Santa Cruz Prof. Claire Max’s lectures and notes from Astronomy 289C, Adaptive Optics

• George Ou’s re-creation of the EIA 1956 chart from a high-resolution scan

• Do Sensors “Outresolve” Lenses? - on lens and sensor resolution interaction

10.3 1951 USAF resolution test chart

The 1951 USAF resolution test chart is a resolution test pattern conforming to MIL-STD-150A standard, set by US Air Force in 1951. It is still widely accepted to test the resolution of optical imaging systems such as microscopes, cameras and image scanners, although MIL-STD-150A was cancelled on October 16, 2006.[1] The pattern consists of groups of three bars (small Ronchi rulings) with dimensions from big to small. The largest bar the imager cannot discern is the limitation of its resolving power.

10.3.1 Pattern format

The common MIL-STD-150A format consists of six “groups” in three layers of patterns. The largest groups, forming the first layer, are located on the outer sides. The smaller layers repeat the same pattern but are progressively smaller toward the center. Each group consists of six elements, numbered from 1 to 6. Within the same layer, the odd- numbered groups appear contiguously from 1 through 6 from the upper right corner. The first element of the even- numbered groups is at the lower right of the layer, with the remaining 2 through 6, at the left. The scales and dimensions of the bars are given by the expression

(lp/mm) Resolution = 2Group+(element−1)/6 although usually the following lookup table will be used. The line pair (lp) means a black and a white line.

10.3.2 Images

See also: commons:Category:Resolution test charts

-2 -1 2 1 2 3 1 0 3 1 2 2 4 3 3 4 5 4 6 5 0 5 4 1 6 6 5 -2 6 1 • USAF-1951USAF-1951 map, vector format 186 CHAPTER 10. DAY 10

Glass chart

• SilverFast USAF 1951 Resolution Target by LaserSoft Imaging 10.3. 1951 USAF RESOLUTION TEST CHART 187

10.3.3 See also

• USAF 1951 target section, in Optical resolution

10.3.4 References

[1] MIL-STD-150A, its Change Notices and the Cancellation Notice are available from http://assist.daps.dla.mil

10.3.5 External links

• efg’s Tech Note: USAF 1951 and Microcopy Resolution Test Charts.

• A USAF 1951 resolution chart in PDF format is provided by Yoshihiko Takinami. This chart should be printed such that the side of the square of the 1st element of the group −2 should be 10 mm long.

• USAF 1951 Resolution Target Further explanations and examples • Koren 2003: Norman Koren’s updated resolution chart better suited for computer analysis Chapter 11

Text and image sources, contributors, and licenses

11.1 Text

• History of photographic lens design Source: https://en.wikipedia.org/wiki/History_of_photographic_lens_design?oldid=762116345 Contributors: Wavelength, Petri Krohn, Gilliam, Chris the speller, N0TABENE, BeenAroundAWhile, Magioladitis, Jim.henderson, Jma- jeremy, Fountains of Bryn Mawr, KylieTastic, Lamro, KoshVorlon, Yobot, El Grafo, AnomieBOT, Lonaowna, OgreBot, John of Reading, Matthiaspaul, Snotbot, Soerfm, Mogism, Sheker kumaresan, Monkbot, Bender the Bot and Anonymous: 12 • Camera lens Source: https://en.wikipedia.org/wiki/Camera_lens?oldid=758604189 Contributors: The Anome, DrBob, Ericd, Leandrod, Edward, Michael Hardy, Egil, Angela, Darkwind, Julesd, Rl, Halfdan, Gutza, Grendelkhan, Kristof vt, Clngre, Rrjanbiah, Reytan, Nelson Minar, Mintleaf~enwiki, BenFrantzDale, Bensaccount, AJim, Hugh2414, Nkocharh, Bobblewik, Christopherlin, Bact, Beland, Lucanos, Fg2, Mormegil, Poccil, Imroy, Discospinster, Cacycle, Rama, LindsayH, Alistair1978, Bobo192, Fir0002, Jeffmedkeff, Thebassman, An- dersju, Sukiari, Maebmij, Hooperbloob, BlairRMartin, Pion, Hu, Velella, Cburnett, H2g2bob, Mindmatrix, Liamgilmartin, Carcharoth, Splintax, Pol098, Macaddct1984, Phlebas, BD2412, Ketiltrout, Rogerd, Filu~enwiki, Bubba73, Mahlum~enwiki, Intersofia, Bitoffish, Ru- mun999, Srleffler, Scoo, Monito, Manop, Shell Kinney, Yyy, Baru~enwiki, NawlinWiki, Janke, Grafen, Megapixie, Howcheng, Brandon, Zzuuzz, PBurns, Petri Krohn, Junglecat, SmackBot, Melchoir, Marc Lacoste, Betacommand, Bluebot, Sparsefarce, Red marquis, Fred Ra- sio, Hateless, Dantadd, Daniel.Cardenas, Zeamays, Autopilot, SilkTork, Paul1513, A. Parrot, Grumpyyoungman01, Astuishin, Dicklyon, Hu12, Paleolith, Spindled, Powerslide, Blouis79, Ken Gallager, Myasuda, Omnicloud, Hebrides, AstroPig7, Pjmtavares, Mactographer, Klausness, Escarbot, Stybn, Ben pcc, Prolog, Helicoptor, Woof69, TuvicBot, JAnDbot, Gcm, Barek, MER-C, BKfi, PhilKnight, .anacond- abot, ChristopherBorcsok, Websterwebfoot, MyNameIsNeo, Gphoto, Akashopoholic, CommonsDelinker, Seàn, RenniePet, Fountains of Bryn Mawr, STBotD, TWCarlson, Dzenanz, Funandtrvl, Multimotyl, AlnoktaBOT, Philip Trueman, TXiKiBoT, Oshwah, Combaten- tropy, Bogdan Dogaru, Natg 19, Charlesviper, Atomicbre, Clonemoan, Juicecapades, CMBJ, Fanatix, Motorrad-67, SieBot, BotMultichill, Hxhbot, Eosslr, Illinois2011, Martarius, Cocokpocok, The Thing That Should Not Be, Nebrot, Drmies, Wikit2007, Polyamorph, Boing! said Zebedee, Manishearth, Alexbot, Resuna, Antti29, Rror, David.Boettcher, SilvonenBot, Jhorthos, Addbot, Jncraton, Xanthous Onyx, Ericg33, Tassedethe, Emdrgreg, Lightbot, Ralf Roletschek, Legobot, Drpickem, Luckas-bot, Yobot, TaBOT-zerem, Amirobot, Magog the Ogre, AnomieBOT, Jim1138, Ulric1313, Flewis, Bruno0.5, OllieFury, GrouchoBot, Wizardist, FrescoBot, Amagnien2, Pinethicket, KnightCourt, PNLawlor, Trappist the monk, PacificJuls, Jan von Erpecom, Lopifalko, EmausBot, Tykesplace, Angrytoast, GoingBatty, RenamedUser01302013, Gsonwiki, Theanimalix, Deirdresm, Kchowdhary, EdoBot, ClueBot NG, Matthiaspaul, Rezabot, Helpful Pixie Bot, G-rob XD, K0 7zQY0oyqcz, Wbm1058, CroMignon, PhnomPencil, Darafsh, Dwergenpaartje, Soerfm, David.moreno72, Jossian, ,Webclient101, Mogism, Mediaadvantages, 50N916 ,پسر یاس ,SCLu, Cyberbot II, Dpa11111, ChrisGualtieri, Tagremover, JYBot Nataliesee, Reatlas, Eyesnore, Electric Celery, DavidLeighEllis, Vickywang12, 11supachok11, Swcastle, Lewislumsden, PotatoNinja, CAPTAIN RAJU, Johnandersonm777, Bender the Bot, Nirob Alam, Thangapriyanka, Toma.preidyte and Anonymous: 158 • Photographic lens design Source: https://en.wikipedia.org/wiki/Photographic_lens_design?oldid=746141817 Contributors: Julesd, AJim, Tooki, Imroy, Hooperbloob, Hugowolf, Ahruman, Velella, EbenVisher, Bubba73, Groogle, Gaius Cornelius, Petri Krohn, SmackBot, Eike Welk, Chris the speller, Stepho-wrs, Amakuru, DangerousPanda, Blouis79, Fletcher, Pstuart84, PKT, Kablammo, Mr pand, Idiotic ally, Kaboldy, Magioladitis, R'n'B, UdovdM, M-le-mot-dit, Fountains of Bryn Mawr, Jessica fae, MagnusA, Skarebo, El Grafo, LilHelpa, J04n, Tamasflex, Sumsci, John of Reading, Glockenklang1, Nikolas Sharp, ClueBot NG, Matthiaspaul, Widr, Morgson, Kingair90, Tagremover, Reatlas and Anonymous: 28 • Aperture Source: https://en.wikipedia.org/wiki/Aperture?oldid=762326679 Contributors: Brion VIBBER, Anders Törlind, Anadem, Ericd, Nevilley, Patrick, PhilipMW, Kwertii, JeremyR, Timcfields, Looxix~enwiki, Ellywa, Rl, Ehn, Redjar, Charles Matthews, Timc, Donarreiskoffer, Robbot, Altenmann, Pingveno, Diberri, Wjbeaty, Msiebuhr, BenFrantzDale, Joconnor, Ssd, AlistairMcMillan, Christo- pherlin, Wmahan, MarkSweep, JoJan, Arsene, EricKerby, Poccil, Rama, Bender235, Kbh3rd, ReallyNiceGuy, RJHall, Cacophony, Fir0002, Thebassman, Hooperbloob, ClementSeveillac, Walter Görlitz, Ashley Pomeroy, Pion, Cburnett, Pennbrook, Pwqn, Mindma- trix, Cbhiii, Carcharoth, Tejastheory, VsevolodSipakov, Ilya, Jamie Kitson, The wub, Yamamoto Ichiro, Mahlum~enwiki, Margos- bot~enwiki, Nivix, Richardbooth, Srleffler, WouterBot, Kafziel, Cookie4869~enwiki, Groogle, SpuriousQ, NawlinWiki, Seb35, Chick Bowen, ONEder Boy, Rlove, Caballero1967, Jeremy Butler, Mohylek, Bill, Daveman 84, DVD R W, Vineethtm, Fireworks, Ultramandk, Cessator, Skizzik, Chris the speller, Bluebot, Ctrlfreak13, Roscelese, Nbarth, Scwlong, Berland, JonHarder, Midnightcomm, Jdlambert, Fitzhugh, Pilotguy, SpoonBender, Tim bates, Breno, Pflatau, Jeenuv, 16@r, Dicklyon, Odedee, Cbuckley, Wwagner, Dl2000, FunPika, Danrok, Kozuch, Mactographer, Headbomb, Klausness, Mentifisto, AntiVandalBot, NgVietNguyen~enwiki, JAnDbot, Ayt999, Mwarren us, JeffConrad, Cryogenius, DavidJoyner, Vssun, GordonMcKinney, Jim.henderson, CommonsDelinker, Nono64, Lax4mike, J.delanoy,

188 11.1. TEXT 189

Wdpics, SharkD, Tommyknchan, Linuxmatt, SJP, KylieTastic, CardinalDan, Funandtrvl, Chinneeb, Indubitably, TheMindsEye, DaRae- Man, Kitashi, Michi zh, Hqb, Darrask, Very little gravitas indeed, WikiCantona, Gwydas, Venny85, Jellyfish84, Paul Breeuwsma, Mc- carver~enwiki, Медиа, Hamiltondaniel, Sfan00 IMG, ClueBot, Schaea, NickCT, Hutcher, Gophi, Wwwnick~enwiki, Lawrence Cohen, CounterVandalismBot, Kakaman, Aua, Alex1ruff, Andy16666, Jcmcc450, XLinkBot, Tuxlie, Justin11213, Rror, Stinen~enwiki, Ad- dbot, ChenzwBot, Tide rolls, OlEnglish, QWerk, MissAlyx, Skippy le Grand Gourou, Yobot, Calle, AnomieBOT, ESCapade, Jim1138, Piano non troppo, Pete463251, RandomAct, Materialscientist, The High Fin Sperm Whale, Sorobansensei, Jcbolton1, Flame CZE, 216Kleopatra, JimVC3, Totoro33, Abce2, WHATHHHHHHHHH, Kyng, 7Cs, Rainald62, Nagualdesign, FrescoBot, Duncandavidson, Mfwitten, Craig Pemberton, Oashi, Armigo~enwiki, Leonrw, Michaelkas9, Pinethicket, I dream of horses, Innerche, Tom.Reding, AGior- gio08, Tim1357, GustavLa, Newt Winkler, Javierito92, Vrenator, Specs112, DARTH SIDIOUS 2, Cathardic, Eggnipples, Jnanadevm, Tommy2010, Cogiati, FinnTime!, H3llBot, Glockenklang1, Gsarwa, Donner60, ClueBot NG, Dliu28, Matthiaspaul, JimsMaher, Wik- ilenox, Guthrun, Haribhagirath, MerlIwBot, Irrc irri, BG19bot, SongO, C.uzum, Northerlywind, Ricordisamoa, GRPH3B18, AntanO, Jakebarrington, MLaGaro, Lugia2453, Frosty, Jamesx12345, Mile47, Fmccarth, YiFeiBot, Ginsuloft, Marabruma, StarrStuff2003 581c 4eva, DivermanAU, Akhomyakov, InternetArchiveBot, GreenC bot, Josepheena, Iancharbonneau and Anonymous: 222 • Diaphragm (optics) Source: https://en.wikipedia.org/wiki/Diaphragm_(optics)?oldid=743616121 Contributors: Earth, Boffy b, Ben- FrantzDale, Gadfium, OverlordQ, MarkSweep, BrokenSegue, Wendell, Walter Görlitz, Hanswaarle, Cburnett, Suruena, Dragunova, Car- charoth, The wub, Margosbot~enwiki, Srleffler, Zotel, Seb35, Nikkimaria, Mikus, Mohylek, Cmglee, Stf, Schmiteye, Bluebot, Colonies Chris, Audriusa, Jec, Dicklyon, Vanisaac, Edal, ENpeeOHvee, Jim.henderson, Kimse, Moscvitch, Kitashi, Victimofleisure, Jaqen, Twins- day, Martarius, Starmaker it, Addbot, Мыша, Catsquisher, Yobot, TaBOT-zerem, Underthedial, KDS4444, Shieldforyoureyes, Ulric1313, J04n, Innerche, Yangosplat222, EmausBot, GoingBatty, Bersibot, Bersam, ClueBot NG, Gareth Griffith-Jones, Matthiaspaul, MerlIwBot, Helpful Pixie Bot, MrNiceGuy1113, Bender the Bot and Anonymous: 26 • Normal lens Source: https://en.wikipedia.org/wiki/Normal_lens?oldid=743975847 Contributors: Koyaanis Qatsi, Caltrop, Heron, Camem- bert, Ericd, Leandrod, Patrick, Egil, Munford, Dale Arnett, RedWolf, BenFrantzDale, Hugh2414, MarkSweep, Grunners, Imroy, Mattdm, Hooperbloob, Arthena, Keenan Pepper, ABCD, Ashley Pomeroy, Mindmatrix, Rjwilmsi, Rogerd, FlaBot, Margosbot~enwiki, Srlef- fler, Roboto de Ajvol, YurikBot, Hede2000, Groogle, Amakuha, BOT-Superzerocool, Sandstein, Marc Lacoste, Ppntori, MalafayaBot, Kuru, Dicklyon, BDS2006, MER-C, DANYvanvee, Eftpotrm, MartinBot, Jamesmcardle, Fountains of Bryn Mawr, Squids and Chips, VolkovBot, TXiKiBoT, GavinTing, Gibbo 07 2, ImageRemovalBot, Addbot, Yobot, Sshjs930, Shadowjams, FrescoBot, Citation bot 1, Rudolfo42, AndyHe829, Davandjoni, ZéroBot, ChuispastonBot, Helpful Pixie Bot, Runner1616, Darafsh, SkipDouglas, Junkyardsparkle, Tomeks89, GreenC bot, Bender the Bot and Anonymous: 35 • Prime lens Source: https://en.wikipedia.org/wiki/Prime_lens?oldid=760346859 Contributors: Michael Hardy, Andrewa, Whkoh, David Latapie, Fuzheado, Grendelkhan, Morven, Finlay McWalter, Pengo, Christopherlin, MarkSweep, Imroy, Saintswithin, Fir0002, Jeffmed- keff, Googol plex, Hooperbloob, Mtreinik, A2Kafir, Musiphil, RoySmith, Mindmatrix, Azov, Mandarax, PatrickSauncy, Bubba73, Avo- cado, Srleffler, Borgx, Midgley, Manic-nirvana, Chris Capoccia, Bergsten, Grafen, David McCormick, Don Williams, Scoutersig, Smack- Bot, Gilliam, Anachronist, Snori, Jnavas, Tsca.bot, Hardywang, Akulkis, Autopilot, Dicklyon, Jack Falstaff, Alant, The Missing Piece, Dlcmh, IMattUK, Archange56, Thijs!bot, TonyTheTiger, Cherianthomas, Rosuna, J Clear, Escarbot, Stybn, Neonblak, UdovdM, Foun- tains of Bryn Mawr, VolkovBot, Skaraoke, Suprcel, Philip Trueman, Jhawkinson, Rkarlsba, ClueBot, Puceron, Tony May, Addbot, Aljays, MrOllie, SpBot, Yobot, AnomieBOT, Citation bot, FrescoBot, RedBot, Johann3s, Ponydepression, H3llBot, DASHBotAV, ClueBot NG, Astrocog, Matthiaspaul, Helpful Pixie Bot, CitationCleanerBot, Maylemon, Cyberbot II, Reatlas, Ulinnuha09, GreenC bot, Bender the Bot, Doktor Daniel and Anonymous: 35 • Zoom lens Source: https://en.wikipedia.org/wiki/Zoom_lens?oldid=762729475 Contributors: AxelBoldt, DrBob, Ericd, Michael Hardy, Egil, Angela, Munford, Grendelkhan, Samsara, Jwpurple, Nurg, Seano1, DocWatson42, Hugh2414, Lenehey, MarkSweep, Sam Hoce- var, Fg2, Muijz, Moxfyre, Imroy, Loganberry, Rama, Joergen, Robotje, Jeffmedkeff, Hooperbloob, Fourthords, Cburnett, Woohookitty, Mindmatrix, Scriberius, Pol098, GregorB, Macaddct1984, SDC, Leemeng, Saperaud~enwiki, Coneslayer, Filu~enwiki, FlaBot, Arnero, Srleffler, Roboto de Ajvol, YurikBot, Borgx, RobotE, Peter S., Conscious, Van der Hoorn, Shotgunlee, Gadget850, Bota47, Petri Krohn, Fourohfour, NFH, That Guy, From That Show!, Timrb, InverseHypercube, Marc Lacoste, Unyoyega, Kokoo, Betacommand, Thumper- ward, Snori, DHN-bot~enwiki, Jnavas, Akulkis, Kuru, H, CmdrObot, Zarex, WeggeBot, Anoneditor, A876, ForrestCroce, Thijs!bot, Iulius, Stybn, Adorama, JAnDbot, LittleOldMe, Sir Link, Church of emacs, Fountains of Bryn Mawr, Gonzalo M. Garcia, Keecheril, RJASE1, VolkovBot, TXiKiBoT, RedAndr, Francis Flinch, Erkan Umut, AlleborgoBot, SieBot, BotMultichill, Gerakibot, MaltaGC, Lynophi, Se16teddy, HujiBot, StigBot, Trivialist, Excirial, Rror, Trabelsiismail, SilvonenBot, Tubesship, Addbot, Benitoisbackagain, Olli Niemitalo, Jncraton, Thermofan, West.andrew.g, Lightbot, AnomieBOT, Xqbot, SassoBot, Tamasflex, Ɱ, Fsgs, NameIsRon, TGCP, J36miles, Warmanddry, Jmencisom, ZéroBot, H3llBot, Gsarwa, Mikhail Ryazanov, ClueBot NG, Matthiaspaul, Rezabot, JordoCo, Help- ful Pixie Bot, Tagremover, Pandages, Tony Mach, Vanished user 23520819, Lagoset, S536870912, Garytheyim, Karlfonza, Bender the Bot and Anonymous: 75 • Telephoto lens Source: https://en.wikipedia.org/wiki/Telephoto_lens?oldid=747332285 Contributors: B4hand, Stewstryker, Ericd, Spiff~enwiki, Gabbe, Egil, Marumari, Vancouverguy, Echoray, Munford, Louis Kyu Won Ryu, Robbot, Fredrik, RedWolf, BenFrantzDale, Hugh2414, Bobblewik, Lenehey, Girolamo Savonarola, Imroy, Rich Farmbrough, Rama, Mattdm, Jeffmedkeff, Nk, Hooperbloob, Free Bear, Arthena, Sl, Digitalmoron, Ahruman, Evil Prince, Velella, Pennbrook, Mindmatrix, Nipsy, Ylem, Filu~enwiki, FlaBot, Artimbo, Quuxplusone, Sr- leffler, YurikBot, Hellbus, FF2010, KGasso, CapitalLetterBeginning, SmackBot, InverseHypercube, Marc Lacoste, Unyoyega, Wuffyz, Hibernian, Nbarth, Tsca.bot, Adamantios, Morio, Dicklyon, Jordanville, Halfblue, Dlohcierekim, Anoneditor, BDS2006, Thijs!bot, Mactographer, Escarbot, Luna Santin, GodGell, Ekabhishek, MarcLevoy, I B Wright, CommonsDelinker, Numbo3, Fountains of Bryn Mawr, VolkovBot, Amikake3, WOSlinker, Qxz, Jackfork, Theoneintraining, BotMultichill, Phorgan1, Pasiasty, Paul Pot, Versus22, Yo- jimbo501, Rror, WikHead, Namzie11, Addbot, CarsracBot, Tassedethe, Krano, Luckas-bot, Afrank99, AnomieBOT, Yankiwi, Citation bot 1, Tamasflex, Sjalexander, Ripchip Bot, TGCP, Orphan Wiki, Dewritech, Bua333, ZéroBot, AndyCivil, Ashkenazzi, ClueBot NG, Helpful Pixie Bot, Karlfonza, Kambojharsangeet, Bender the Bot and Anonymous: 71 • Teleconverter Source: https://en.wikipedia.org/wiki/Teleconverter?oldid=744626689 Contributors: Egil, Andrewa, Rl, Rnbc, Reub2000, Swn, Jason Quinn, Maximaximax, Rama, Phule, Hooperbloob, Gene Nygaard, Sirimiri, Rogerd, Filu~enwiki, Bubba73, FlaBot, Who, Sr- leffler, Petri Krohn, SaxTeacher, Storm2005, Dontworry, Zahn, Jayrandom, Quentar~enwiki, Cuardin, GermanX, MartinBot, LordAnu- bisBOT, Fountains of Bryn Mawr, Dhaluza, Broadbot, Zaslaw, Michael Frind, Martarius, Nebrot, Wispanow, ChrisHodgesUK, Versus22, Addbot, CarsracBot, Lightbot, Ptbotgourou, The High Fin Sperm Whale, ArthurBot, FrescoBot, Tamasflex, EmausBot, Matthiaspaul, Jacopo188, Tagremover, E6filmuser, Bender the Bot and Anonymous: 14 • Long-focus lens Source: https://en.wikipedia.org/wiki/Long-focus_lens?oldid=740913457 Contributors: Imroy, Dicklyon, Fountains of Bryn Mawr, Mortense, 10metreh, Helpful Pixie Bot, BG19bot, NoodleWhacks, Dexbot, Bender the Bot and Anonymous: 2 190 CHAPTER 11. TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES

• Close-up filter Source: https://en.wikipedia.org/wiki/Close-up_filter?oldid=762580539 Contributors: Andrewa, Petri Krohn, Leridant, Pieter Kuiper, CoolKoon, Zepheriah, Smial, Viridiflavus~enwiki, , SieBot, Hamiltondaniel, SchreiberBike, Drahkrub, Addbot, ComputerHotline, The High Fin Sperm Whale, FrescoBot, Tamasflex, Jesse V., Gsarwa, Ulrich67, MerlIwBot, Helpful Pixie Bot, Calidum, Jacopo188, Theraincloud, Duvivier.Michel and Anonymous: 12 • Macro photography Source: https://en.wikipedia.org/wiki/Macro_photography?oldid=759616808 Contributors: Leandrod, Spiff~enwiki, Michael Hardy, Arpingstone, Ahoerstemeier, Haakon, SharQ, Andrewa, Nv8200pa, Ed g2s, Samsara, Finlay McWalter, Dale Arnett, Sander123, JerryFriedman, Meanos~enwiki, BenFrantzDale, BigBen212, Dawidl, Jason Quinn, Solipsist, Adamrice, Fg2, Imroy, Dis- cospinster, Rich Farmbrough, T Long, NrDg, Rama, Smyth, MattTM, Circeus, Fir0002, Jeffmedkeff, Jlencion, Hooperbloob, Musiphil, Rd232, Digitalmoron, Dschwen, Sciurinæ, Gene Nygaard, Dejvid, The JPS, Mindmatrix, Pol098, Rjwilmsi, Filu~enwiki, Skirtley, Awm, The wub, Sango123, Pathaugen, BjKa, Srleffler, YurikBot, Az7997, Diliff, Splette, Zelmerszoetrop, Gaius Cornelius, TheMandarin, Jaspinall, Y6y6y6, Howcheng, Fredkamphues, Bota47, Kkmurray, Niksilver, Bidiot, Shawnc, Chic happens, Lviatour, KnowledgeOf- Self, Bigbluefish, Stimpy, Ohnoitsjamie, BuBZ, IanBailey, D-Rock, Can't sleep, clown will eat me, OrphanBot, Rrburke, Abrahami, Soumyasch, Peterlewis, Erwin, Dicklyon, H, AntOnTrack, Hacksawbob, Craigboy, Atomobot, Jamoche, Sbn1984, DanieleProcida, Alves- gaspar, AnonyGnome, SKPhoton, ForrestCroce, Imv, Epbr123, Mactographer, Z10x, Stybn, Erniehatt, Cyclonenim, AntiVandalBot, Bernopedia, Amberroom, Mewslee37, JAnDbot, DSiegfried, Ekabhishek, MER-C, The Transhumanist, .anacondabot, VoABot II, Sujit kumar, Soulbot, Nyttend, Alanbrowne, Gimlei, Emil76~enwiki, $01734071290912$, Atulsnischal, Cotton2, CommonsDelinker, Tobi- asK, Smial, FANSTARbot, Uncle Dick, Thegreenj, LogiJake, WarthogDemon, Krisirk, Speed8ump, Bookworming, Ycdkwm, Fountains of Bryn Mawr, Naturphoto~enwiki, Helmut Schütz, Signalhead, Wikieditor06, Jmrowland, Nburden, TheMindsEye, Philip Trueman, Macro-photo, Rei-bot, DerGolgo, Jyi1693, BwDraco, Muhammad Mahdi Karim, B2photographs, Crazymapleleaf, Flash19901, Isis4563, Edvvc, Madhero88, Guy Van Hooveld, AlleborgoBot, Red, Jim77742, Solah~enwiki, Scarian, RikLittlefield, Phe-bot, Flyer22 Reborn, Yerpo, Mbrown54, Oxymoron83, Paintman, Acceptable, Frander, EricPaynter, Madjidm, WikipedianMarlith, ClueBot, Aashish.59, Rockfang, Mumiemonstret, Excirial, Alexbot, 7, Sormus, XLinkBot, Rror, Skarebo, Namzie11, Addbot, Some jerk on the Internet, Tomwins76, Axilera, Misterx2000, NeotonicDragon3, MrOllie, Chzz, Tyw7, NikOly, ComputerHotline, Luckas-bot, Yobot, Amirobot, Jethrothompson, Simplymono, Mgmizell, Momoricks, Kingpin13, Chris Pine, B137, The High Fin Sperm Whale, Thelittlegreyman, ArthurBot, Arielasteif, Yousif keasou, SassoBot, AlixW, Dougofborg, Jhkauf, Celuici, Amethystus, FrescoBot, Nokia ST, Pinethicket, Tamasflex, Qazwsx13, Kilnuri, DARTH SIDIOUS 2, The Utahraptor, Fgcurtis, TjBot, Robertppt, Tricajus, John of Reading, Immu- nize, Dewritech, TuomTuo, Steroid Maximus, Tommy2010, Aminyllah, ZéroBot, Cogiati, Stover98074, DXR, Blue Marble, Larkot, Jetlekk, Gsarwa, Angerdan, Imohano, ClueBot NG, Coolhand2120, Sylvain Bui, Recyclojunk64, Mario7676, Titodutta, Graceofrox, Badon, Jaymargolis, Jenoptik, Soerfm, Fraulein451, Cyberbot II, Tagremover, YFdyh-bot, StudioLoft, Pf soycd, GodeNehler, Therey- oflite, 11supachok11, Thereyoflite8, Kelvin Santarita, Devwebtel, Wimw, CAPTAIN RAJU, Kaikai Guo, GreenC bot, Bender the Bot, Bladiblatalkinokedag, YoavNir, Ficaso, Jun V Lao and Anonymous: 187 • Wide-angle lens Source: https://en.wikipedia.org/wiki/Wide-angle_lens?oldid=759975600 Contributors: B4hand, Ericd, Ram-Man, Michael Hardy, Egil, Munford, Dale Arnett, RedWolf, Kent Wang, Seano1, BenFrantzDale, Hugh2414, Slindner, Christopherlin, Beland, Imroy, Rama, Mattdm, Cacophony, Fir0002, Jeffmedkeff, Polylerus, Hooperbloob, Velella, Gene Nygaard, OwenX, Mindmatrix, Ylem, Amigadave, Macaddct1984, Bubba73, FlaBot, Margosbot~enwiki, Srleffler, Roboto de Ajvol, Chensiyuan, Gaius Cornelius, Bovineone, Draicone, SmackBot, Unyoyega, Eskimbot, Morio, Jmak1949, Dicklyon, Zahn, Anoneditor, Rmeskill, Thijs!bot, N5iln, Mentifisto, Dricherby, Bkpsusmitaa, VoABot II, GermanX, Darkxsun, Discboy, DogNewTricks, Fountains of Bryn Mawr, STBotD, VolkovBot, EEye, Amikake3, TXiKiBoT, Xjs, AlleborgoBot, Phorgan1, Smilesfozwood, Martarius, The Thing That Should Not Be, XLinkBot, Ad- dbot, Misterx2000, Oldmountains, Yobot, AnomieBOT, Materialscientist, Xqbot, Javert, Rudolfo42, Tamasflex, Longerro, Miracle Pen, Lopifalko, ClueBot NG, Ammar adel, Matthiaspaul, JordoCo, K0 7zQY0oyqcz, Sapemeg, Reatlas, Center City Productions, Isaac.Enio, Ugyballoons, Bender the Bot, Iadmc and Anonymous: 58 • Fisheye lens Source: https://en.wikipedia.org/wiki/Fisheye_lens?oldid=762818511 Contributors: Damian Yerrick, Css, Michael Hardy, Furrykef, Samsara, Robbot, Dale Arnett, RedWolf, Auric, Bkell, Jleedev, DavidCary, BenFrantzDale, Solipsist, Bobblewik, MarkSweep, Imroy, Bender235, Syp, Evand, EurekaLott, Silverdragon706, Hooperbloob, Ashley Pomeroy, Wtmitchell, Woohookitty, Mindmatrix, Tabletop, Nightscream, BlueMoonlet, Seinman, Bubba73, Srleffler, Roboto de Ajvol, RobotE, Peter.wieden, Phantomsteve, Hede2000, Splette, Hellbus, Bovineone, Brandon, Closedmouth, Dspradau, SmackBot, Mjposner, Eskimbot, Kmarinas86, Anachronist, Chris the speller, Nbarth, Darth Panda, Tsca.bot, Themeparkphoto, Mjefm, Morio, Carampaima, KengRu, TFNorman, Dicklyon, ShakingSpirit, Tawkerbot2, Konnetikut, MasterMan, DumbBOT, Thijs!bot, Civertan, Dawnseeker2000, AntiVandalBot, Bautsch, JAnDbot, Sterrys, BrotherE, JWGreen, John Spikowski, Nikevich, Indon, 28421u2232nfenfcenc, Tokino, Wyrdlight, J.delanoy, Captain panda, Pharaoh of the Wizards, RadioGuyTed, Ksempac, SharkD, Jeepday, Beatledavid, RenniePet, Fountains of Bryn Mawr, Erik Krause, Rdfr, TheMindsEye, WilliamSommerwerck, Piperh, Littlealien182, BwDraco, Falcon8765, C45207, Sardaka, Pjoef, SieBot, Bryan Dug- gan, Hertz1888, Napocapo~enwiki, Keilana, Flyer22 Reborn, Pmrich, ClueBot, Nebrot, Jusdafax, Bobby Tables, Puceron, DumZiBoT, XLinkBot, Skarebo, Addbot, Willking1979, Edgy01, Aelkris, GD 6041, Kyle1278, Mliu92, Lightbot, SkaterBoy182, Luckas-bot, Yobot, AVB, AnomieBOT, Ta2Ed, Archon 2488, Jim1138, Timwether, Pepo13, Citation bot, LilHelpa, RibotBOT, SCΛRECROW, Sophus Bie, Tiger1027tw, Brett7boi, Davitof, Ml-gvalt, Ciaranhughes, Rudolfo42, Doubleclix, Markringo, Beerrocks, Lotje, VORON SPb, DASH- Bot, EmausBot, Jmencisom, BraxtonSmith, ZéroBot, Cogiati, Wackywace, Cymru.lass, VJTownsend, Pau Valiente, Kitsaprob, Matejmm, ClueBot NG, Matthiaspaul, Luc9488, Ilveon, Helpful Pixie Bot, KLBot2, Regulov, BG19bot, Darafsh, Tracy Davis, Malyszkz, Soerfm, G37x8004uc, LlamaAl, Dpa11111, Tagremover, Xyzspaniel, Ayeshun, Mogism, ,DavidLeighEllis, Isaac.Enio, Henryc- murray, ThePaurBear, Story in Pictures and Anonymous: 155 • Optical coating Source: https://en.wikipedia.org/wiki/Optical_coating?oldid=715566427 Contributors: DrBob, Michael Hardy, DIG~enwiki, Marshman, Shantavira, RedWolf, Ryanrs, Niteowlneils, Tateroid, Madoka, Sam Hocevar, Kevin Rector, Rich Farmbrough, Loren36, Vinsci, Cmdrjameson, Justinlebar, Polyparadigm, Pol098, Pfalstad, Kolbasz, Srleffler, Roboto de Ajvol, Conscious, Gaius Cornelius, Shaddack, Zwobot, Kungfuadam, SmackBot, Bluebot, Radagast83, Dreadstar, Zaphraud, Pflatau, Dicklyon, Hetar, Joseph Solis in Aus- tralia, CmdrObot, Alphachimpbot, WmRowan, R'n'B, Ctroy36, Trilobitealive, Signalhead, Akhram, TheBendster, Anchor Link Bot, Addbot, Lightbot, AnomieBOT, Materialscientist, Jkeck-wiki, TheC4pt, , NameIsRon, Lopifalko, RaptureBot, Haianqutang, Cn- tras, Marechal Ney, Manfred Weiler, Dexbot, Zenmanenergy, Tl14054, KasparBot and Anonymous: 30 • Optical filter Source: https://en.wikipedia.org/wiki/Optical_filter?oldid=729898673 Contributors: DrBob, Michael Hardy, Kragen, An- dres, Maximus Rex, Leonard G., Jorge Stolfi, Quadell, Antandrus, Kevin Rector, ArnoldReinhold, Quistnix, Neko-chan, Fatphil, Hooperbloob, Atlant, Velella, Ceyockey, Woohookitty, Pol098, Zbxgscqf, SeanMack, Weihao.chiu~enwiki, Chobot, Gdrbot, YurikBot, RobotE, Voidxor, Nolanus, Trickstar, SmackBot, Binarypower, BahramH, Hmains, Chris the speller, VMS Mosaic, Slakr, Luokehao, Dicklyon, Martious, Gnome (Bot), Jbusenitz, James pic, CmdrObot, Gogo Dodo, Calvero JP, Epbr123, Drmemory, WillMak050389, A3RO, TekE, Zylorian, RisingStick, R'n'B, CommonsDelinker, Pharaoh of the Wizards, Tradexpert1, Remo (CPI), Bonadea, Signalhead, Spinningspark, Sevela.p, 11.2. IMAGES 191

Pjoef, DonBarredora, Biscuittin, Hertz1888, Martarius, ClueBot, LAX, Binksternet, Stoltexcellence, ChrisHodgesUK, Eranus~enwiki, Dododerek, Torchflame, Addbot, CL, Jeeves rules, Luckas-bot, Yobot, Bunnyhop11, AnomieBOT, Otaviogood, Mnmngb, Novaseminary, TobeBot, Greatpopcorn, Lizinvt, EmausBot, Dcirovic, ZéroBot, AVarchaeologist, 2pem, Omegaoptical, SimmeD, Fluffystar, Mogism, NoslivRage, Lingau.alex, DianaVicky1974 and Anonymous: 43 • Photographic filter Source: https://en.wikipedia.org/wiki/Photographic_filter?oldid=758361084 Contributors: DrBob, Blueshade, Kricke, Nikai, Jiang, Silvonen, Dmetric, Robbot, Dale Arnett, Modulatum, Seano1, ShutterBugTrekker, DocWatson42, BenFrantzDale, Hugh2414, Jorge Stolfi, Bobblewik, Niffux, Imroy, Qutezuce, ArnoldReinhold, Giraffedata, PiccoloNamek, Hooperbloob, Alansohn, Keenan Pep- per, Ashley Pomeroy, Andrew Norman, Dave.Dunford, H2g2bob, Gene Nygaard, Jun-Dai, Ikiwaner, Pol098, NickF, Rjwilmsi, Bubba73, The wub, FlaBot, Kallemax, Matt Jason H, J S Lundeen, Srleffler, Chobot, Bgwhite, Drumex, Adoniscik, YurikBot, Beltz, DanMS, Dav- eswagon, Voidxor, Bressen, A bit iffy, SmackBot, Tom Lougheed, InverseHypercube, Rmosler2100, Marc Kupper, BenAveling, Chris the speller, Ksenon, Nbarth, ZyMOS, Invenio, Hgrosser, Frap, Mosca, Melbournian, Steve Pucci, Lanserj630, Roguegeek, Ashmedai, Rfernand, Dicklyon, Zabdiel, Peter Horn, Wwagner, JoeBot, Sjb72, Internedko, JForget, Tubenutdave, Crossmr, ClarkMills, Thijs!bot, Akb4, Redset, The Transhumanist, CeeJay.dk, Memtek, Vmuth~enwiki, JeffJonez, Noodle snacks, Wayne Miller, Akashopoholic, R'n'B, Mange01, Yongbojiang, Tyrerj, DMCer, BwDraco, Frogcement, Synthebot, , Ondra h, Jauerback, Dawn Bard, Jdaloner, Martar- ius, ClueBot, Ggia, Maniac18, Imotor, Alexbot, Bjdehut, DumZiBoT, XLinkBot, Sbittante, Addbot, Ronhjones, Cosmos72, Luckas- bot, Yobot, Nallimbot, Robert Treat, Synchronism, AnomieBOT, Nm168, Piano non troppo, Mann jess, The High Fin Sperm Whale, Amithshs, Capnwally, Dave3457, FrescoBot, MLKLewis, LucJ, SiPlus, Cullen328, Squidoo, Kapgains, IMYY4U, Slashdot.dot, Emaus- Bot, WikitanvirBot, MrFawwaz, Dewritech, Klbrain, Zubrowka74, AVarchaeologist, Gsarwa, ChuispastonBot, Angerdan, ClueBot NG, Matthiaspaul, Frietjes, Cntras, Widr, Helpful Pixie Bot, Darafsh, Snow Blizzard, Baronsen, Mb77777, Olegstr23, Melonkelon, Tolunayt, Bender the Bot and Anonymous: 105 • Optical transfer function Source: https://en.wikipedia.org/wiki/Optical_transfer_function?oldid=762862593 Contributors: The Anome, Jordi Burguet Castell, Donarreiskoffer, Merovingian, BenFrantzDale, Jason Quinn, BoP, Danh, Algocu, Default007, Srleffler, J.Ammon, Jaraalbe, Alex Bakharev, Voidxor, Petri Krohn, SmackBot, Lindosland, Chris the speller, Stevage, Beetstra, Dicklyon, Martious, JonesMI, Omicronpersei8, Thijs!bot, R'n'B, Normankoren, Zhongsifen, Memestream, Squids and Chips, DarkArcher, NathanHagen, AlleborgoBot, SieBot, WereSpielChequers, Tom.vettenburg, Wispanow, Mild Bill Hiccup, 1ForTheMoney, DumZiBoT, Chymæra, Jytdog, Dthomsen8, Addbot, Legobot, AnomieBOT, Wrongfilter, The Lamb of God, Yoconst, Optikosco, DurkJPearson, BradMarX, John of Reading, Going- Batty, Ὁ οἶστρος, Salo2010, KlappCK, Frietjes, Rezabot, Bibcode Bot, BG19bot, Sfnagle, Soerfm, ChrisGualtieri, Jeffreyleach21e21e, CitrusEllipsis and Anonymous: 41 • Optical resolution Source: https://en.wikipedia.org/wiki/Optical_resolution?oldid=715695332 Contributors: Euske, Smack, Tonsof- pcs, Ploum’s, BenFrantzDale, Bobblewik, Ehusman, Neffk, JimWae, Rubik-wuerfel, El C, Worldtraveller, Cmdrjameson, Mindmatrix, Alhutch, Srleffler, Physchim62, Jaraalbe, YurikBot, Wavelength, Doncram, RSaunders, SmackBot, Richmeister, Chris the speller, Kev- inpurcell, Dicklyon, CRGreathouse, CmdrObot, Greif~enwiki, Waxigloo, Thijs!bot, Magioladitis, Appraiser, Nono64, Bealevideo, Ian Strachan, Theaveng, Lightmouse, Myceteae, Fgnievinski, Epzcaw, Lightbot, Otrfan, MARKEMUP, The Lamb of God, The High Fin Sperm Whale, Xqbot, Steve Quinn, Pestling, Ego White Tray, Orange Suede Sofa, Clickeric, Gwestheimer, LaserSoft Imaging, MerlI- wBot, Ydame001, MusikAnimal, ChrisGualtieri, Dexbot, Jodosma, Chacapito, Comp.arch, Temdor, Panypeces, Strandaffe87, Darthaw- some and Anonymous: 42 • 1951 USAF resolution test chart Source: https://en.wikipedia.org/wiki/1951_USAF_resolution_test_chart?oldid=741572418 Contrib- utors: Asparagus, BenFrantzDale, Imroy, Keenan Pepper, Theant2000, Icey, DrTorstenHenning, Jaraalbe, Alemily, SmackBot, Autopilot, Dicklyon, CmdrObot, Joechao, Greif~enwiki, Mattisse, MarshBot, KConWiki, Steevven1, Ndunruh, Setreset, Lightmouse, Kumioko (re- named), Ktr101, DumZiBoT, Addbot, Yobot, Amirobot, Leon3289, Ren Kusack, Pestling, David Casale, Klbrain, Frietjes, Chiph588 and Anonymous: 13

11.2 Images

• File:16_minolta_50mm.jpg Source: https://upload.wikimedia.org/wikipedia/commons/b/bc/16_minolta_50mm.jpg License: CC BY 3.0 Contributors: No machine-readable source provided. Own work assumed (based on copyright claims). Original artist: No machine- readable author provided. Leonrw assumed (based on copyright claims). • File:1951usaf_test_target.jpg Source: https://upload.wikimedia.org/wikipedia/commons/d/d6/1951usaf_test_target.jpg License: CC BY-SA 2.5 Contributors: Transferred from en.wikipedia to Commons by OS. Original artist: The original uploader was Alemily at English Wikipedia • File:1D_diffraction_limited_optical_transfer_function..svg Source: https://upload.wikimedia.org/wikipedia/commons/f/fb/1D_diffraction_ limited_optical_transfer_function..svg License: CC BY-SA 3.0 Contributors: Own work Original artist: Tom.vettenburg • File:24mm-tilt-lens.jpg Source: https://upload.wikimedia.org/wikipedia/commons/f/fc/24mm-tilt-lens.jpg License: Attribution Con- tributors: Own work (Original text: I created this work entirely by myself.) Original artist: Motorrad-67 at English Wikipedia • File:35mm_Camera_I.JPG Source: https://upload.wikimedia.org/wikipedia/commons/e/e7/35mm_Camera_I.JPG License: CC BY- SA 4.0 Contributors: Own work Original artist: Karl Thomas Moore • File:35mm_Camera_II.JPG Source: https://upload.wikimedia.org/wikipedia/commons/8/82/35mm_Camera_II.JPG License: CC BY- SA 4.0 Contributors: Own work Original artist: Karl Thomas Moore • File:35mm_Equivalent_Reproduction_Ratio.jpg Source: https://upload.wikimedia.org/wikipedia/commons/9/90/35mm_Equivalent_ Reproduction_Ratio.jpg License: CC BY 3.0 Contributors: Own work Original artist: DSiegfried (talk)(Uploads) • File:3DPSF_3DMTF_widefield_confocal.png Source: https://upload.wikimedia.org/wikipedia/commons/b/b9/3DPSF_3DMTF_widefield_ confocal.png License: CC BY 3.0 Contributors: Own work Original artist: Tom Vettenburg • File:500mm_telephoto_lens_01.jpg Source: https://upload.wikimedia.org/wikipedia/commons/d/d8/500mm_telephoto_lens_01.jpg Li- cense: CC-BY-SA-3.0 Contributors: Own work Original artist: :) Dlohcierekim • File:80a_comparison.jpg Source: https://upload.wikimedia.org/wikipedia/commons/3/3b/80a_comparison.jpg License: CC-BY-SA- 3.0 Contributors: Dmetric (talk)(Uploads) Original artist: Dmetric at en.wikipedia 192 CHAPTER 11. TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES

• File:AchromatDoublet-text.svg Source: https://upload.wikimedia.org/wikipedia/commons/c/c1/AchromatDoublet-text.svg License: CC BY-SA 3.0 Contributors: Transferred from en.wikipedia to Commons by Logan using CommonsHelper. Original artist: Paul1513 at English Wikipedia • File:AchromatLandscape-text.svg Source: https://upload.wikimedia.org/wikipedia/commons/f/f7/AchromatLandscape-text.svg Li- cense: CC BY-SA 3.0 Contributors: Originally uploaded on en.wikipedia Original artist: Originally uploaded by Paul1513 (Transferred by Logan) • File:Angenieux.png Source: https://upload.wikimedia.org/wikipedia/commons/0/03/Angenieux.png License: CC BY-SA 3.0 Contribu- tors: Own work Original artist: Tamasflex • File:Angenieux35f25Retrofocus-t.svg Source: https://upload.wikimedia.org/wikipedia/en/a/ad/Angenieux35f25Retrofocus-t.svg Li- cense: CC-BY-SA-3.0 Contributors: Own work Original artist: Paul1513 (talk)(Uploads) • File:Angleofview_210mm_f4.jpg Source: https://upload.wikimedia.org/wikipedia/commons/f/fd/Angleofview_210mm_f4.jpg License: Public domain Contributors: ? Original artist: ? • File:Angleofview_28mm_f4.jpg Source: https://upload.wikimedia.org/wikipedia/commons/1/12/Angleofview_28mm_f4.jpg License: Public domain Contributors: ? Original artist: ? • File:Angleofview_50mm_f4.jpg Source: https://upload.wikimedia.org/wikipedia/commons/9/9c/Angleofview_50mm_f4.jpg License: Public domain Contributors: ? Original artist: ? • File:Angleofview_70mm_f4.jpg Source: https://upload.wikimedia.org/wikipedia/commons/6/68/Angleofview_70mm_f4.jpg License: Public domain Contributors: ? Original artist: ? • File:Anti-reflective_coating_comparison.jpg Source: https://upload.wikimedia.org/wikipedia/commons/f/f2/Anti-reflective_coating_ comparison.jpg License: CC-BY-SA-3.0 Contributors: Own work Original artist: Justin Lebar • File:ApertureDefn1707.png Source: https://upload.wikimedia.org/wikipedia/commons/1/1f/ApertureDefn1707.png License: Public domain Contributors: Transferred from en.wikipedia to Commons. Original artist: The original uploader was Dicklyon at English Wikipedia • File:Aperture_Example_Wall.jpg Source: https://upload.wikimedia.org/wikipedia/commons/9/9c/Aperture_Example_Wall.jpg License: CC BY-SA 4.0 Contributors: Own work Original artist: Aleksandr Khomyakov • File:Aperture_Example_Wall_2.jpg Source: https://upload.wikimedia.org/wikipedia/commons/c/c1/Aperture_Example_Wall_2.jpg License: CC BY-SA 4.0 Contributors: Own work Original artist: Aleksandr Khomyakov • File:Aperture_diagram.svg Source: https://upload.wikimedia.org/wikipedia/commons/8/87/Aperture_diagram.svg License: CC-BY- SA-3.0 Contributors: Transferred from en.wikipedia to Commons. Original artist: Cbuckley at English Wikipedia Later versions were uploaded by Dicklyon at en.wikipedia. • File:Aperture_in_Canon_50mm_f1.8_II_lens.jpg Source: https://upload.wikimedia.org/wikipedia/commons/8/8a/Aperture_in_Canon_ 50mm_f1.8_II_lens.jpg License: GFDL Contributors: Own work Original artist: Gophi • File:Apertures.jpg Source: https://upload.wikimedia.org/wikipedia/commons/d/d7/Apertures.jpg License: CC-BY-SA-3.0 Contribu- tors: No machine-readable source provided. Own work assumed (based on copyright claims). Original artist: Mohylek • File:Automatik-Balgengeraet_mit_Kamera,_Objektiv_und_Umkehrring.jpg Source: https://upload.wikimedia.org/wikipedia/commons/ 3/31/Automatik-Balgengeraet_mit_Kamera%2C_Objektiv_und_Umkehrring.jpg License: CC BY-SA 2.0 de Contributors: Own work Original artist: User Smial on de.wikipedia • File:Axonometric_projection.svg Source: https://upload.wikimedia.org/wikipedia/commons/4/48/Axonometric_projection.svg License: Public domain Contributors: This vector image was created with Inkscape. Original artist: Yuri Raysper • File:Big_pinhole.svg Source: https://upload.wikimedia.org/wikipedia/commons/1/1c/Big_pinhole.svg License: CC BY-SA 3.0 Contrib- utors: Own work Original artist: BenFrantzDale • File:Big_pinhole_with_lens.svg Source: https://upload.wikimedia.org/wikipedia/commons/5/54/Big_pinhole_with_lens.svg License: CC BY-SA 3.0 Contributors: Own work Original artist: BenFrantzDale • File:Biogon-text.svg Source: https://upload.wikimedia.org/wikipedia/en/f/fd/Biogon-text.svg License: CC-BY-SA-3.0 Contributors: Own work Original artist: Paul1513 (talk)(Uploads) • File:BuschBisTelar-text.svg Source: https://upload.wikimedia.org/wikipedia/en/f/fb/BuschBisTelar-text.svg License: CC-BY-SA-3.0 Contributors: By Paul Chin (paul1513 (talk)); self created; Original artist: paul1513 (talk) • File:Canon400DOtext.svg Source: https://upload.wikimedia.org/wikipedia/en/9/9d/Canon400DOtext.svg License: CC-BY-SA-3.0 Con- tributors: Own work Original artist: Paul1513 (talk)(Uploads) • File:Canon_17-40_f4_L_lens.jpg Source: https://upload.wikimedia.org/wikipedia/commons/c/ce/Canon_17-40_f4_L_lens.jpg License: GFDL 1.2 Contributors: Own work Original artist: fir0002 | flagstaffotos.com.au 11.2. IMAGES 193

• File:Canon_85mm_comparison_(front).jpg Source: https://upload.wikimedia.org/wikipedia/commons/8/81/Canon_85mm_comparison_ %28front%29.jpg License: CC BY-SA 3.0 Contributors: Own work Original artist: Autopilot • File:Canon_EF_50mm_II_lens_front_and_rear_side-by-side_version3.JPG Source: https://upload.wikimedia.org/wikipedia/commons/ 1/16/Canon_EF_50mm_II_lens_front_and_rear_side-by-side_version3.JPG License: CC BY-SA 3.0 Contributors: Own work Original artist: TonyTheTiger • File:Canon_MP-E65mm.jpg Source: https://upload.wikimedia.org/wikipedia/commons/d/da/Canon_MP-E65mm.jpg License: CC BY- SA 2.5 Contributors: Own work Original artist: Richard Bartz, Munich aka Makro Freak Makro Freak bar.jpg • File:Canon_Teleobjektiv_(29909576375).jpg Source: https://upload.wikimedia.org/wikipedia/commons/e/e7/Canon_Teleobjektiv_ %2829909576375%29.jpg License: CC BY 2.0 Contributors: Canon Teleobjektiv Original artist: Marco Verch • File:Car_Fisheye.jpg Source: https://upload.wikimedia.org/wikipedia/en/c/cd/Car_Fisheye.jpg License: CC-BY-SA-3.0 Contributors: At public cruise-in Previously published: http://carfisheye.blogspot.com/ Original artist: Mjposner • File:Chromatic_aberration_lens_diagram.svg Source: https://upload.wikimedia.org/wikipedia/commons/a/aa/Chromatic_aberration_ lens_diagram.svg License: CC-BY-SA-3.0 Contributors: Bob Mellish (talk)(Uploads) Original artist: Bob Mellish (talk)(Uploads) • File:Close-Up_lens_Canon_500D_58_mm.jpg Source: https://upload.wikimedia.org/wikipedia/commons/1/11/Close-Up_lens_Canon_ 500D_58_mm.jpg License: CC BY-SA 2.5 Contributors: ? Original artist: ? • File:Close-up.png Source: https://upload.wikimedia.org/wikipedia/commons/8/8d/Close-up.png License: CC BY-SA 3.0 Contributors: Own work Original artist: Tamasflex • File:Coating-Mirror-Lens.jpg Source: https://upload.wikimedia.org/wikipedia/commons/6/68/Coating-Mirror-Lens.jpg License: CC- BY-SA-3.0 Contributors: http://en.wikipedia.org/wiki/Image:Coating-1.jpg Original artist: Bob Mellish • File:Cokin_Filters_(Stacked_Cases).jpg Source: https://upload.wikimedia.org/wikipedia/commons/2/22/Cokin_Filters_%28Stacked_ Cases%29.jpg License: CC BY-SA 4.0 Contributors: Own work Original artist: Vilson V. Venezuela • File:Commons-logo.svg Source: https://upload.wikimedia.org/wikipedia/en/4/4a/Commons-logo.svg License: PD Contributors: ? Orig- inal artist: ? • File:CookeTriplet-text.svg Source: https://upload.wikimedia.org/wikipedia/commons/7/77/CookeTriplet-text.svg License: CC BY- SA 3.0 Contributors: Transferred from en.wikipedia to Commons by SreeBot. Original artist: Paul1513 at en.wikipedia • File:Definitions_PSF_OTF_MTF_PhTF.svg Source: https://upload.wikimedia.org/wikipedia/commons/6/64/Definitions_PSF_OTF_ MTF_PhTF.svg License: CC BY-SA 3.0 Contributors: Own work Original artist: Tom.vettenburg • File:DoubleGauss_horizontal.png Source: https://upload.wikimedia.org/wikipedia/commons/8/8c/DoubleGauss_horizontal.png License: CC BY-SA 3.0 Contributors: Own work Original artist: Soerfm • File:Dragon_Fly_portrait_using_reverse_ring_macro.png Source: https://upload.wikimedia.org/wikipedia/commons/1/16/Dragon_ Fly_portrait_using_reverse_ring_macro.png License: CC BY-SA 4.0 Contributors: Own work Original artist: Jun V Lao • File:EIA_Resolution_Chart_1956.svg Source: https://upload.wikimedia.org/wikipedia/commons/2/2b/EIA_Resolution_Chart_1956. svg License: Public domain Contributors: Self painted Original artist: Self painted • File:El_Gouna_Egypt_BW_Filter_Comparison_EN_large.png Source: https://upload.wikimedia.org/wikipedia/commons/c/c3/El_ Gouna_Egypt_BW_Filter_Comparison_EN_large.png License: CC BY-SA 1.0 Contributors: Transferred from en.wikipedia to Commons by SreeBot. Original artist: Blueshade at en.wikipedia • File:Ernostarf18text.svg Source: https://upload.wikimedia.org/wikipedia/commons/e/ec/Ernostarf18text.svg License: CC BY-SA 3.0 Contributors: Own work (Original caption: “By Paul Chin (paul1513 (talk)); self created;”) Original artist: Paul1513 at en.wikipedia • File:ExTubeMacro.png Source: https://upload.wikimedia.org/wikipedia/commons/7/78/ExTubeMacro.png License: CC BY-SA 3.0 Contributors: Own work Original artist: Tamasflex • File:ExtensionTube5733.jpg Source: https://upload.wikimedia.org/wikipedia/commons/3/30/ExtensionTube5733.jpg License: Public domain Contributors: Own work Original artist: User:Fg2 • File:Filter-optics-1.jpg Source: https://upload.wikimedia.org/wikipedia/commons/4/46/Filter-optics-1.jpg License: CC-BY-SA-3.0 Contributors: DrBob (talk)(Uploads) Original artist: DrBob at en.wikipedia • File:Filters_6187.jpg Source: https://upload.wikimedia.org/wikipedia/commons/3/3e/Filters_6187.jpg License: CC BY 3.0 Contribu- tors: Own work Original artist: Ashley Pomeroy • File:Fisheye-Nikkor_Auto_6mm_f2.8_lens_2015_Nikon_Museum.jpg Source: https://upload.wikimedia.org/wikipedia/commons/ 1/1e/Fisheye-Nikkor_Auto_6mm_f2.8_lens_2015_Nikon_Museum.jpg License: CC BY-SA 4.0 Contributors: Own work Original artist: Morio • File:Fisheye-text_2.svg Source: https://upload.wikimedia.org/wikipedia/commons/3/3f/Fisheye-text_2.svg License: CC BY-SA 3.0 Contributors: self created Original artist: Paul1513 at English Wikipedia (Original text: By Paul Chin (paul1513)) • File:Focal_length.jpg Source: https://upload.wikimedia.org/wikipedia/commons/e/e5/Focal_length.jpg License: CC BY-SA 3.0 Con- tributors: Own work Original artist: Jcbrooks • File:Focale-rama-028.jpg Source: https://upload.wikimedia.org/wikipedia/commons/0/05/Focale-rama-028.jpg License: CC BY-SA 2.0 fr Contributors: Own work Original artist: Rama • File:Focale-rama-050.jpg Source: https://upload.wikimedia.org/wikipedia/commons/b/bc/Focale-rama-050.jpg License: CC BY-SA 2.0 fr Contributors: Own work Original artist: Rama • File:Focale-rama-135.jpg Source: https://upload.wikimedia.org/wikipedia/commons/4/44/Focale-rama-135.jpg License: CC BY-SA 2.0 fr Contributors: Own work Original artist: Rama 194 CHAPTER 11. 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Essl (www.essl.de)/ESO • File:Tiny_pinhole-diffraction.svg Source: https://upload.wikimedia.org/wikipedia/commons/6/6d/Tiny_pinhole-diffraction.svg License: CC BY-SA 3.0 Contributors: Own work Original artist: BenFrantzDale • File:TokinaSZX70-210text.svg Source: https://upload.wikimedia.org/wikipedia/en/a/ab/TokinaSZX70-210text.svg License: CC-BY- SA-3.0 Contributors: ? 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Original artist: ? • File:Viewfinder-SLR-300mm.swn.jpg Source: https://upload.wikimedia.org/wikipedia/commons/7/79/Viewfinder-SLR-300mm.swn. jpg License: CC-BY-SA-3.0 Contributors: ? Original artist: ? • File:VivitarS1-70-210v1PBtext.svg Source: https://upload.wikimedia.org/wikipedia/en/d/d3/VivitarS1-70-210v1PBtext.svg License: CC-BY-SA-3.0 Contributors: ? Original artist: ? 198 CHAPTER 11. TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES

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11.3 Content license

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