DOCSLIB.ORG

An Expansion of the Ev System

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
An Expansion of the Ev System .d .. P 4 AN EXPANSION OF THE EV SYSTEM By W. F. Lindsey NASA Langley Research Center Langley Station, Hampton, Va. Presented at the 10th Annual Technical Symposium of The Society of Photo-Optical Instrument Engineers ‘- San Francisco, California August 16-20, 1965 AN EXPANSION OF THE EV SYSTEM By W. F. Lindsey NASA langley Research Center analysis has been expanded to include the factors involved in photoflash and electronic flash PhOtOgraPhy. The exposure value system or additive value system has been expanded to include filter factors This paper presents the derivation of the and transmittance. In addition, the equations for equations relating the photographic factors for photoflash and electronic flash photography are both basic photography and flash photography. converted into a form compatible with the EV sys- These equations are converted into an additive tem. The photographic factors are presented in value system that is a duplicate of or is com- tabular form together with their corresponding patible with the exposure value system. Tabulated values in the additive value system in 25-percent values are presented of the photographic factors steps or quarter stops to permit an acceptable and their corresponding values in the addltive solution to be obtained more readily. system which permit the application of the expanded system to photographic problems within ranges wherein the reciprocity effects are approx- INTROIKTCTION imately constant. In the utilization of photography in SYMBOLS research, unusual conditions are encountered that in some cases range from making exposures of about 0.01 second of objects having brightness levels of aperture value, f = 2AvI2 the order of 100 times brighter than a beach scene, to other unrelated situations. Generally brightness of object (subject) , candles/ft2 for these conditions a correct exposure for a given time and film is determined experimentally brightness value, b = 0.3515 X 2% and it is often required to transpose these set- tings to another one involving changes in film and transmittance factor, ratio of incident exposure time. It appeared that this transposi- light to transmitted light tion could be accomplished more rapidly and with less restriction on the variation of the variables transmittance value, = 2-'v involved if an additive system such as the expo- c sure value (or light value) system could be used. diameter of lens, or free aperture, ft This application of the exposure value sys- tem however required that the system be extended distance from flash to object (subject), ft to high brightness level, and expanded to include filter factors. Exposure values especially in distance value, D = tabular form (refs. 1 and 2) have been in steps of 1 or one stop, A minimum of four photographic exposure values (also EV) , factors are involved in the evaluation of an expo- E, =Av + Tv = B, -+ S, sure which when determined from tables of 1-stop interval could introduce noticeable error. It f/number, z/d was desirable therefore that the values be pro- vided in 25-percent steps or quarter stops to per- light flux output of source, lumens mit an acceptable solution to be obtained more readily. The initial study in 1960 produced flash value of photoflash bulb, numerical values in 0.25 increment of exposure for L = 32.5 x 2Fv each of the following photographic factors: f/number, exposure time, film speed, object guide number for flash, G = f X brightness, and filter factor. Since then the D L-4609 GV DERIVATIONS i image distance or lens to film distance, ft In the application of the exposure value cameras and exposure meters, an EV num- k a constant system to ber is determined by a combination of exposure 2 focal length of lens time and the f/number of the lens. A light value or exposure value is also deteTdced 5y a combica- lumen-second output of electronic flash tion of object brightness and film speed. For a Le successful exposure the two exposure values must be equal; therefore, the basic photometric rela- lumen-seconds output of photoflash bulbs LP tion between the four photographic factors is needed before the contribution of each factor to L, light value, interchangeable with E, in the exposure value can be determined and the sys- popular usage, also LVS tem expanded. The presentation of the derivations will in themselves indicate limitations on the NV the numerical value expressed in the addi- application of the system, as well as provide a tive or EV system that is derived from foundation for future expansion. any photographic factor, N, = 0 for t = 1 (Tv = 0), f = 1 (Av = 0), s = 3 (s, = 0), etc. Basic Photometric Relation 0 object distance from lens, ft An object or surface of uniform luminance b (candles/ft2) having an area P, is located on Pi area of image, sq ft and normal to the optical axis of a perfect lens of diameter d at a distance 0 from the lens PS area of object or subject, sq ft (with linear dimensions in feet). Q beam candle power seconds output of elec- The illuminance on the lens is tronic flash Qv electronic flash value, Q = 5 x 2Qv The luminous flux passing through the lens r reflectivity of object or subject (used as 17 - 7%) S film speed ASA rating, s = k Exposure An image of area Pi will be formed on the film, having an intensity of illumination of SV speed value of film (often denoted by the superscript O), s = 5.125 X 2% t exposure time, seconds From geometric optics the object and image T reciprocal of exposure time, l/t areas are related by Psi2 = Pi02 where i is the image to lens distance and is approximately TV exposure time value, T = 2Tv equal to the focal length of the lens. i = 1 but f = l/d then i = fd. W reflector factor The intensity of illumination in the image Illuminance with reflector - on the film is 21 lumens/ft2 Illuminance without reflector 4 f2 X filter factor If the illumination is incident upon the photographic film at the image plane for a time t XV filter value, x = 2Xv seconds, the film exposure is the product of the intensity of illumination and the duration of the Subscript: exposure. xbt o numerical value of a photometric factor Exposure = - foot candle seconds. for which Nv = 0 or for which its con- 4f2 tribution to the exposure value is zero .I The ASA (American Standards Association) Tofo2 = 0.9lbOso = 1 ppeed rating of the film s by definition is inversely proportional to the exposure or The values for Nv = 0 (also & = 0) are To = 1, fo = 1, bo = 0.35, SO = 3.l25 The corresponding values given in references 1 The graduations of the dials on exposure and 2 for exposure time and film speed are 1 sec- meters used for computing exposure, as well as the ond and ASA of 3 which are in agreement. The calibrations of the meters, are based on this derived value for bo from reference 2 is 0.3125. equation. When t is in seconds, s is the effective AFA speed rating and b is in Since Tof$ = 1 and Tf2 = & then canbles/ft2 the value of the constant, kl is 2 x f2 = Sv. Now E, can be resolved into the about 1.05 with variations in practice mging To fo from 1.0 to 1.1. The differences however do not individual components that correspond to the sep- constitute any significant effect upon exposure. arate photometric factors as A value of about 1.1will be used herein in order to retain compatibility with the tables of ref- erences 1 and 2 on incident light and have a T/To = and f2/fo2 = reflectivity approximately that of the standard 2Tv $V gray card (about 188). The basic photometric equation is Similarly or (1) b/bo = 2h and ./So = fi The effective ASA rating depends upon reci- b/bo X ./so = T/To X f2/fo2 = 2% X fi procity and in some applications can be affected by differences between the spectral response of the film and the spectrum of the luminance of the hence object. The Exposure Value or Light-Value System These permit the EV system to be extended in range and to be evaluated in smaller steps than General Photograp& are usually available. The system is designated in various ways on Sometimes it is desirable to include filter exposure meters and on cameras as EV, LVS, EV-LVS, factor x, and the transmittance of other elements Light-Value. An EX number for a camera is fixed in the optical path c. The basic equation by any combination of exposure time t and becomes f/number for which Tf2 = constant. On exposure meters for a @veri film speed the brightness also ICl’f2x = bsc defines a value which is sometimes called the light value. The numerical value depends on the for product of brightness and film speed (b x s). The “value system” will be referred to herein as Nv=O xo=l co = 1.0 or percent/lW the EX system for simplicity, and a particular exposure value or light value will be denoted as x/xo = 2xv c/co = 24, E,. and An analysis of the Ev system shows that E, = Av + Tv iX, = B, iSv - C, (4) Tf2 = 2E” Photoflash Photography SO that Tf2 = 1 for E, = 0. Consider a light source of F lumens illu- minating an object at a distance of D feet Datum or base values were determined for T, The intensity of the source is F/4n candles.
Load more

Recommended publications
  • Appendix A: Symbols and Prefixes
    Appendix A: Symbols and Prefixes (Appendix A last revised November 2020) This appendix of the Author's Kit provides recommendations on prefixes, unit symbols and abbreviations, and factors for conversion into units of the International System. Prefixes Recommended prefixes indicating decimal multiples or submultiples of units and their symbols are as follows: Multiple Prefix Abbreviation 1024 yotta Y 1021 zetta Z 1018 exa E 1015 peta P 1012 tera T 109 giga G 106 mega M 103 kilo k 102 hecto h 10 deka da 10-1 deci d 10-2 centi c 10-3 milli m 10-6 micro μ 10-9 nano n 10-12 pico p 10-15 femto f 10-18 atto a 10-21 zepto z 10-24 yocto y Avoid using compound prefixes, such as micromicro for pico and kilomega for giga. The abbreviation of a prefix is considered to be combined with the abbreviation/symbol to which it is directly attached, forming with it a new unit symbol, which can be raised to a positive or negative power and which can be combined with other unit abbreviations/symbols to form abbreviations/symbols for compound units. For example: 1 cm3 = (10-2 m)3 = 10-6 m3 1 μs-1 = (10-6 s)-1 = 106 s-1 1 mm2/s = (10-3 m)2/s = 10-6 m2/s Abbreviations and Symbols Whenever possible, avoid using abbreviations and symbols in paragraph text; however, when it is deemed necessary to use such, define all but the most common at first use. The following is a recommended list of abbreviations/symbols for some important units.
    [Show full text]
  • Paper Code and Title: H01RS Residential Space Designing Module Code and Name: H01RS19 Light – Measurement, Related Terms and Units Name of the Content Writer: Dr
    Paper Code and Title: H01RS Residential Space Designing Module Code and Name: H01RS19 Light – measurement, related terms and units Name of the Content Writer: Dr. S. Visalakshi Rajeswari LIGHT – MEASUREMENT, RELATED TERMS AND UNITS Introduction Light is that part of the electromagnetic spectrum which will stimulate a response in the receptors of the eye. Its frequency usually expressed as wavelength determines the colour of light and its amplitude determines its intensity. Accommodation from the individual’s part enables focusing of vision. Hence the need to study lighting in interiors. Especially when activities are carried out indoors it is necessary to provide some sort of artificial illumination. In such circumstances, the designer should be aware of what (lighting) is provided and the satisfaction the ‘user’ derives out of it. 1. The radiant energy spectrum Vs visible spectrum Light is visually evaluated radiant energy (electromagnetic), which moves at a constant speed in vacuum. The entire radiant energy spectrum consists of waves of radiant energy that vary in wavelength of a wide range; an array of all rays - cosmic, gamma, UV, infra red, radar, x rays, the visible spectrum, FM, TV- and radio broadcast waves and power transmission. The portion of the radiant energy which is seen as light, identified as the spectrum visible to the human eye ranges from about 380 (400) to 780 (700) mµ (referred to as nanometers or millimicrons). A nanometer (nm) is a unit of wavelength equal to 10 -9 m. Light can thus be thought of as the aspect of radiant energy that is visible. Colour perception is attributed to the varying wavelengths noticeable within the spectrum of visible light.
    [Show full text]
  • Radiometric and Photometric Measurements with TAOS Photosensors Contributed by Todd Bishop March 12, 2007 Valid
    TAOS Inc. is now ams AG The technical content of this TAOS application note is still valid. Contact information: Headquarters: ams AG Tobelbaderstrasse 30 8141 Unterpremstaetten, Austria Tel: +43 (0) 3136 500 0 e-Mail: [email protected] Please visit our website at www.ams.com NUMBER 21 INTELLIGENT OPTO SENSOR DESIGNER’S NOTEBOOK Radiometric and Photometric Measurements with TAOS PhotoSensors contributed by Todd Bishop March 12, 2007 valid ABSTRACT Light Sensing applications use two measurement systems; Radiometric and Photometric. Radiometric measurements deal with light as a power level, while Photometric measurements deal with light as it is interpreted by the human eye. Both systems of measurement have units that are parallel to each other, but are useful for different applications. This paper will discuss the differencesstill and how they can be measured. AG RADIOMETRIC QUANTITIES Radiometry is the measurement of electromagnetic energy in the range of wavelengths between ~10nm and ~1mm. These regions are commonly called the ultraviolet, the visible and the infrared. Radiometry deals with light (radiant energy) in terms of optical power. Key quantities from a light detection point of view are radiant energy, radiant flux and irradiance. SI Radiometryams Units Quantity Symbol SI unit Abbr. Notes Radiant energy Q joule contentJ energy radiant energy per Radiant flux Φ watt W unit time watt per power incident on a Irradiance E square meter W·m−2 surface Energy is an SI derived unit measured in joules (J). The recommended symbol for energy is Q. Power (radiant flux) is another SI derived unit. It is the derivative of energy with respect to time, dQ/dt, and the unit is the watt (W).
    [Show full text]
  • Radiometry and Photometry
    Radiometry and Photometry Wei-Chih Wang Department of Power Mechanical Engineering National TsingHua University W. Wang Materials Covered • Radiometry - Radiant Flux - Radiant Intensity - Irradiance - Radiance • Photometry - luminous Flux - luminous Intensity - Illuminance - luminance Conversion from radiometric and photometric W. Wang Radiometry Radiometry is the detection and measurement of light waves in the optical portion of the electromagnetic spectrum which is further divided into ultraviolet, visible, and infrared light. Example of a typical radiometer 3 W. Wang Photometry All light measurement is considered radiometry with photometry being a special subset of radiometry weighted for a typical human eye response. Example of a typical photometer 4 W. Wang Human Eyes Figure shows a schematic illustration of the human eye (Encyclopedia Britannica, 1994). The inside of the eyeball is clad by the retina, which is the light-sensitive part of the eye. The illustration also shows the fovea, a cone-rich central region of the retina which affords the high acuteness of central vision. Figure also shows the cell structure of the retina including the light-sensitive rod cells and cone cells. Also shown are the ganglion cells and nerve fibers that transmit the visual information to the brain. Rod cells are more abundant and more light sensitive than cone cells. Rods are 5 sensitive over the entire visible spectrum. W. Wang There are three types of cone cells, namely cone cells sensitive in the red, green, and blue spectral range. The approximate spectral sensitivity functions of the rods and three types or cones are shown in the figure above 6 W. Wang Eye sensitivity function The conversion between radiometric and photometric units is provided by the luminous efficiency function or eye sensitivity function, V(λ).
    [Show full text]
  • The International System of Units (SI) - Conversion Factors For
    NIST Special Publication 1038 The International System of Units (SI) – Conversion Factors for General Use Kenneth Butcher Linda Crown Elizabeth J. Gentry Weights and Measures Division Technology Services NIST Special Publication 1038 The International System of Units (SI) - Conversion Factors for General Use Editors: Kenneth S. Butcher Linda D. Crown Elizabeth J. Gentry Weights and Measures Division Carol Hockert, Chief Weights and Measures Division Technology Services National Institute of Standards and Technology May 2006 U.S. Department of Commerce Carlo M. Gutierrez, Secretary Technology Administration Robert Cresanti, Under Secretary of Commerce for Technology National Institute of Standards and Technology William Jeffrey, Director Certain commercial entities, equipment, or materials may be identified in this document in order to describe an experimental procedure or concept adequately. Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the entities, materials, or equipment are necessarily the best available for the purpose. National Institute of Standards and Technology Special Publications 1038 Natl. Inst. Stand. Technol. Spec. Pub. 1038, 24 pages (May 2006) Available through NIST Weights and Measures Division STOP 2600 Gaithersburg, MD 20899-2600 Phone: (301) 975-4004 — Fax: (301) 926-0647 Internet: www.nist.gov/owm or www.nist.gov/metric TABLE OF CONTENTS FOREWORD.................................................................................................................................................................v
    [Show full text]
  • Lens Tutorial Is from C
    �is version of David Jacobson’s classic lens tutorial is from c. 1998. I’ve typeset the math and fixed a few spelling and grammatical errors; otherwise, it’s as it was in 1997. — Jeff Conrad 17 June 2017 Lens Tutorial by David Jacobson for photo.net. �is note gives a tutorial on lenses and gives some common lens formulas. I attempted to make it between an FAQ (just simple facts) and a textbook. I generally give the starting point of an idea, and then skip to the results, leaving out all the algebra. If any part of it is too detailed, just skip ahead to the result and go on. It is in 6 parts. �e first gives formulas relating object (subject) and image distances and magnification, the second discusses f-stops, the third discusses depth of field, the fourth part discusses diffraction, the fifth part discusses the Modulation Transfer Function, and the sixth illumination. �e sixth part is authored by John Bercovitz. Sometime in the future I will edit it to have all parts use consistent notation and format. �e theory is simplified to that for lenses with the same medium (e.g., air) front and rear: the theory for underwater or oil immersion lenses is a bit more complicated. Object distance, image distance, and magnification �roughout this article we use the word object to mean the thing of which an image is being made. It is loosely equivalent to the word “subject” as used by photographers. In lens formulas it is convenient to measure distances from a set of points called principal points.
    [Show full text]
  • EL Light Output Definition.Pdf
    GWENT GROUP ADVANCED MATERIAL SYSTEMS Luminance The candela per square metre (cd/m²) is the SI unit of luminance; nit is a non-SI name also used for this unit. It is often used to quote the brightness of computer displays, which typically have luminance’s of 50 to 300 nits (the sRGB spec for monitor’s targets 80 nits). Modern flat-panel (LCD and plasma) displays often exceed 300 cd/m² or 300 nits. The term is believed to come from the Latin "nitere" = to shine. Candela per square metre 1 Kilocandela per square metre 10-3 Candela per square centimetre 10-4 Candela per square foot 0,09 Foot-lambert 0,29 Lambert 3,14×10-4 Nit 1 Stilb 10-4 Luminance is a photometric measure of the density of luminous intensity in a given direction. It describes the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle. The SI unit for luminance is candela per square metre (cd/m2). The CGS unit of luminance is the stilb, which is equal to one candela per square centimetre or 10 kcd/m2 Illuminance The lux (symbol: lx) is the SI unit of illuminance and luminous emittance. It is used in photometry as a measure of the intensity of light, with wavelengths weighted according to the luminosity function, a standardized model of human brightness perception. In English, "lux" is used in both singular and plural. Microlux 1000000 Millilux 1000 Lux 1 Kilolux 10-3 Lumen per square metre 1 Lumen per square centimetre 10-4 Foot-candle 0,09 Phot 10-4 Nox 1000 In photometry, illuminance is the total luminous flux incident on a surface, per unit area.
    [Show full text]
  • I L L U M I N a T I O N
    I L L U M I N A T I O N A R ILLUMINATION Index LIGHT ..................................................................................... 3 Units ...................................................................................... 5 Laws of illumination ............................................................... 8 Lighting design ..................................................................... 13 TYPES OF LAMP ........................... Error! Bookmark not defined. Exterior Lighting .......................... Error! Bookmark not defined. Types .......................................... Error! Bookmark not defined. More examples ........................... Error! Bookmark not defined. 2 Career Avenues GATE Coaching by IITians LIGHT The basic light quantities and units encountered in radiology can be conveniently divided into two categories: those that express the amount of light emitted by a source and those that describe the amount of light falling on a surface, such as a piece of film. The relationships of several light quantities and units are shown below. Luminance Luminance is the light quantity generally referred to as brightness. It describes the amount of light being emitted from the surface of the light source. The basic unit of luminance (brightness) is the nit, which is equivalent to 1 candela per m2 of source area. The quantity for specifying an amount of light is the lumen. 3 Career Avenues GATE Coaching by IITians One lumen of light with wavelengths encountered in x-ray imaging systems (540 nm) is equivalent to 3.8 x 1015 photons per second. Another factor that determines luminance is the concentration of light in a given direction. This can be described in terms of a cone or solid angle that is measured in units of steradians (sr). If a light source produces an intensity of 1 cd/m2 of surface area, it has a luminance of 1 nit. Viewbox and other image display device brightness is measured in the units of nits.
    [Show full text]
  • Recommended Practice for the Use of Metric (SI) Units in Building Design and Construction NATIONAL BUREAU of STANDARDS
    <*** 0F ^ ££v "ri vt NBS TECHNICAL NOTE 938 / ^tTAU Of U.S. DEPARTMENT OF COMMERCE/ 1 National Bureau of Standards ^^MMHHMIB JJ Recommended Practice for the Use of Metric (SI) Units in Building Design and Construction NATIONAL BUREAU OF STANDARDS 1 The National Bureau of Standards was established by an act of Congress March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology and facilitate their effective application for public benefit. To this end, the Bureau conducts research and provides: (1) a basis for the Nation's physical measurement system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to pro- mote public safety. The Bureau consists of the Institute for Basic Standards, the Institute for Materials Research, the Institute for Applied Technology, the Institute for Computer Sciences and Technology, the Office for Information Programs, and the Office of Experimental Technology Incentives Program. THE ENSTITUTE FOR BASIC STANDARDS provides the central basis within the United States of a complete and consist- ent system of physical measurement; coordinates that system with measurement systems of other nations; and furnishes essen- tial services leading to accurate and uniform physical measurements throughout the Nation's scientific community, industry, and commerce. The Institute consists of the Office of Measurement Services, and the following center and divisions: Applied Mathematics — Electricity
    [Show full text]
  • Radiometry and Photometry
    Radiometry and Photometry Wei-Chih Wang Department of Power Mechanical Engineering National TsingHua University W.Wang 1 Week 11 • Course Website: http://courses.washington.edu/me557/sensors • Reading Materials: - Week 11 reading materials are from: http://courses.washington.edu/me557/readings/ • H3 # 3 assigned due next week (week 12) • Sign up to do Lab 2 next two weeks • Final Project proposal: Due Monday Week 13 • Set up a time to meet for final project Week 12 (11/27) • Oral Presentation on 12/23, Final report due 1/7 5PM. w.wang 2 Last Week • Light sources - Chemistry 101, orbital model-> energy gap model (light in quantum), spectrum in energy gap - Broad band light sources ( Orbital energy model, quantum theory, incandescent filament, gas discharge, LED) - LED (diode, diode equation, energy gap equation, threshold voltage, device efficiency, junction capacitance, emission pattern, RGB LED, OLED) - Narrow band light source (laser, Coherence, lasing principle, population inversion in different lasing medium- ion, molecular and atom gas laser, liquid, solid and semiconductor lasers, laser resonating cavity- monochromatic light, basic laser constitutive parameters) w.wang 3 This Week • Photodetectors - Photoemmissive Cells - Semiconductor Photoelectric Transducer (diode equation, energy gap equation, reviser bias voltage, quantum efficiency, responsivity, junction capacitance, detector angular response, temperature effect, different detector operating mode, noises in detectors, photoconductive, photovoltaic, photodiode, PIN, APD, PDA, PSD, CCD, CMOS detectors) - Thermal detectors (IR and THz detectors) w.wang 4 Materials Covered • Radiometry - Radiant Flux - Radiant Intensity - Irradiance - Radiance • Photometry - luminous Flux - luminous Intensity - Illuminance - luminance Conversion from radiometric and photometric W.Wang 5 Radiometry Radiometry is the detection and measurement of light waves in the optical portion of the electromagnetic spectrum which is further divided into ultraviolet, visible, and infrared light.
    [Show full text]
  • Philips Technical Review • DEALING ~TH TEC~CAL PROBLE~ RELATING to the PRODUCTS, PROCESSES and INVESTIGATIONS of the PIIILIPS INDUSTRIES
    VOL.12 No. 7, pp. 185-212 JANUARY 1951' Philips Technical Review • DEALING ~TH TEC~CAL PROBLE~ RELATING TO THE PRODUCTS, PROCESSES AND INVESTIGATIONS OF THE PIIILIPS INDUSTRIES EDITED BY THE RESEARCH LABORATORY OF N.V. PHILIPS' GLOEILAMPENFABRIEKEN. EINDHOVEN.NETH,ERLANDC; THE "PHOTOFLUX" SERIES OF FLASHBULBS by G. D. RIECK and L. H. VERBEEK. 771.448.4 It is known that right in the beginning of photography, about 100 years ago, photographs were already being taken with a flash of light. This is probably even the oldest form of artificial-light photography, since with the means of permanent artificiallight available in those days and the very poor sensitivity of the sensitive plates of that time, the exposures would certainly hove been unduly long. The flash was obtained by burning i.a. magnesium powder. Nowadaysflashlight technique has reached a very high degree of refinement, as will be shown in this article. Introduction It was about 20 years ago that the "Photoflux" with in this journal as far back as 19362). The and similar flashbulbs were introduced to replace principle has not heen altered much, nor is there the old flashlight produced by combustion of a much difference in the appearance of the present- mixture of magnesium powder and an oxidizer day lamp compared with that described at the in air. Their success was remarkable -, Only in one time. The properties of the lamp however have application, for "magnesium flash bombs " when been improved or changed in a great many respects, photographing from aircraft, is the "open" flash- so that it is deemed opportune to discuss these light still in use, but otherwise it was very soon "Photoflux" lamps anew; they are now being ousted by the "closed" flashlight.
    [Show full text]
  • How Many Photons Are There?
    IS&T's 2002 PICS Conference How Many Photons are There? Russ Palum Eastman Kodak Company Rochester, New York, USA Abstract If the ISO speed for an image is specified then the number of photons per unit area due to an 18% gray For many digital imaging systems, it is important to know (average scene luminance) can be determined. To determine or model the absolute illumination levels for a scene, light the signal-to-noise due to “photon shot noise” the number of source, etc. Often this information is used to select sensors, photons/pixel has to be determined. This can be calculated lenses, and light sources. Because the signal-to-noise ratio from the number of photons per meter2, which leads to the of an acquired image is ultimately controlled by the final question: how many photons are in a lux-second? A quantum nature of light, this exposure is best quantified in lux second is a (lumen second)/meter 2 a photometric unit terms of number of available quanta. Even if all the which somewhat complicates the calculation. A lumen is the electronic sources of noise have been reduced to photometric counterpart of the radiometric watt. The undetectable levels, the noise caused by “photon shot noise” number of photons in a lumen-second will vary depending or quantum noise will remain. on the spectral distribution of the light source. For sources This tutorial paper illustrates the calculation of the with a spectral distribution that can be described as a number of photons per unit area falling on a photographic blackbody radiator the number of photons per lumen-second sensor based on the ISO speed of the sensor.
    [Show full text]