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Home , Chromatic aberration, Field of view, Film base, Instant camera, Lens speed

GEMINI CRIMINOLOGY ONLINE REVIEW AND TRAINING CENTER P E N E T E E A P Dr. MANUEL V JAUDIAN, LLB. PhD ETEEAP DIRECTOR NOTES COMPILED AND EDITED BY: PROF. HERMOGENES MALAGAMBA POLICE

Photography is the production of visible images by using the action of on a sensitized material. The word photography was derived from two Greek terms PHOTO which means light and GRAPHY which means to write . Thus, literally, photography means to draw with light.

SPEED OF LIGHT

The speed of light, measured in a vacuum is 299, 792.5 km/sec (approximately 186,281 miles/sec / 186,000).

BEHAVIOR OF LIGHT

INTERFERENCE - Any phenomenon having a periodic disturbance of some sort and travels outward from a source is called a wave. To understand how energy can travels in waves, think of a wooden log floating in the ocean. Light maybe visualized as such as the high points are called crest while the low points are called troughs. The distance between two successive crest and troughs is called a .

DIFFRACTION – light in space and not within the gravitational field of any object travels in a straight line. The bending of light around an object gives rise to the phenomenon called diffraction. This phenomenon is responsible for the partial illumination of object parts not directly in the path of the light. THE LAW OF REFLECTION – refers to the rebounding or deflection of light. The angle of reflection depends upon the angle of the light striking the material, which is referred to as the angle of incidence.

THE LAW OF REFRACTION – when the material in the path of the light is transparent a change in the direction of the light occurs.

THE ELECTROMAGNETIC

By using a prism made of or plastic, it is possible to see the that made up the sunlight. The colors separated in this way are called a spectrum. Another way to see the spectrum of sunlight is to look at a rainbow. The light is bend as observed, and because some of bend more than others, the colors are separated. The violet rays are bent the most, and the red rays least.

SOURCES OF LIGHT

NATURAL LIGHT

The source of all daylight is the sun. The combination of and contrast ascertains the quality of the daylight. The lighting contrast depends upon the sunlight available in the daylight, when clouds do not cover the sun.

Color of the daylight will also affect the appearance of the objects being photographed specially in . Some of the factors affecting the color of the daylight:

a) atmospheric vapor b) atmospheric dust c) reflected light reached the objects and directly coming from the source.

Daylight maybe classified according to its intensity. They are: a) Bright sunlight b) Hazy sunlight c) Dull sunlight.

These classifications are modified by the manufacturers like a) Open bright sunlight b) Under shade bright sunlight c) Hazy sunlight d) Cloudy bright sunlight e) Cloudy dull sunlight.

ARTIFICIAL LIGHT

Almost all artificial light sources can be used in photographing of objects, as long as the light is capable of exposing the sensitized materials (film). Some of the artificial are electronic , photoflood lamp, fluorescent lamp, and Infrared and Ultra-Violet lamp.

COLORS OF LIGHT FOUND IN VISIBLE SPECTRUM

Visible Spectrum - a small part of the where the visible light is found, the portion of the electromagnetic spectrum that affect the human sense of sight. Visible light includes all those radiation having a wavelength ranging from 400 – 700 mu.

COLOR

Primary Colors Approximate Wavelength

A. Red (longest wavelength) 700 mu B. Blue 450 mu C. Green 550 mu

Complementary Colors

A. Magenta (shortest wavelength) 400 B. Cyan 500 C. Yellow 590

Neutral Color

A. Gray B. White C. Black

COLOR MIXING

1. Color Addition R+B+G = W R+B= M M+Y= R R+G= Y Y+C= B B+G= C Y+C= G

2. Color Subtraction W-R= C W-C=R C-G=B W-B=Y W-Y=B Y-G=R W-G=M W-M=G Y-R=G

PRIMARY AND SECONDARY COLORS

The three primary colors in light are red, green and blue. White light can be made by mixing red, blue and green. The process of making colors by mixing primary colors of light is called addition, because one color is added to another.

OPTICS

Optics is the study of light. It is concerned with the nature of light and the way it behaves in optical instruments.

ATTRIBUTE OF COLORS

Radiant energy within a limited frequency range has the property of stimulating the retina of the to create color sensation, which the brain interprets. Radiant energy, which has this property, is called light, the physical stimulus of vision.

Color can be defined in qualitative terms according to certain psychological attributes. These attributes are hue, brightness and saturation. Hue is the attributes of chromatic colors, which distinguishes them from achromatic colors.

MEDIUM OF LIGHT

TRANSPARENT OBJECTS – mediums that merely slow down the speed of light but allow to pass freely in other respects, transmit 90% or more of the incident light.

TRANSLUCENT OBJECTS – mediums that allow light to pass through it in such a way that the outline of the source of light is not clearly visible, transmit 50% or less of the incident light.

OPAQUE OBJECTS – A medium that divert or absorb light, but does not allow lights to pass though, they absorb most of the light while reflecting some of it.

THE RAT LAW

When incident light hits a medium, three things might happen, the light maybe:

A. Reflected B. Absorbed C. Transmitted

MECHANICAL DEVICE ()

The principle of photography are derived from science and the images on the film or paper made by the rays or light through the camera are dependent on the same general laws which produces images upon the retina through the which produce images upon the retina through the lens of the eye.

A camera basically is nothing more than a light tight box with pinholes or lens, a at one end and a holder of the sensitized material at one end. While there is various kind of camera from the simplest in construction (the box type) to the most complicated, all operate in the same principle. The of the sensitized material to light is controlled by the lens and its and the shutter through its speed in opening and closing the lens to light.

CAMERA TYPES

THE - The simplest camera is a pinhole camera, which consists of a box with a small hole in one of its sides. To produce a sharp image, the hole must be very small and this restricts the amount of light entering the camera. Quite a long time may be necessary to let enough light through to affect the film and this causes problems because if the subject moves the picture will be blurred. It is impossible to anything like a moving car or a galloping horse with a pinhole camera.

CAMERA OBSCURA - Is a box used for sketching large objects? The term means dark chamber. The box contains a set at 45-degree angle. Mounted in the front end of the box is a double convex lens like that in a photographic camera. Light from the object or scene is transmitted through the lens. The mirror reflects this light upward to ground glass screen on the top of the box. There the light forms an image of the object or scene that can be sketched easily.

FIXED CAMERA - The most basic of all camera, have a non-adjustable lens. Most models have a single diaphragm setting and only one or two shutter speeds. Most fixed focus , including many inexpensive, pocket-sized models, use 110 or 126 size film. The of such film require considerable enlargement, which may produce a fuzzy image. In general, a fixed focus camera can take satisfactory in ordinary daylight but not in dim light, because its lens does not admit much light. The camera may produce a blurred picture is moving or less than two meters away. Many fix-focused cameras can take flash pictures.

Disposable cameras are a kind of fixed - focus camera that combine a plastic lens, a shutter, a film in one small box. The entire camera is taken to the photo laboratory when the roll of film has been exposed.

POINT AND SHOOT CAMERA - Have many automatic features that make them easy to use. Electronic devices inside the cameras automatically adjust the focus, set the light exposure and the and advance and rewind the film. A built in electronic flash automatically supplies light when too little light reflects from the subject. The cameras are equipped with high quality that produce a sharp image. Some of them have a . Point and Shoot cameras use that measure 35 mm. Since their introduction in 1970’s theses cameras have gained wide popularity among amateur’s photographers.

SINGLE LENS REFLEX CAMERAS - Appealed to skilled amateur photographers and to professional photographers. The camera’s name refers to its viewing system. The photographer views the subject through the rather than through a separate viewing lens. A mirror between the lens and the film reflects the image onto a viewing screen. When the shutter release button is pressed to take a picture, the mirror lifts out of the way to allow the light to expose the film. Thus the photographer sees almost the exact image that is recorded on the film. SLR cameras use 35 mm film. The photographer can adjust the focus, select the shutter speed, and control the opening of the diaphragm. Many new models can also adjust the focus and control the light exposure automatically.

TWIN LENS REFLEX CAMERAS - Have a viewing lens directly above the picture - taking lens. The image in the viewfinder appears on a flat screen on top of the camera. Photographer found such a viewing screen helpful in composing a picture.

VIEW CAMERAS - View cameras are generally larger and heavier than medium- and small-format cameras and are most often used for studio, landscape, and architectural photography. These cameras use large-format films that produce either negatives or transparencies with far greater detail and sharpness than smaller format film. View cameras have a metal or wooden base with a geared track on which two metal standards ride, one at the front and one at the back, connected by a bellows.

It is the largest and most adjustable type of camera.

INSTANT CAMERAS - Use film that provides a print without first being developed into a negative. The cameras produce a print 15 seconds to 2 minutes after the photographer takes a picture. The time varies according to the camera and to the type of film. use film that provides pictures ranging in size from 73 by 94 mm to 508 by 610 mm. Special types of film for instant camera also provide negatives. Some instant cameras can take flash pictures and focus automatically as the photographer lines up a subject in the viewfinder.

ELECTRONIC CAMERA - Create pictures that can be viewed on a television screen. The lens in most electronic cameras focuses light on light sensitive mechanism called CHARGED COUPLED DEVICE OR CCD. The CCD changes the light into electronic signals. The electronic pictures can then be stored on small magnetic discs similar to those I=used in computers. With additional equipment, electronic images can also be sent over telephone lines or printed on paper.

FILM CAMERAS - Takes pictures that re-create the motion of a subject when they are viewed. Professional filmmakers generally use large cameras that take 35 or . Most amateur’s records on 8 mm film called super 8. Today, many amateur filmmakers use portable video cameras called CAMCORDERS. These cameras convert light reflected by the subject into electronic signals that are recorded on magnetic tape. Most film cameras and camcorders can record sound at the same as they record images. Most of them also have a zoom lens.

THE CAMERA AND ACCESSORIES

LENS – The lens of a camera consist of one or more glass or plastic disk with flat, concave, or convex surfaces, each disk is called element. The purpose of the lens is to focus light on the film. The of the lens is the distance between the optical center and the film. SHUTTER – The shutters on most cameras can be adjusted to different shutter speeds. The shutter speed means the length of time the shutter is open. This might be several seconds ( or even hours if you are photographing a night sky ) or one thousandth of a second or even less with special cameras. Most cameras have a shutter speed dial showing speeds from one second to, for example, one thousand of a second.

DIAPHRAGM – The diaphragm changes the size of the aperture of the lens. Like a shutter with valuable speed, a diaphragm regulates the amount of light reaching the film. The diaphragm also affects – the smaller the aperture the greater the depth of field.

The diaphragm controls the size of the aperture in the same way as the iris of the eye, if you look at a cat’s eye when it comes in out of the darkness you will that the irises have contracted to make the pupils bigger. After a few moments in a bright light the irises expand and cause the pupils to become much smaller. The aperture of the camera must also be larger in dim light and smaller in bright light. The diaphragm is usually a ring of overlapping metal leaves, which can be adjusted. The control settings for the diaphragm are referred to as f – stops and going from one f – stop to the next reduces the amount of light by one half. The common setting are f /2.8, f/4, f/5.6, f/8, f/11, f/16 and f/22. VIEWING AND FOCUSING DEVICES – The viewfinder shows the photographer the scene being photographed. It maybe a viewing screen, a miniature lens system, or a sample wire frames.

LENS APERTURE – Adjustable cameras are equipped with an iris diaphragm, a device located in or near the lens and consisting of thin overlapping leaves that fold together to create a hole of continuously variable size. In this way the aperture or lens opening, can be adjusted to admit more or less light as required. The diaphragm is usually marked with a series of settings called STOPS, which are designated by F- NUMBERS, such as f/5.6 or f/5.8. The f/ number expresses the ratio of focal length to aperture. The larger the number, the smaller the aperture.

DEPTH OF FIELD - The lens aperture not only controls the amount of light entering the camera, it also affects another fundamental aspect of the photograph – depth of field. Depth of field is the range in front of and behind a sharply focused subject in which details also look sharp in the final photographic image. It depends on lens aperture, the focused distance, and the focal length of the lens. A small lens aperture, great camera to subject distance, and focal length result in greater depth of field.

SHUTTER SPEED AND MOTION – Shutter speed determines how effectively a moving object can be stopped, that is, how sharply it can be reproduced without blurring, or streaking in the final image. With a fast shutter speed, the shutter is opened only briefly and the moving object has little time to change its position before exposure is completed. With a slow shutter speed, on the other hand, the shutter remains open for a relatively long time. Thus, the faster the shutter speed, the sharper the moving object will appear on the final image, and the slower the shutter speed, the more blurred object will appear.

FILM TRANSPORT MECHANISM – Moves new, unexposed film into position for the next picture.

FILM ADVANCER – Necessary so that the exposed film can be transferred to the take up spool while the unexposed film remain on the opposite side of the lens for another exposure.

FILM ADVANCE LEVER FILM REWIND CRANK FILM REWIND KNOB FILM TAKE-UP SPOOL

SHUTTER SPEED DIAL – Controls the opening and closing of the shutter, regulates the quantity of light that reaches and affects the sensitized material, a dial which sets the length of time in which the light is allowed to enter the camera.

SHUTTER RELEASE BUTTON – The “click” of the camera that releases the shutter

FOCUSING MECHANISM – The mechanism that estimates the appropriate objects distance from the camera to form a sharp or clear image on the photograph.

FOCUSING RING – The outer ring of the lens which is rotated or adjusted to obtain a clear and sharp photograph and it enables the photographer to adjust focal range.

F-STOP RING F-NUMBERS ASA DIAL/SHUTTER SPEED DIAL FLASH UNIT FLASH TERMINAL FLASH ACCESSORY SHOE TIMER/SELF-TIMER CABLE RELEASE

CAMERA LENSES The lens , which must be focus at the object at the time of picture taking, is one of the most important parts of any camera. The function of the lens is to focus the light coming from the subject. It operates more or less in the same way as the lens of the eye. It is chiefly responsible for the sharpness of the image formed through which light passes during the exposure of the sensitized materials inside the camera.

Artificial lenses are made of various transparent materials such as glass, plastics or crystals. Quartz crystals are used to refract ultra violet light, which a very short wavelength.

Interchangeable lenses allow a photographer to capture a variety of pictures that would otherwise be difficult or impossible to obtain with a single camera. For instance, a zoom lens may be used to photograph individual drops of dew on a spider’s web.

MAGE FORMATION

The focal length of a single lens is the distance from the lens to the point at which incoming parallel rays focus. Light converged in the manner can produce a real images, that is, an image that can actually be projected onto screen. In a negative lens, rays do not actually come to a real focus but appear to originate from a point called the virtual focus.

1. CONVEX LENS – DIVERGING LENS

A convex lens causes light rays to converge, or come together, and is called a positive lens. A positive lens focuses light form a distant source into visible image that appears on then opposite side of the lens to the object.

1. SIMPLE CONVEX – convexo – convex

2. SPECIAL CONVEX – special positive lens a. – Plano – convex b. – convexo – concave

2. CONCAVE LENS – DIVERGING LENS

Concave lens or negative lens spreads the light depends on the amount of curved on the faces of the lens. The distance between the lens and the image it produces is called the FOCAL LENGTH. The shorter the focal length, the smaller the image. The greater the curvature of the faces of the lens, the shorter its focal length will be. Lens that posses at least one surface that curves inward. It is a diverging lens, spreading out those light rays that have been refracted to it. Concave lens is thicker at the edges than they are at the center. Light rays passing through a diverging lens are bent outward. Diverging lens form only virtual image.

1. SIMPLE CONCAVE – concavo – concave - Biconcave lens (with both surfaces curved inward) 2. SPECIAL CONCAVE – special negative lens a. Plano - concave – lens with one flat surface and one concave. b. Concavo – convex

3. A concave lens is curved inward; it is shaped like two dishes placed back-to-back. Light passing through a concave lens bends outward, or diverges. Unlike convex lenses, which produce real images, concave lenses produce only virtual images. A virtual image is one from which light rays only appear to come.

COMPOUND LENSES

Simple lenses generally produce aberrated (imperfect) images. This imperfection in image formation can be reduced using compound lenses.

TYPES OF LENSES BASED ON LENS SPEED

Lens speed refers to the largest opening of the diaphragm that the light can pass through it determines the maximum intensity of the light entering the light tight box.

A. FAST LENS – Lens with high lens speed, a high lens speed is used during nighttime or in dark room. B. SLOW LENS – lens with low lens speed, used during daytime or where the room is very bright.

Focus : the means by which the object distance is estimated or calculated to form sharp images. It also refers to the point at which light rays converge. It is the point where a set of lights rays converges after passing through a lens or other optical arrangement. It also refers to the point from which rays appear to diverge, the place where the visual image is clearly formed, as in the eye or a camera. The point of principal focus is called focal point.

Focusing is the process of changing the distance between the centers of the lens to the focal plane. It is the technique of adjusting the focal length to get the sharp image of the object or scene to be photographed.

Infinity refers to the distance so far removed from the observer that the rays of light reflected to a lens from a point at the distance maybe regarded as parallel. It is a distance setting on a camera focusing scale, beyond which all objects are in focus.

REAL FOCUS – the point of convergence of the light rays. VIRTUAL FOCUS - the point where diverging rays would meet if their direction were reversed. In terms of focus, there are two types of lenses sold today:

1. AUTO FOCUS – are the predominant types to the market. AFLSR’s focus using a phase detection system that slits the incoming light into two or more parts and compares them to determine the amount of DEFOCUS. AF is not perfect, but the technology has greatly improved since the first AF lenses made their appearance. As it is, sometimes this phase detection system can have difficulty with dim lighting and fast – moving objects, but they are more accurate than the infrared systems found on point and shot cameras. 2. MANUAL – FOCUS LENSES – YOU SIMPLY TURN THE FOCUSING RING BY HAND UNTIL THE SUBJECT IS SHARP IN THE VIEW FINDER. Although AF lenses dominate the market today, nearly all interchangeable AF Lenses allow the user to over ride the AF mode with the manual focus option. These lenses usually have a switch on the barrel, so that you can choose one or the other to suit the shooting circumstances.

WHY DO LENSES VARY TO EACH OTHER?

The most important way lenses differ is in their FOCAL LENGTH.

FOCAL LENGTH – the distance between the lens and the film plane when the lens is focused on infinity. Focal length controls (the size of the image formed by the lens). A lens is also described in terms of its view angle, the mount of the image shown on the film.

GROUP OF LENSES ACCORDING TO THE

1. – A lens with a focal length equal to the diagonal measure the image area. The image area of 35 mm camera is 24x36 mm, thus a normal lens for any 35 mm SLR is 50 mm international standards, 50 mm lens may have an actual focal length of 48 – 52 mm, and the normal lens has a picture angle of 5 degrees that correspond to the viewing angle of the .

CHARACTERISTICS: Optimum area coverage than any lens type. Minimum and fewer common lens defects. Angle of view equal to 75 degrees but not less than 45 degrees.

2. Wide Angle Lens – The wide-angle lens has a shorter focal length than the normal lens. As a result, it covers a picture angle of 60 – 90 degrees. It enables photographing a widely extended scene from a close proximity or within a confined area. The range for wide angles for 35 mm SLR cameras includes 8mm, 24mm, 28 mm, and 35 mm. The 28 mm and 35 mm are the most important for general wide angle for police work.

CHARACTERISTICS: Reduced scale but increases area coverage compared with any lens at the same distance. Increased deep perception at a given scale. Increased distortion toward the edges of the negative material. Reducing illumination from the center toward the edges of the negative material. Angle of view exceeds 75 degrees.

3. – as telephoto lens, or long focus lens has a longer focal length and provides a close up image of a distant object. In contrast to the wide-angle lens, the telephoto lens covers a small field of view and a shallower depth of field. Because of shallow depth of field, there will be lack of sharpness of the subject focus areas in the photograph to be produced. Another characteristics of the telephoto lens is production of flat composition, far objects appear enlarged while near objects do not appear proportionally large.

4. Super wide Angle Lenses – In this category are fish eye lenses with a 180 degrees angle of view. Focal lengths run from an amazing 6 mm to about 18mm. F stop ranges begin at F 1.8 but average f 3.5 and f 4.

Macro Lenses – The word macro is derived from the Greek word and means, “ to enlarge “. In photographic terms, a macro lens is designed with extended focusing capabilities to shoot a few inches from a subject. A lens used for close up photography particularly in taking pictures in minute objects.

Two Main Types of MACRO LENS:

- One is meant to be used on a held tripod mounted camera and ranges from 40 mm to about 90 mm with the average about 25 mm. - The other type is either a wide angle or a lens with a focal length with 100 mm or more and is designed with a close up bellows attachment to the camera. The longer lenses give a larger image and are most suitable for static subjects and painstaking photography.

5. Zoom Lenses – The macro zoom is relatively new in both long and short-range classes. By turning a ring on the lens barrel, you are able to focus as close as three four inches and still use zoom capability. Such lens gives you close – ups as well as variable focal lengths. and the macro zoom is taking this field. A final zoom category is the variable- focal length lens that operates in the same manner as the zoom.

6. Special Purpose Lenses – Two special- purpose lenses in particular should be familiar to you. The first is adjustable through movement of the front portion up and down for perspective control (PC). Architectural photographers benefit using a PC lens that offers some control of perspective similar to the using the tilting front and back of a .

7. Add – On Teleconverter Lenses – Add-on lenses. Principal among add- on lenses is the fishnet lens that is screwed into the front of a normal 35 mm camera lens, offering a super wide effect for less cost than a separate .

LENS DEFECTS

ABERRATION in optics , is the failure of light rays to focus properly after they pass through a lens or reflect from a mirror. Proper focus occurs when the light rays cross one another at a single point. ABERRATION occurs because of minute variations in lenses and , and because different parts of the light spectrum are reflected or refracted by varying amounts.

ABERRATION also defined as an optical imperfection responsible for image distortion. It can be avoided by combining several lenses and by elimination of marginal rays refracted through the outer edges of the lens. Lenses or mirrors that are sections of spheres produce spherical aberrations.

There are six ( 6 ) types of optical aberrations:

1. 2. Chromatic Aberrations 3. Astigmatism 4. 5. Curvature of Field 6. Distortion

SPHERICAL ABERRATION

Aberration predicts that rays of light emanating from a point are imaged by spherical optical elements as a small blur. The outer parts of a spherical surface have a focal length different from that of the central area, and this defect causes a point to be imaged as a small circle. The difference in focal length for the various parts of the spherical section is called spherical aberration

Spherical Aberration is found in all lenses bounded by spherical aberration / surfaces. The marginal portions of the lens bring rays of light to shorter focus than the central region. The image of a point in space is therefore not a point, but a blur circle. Spherical aberration is the focusing at the different parts of spherical lens. This aberration occurs because light hitting the outer parts of the lens is bent more sharply and comes to a focus sooner than that passing through the middle. In spherical aberration, the image is blurred because different parts of a spherical lens or mirror have different focal lengths.

CHROMATIC ABERRATION

All lenses (single) made of one material refract rays of short wavelength more strongly than those of longer wavelenght and so brings blue more to a shorter focus than red. The result is that the image of a point white light is not a white point, but a blur circle bordered with colors.

Chromatic aberration is the failure of different colored light rays to focus after passing through a lens, focusing of light of different colors at different points resulting in a blurred image. When white light, which consists of colors, passes through a lens, the lens bends the rays. The rays then cross one another on the other side. The violet rays bend more than the other colors and focus close to the lens. The red rays bend the least and focus farther from the lens. Rays on the other colors focus at points between these two points. In chromatic aberration the image is surrounded by colored fringes, because light at different colors is brought to different focal points by a lens.

ASTIGMATISM

Astigmatism is the defect in which the light coming from an off-axis object point is spread along the direction of the optic axis. If the object is a vertical line, the cross section of the refracted beam at successively greater distances from the lens is an ellipse that collapses first into a horizontal line, spreads out again, and later becomes a vertical line

Astigmatism is the failure of a lens to produce a point image of an object point. Such condition occurs when the lens surfaces are not symmetrical with respect to the principal axis of the lens. An extreme example would be one surface is spherical and the other is cylindrical, or when the lens surfaces are perfectly spherical but the beam of light from the object point passes through the lens very obliquely.

COMA

The result of differences in lateral magnification for rays coming from an object point not on the optic axis is an effect called coma . If coma is present, light from a point is spread out into a family of circles that fit into a cone, and in a plane perpendicular to the optic axis the image pattern is comet-shaped. Coma may be eliminated for a single object-image point pair, but not for all such points, by a suitable choice of surfaces.

CURVATURE OF FIELD

A curved, concave, or saucer – shaped image of an object which has a flat surface produced by .

In curvature aberration the relation of the images of the different points are incorrect with respect to one another. In curvature, the images of the different points of the plane image lie on a curved surface, with points at the edge of the field lying nearer to the lens than those at the center. In curvature, the images distance is different for different points of the same object due to their differing distance from the axis.

The fuzziness increases toward the edge of the film. Refocusing brings different circle into focus but others now are blurred.

DISTORTION

Distortion arises from a variation of magnification with axial distance and is not caused by a lack of sharpness in the image.

When there exists a different magnification for rays at different angles distortion exists. Any straight light extending across the field is considered curved and for different lenses the curvature maybe from or toward the center. The distortion is called barrel distortion (in the first case). It is the common type of curvilinear defect. The second distortion is the pincushion defect.

For correction two similar lenses, each of half necessary power are placed a short distance apart, with a diaphragm between. Such a lens is called RECTILINEAR LENS.

OTHER OPTICAL DEFECTS

These defects are usually corrected when the lens is designed; however, they can occur if the lens is misused or through normal wear.

FLARE or OPTICAL FLARE

In a result of double reflection from inner lens surfaces. It exhibits itself as a misty haze, or a cloudy semicircular patch of light, which may cover part or the entire image. This doubly reflection may form an image called a ghost image.

MECHANICAL FLARE

Are bright spots on the film caused by stray light from worn shiny parts of the lens such as the stop, shutter , or from the camera itself.

LIGHT LOSS

Most corrected lenses is coated with a substance which will reduce one type of flare ( optical ) and which will also increase the optics ability to transmit light thus reducing light loss.

STRAY LIGHT

Can be reduced or eliminated by using the proper lens shade placed on the front of the lens as shield.

FOCAL LENGTH

What is focal length?

It is usual to think of the focal length of the lens as the distance from the lens center or the position of the image it forms of a distant object. It is important to know that it is the focal length that determines how large an image is formed by the lens. All lenses of the same focal at the same distance produce the same of size; whether they are called wide angle, or by any other names.

The focal length of a lens can be define as the distance from the optical center of the lens to its focal plane, when the lens is focused upon an object at infinity in practical terms, means focused on a subject a great distance away ( 200 ft. or more ) the light rays reflected by that the subject will be traveling on parallel paths, for all practical purposes, when they reach the film. The photographer seldom or need not measure the focal length of a lens, for this characteristic is almost always marked on the front of the lens mount.

LENS SPEED , the largest opening of diaphragm (aperture) at which a lens can be used is also known as the speed of the lens. Hence the light gathering capability of a lens is called lens speed. Speed here refers to intensity of light reaching the film, and not to any movement. Thus, an F/2 lens is faster than F74, because an F2 has a larger aperture and will admit more light at a given time. Lenses having a large aperture are called “fast” lenses because their large aperture makes it possible to take photograph at a very short exposure interval or under very dim light conditions. The closer this largest aperture to one (1) or to being equal in diameter to the focal length of the lens, the faster the lens.

SENSITIZED MATERIAL

Sensitized Material refers to films and papers that are composed of emulsion containing SILVER HALIDE crystals suspended in gelatin and coated on a transparent or reflective support.

FILM

A film consists basically, of a random scattering of light sensitive silver halides suspended in a layer of animal gelatin which is coated onto acetate support or base.

THE FILM STRUCTURE

A. STRUCTURE OF WHITE and BLACK FILM

1. TOP COATING (TOP LAYER) – scratch resistant coating also called gelatin coating, an over coating composed of a thin transparent layer of a hard gelatin which help protect the silver halide emulsion from scratches and abrasions. The hard gelatin, which is derived from cows, contains SULFUR. The SULFUR is very much compatible with silver halides. 2. EMULSION LAYER – SILVER SALT + GELATIN – A layer composed of silver compounds which are light sensitive and halogens (such as bromide, chloride and iodide bromide in fast film emulsion). A silver compound when combined with a halogen becomes SILVER HALIDE. Silver Halides are rare compound that are responsible in forming the so called the LATENT IMAGE in the . 3. – commonly made of cellulose or other material such as paper, plastic, or glass, which supports the emulsion layer and is coated with a non-curling antihalation backing. 4. ANTIHALATION BACKING – a black dye applied on the rare surface of the film. Its function is to absorb light that may penetrate the emulsion thus making the image sharper since it suppresses double image. It prevents halo formation in the photograph. The black dye is removed during processing by one of the chemicals in the developer. Its second function is to control the film from curling inwards. (Towards the emulsion surface).

B. STRUCTURE OF COLOR FILM

1. TOP LAYER – sensitive to blue light only, green and red light passes through it without exposing the color halide. 2. EMULSION LAYER

a. Blue filter b. Yellow filter – CAREY LEA silver suspended in gelatin, it is coated between the top and second layer to absorb any penetrating blue light but allowing green and red light to pass through. c. Green filter – a layer that is orthochromatic, the layer sensitive to blue light (which can not reach it) and green, but not to red light pass on to the bottom of the emulsion layer. d. Red filter – a panchromatic layer, sensitive to blue (which can’t reach it) and red. It is also sensitive to green light but to a slight degree that is insignificant.

3. ANTIHALATION BACKING / COATING 4. FILM BASE – Plastic film base

Emulsions are thin, gelatinous, light-sensitive coatings on film that react chemically to capture the color and shadings of a scene. The four layers pictured above show the same image as it would appear on different emulsions in photographic film after the first stage of developing. For black-and-white photographs, only one emulsion is required, because it is the amount of light, not the colour that activates the chemical reaction.

C. TYPOLOGY OF FILMS

Exposure is made simultaneously in the three layers. Each layer responding to only one of the additive primary colors (red, blue and green). After exposure and during the film processing, the yellow color of the filter layer is destroyed.

Films maybe classified according to their forms and types. Basically, films that are available in the markets today are in various forms. They can be in rolls, in cartridges and cut sheets. Light sensitivity of the film can be ascertained through its various types.

There are some films that are sensitive to all colors while there is some that are sensitive only to one or specific set of colors.

Classification according to USE

1. FILM – for B and W Photography 2. COLOR FILM – films that have names ending in COLOR - Color negatives for prints The negative in this type of film is divided into blocks and is color positive. It is composed of hue dyes. In between the blue and green hues, yellow gelatin is placed so that the blue rays of light would not affect the green hue and in between the green and the red dye, magenta gelatin is placed so that the green rays of light would not affect the red hue dye of the emulsion.

3. CHROME FILMS – films with names ending in CHROME - For color transparency (slides); films that are exposed by slides, mounted in a cardboard for slide projectors: reversal type. 4. X – RAY FILM – films that are sensitive to X- radiations.

Types based on (according to light sensitivity)

1. FAST FILM – contains numerous number of large grains of silver halides that usually develop in groups; film that are very sensitive to light. When the available is dim, this

type of film is the best choice because of the low reflection power of the subject against a background. It is low in contrast but high in brightness. However, the use of fast speed film is not advisable due to its graininess result.

2. SLOW FILM – film that require longer period of time to completely expose their emulsion to light; film with fine grains of silver halides.

Types based on SPECTRAL SENSITIVITY (color sensitivity)

Spectral sensitivity – responsiveness of the film emulsion to the different wavelength of light source.

1. MONOCHROMATIC FILM – film that is sensitive to a single color of light (for white and black) a. BLUE SENSITIVE FILM – a film specially treated that makes it more sensitive to blue rays of light b. ULTRA-VIOLET SENSITIVE FILM – sensitive to UV rays only

2. PANCHROMATIC FILM – sensitive to ultra-violet rays, and all light found in the visible spectrum, especially to blue and violet light. It is suitable for general use in the preparation of black and white photography because it produces the most natural recording of colors.

Panchromatic films are further sub classified according to their degree of sensitivity to each primary colors or light. There are three classes of panchromatic film. They are the following:

a. Process Panchromatic Film – permit short exposures under average lighting condition and has the advantage of fine grain structure. b. Grain Panchromatic Film c. High Speed Panchromatic Film – designed originally for photographing objects under adverse lighting condition.

Contrast of the panchromatic film usually varies with the color of the light and using filters can attain proper contrast in photograph.

3. ORTHOCHROMATIC FILM – film that is sensitive to UV rays, blue and green colors, but not to red. Red portions are recorded as dark tones, while green and blue parts appear as light tones when printed. This type of film is popular in the market as the KODALITH FILM.

4. INFRARED FILM – a special type of film that is sensitive to infrared and ultra-violet radiation (radiation beyond the human eye’s sensitive). It is also sensitive to all the colors found in the visible spectrum. Although the infrared film is sensitive to blue color, a red filter can exclude the blue color. The red filter transmits only long red and infrared radiation. IR film is useful in penetrating haze because of its longer wavelength. In Investigative Photography, it is useful in laboratory analysis of questioned documents, in discovering old ( or faded ) tattoos under the skin, and in the construction of camera types.

D. FILM SPEED – (EMULSION SPEED)

EMULSION SPEED – the sensitivity of the film to light; the extent to which emulsion is sensitive to light. The light sensitivity of the film is also known as the FILM SPEED. Speed of the film is determined through the numerical film speed labels given by the film manufacturer. There are two classical speed ratings that became popular:

1. ASA (American Standard Association) rating - This is expressed in arithmetical value system. The speed in numbers is directly proportional to the sensitivity of the material. A film with an arithmetical value of 400 is four times as fast as one with a speed of 100. 2. DIN (Deutche Industrie Norman) rating – This is expressed in logarithmic value system. In this system, an increase of 3 degree doubles the sensitivity of the film.

• ISO rating (International Standards Organization) – combination of ASA and DIN rating. The higher the ISO number, the more sensitive the film to light and the pictures can be taken indoors or in dim light condition. • ISO 100-200 – film for general purpose

One film maybe rated ISO – 100, and another film ISO- 200. This means that the 200 films are twice as fast ( twice more sensitive to light ) than the ISO-100 film. Hence, it would only require half the amount of light to produce a satisfactory negative. Each time the film speed is doubled, it is equal to one f / stop higher. For instance, in the example given, if ISO-1 is exposed at f / 8, then ISO-200 should be exposed at f / 11 to produce the same negative . Any film above ISO-200 can be considered grain. The suggested uses of the following film exposure under varying conditions are:

1. ISO – 25 – slowest speed that natural condition will permit, for best color and sharpness. 2. ISO – 100 to ISO – 200 – for general purpose 3. ISO – 100 – slow speed film; needs sufficient light and low shutter speed; has fine grains of silver halides; produce sharp image. 4. ISO – 200 – twice as fast and as sensitive as ISO – 100; has large grains; produce large sharp image. 5. ISO – 400 – for dim light or with moving subject 6. ISO – 1000 and up – for extremely low light conditions or for fast moving objects

• When DX is attached to the film speed, it means that the film automatically sets the film speed dial (ASA dial).

E. FILM SIZE

1. 110 – for cartridge loading pocket cameras 2. 126 – for older and larger cartridge loading type 3. 120 – variation of the 2.25 inch-wide roll film that was first introduced for box cameras a decade ago and now used in professional cameras like the Hasselbald or Mamiya. 4. 135 – commonly known as the mm. so named because the film is 35 mm wide 5. 220 – the same with 120 but twice as many exposure

FILM AND LIGHT

An alteration in the spectral response of a photographic material brought about by a change in the spectral distribution of energy in the light source used for exposure is a difference in a relative brightness in which different colors are reproduced by the photographic material.

EXPOSURE

Photographic exposure is defined as the product of illumination and time. The unit of exposure is usually in meter candle second which is equivalent to exposure produced by a light source of one candlepower, in the second at a distance of one meter from the surface of the sensitive material.

FILTERS

Filters made of gelatin or glass; filters are used in front of a camera lens to alter the of light, to change contrast or brightness, to minimize haze, or to create special effects. In black-and-white photography, color filters are used with panchromatic film to transmit light of the matching color while blocking light of a contrasting color. In a landscape photograph taken with a red filter, for example, some of the blue light of the sky is blocked, causing the sky to appear darker and thereby emphasizing clouds. Under a blue sky, a yellow filter produces a less extreme effect because more blue light is transmitted to the film. The No. 8 yellow filter is often used for outdoor black-and-white photography because it renders the tone of a blue sky in much the same way that the human eye perceives it. COLOR FILTERS – Are used to control the relative tone values in which colors are rendered by the photographic process, to lighten or darkened particular colors or to obtain color separation records for color photography works.

A color filter maybe defined as an optically homogenous filter in which the absorption of light and transmission of light varies with the wavelength.

• Blue Filters – A blue filter can be used effectively when photographing blood in black and white. When used outdoors as blue filters will make the sky, or any blue object appears white in photograph. • Green Filters – Are now used in place of blue filters for photographing blood. • Yellow Filters – Yellow filters cut through haze to certain extent and can be used with good results to photograph an accident on a hazy day.

VIEWING FILTER – Are designed to show by direct observation the relative values in which colors will be reproduced by a particular type of sensitized without or with a given filter.

NEUTRAL DENSITY FILTER – Are used to reduce the light intensity to prevent over exposure.

POLARIZING FILTER – Are used primarily to control light reflected from highly polished surfaces, metallic objects and others.

The Principle of Color Filters

Objects are distinguished from their surroundings by the contrast, which may be the result of a difference in brightness or color.

Filter Factor

A photographic material exposed to such filtered radiation will receive a small amount of light than one without any filter. To compensate for the loss of radiation because of the absorption of the filter, the shutter speed should be increased or a longer time in opening and closing or wider lens aperture, or an increase in the intensity of the light source is necessary. Filter factors depend upon: 1. Absorption characteristics of the filter. 2. The subject 3. The spectral sensitivity of the emulsion 4. The processing conditions.

The general effects of filter may be given as below:

Color of Subject Rendered Lighter Rendered Darker

Red Filters F, A or G Filter B or C-5 Green G, X-1, X-2 Filter A or C-5 Blue Filter A A, F, G, or B

Magenta Filter F or A Filter B Yellow Filter F or G Filter C-5 Orange Filter G or A Filter C-5

Filter Guide

G - - - - Deep Yellow B - - - - Green X-1, X-2 - - - Lighter Green A or F - - - - Shades of Red

SENSITIZED PAPER (PHOTOGRAPHIC PAPER)

The result of photography in its final form is the photograph. The materials necessary to produce a photograph (POSITIVE PRINT) are a sensitized paper. It has emulsion that is coated with opaque material like paper.

A. STRUCTURE OF THE PHOTOGRAPHIC PAPER

After the process of producing the negative image is produced from the negative, which is a true presentation of the relative brightness of all parts of the object and is now called a print. A print is ordinarily made on paper that is coated with light sensitive emulsion. This emulsion is similar to the. Basic layers of printing paper are: 1. Emulsion Layer – the layer containing minute silver suspended in gelatin; the layer of chemical needed to reproduce the opposite tone of the negative print. 2. Baryta Layer – a gelatin layer containing Baryta crystals (barium oxide particles) to increase the reflectivity of the paper. 3. Base – made of hardened white paper, which must be chemically pure to ensure that it will not interfere with the chemical processes to which the emulsion is subjected. Available either in single or double weight paper.

In the preparation of photographic papers, there are three important factors to be considered, the: 1. Type of emulsion 2. Contrasting light rays and 3. Physical characteristics

Each type of emulsion has its own substance and use in the preparation of photographs. The types of emulsion use in photo papers are: 1. Silver Chloride emulsion

2. Silver Bromide emulsion 3. Silver Chlorobromide emulsion

B. TYPES OF PHOTOGRAPHIC PAPERS

BASED ON EMULSION USED

1. SILVER CHLORIDE PAPER – contains silver chloride emulsion; grained and produce deep black images; used for contact printing. Its sensitivity to light is low. Generally, the size of the positive print is the same as the size of the negative used and usually it will give blue-black tone if properly developed. 2. SILVER BROMIDE PAPER – contains silver bromide emulsion. Light sensitivity of this type is faster than the silver chloride paper. This photographic paper is used for projection printing or enlarging process wherein the negative image is projected or enlarged. If properly developed, the silver bromide paper will give a black tone. 3. SILVER CHLOROBROMIDE PAPER – contains a combination of silver chloride emulsion; its emulsion speed lies between that of chloride and bromide papers; used both for contact and projection printing. The sensitivity of this paper is either slow or fast. The slow emulsion is used for contract printing while the fast emulsion is used for projection printing. 4. VARIABLE CONTRAST PAPER – combines the contrast ranges in one paper, it uses a special Chlorobromide emulsion that produces varying contrast responses upon exposure to different colored light.

VELOX No. 0 – used for printing from extremely contrast negatives, the low contrast in the paper sensitizing counteracts the high contrast in the negative to give a new print. VELOX No. 1 – used for high contrast negative VELOX No. 2 – a paper for normal contrast used with normal negatives VELOX No. 3 – used for negatives that have weak contrast VELOX No. 4 – provides for sufficient contrast to compensate for very thin or weak negatives. It is useful in printing pictures which high contrast is desired VELOX No. 5 – for flat negative that is unprintable