THEORY OF LIGHT AND OPTICAL PRINCIPLES
Light is the photographer's image of a pattern of light recorded on film? The photography means writing and drawing with light. Without light there could be no vision or photography because it is light reflected from the world around us that makes things visible to both our eyes and the eye of the camera. The nature of light has a critical effect on the pictures. Actually understand much about light. But they are not alone. Scientists have never been able to agree fully. However, certain useful things are clear and well understood about how light behaves. Light is a form of electromagnetic radiant energy to which the eye is sensitive. It travels at tremendous speed from its source, such as the sun, a fluorescent lamp, an electronic flash, or whatever source is used. It has an effect on the materials it falls on, skin becomes tanned, and fruit is ripened by the light of the sun. Depending on the way in which light is received or rejected, a complex pattern of light, shade, and color results. Other types of radiant energy, such as radio waves and x rays, are similar to light but the eye cannot see them. Thus they are not light. By definition, light is electromagnetic energy visible to the human eye. All other electromagnetic energy is invisible, therefore, is not considered light. Ultraviolet and infrared radiations are two such invisible radiations that are of concern to the photographer.
LIGHT-SENSITIVE MATERIALS
Many substances are affected in some way by light. The light-sensitive substances used in photographic film to record an image are silver salts and are called silver halides. The silver halides react to ultraviolet radiation,
Violet and blue light only; however, they can bemadesensitive to other colors of light and infrared radiation by the addition of dyes. Depending on the amount of
light and the type of silver halide, the light produces a visible or invisible change in the halides of a film or printing paper. An invisible change is made visible by
development. Photographic films and papers are composed of two basic parts: the emulsion and the base, or support. The emulsion is the light-sensitive portion of a film or paper that records the image. The emulsion contains the silver halides and any special sensitizing dyes suspended in a binder of gelatin. The gelatin holds the silver halides evenly dispersed and prevents action by a developer until the silver halides have been made developable either by exposure to light or chemical action. Also, the Gelatin acts as a sensitizer for the silver salts.
light and the type of silver halide, the light produces a visible or invisible change in the halides of a film or printing paper. An invisible change is made visible by
development. Photographic films and papers are composed of two basic parts: the emulsion and the base, or support. The emulsion is the light-sensitive portion of a film or paper that records the image. The emulsion contains the silver halides and any special sensitizing dyes suspended in a binder of gelatin. The gelatin holds the silver halides evenly dispersed and prevents action by a developer until the silver halides have been made developable either by exposure to light or chemical action. Also, the Gelatin acts as a sensitizer for the silver salts.
In photographic films and papers, the primary Purpose of the base is to support or hold the emulsion in place. The base, or support, may be transparent or opaque, depending upon how the recorded image is to be used. A transparent base is used for transparencies that are viewed by transmitted light and for negatives that are printed with transmitted light. An opaque base is used for prints that are viewed by reflected light. The latest state of the art in light-sensitive materials Used in photography is the use of the electronic medium.
Video disks do not contain an emulsion or a base. When electronic mediums are used, light is converted to electrical impulses and these impulses are stored
magnetically on a tape or disk. Since it is the camera itself that converts light to electrical impulses, the recording medium and all stages of the photographic process can be carried out in normal room light.
Video disks do not contain an emulsion or a base. When electronic mediums are used, light is converted to electrical impulses and these impulses are stored
magnetically on a tape or disk. Since it is the camera itself that converts light to electrical impulses, the recording medium and all stages of the photographic process can be carried out in normal room light.
PHOTOGRAPHIC FILTERS
Filters are used in all the various steps of the Photographic process. Though often neglected in the Shooting stage, the use of filters can tremendously
enhance the final product in both black-and-white and color photography.
enhance the final product in both black-and-white and color photography.
PURPOSE OF PHOTOGRAPHIC FILTERS
The purpose of photographic filters is to alter the characteristic of light that reaches the light-sensitive emulsion as light is transmitted through a filter; at least one of the following alterations occurs:
Ø The color of light is modified.
Ø The amount of light is reduced.
Ø The vibration direction of the light rays is
Ø Limited.
The two most important reasons for using Photographic filters are to create an effect with an emulsion and to control the exposure of an emulsion.
Interlocked with the use of filters are characteristics of light and characteristics of photographic emulsions. The effectiveness of a filter depends upon the ability of an emulsion to respond to the color of light transmitted by the filter. Colored filters modify the way colors are recorded. Without the use of filters, black-and-white panchromatic film records colors as gray tones. These gray tones correspond roughly to the tonal range as seen by the human eye. Colored filters selectively brighten or darken these tones. In color photography, colored filters are used to correct or distort color balance. Filters of a specific color transmit most of the light of that color and partially or completely absorb light of
all other colors. For example, a red filter transmits red light and may partially or completely absorb blue and green light,
Interlocked with the use of filters are characteristics of light and characteristics of photographic emulsions. The effectiveness of a filter depends upon the ability of an emulsion to respond to the color of light transmitted by the filter. Colored filters modify the way colors are recorded. Without the use of filters, black-and-white panchromatic film records colors as gray tones. These gray tones correspond roughly to the tonal range as seen by the human eye. Colored filters selectively brighten or darken these tones. In color photography, colored filters are used to correct or distort color balance. Filters of a specific color transmit most of the light of that color and partially or completely absorb light of
all other colors. For example, a red filter transmits red light and may partially or completely absorb blue and green light,
Color (fig. 3-1). Likewise, a yellow filter transmits red
and green light and partially or completely absorbs blue light. Remember, a secondary color of light is produced by combining two primary colors of light. Red and green equal yellow; thus a yellow filter passes red and green
light.
and green light and partially or completely absorbs blue light. Remember, a secondary color of light is produced by combining two primary colors of light. Red and green equal yellow; thus a yellow filter passes red and green
light.
Filters are available in three forms: optical glass Disks bound with metal rims, lacquered gelatin film squares, and glass squares. Glass disk filters are the most
practical for general use. They are available in different sizes called series numbers, such as Series 4,5, and 6 or in millimeter sizes, such as 52mm and 59mm. Glass disk filters attach to a camera lens in two ways. Some have threads and screw directly into the lens barrel, and the others are held on the lens barrel by an adapter ring. Gelatin filters and square filters made of glass are either
inserted into special filter holders that are part of the camera, or they are held on the camera by a square filter Holder.
practical for general use. They are available in different sizes called series numbers, such as Series 4,5, and 6 or in millimeter sizes, such as 52mm and 59mm. Glass disk filters attach to a camera lens in two ways. Some have threads and screw directly into the lens barrel, and the others are held on the lens barrel by an adapter ring. Gelatin filters and square filters made of glass are either
inserted into special filter holders that are part of the camera, or they are held on the camera by a square filter Holder.
FILTER DESIGNATIONS
Filters are usually identified by numbers. This System of designating filters is used to identify Kodak Written filters. It uses designators, such as No. 6, No.
8, and No. 11. Some filters have a descriptive name rather than a number; for example, polarizing, skylight, and neutral density. Color compensating and color print filters have yet another designation system.
8, and No. 11. Some filters have a descriptive name rather than a number; for example, polarizing, skylight, and neutral density. Color compensating and color print filters have yet another designation system.
FILTERS FOR BLACK-AND WHITEPHOTOGRAPHY
Filters used with black-and-white film are classified as contrast, correction, and special purpose. All contrast and correction filters have a noticeable color. It is
important to note that a filter must be used with an emulsion sensitive to the specific color of light it transmits. Colored filters should normally be used with
black-and-white film only. Special-purpose filters for black-and-white film
important to note that a filter must be used with an emulsion sensitive to the specific color of light it transmits. Colored filters should normally be used with
black-and-white film only. Special-purpose filters for black-and-white film
May be colorless, contain a hint of color, be noticeably colored, or almost visually opaque. Some special- purpose filters can be used with both black-and-white
and color film. Special-purpose filters are covered later in this chapter.
and color film. Special-purpose filters are covered later in this chapter.
Contrast Filters Contrast filters are available in all colors and are designed to exaggerate, reduce, or eliminate specific colors of light. As their name indicates, these filters are used to increase or decrease contrast in a negative that
provides differences between tones in the print. To illustrate this, compare a red apple and a yellow banana in a black-and-white print. With a red filter over
the camera lens, the apple appears lighter on the print hand the yellow banana. Both objects in this example reflect the same intensity of light. When you look through a red filter, the filter definitely appears red. This color is the effect it produces in your eye and the reason it is called a red filter. The red filter is transmitting most of the red part of the spectrum, some yellow, and some magenta. The color it is not transmitting is cyan. If you think of this red filter
provides differences between tones in the print. To illustrate this, compare a red apple and a yellow banana in a black-and-white print. With a red filter over
the camera lens, the apple appears lighter on the print hand the yellow banana. Both objects in this example reflect the same intensity of light. When you look through a red filter, the filter definitely appears red. This color is the effect it produces in your eye and the reason it is called a red filter. The red filter is transmitting most of the red part of the spectrum, some yellow, and some magenta. The color it is not transmitting is cyan. If you think of this red filter
as an anticay (blue and green) filter, you will better understand the way it works.
When a red filter is used, most of the reflected red light from the red apple is transmitted through the filter and recorded as a dense area on the film. Only a portion of the yellow light is transmitted, so it is recorded as a less dense area on the film. Only some of the yellow light is transmitted because the reflected light from the banana consists of red and green light. Although the red portion of the yellow light is readily transmitted through the red filter, the green portion is absorbed to some degree. Thus less light from the yellow banana reaches
the film emulsion. When the negative is printed, the two print images Have separation in contrast because of the differences in negative densities. The print image of the apple is lighter than the print image of the banana because the negative image of the red apple is denser than the negative image of the yellow banana. When using a specific color of contrast filter to provide separation between black-and-white images of colored objects, you should also take into account what effect the filter has on the images of other colored objects in the scene. For example, when there are blue and green objects in the scene, the red filter absorbs some or all of the reflected blue and green light. The red filter renders the negative images of these objects as low-density areas. Thus the print images have darker tones or densities. Contrast filters can also be used to filter out an image or filter out the image of a transparent stain on an original document by copying it. This filtering-out process takes place by blending or matching the density of the image to be filtered out with the image density of
the surrounding area For example, to eliminate the image of a yellow line on a white background, use a yellow filter. The yellow filter should be as deep (same
color density) or deeper in color than the color of the line. The yellow filter reduces the intensity of the light reflected from the white background by absorbing blue light. The intensity of the light reflected from the yellow
line is not greatly affected since the yellow filter readily transmits the yellow light. The reduction of the intensity of the light reflected from the white background and the intensity of the light reflected from the yellow line produces equal densities on the negative and thereby does not render an image of the yellow line. Conversely, when the yellow line is on a black background, a blue filter does not allow yellow light to be transmitted. Therefore, light from the yellow object is not allowed to affect the film emulsion. Thus the line appears as a thin area that matches the black background and is thereby "eliminated" Stains on a drawing or a picture can be filtered out whenever the stain is transparent and reasonably pure in color. The filter should be approximately the same color as the stain. The stain may still show in the negative but, in the case of line material, proper paper contrast and printing exposure get rid of the rest of the stain image. Remember, the color of filter required eliminating the image of an object or stain is determined by the color of the object or stain and the darkness or lightness of the
surrounding scene area. Also, always use a filter that is as deep as or deeper in color than the color of the object.
the film emulsion. When the negative is printed, the two print images Have separation in contrast because of the differences in negative densities. The print image of the apple is lighter than the print image of the banana because the negative image of the red apple is denser than the negative image of the yellow banana. When using a specific color of contrast filter to provide separation between black-and-white images of colored objects, you should also take into account what effect the filter has on the images of other colored objects in the scene. For example, when there are blue and green objects in the scene, the red filter absorbs some or all of the reflected blue and green light. The red filter renders the negative images of these objects as low-density areas. Thus the print images have darker tones or densities. Contrast filters can also be used to filter out an image or filter out the image of a transparent stain on an original document by copying it. This filtering-out process takes place by blending or matching the density of the image to be filtered out with the image density of
the surrounding area For example, to eliminate the image of a yellow line on a white background, use a yellow filter. The yellow filter should be as deep (same
color density) or deeper in color than the color of the line. The yellow filter reduces the intensity of the light reflected from the white background by absorbing blue light. The intensity of the light reflected from the yellow
line is not greatly affected since the yellow filter readily transmits the yellow light. The reduction of the intensity of the light reflected from the white background and the intensity of the light reflected from the yellow line produces equal densities on the negative and thereby does not render an image of the yellow line. Conversely, when the yellow line is on a black background, a blue filter does not allow yellow light to be transmitted. Therefore, light from the yellow object is not allowed to affect the film emulsion. Thus the line appears as a thin area that matches the black background and is thereby "eliminated" Stains on a drawing or a picture can be filtered out whenever the stain is transparent and reasonably pure in color. The filter should be approximately the same color as the stain. The stain may still show in the negative but, in the case of line material, proper paper contrast and printing exposure get rid of the rest of the stain image. Remember, the color of filter required eliminating the image of an object or stain is determined by the color of the object or stain and the darkness or lightness of the
surrounding scene area. Also, always use a filter that is as deep as or deeper in color than the color of the object.
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