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Emulsion   Definition
Color  Negative  Film

Photography (Basic) - Introduction to photography and other graphic techniques
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Figure 2-2.–Cross section of black-and-white film. highlight area and a shadow area is not perfectly sharp. This is because the high-density area tends to “bleed” onto the low-density area due to the scattering or diffusing  of  light  in  the  emulsion  during  exposure. CONSTRUCTION OF BLACK-AND-WHITE FILM Light-sensitive  materials  are  composed  of  two  basic parts: the emulsion and the base. The emulsion is the light-sensitive portion that records the image. The base is the support to which the emulsion is coated. Also, negative  materials  have  additional  layers  that  perform  a special purpose. They are as follows: overcoating, antihalation backing, and noncurl coating (fig. 2-2). The purpose of the five parts of photographic film are as follows: 1. Overcoating–The overcoating protects the film from  friction,  scratches,  or  abrasions  before  develop- ment. The overcoating is a clear, gelatin layer that is sometimes  called  the  antiabrasion  layer. 2.  Emulsion–thin  layer  of  gelatin  that  suspends and  supports  the  light-sensitive  silver  halides. 3. Base-This supports or holds the emulsion in place. The base may be transparent, translucent, or opaque, depending upon how the recorded image is to be used. The base is generally made of a cellulose acetate. 4.  Antihalation  backing-The  antihalation  backing prevents light from reflecting from the base back into the  emulsion.  The  antihalation  dye  is  sometimes incorporated in the anticurl backing. The dye used to eliminate halation is a color to which the emulsion is least sensitive. This dye is water soluble and is com- pletely dissolved during processing. 5.  Noncurl  coating-The  noncurl  coating  is  a hardened gelatin, about the same thickness as the PROTECTIVE OVERCOATING BLUE SENSITIVE EMULSION LAYER - PRODUCES YELLOW DYES YELLOW FILTER - ABSORBS BLUE LIGHT GREEN SENSITIVE EMULSION LAYER - PRODUCES MAGENTA DYES RED SENSITIVE EMULSION LAYER - PRODUCES CYAN   DYES BASE ANTIHALATION  BACKING NONCURL    COATING Figure 2-3.-Cross section of ordinary color negative film. Figure 2-4.–Modern high-speed color film. emulsion, and is applied to the back of the film. A film emulsion swells when wet and shrinks when dry. This contraction produces a strain on a film base because it is highly flexible. The noncurl coating prevents the film from  curling  during  the  drying  process. COLOR FILM Modern color films are constructed much the same as black-and-white film, but color films consist of three separate emulsions on a single film base. Each of the three emulsion layers records one of the three additive primary colors-red, green, or blue. The top emulsion layer is sensitive to blue light and produces yellow dyes. Between the top emulsion layer and the middle emulsion layer is a yellow filter (fig. 2-3). The yellow filter absorbs the blue light that would otherwise affect the middle  and  bottom  emulsion  layers.  During  processing, this yellow filter is dissolved. The middle emulsion layer records green light and produces magenta dyes. The bottom emulsion records red light and produces cyan dyes. Many of the modern high-speed color films have fast and slow emulsion layers for each primary color (fig.  2-4). 2-5







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