Film Structure

Black & White

Photographic film will only react when it is exposed to light. Different levels of light determine the black areas and the gray tones to create a negative image on the film. The base of the film is made up of a transparent celluloid material which is about 5/1000 of an inch thick. One side is shiny and the other side is opaque. On the photochemical side of the film up to 20 different layers are added. Each layer is held in place by gelatin. These layers not only help form images, but also control chemical reactions and filter light. The silver halide crystals are light sensitive, basically they react to different levels of light to create an image. Depending on where you are taking pictures determines the exposure speed of the film. If you are outside in bright light you may want 100. Indoor photos may call for 400 or so.

Color

Color film is a bit more complex. The first layer contains blue-sensitive silver halide and a yellow forming color coupler. This reacts with the developing agent to generate dye in all of the areas where a silver image is produced. Then there is a yellow filter. The second layer contains blue and green sensitive silver halide as well as a magenta-forming color coupler. The next layer is blue-and-red sensitive and has cyan forming color coupler. There is then an antihalation layer, a safety film base, and a backing layer.

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