Photographic film

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Photographic film is a strip or sheet of transparent film base coated on one side with a gelatin emulsion containing microscopically small light-sensitive silver halide crystals, for the purpose of taking photographs. The sizes and other characteristics of the crystals determine the sensitivity, contrast, and resolution of the film. Film is typically segmented in frames, which give rise to separate photographs. The emulsion will gradually darken if left exposed to light, but the process is too slow and incomplete to be of practical use. Instead, a very short exposure to the image made possible by a camera lens is used to produce only a very slight chemical change, proportional to the amount of light absorbed by each crystal. This creates an invisible latent image in the emulsion, which can be chemically developed into a visible photograph. In addition to visible light, most films are sensitive to ultraviolet light, X-rays, gamma rays, and high-energy particles. Unmodified silver halide...

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