Cameras work by focusing light in order to produce an image on a light-sensitive surface. Some cameras work by forming the image on light-sensitive film. Sometimes film uses dyes that change colour when exposed to light, as happens with film used to make coloured slides or prints. Earlier film or glass plates used a silver compound as the light-sensitive material. To produce a photographic print the image is projected onto the surface of light-sensitive paper. It is treated with chemicals to make the print visible and prevent further changes when exposed to light.
Digital cameras are a recent development. They convert the image they receive into electrical signals that are stored. These signals can then be read by a computer and used to produce a picture on screen, which can then be printed out.
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