photography

photography Process of obtaining a permanent image of an object, either in black-and-white or in colour, on treated paper or film. A camera is used to expose a film to an image of the object to be photographed, for a set time. In black-and-white photography, the film is covered on one side with an emulsion containing a silver halide (silver bromide or silver chloride). The silver compound is exposed, so that it reduces easily to metallic silver when treated with a developer. The action of the developer is to produce a black deposit of metallic silver particles on those parts of the film that were exposed to light, thus providing a ‘negative’ image. After fixing in ‘hypo’ (thiosulphate) and washing, the negative can be printed by placing it over a piece of sensitized paper and exposing it to light so that the silver salts in the paper are affected in the same way as those in the original film. The dark portions of the negative let through the least light, and the image on the paper is reversed back to a positive. Colour photography works on a similar, but more complex, process. Newer digital cameras have a built-in computer to record electronic images without using film. Incoming light is converted into electrical charges that may contain millions of photosensitive dots. Digital images are easily stored on computers. See also Daguerre, Louis Jacques Mandé; Talbot, William Henry Fox; individual photographers

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