Date of this Version
The photographic camera uses a converging lens to form a real, inverted image of an object. The image is focused on a film or plate which is coated with an emulsion containing silver bromide crystals. When a few incident quanta of light are absorbed in a grain of emulsion, the grain becomes activated and developable, and when the plate is developed, the bromine is removed from each activated grain, leaving a clump of silver behind. When the plate is "fixed," the remaining emulsion is removed from the plate, so that the image is made permanent. In most cameras the converging lens consists of several elements designed and arranged to reduce objectionable aberrations to a minimum. In general, the lens is designed for a particular arrangement of image and object, as in a camera, where the object is usually much farther from the lens than is the image. A camera lens designed to minimize aberrations for an infinitely distant object may not be well corrected for "close-ups."