When focused on infinity any lens is at its closest to the film in the camera. As the lens is focused on nearer objects its distance form the film must be increased-and by a progressively greater degree ads the object focused on gets closer. There are three accessories which alter focusing, and make it possible to go really close. These are supplementary or close-up lenses, bellows, and extension tubes. Supplementary lenses can be used with very basic cameras, even vintage box cameras, to allow the photographer to get close enough for a good-sized portrait head. Bellows are suitable only for use with single lens reflex cameras, for it is necessary to be able to see through the lens to know just what in focus and what is not. Extension tubes work in the same fashion as bellows, but usually consist of two or three detachable tube pieces, giving a limited range of close-up focusing distances.
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