Camera is a lightproof box or container fitted with a lens, which gathers incoming light and concentrates it so that it can be directed toward the film (in an optical camera) or the imaging device (in a digital camera) contained within. They are made up of the same basic parts a body (the lightproof box), a lens and a shutter to control the amount of light reaching the light-sensitive surface, a viewfinder to frame the scene, and a focusing mechanism. The 35-mm cameras, both rangefinder and reflex models, incorporate a rapid film-transport mechanism, lens interchangeability (whereby lenses of many focal lengths, such as wide-angle and telephoto, may be used with the same camera body), and a built-in light meter. Many also have an automatic exposure device whereby either the shutter speed or the aperture is regulated automatically (by means of a very sophisticated solid-state electronics system) to produce the correct exposure. Accessories include filters, which correct for deficiencies in film sensitivity, flash bulbs and flash mechanisms for supplying light and monopods & tripods for steady support.