A combination of shaped glasses and air spaces set in a specific arrangement within a barrel. Within the lens is a diaphragm that can be opened and closed to allow in specific amounts of light. This is controlled manually by a ring on the outside of the lens barrel, or electronically via pins in the coupling ring that mounts the lens to the camera. Lenses have two primary functions: one is to focus light with as little distortion or aberration as possible on to film or sensor. Focusing is accomplished by changing the relationship of the elements in the lens to the film plane. The other function is to control the amount of light hitting the film by use of its aperture. Autofocusing lenses may contain small motors for racking the lens back and forth in response to changes in focus.ritzcamera
A cylinder of shaped pieces of glass or plastic at the front of a camera, it projects a tiny image of the subject onto the film.