The second component after the camera body is the lens. The lens is often likened to the 'eye' on a camera. This section functions to capture, focus, and deliver light into the camera body, to then be processed to become an image. In carrying out its function, the lens will usually be assisted by three rings. First, the diaphragm ring (aperture) which functions to regulate the amount of light that enters. Second, the focus ring which serves to focus the object. Third, the zooming ring which functions to magnify the view of objects, where this magnification depends on the distance and size of the lens.
Lenses have sizes. The standard lens size is determined by the focal length. Focal length is expressed in millimeters (mm). By definition, the focal length is the distance between the lens and the focal plane on the sensor where the photo will be formed. Consider the following scheme.
