Professional cameras allow you connect different lenses so you can see the scene at various magnifications. The magnification power of a lens is described by its focal length. In cameras, the focal length is defined as the distance between the lens and the real image of an object in the far distance. A higher focal length number indicates a greater image magnification.

Different lenses are suitable for different situations. If you're taking a picture of a mountain range, you may want to use a telephoto lens, a lens with an particularly long focal length. This lens lets you zero in on specific elements in the distance, so you can create tighter compositions. If you're taking a close-up portrait, you might use a wide-angle lens. This lens has a much shorter focal length, so it shrinks the scene in front of you. The entire face is exposed to the film even if the subject is only a foot away from the camera.