Focal Length •Focal length effects the perspective and angle of view. •The greater the focal length number the more “zoomed in” you are. •The focal length of the lens is marked in millimeters on the lens.
Perspective •How far the foreground and background appear to be separated from one other •If objects appear in their normal size relations, the perspective is considered "normal“ http://www.usa.canon.com/app/html/EFLenses101/focal_length.html
50mm rule •Lenses with a focal length of approx. 50mm are called normal lenses because they have normal perspective. •A 100mm lens has 2x magnification of normal viewing. •A 24mm lens has a ½ magnification of normal viewing.
Wide Angle •A lens that has a small number focal length, a loose perspective and a wider angle of view than a normal lens
Telephoto •A lens that makes a subject appear larger than a normal lens does •A telephoto lens has a longer focal length, a compressed perspective and narrower field of view than a normal lens
Zoom A lens that you adjust the focal length over a wide range of focal lengths