In
photography and
cinematography, a
telephoto lens is a specific type of a
long-focus lens in which the physical length of the lens is shorter than the
focal length. This is achieved by incorporating a special lens group known as a
telephoto group that extends the light path to create a long-focus lens in a much shorter overall design. The
angle of view and other effects of long-focus lenses are the same for telephoto lenses of the same specified focal length. Long-focal-length lenses are often informally referred to as
telephoto lenses although this is technically incorrect: a telephoto lens specifically incorporates the telephoto group.