Lenses over 100mm are considered to be Long. These lenses function much like a telescope in that they allow you to photograph distant objects. A Telephoto lens is a long lens whose actual physical length is shorter than its focal length. This is achieved through the use of a complex grouping of optical elements within the lens. Despite the shorter physical length, it will demonstrate the same optical properties as a long lens of the same focal length. These lenses are more convenient due to their compact size but can be more expensive and some quality may be sacrificed.
Long Lens Vs. Telephoto LensDiscovery Center Team