A telephoto lens is any lens with a focal length longer than the standard 50mm field of view on a full-frame sensor, providing a narrower angle of view and greater apparent magnification. The category covers a wide range: short telephotos from 70mm to 135mm are the favored tools for portraiture and event coverage, while long telephotos from 300mm to 800mm and beyond are essential for wildlife, sports, and aviation work. Strictly, the term refers to lens designs where the physical length is shorter than the focal length, but in common photographic usage it describes any long-focal-length lens.
Telephoto lenses compress perspective, making distant objects appear closer to each other and to the foreground. A mountain photographed at 400mm seems to loom directly behind a foreground tree even when miles separate them. This perspective effect is purely a consequence of camera-to-subject distance, not the lens itself, but telephotos enable the photographer to stand far enough away that the compression becomes visible and useful. The flattering effect of an 85mm or 135mm portrait lens on a face comes from exactly this mechanism.
Shallow depth of field is the other defining property. A 200mm lens at f/2.8 produces a paper-thin focused plane, which isolates the subject against a smoothly defocused background. Combined with the narrow angle of view, this makes telephotos the standard choice when the background needs to dissolve and the subject must dominate the frame. Wildlife and sports photographers rely on this isolation to lift animals or athletes out of chaotic environments.
Handling a telephoto introduces its own discipline. The shutter speed required to hand-hold a long lens scales with focal length, the classic reciprocal rule suggesting at least 1/focal-length seconds, though modern IBIS and optical stabilization extend that significantly. Tripods and monopods become routine equipment at 300mm and beyond, and gimbal heads are the norm for 500mm and 600mm lenses. Teleconverters can extend reach further at the cost of one to two stops and some sharpness.
Lens design for long telephotos is dominated by the need to manage chromatic aberration and weight. Fluorite, low-dispersion glass, and aspherical elements all show up in the marketing brochures of professional supertelephotos because correcting longitudinal CA at 600mm is difficult and expensive. Prime telephotos at f/2.8 and f/4 can cost tens of thousands of dollars, while zoom telephotos like the 70-200mm f/2.8 and 100-400mm f/4.5-5.6 dominate everyday professional work because they cover a useful range at a fraction of the weight and price.
Common pitfalls include forgetting that atmospheric haze, heat shimmer, and dust become visibly destructive at long focal lengths, and underestimating the importance of a fast, accurate autofocus system when subjects are small in the frame and moving. The longer the lens, the less margin there is for any kind of error in technique.