longfocallength

Long focal length refers to lenses with relatively long focal length in optics and photography. In photographic terms, a long focal length is typically anything longer than about 85 mm on a full-frame sensor, and shorter on cameras with smaller sensors due to the crop factor. Telephoto lenses—both primes and zooms—fall into this category and are characterized by their narrow field of view and increased image magnification, allowing distant subjects to appear larger in the frame.

The principal effects of a long focal length are increased subject magnification and a shallower depth of field at a given distance and aperture. The restricted field of view also changes perspective, often producing compression where distances between objects in the frame appear shorter than they are in reality. On APS-C or Micro Four Thirds bodies, the effective field of view is further narrowed by the crop factor, expanding the telephoto effect without changing the lens' physical focal length.

Common uses include wildlife and sports photography, where subjects are far away, as well as portraiture where background blur and subject separation are desirable. Telephotos are also used in astronomy.

Practical considerations include larger size and weight, higher cost, and the need for faster shutter speeds or stabilization to compensate for movement and handshake. Autofocus can be reliable but may be challenged by very long focal lengths in low light. Tripods or monopods, appropriate shutter speeds, and careful focusing are often recommended.