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Like telescopes or binoculars, telephoto lenses magnify distant objects. They are essential for wildlife photography and for taking good pictures of many sports. Telephoto lenses can also be useful for picking out details in landscapes, or for head-and-shoulders portrait shots.

Like other lenses, telephotos are categorized according to their focal length. On a 35mm film camera, a 100mm lens would be a ‘short’ telephoto, a 200mm lens would be a ‘medium’ telephoto and a lens of 400mm or longer would be a ‘long’ telephoto.

Due to the magnification factor from their smaller sensor sizes, digital SLRs make telephoto lenses ‘longer’. Fitted to a digital SLR, a 200mm lens would have an equivalent focal length of around 320mm, and a 400mm lens would become a 640mm.

Professional photographers use fixed focal length, or ‘prime’, telephoto lenses. This is because they have wider maximum apertures which enable them to shoot in low light. This is essential for many sports, especially those held indoors under artificial lighting.