What is the focal length of a telephoto lens?

Focal length of telephoto lens: 200mm or more: telephoto lens with a focal length of 200mm or more is often used to shoot birds, sports, forest scenery and so on. A long focal length lens refers to a photographic lens whose focal length is longer than that of a standard lens. Telefocal lenses are divided into ordinary telephoto lenses and ultra-telephoto lenses. The focal length of ordinary telephoto lens is close to that of standard lens, while the focal length of ultra telephoto lens is much larger than that of standard lens. Take 135 camera as an example, the photographic lens with a focal length of 85 mm-300 mm is a normal telephoto lens, and the lens with a focal length of more than 300 mm is a super telephoto lens. Standard lens, the general term for lenses with a viewing angle of about 50 degrees. A photographic lens with a focal length approximately equal to the diagonal length of the photographed picture. Its viewing angle is generally 45 ~ 50. A lens with a focal length of 40-60 mm is 35 mm, a lens with a focal length of 6*6 cm is 75-80 mm, and a lens with a focal length of 4*5 inches is120-150 mm. A standard lens usually refers to a photographic lens with a focal length of 40-55 mm, and the perspective effect of the scene represented by a standard lens is close to vision. This is the most basic photographic lens.