What are standard lenses, wide-angle lenses and telephoto lenses?

The standard lens mentioned in photography is relative to the film size used by the camera. That is, the effect of photos taken with a standard lens, that is, the effect we usually see when we observe the scenery from a horizontal angle. In other words, when we watch a scene, the range we can see clearly is roughly the range we can shoot through this standard lens. When it is greater than this range, it is called a wide-angle lens; When it is narrower than this range, it is called a telephoto lens.

For example, for a camera using 35 mm film, a lens with a focal length of 50 millilens is a standard lens. If you shoot with a lens with a focal length of 28 mm or 20 mm, the effect is wide angle. Lenses with focal lengths of 105mm, 135mm and 200mm are considered as long lenses or telephoto lenses. However, for a camera using 2×2 inch film, the lens with a focal length of 75 mm is its normal lens.

A simple method can be used to judge whether it is a standard lens. That is, measuring the diagonal distance of the film used, then this value should be similar to the focal length of the standard lens.