What is the focal length of fish eyeglasses?

A fisheye lens is a lens with a focal length of 16mm or shorter and a viewing angle close to or equal to 180°. It is an extreme wide-angle lens, and "fisheye lens" is its common name. In order to achieve the maximum photographic angle of the lens, the front lens of this photographic lens is very short in diameter and protrudes parabolically towards the front of the lens, which is quite similar to the eye of a fish, hence the name "fisheye lens".

The fisheye lens is a special type of ultra-wide-angle lens. Its viewing angle strives to reach or exceed the range that the human eye can see. Therefore, there is a big difference between the fisheye lens and the real world scenes in people's eyes, because the scenery we see in real life has regular and fixed shapes, and the picture effect produced by the fisheye lens goes beyond this category. .