Fisheye lens is a focal length is 16 mm or less close to or equal to the Angle 180 ° of the lens. It's an extreme wide-angle lens, and the "fish-eye lens" is its colloquial name. In order to achieve the maximum camera Angle, the front lens of this camera lens is very short in diameter and protrudes toward the front of the lens in parabolic shape, which is similar to the eyes of fish, hence the name "fish-eye lens".
Fish-eye lens is a special kind of lens in the ultra wide Angle lens, its Angle of view try to reach or beyond the scope of the human eye. Therefore, the fish-eye lens is very different from the real world scene in people's eyes, because the scenes we see in real life are regular fixed forms, and the picture effect produced by the fish-eye lens is beyond this category.