What is a fisheye lens? What's the role?

"fisheye lens" is a common name. Take the lens of a 135mm SLR camera as an example. The fisheye lens is a short-focus ultra-wide-angle photographic lens with a focal length within 16mm and a viewing angle of about 180. In order to make the lens reach the maximum viewing angle, the front lens of this photographic lens has a short diameter and projects to the front of the lens in a parabolic shape because it is in harmony with the fish's eyes.

Fish's eyes are usually located on both sides of the head, and most of them have no eyelids and cannot be closed. The lens of the eye is spherical. The fish's vision adjustment depends on the forward and backward movement of the lens position, rather than changing the convexity of the lens. According to the imaging principle of fisheye lens, people designed fisheye lens.

Visual effect of fisheye lens

The focal length range of fisheye lens is generally 6 ~ 16 mm, which is characterized by a large viewing angle, mostly above 180, and some even reach 230. Moreover, the barrel bending distortion is great, and the straight lines at the edge of the picture are all curved, and only the straight lines passing through the central part can maintain the original straight line state. Fisheye lenses are divided into full circle and full width.

The angle of view of the full round fisheye lens is above 180, and only the round part is seen in the picture. This kind of lens completely blocks the four corners of the picture. The appearance of this lens is that the first lens at the front end of the lens is very large and obviously protrudes forward, but for fisheye lenses with a slightly smaller maximum aperture, the front end of the lens is not so exaggerated. Representative lens: Sigma AF8/3.5EX DG round fisheye.

Shooting effect of full circular fisheye lens

When you hold the fisheye lens up to eye level and point it straight ahead, this lens will take pictures of everything in the hemispherical space in front of you, even your own shoes. This kind of image usually forms a circle in the frame instead of filling the rectangular frame. Obviously, the fisheye lens is a kind of special effect lens with great distortion. The perspective line radiates from the center in all directions. In the figure, except for the straight line passing through the center, all the other straight lines remain straight.

Shooting effect of full-frame fisheye lens

The full-width fisheye lens, also called diagonal fisheye lens, is characterized in that the whole picture is a complete 24×36mm frame, but the geometric figure of the picture still has the fisheye lens visual effect concentrated in the middle of the picture. Representative lens: Nikon AF 16/2.8D fisheye.