# Fisheye Lens

## What is Fisheye Lens?

A fisheye lens is an ultra-wide-angle lens that is designed for shooting wide angles generally 180 degrees. These lenses are also known as the ultra-wide or super-wide lens. They are famous for extreme sport, landscape, and artistic photography.

The term fisheye was named in the year 1906 by Robert W.Wood. He was an American physicist and the inventor of this lens. It was first put to use in the year 1920 for studying the formation of clouds. The angle of view of fisheye lenses is generally present between 100 and 180 degrees. The focal lengths depend upon the format they are used for.

## Types of Fisheye Lens

There are two main types of fisheye lenses namely full-frame and circular frame. Each type will have a different effect and gives a different type of image. Let’s have a detailed look at them.

• ### Full Frame Fisheye Lenses

A full-frame fish lens is capable of capturing 180° field of view along its diagonal. The vertical and horizontal sides of the image do not exceed 180°. Even though they are not capable of capturing wide angles, they are widely used because the image produced by this lens is rectangular and will not have black edges.

• ### Circular Fisheye Lens

The circular fisheye lens is capable of capturing a complete 180-degree view in all directions. So, the image looks like a circular image. But the main drawback of this lens is it forms black edges. These lenses are mostly used in artistic photography and skateboard photography.

## Fisheye Lens Projection

From the image given below, we can see that the projection of the object is 90° either on the left or right of the pinhole. The position of the object is linearly proportional to the angle. The captures of the fisheye lens are great but their projection is deemed unpleasant.

The projection for both the types of fisheye lenses is the same. The only difference is in the field of view. Following is the table with a mathematical formula for different fisheye projection:

 Projection Formula Equidistant fisheye R = f . θ Equal area fisheye R = 2f . sin $\frac{\theta}{2}$

Where,

• R is the radial position of a point on the image obtained on the screen
• f is the focal length of the lens
• θ is the angle between the point in the real world and the optical axis. It is measured in radians.

## Characteristics of Fisheye Lens

Following are the characteristics of a fisheye lens:

• Focal length: A typical circular fisheye lens have 8mm to 10mm focal length while the focal length of a full-frame lens is 15mm to 16mm.
• Angle of view: The angle of view of a fisheye lens is 180° at the widest point.
• Image distortion: Images obtained from the fisheye lens have a distortion called barrel distortion where the centre of the frame appears to bulge outwards and the image obtained is known as curvilinear image.
• Depth of field: The depth of field of the fisheye lens is very large because of the extreme angle.