To keep it pretty straightforward, a fisheye is a super wide-angle lens that has a viewing angle close to 180 degrees.
Because of its unique feature, it creates an image that is visually distorted to make it seem like a wide panorama.
Why is a fisheye lens called that?
In 1906, an American physicist Robert Wood, coined the term fisheye with the basis on how a fish’s view would be in an ultra-wide hemispherical view.
The first noted practical use of the glass was in 1920 when it was used to study cloud formation in meteorology. Since then, it was also coined as the “whole-sky lens” because of how it captured a wide view of the subject.
(This means that a fisheye lens does an amazing job capturing the firmament.)
It is also popular for:
artistic photography, and,
… because it is capable of capturing an extremely wide image of around 180 degrees.
Filmmakers and photographers have used it mainly to give an illusion of distortion. The effect makes it seem as if the borders were wrapped into a spherical shape.
With the edges curved and all, the eye immediately goes to the subject and focus on that.
Another thing a fisheye is good for is to create a “peephole” effect.
If you’ve ever watched a film where actors use doors with peepholes, then that is the exact lens they are using to achieve such a shot.
See image below:
Lastly, where this lens is mostly used unlike any other is in space.
The reason comes as no surprise. More of the surrounding is captured into the frame when it’s in use.
The fisheye’s ability to have a large depth of field and wide angle of view means that the NASA is unlikely to miss anything in space.
(It is for this same reason why it’s the glass of choice for most photographers who take photos of the night sky.)
This post is excellent talking about wide angle lenses in greater detail.
Fisheye vs Wide-Angle Lens
You may wonder:
What what is the difference between a fisheye lens and a wide angle lens?
A fisheye lens is an exaggerated wide-angle lens.
One noticeable difference you will see is that the former produces a distorted edge unlike the latter. The fisheye distortion is vertically extreme where it bends in the middle which is why the subject at the center is the least distorted.
Generally, the lens is more prone to distortion at an image’s periphery is the focal length is shorter.
The reason why wide-angle lenses use a corrective lens element is to remove the chances of image distortion or pincushion distortion.
On the other hand, the fisheye lens takes advantage of this effect that’s why the corrective lens element is not put into place.
It is important to note that there are different types of fisheye lenses:
Circular Fisheye Lens
The photo I shared earlier is a great example of a circular fisheye lens.
It gives a 180-degree angle of view on the entire periphery namely: vertical, horizontal, and diagonal with a distortion that is like a barrel.
This simply means that the produced image is contained within a circle because of the vignette effect in the corners of the frame.
This effect is also known as the “tunnel vision” effect.
Diagonal (Full-Frame) Fisheye Lens
It is a 180-degree image with a diagonal angle-of-view where the edges are the areas of the picture that is mostly distorted leaving the center “normal-looking”.
Unlike we saw with the circular fisheye forming a circular image within the frame, a diagonal fisheye lens fills the frame entirely.
Hence the reason why it’s also called “full frame” fisheye lens.