A fisheye lens is an ultra-wide lens for a DSLR camera that captures a hemispheric (round) image. This creates visual distortion that is distinct and is often used in creative photography. The result is an image that looks as if the edges of the picture have been wrapped around a spherical shape, curving lines, and changing the context of anything on the outside edge of the picture.
What Makes a Fisheye Lens Ultrawide?
The angle a fisheye lens can capture an angle of about 180 degrees, which is why it's considered an ultra-wide-angle lens. A wide-angle lens can capture an image that is about 100 degrees wide. What this creates is an image that looks like it's been taken through a peep-hole, like those often seen in entryway doors.
Fisheye lenses also have a distinct look, since the outer glass of the lens has a much more noticeable curve than a wide-angle lens. This curve is what allows the lens to capture a greater range of light and create photographs that are wider than your average wide-angle lens.
How a Fisheye Lens Works
All DSLR lenses except fisheye lenses are referred to as rectilinear lenses. This is because light travels through the lens in a straight path to the image sensor. This creates the straight lines you see in most photographs.@mlsartstudio via Twenty20
Fisheye lenses are designed to bend light as it travels from the outer edges of the lens into the image sensor. The result is the lens funnels light to the image sensor and only the very center of the lens delivers light in a straight path, creating the obvious distortion of the outer edges of a photograph, seen as curves where there would ordinarily be straight lines. This is the very effect that makes these lenses so popular.
The first fisheye lens was created in 1924 by Becks of London, but fisheye lenses didn't become widely available for interchangeable lens cameras until the first interchangeable fisheye lens was released by Nikon in 1962. That first fisheye lens had an 8mm focal length and an f/8 aperture.
The Many Uses of a Fisheye Lens
One of the reasons some photographers choose to use a fisheye lens is to get an effect called barrel distortion. In most kinds of photography, barrel distortion is an effect that photographers avoid, but when shooting images through a fisheye lens, that exactly what some photographers want to achieve.
There are, however, two approaches to photography with a fisheye lens. One group of photographers use the lenses as a way to enhance an image, but without it being obvious that a fisheye lens was used. For example, a fisheye lens can be used with a sunset shot to further expand the horizon or used with a curved subject to capture the feeling of the curve without losing a portion of the image.@kymdros via Twenty20
The other group of photographers uses a fisheye lens specifically to capture the distortion the lens creates. This is useful in a variety of creative styles photography but is most often used in extreme sports photography such as skateboarding or skydiving, where the view created by a fisheye lens simulates the view a person would see.Rick Neves / Getty Images
Additional Types of Fisheye Photography
Of course, whether a photographer wants it to be obvious a fisheye lens was used or not, there are many more uses for fisheye lenses than just horizon and extreme sports shots. It's not at all uncommon for underwater photographers to use a fisheye lens, because it creates a better 'feeling' for what it's like to be underwater by allowing the viewer to see the scene in a much more natural way.Ken Kiefer 2 / Getty Images
Another creative use for a fisheye lens is to take pictures with the lens pointing straight up. This is useful in cityscape photography or even in landscape photography. The upward angle of the lens gives a sense of height when viewing buildings, trees, and other elements.@simogarb via Twenty20
Some photographers also use fisheye lenses for other types of photography, like portraits (the subject needs to be centered, and the edges will be distorted), astrophotography, and behind-the-scenes photos which can capture a more complete view of what's going on behind the scenes. Circular subjects are also well suited to photographs captured through fisheye lenses, as the spherical nature of the images works well with the round nature of a fisheye lens.
One more, slightly obscure use for fisheye lenses is in mobile photography. Mobile fisheye lenses create images that are enclosed in a distinct circle, and some creative photographers find this an interesting way to capture their subjects. The outer edge distortion and center focus are still present, as with other types of fisheye photography, but the obvious mobile nature of the circular mobile images is a genre of its own.Taro Hama @ e-kamakura / Getty Images
Post-Processing for Fisheye Images
Post-processing can play a couple of different roles in fisheye photography:Creating fisheye-like photographs: Some photographers prefer to add a fisheye effect during post processing, rather than capturing images through a fisheye lens. This allows the photographer to have more control of the degree of fisheye distortion, the location of the distortion, and circumference of the fisheye effect. Images with this effect added in post might have only a small portion of the overall image that includes the fisheye effect. It can be an interesting way to alter creative images to create something new.Removing distortion introduced by the lens: Some photographers will capture the image using the fisheye lens and then use photo editing software to correct and straighten the image around the edges. The result can be a an ultra-wide image that resembles a panoramic photograph.