Fisheye lens

Fish-eye lenses are extreme wide angle and render an image that is very distorted, in contrast with most lenses that are designed to minimise distortion. Fish-eye lenses project severe barrel distortion away from the image centre, only straight lines that pass through the centre will appear straight. The lenses are made in two forms: circular fish-eye that project a circular 180 degree angle of view image within the film frame, and full frame fish-eye that fill the frame with 180 degree angle of view diagonally.

Originally developed for metereological usage their distortion limits use in general photography.

Origin

The term "fish-eye" comes from the similarly distorted view of the dry world when looking up from underwater. Because of light refraction when entering water, the image seen of the above water world when looking up from underwater is a circle with extreme barrel distortion at the edges, exactly as rendered by a circular fish-eye lens. This is the only way to project a 180 degree image onto a flat plane and the original use of these lenses was photographing cloud cover.

Full frame fish-eye lenses were developed for general photography but the extreme distortion is obvious. Jonathan Eastland commented "...difficult to use with originality".