As the name suggests, fisheye, this lens tends to have a viewing angle of 180 degrees. With this uniqueness, fisheye lenses have a focal length of 4-14mm.

Much like a fish sees the world, these lenses use a particular type of "mapping" that deliberately distorts lines to make them appear more convex. However, the distortion that basically spoils this image actually has its own unique effect.

This lens tends to be used for photographing landscapes, but most surveillance cameras also use this lens because they get a wider image coverage.