Fisheye Lens is a type of wide-angle lens used by photographers. The purpose of the said lens is to provide an expansive, circular image of the entire surrounds.

This kind of lens derives its name from upward view of a fish lurking at the bottom of a pond. Apparently, due to the deflection of light through water-air surfaces, the fish's view appears widely distorted.

The first fisheye lens is attributed to Robin Hill Sky Lens of Beck and dates back to the 1930's. This particular lens was used to capture cloud formations.

It is claimed this type of lens is typically useful for image angles that exceed 110o. Apparently, for such wide-angle shots, the incoming rays would not spread out enough between the film and the lens without the use of accessories like the fisheye lens. It seems these lens are capable of covering 140o - 210o angles.

There are different types of fisheye lenses. One type is the circular fisheye lens. These ones will capture an entire 180 horizon as a rounded image. Another favorite type is the full-frame lens. This type has a more limited view than the former and so does not snap a whole hemispherical image.

Circular frame ones are noted to be on the pricier side, sometimes costing almost twice the price of a full-frame lens. There are many enthusiasts who try out DIY fisheye lens. Some suggest lining up the camera lens to a peephole while others recommend using a pair of old glasses ('positive' lenses).