The Kenko Fish-Eye 180º is an accessory fisheye lens for lenses with 52mm threads. This is a pretty elaborate adapter, with its own diaphragm and a lens focal length selector that provides appropriate apertures with lenses from 30mm to 200mm. Why would you put a fisheye adapter on a 200mm lens? That is between you and your camera. But this adapter will make any compatible lens into a 180-degree circular fisheye lens of acceptable quality. I mean, it's still a toy- the edges are gonna get soft- but it's a pretty neat toy. Fits lenses with 52mm filter threads.

Please note: this is not a standalone lens! You will need a lens with a 52mm filter thread (not included)