Adorama Pro Optic Auxiliary Super Fish-Eye Lens 0.25x. Reviews:
Great economy solution for super-wide
Have had a lot of fun. Adds wide-angle capability even to digital. I use it attached to my 28-70. The back lens cover doesn't fit the adapter, and there was no cover with the adapter. Pretty easy to attach/remove.
... you get what you pay for. It's about a tenth of the price of a true fish eye, so it's about a tenth of the quality and ease of use of a true fish eye too! The focus is only good in the center of the lens, the edges become blurry very quickly, and it takes time to attach it to your main lens.
There was some initial confusion around the need for the series 7 adapter ring (one did not come with the product), but this was sent later after some discussions with Adorama.The lens is very fun to have, and relatively inexpensive. There is a loss of focus near the edges, and depending on the size of your lens, you may experience vignetting which can be partially eliminated by zooming.Very fun to get up close to an object to allow the image to deform in interesting ways via the lens.