Summary: I was in the market for a cheap fisheye lens. I found this at a good price and thought it was worth a shot. The image quality is pretty bad. Blurry in the middle, worse at the edges. These days bad photography is all the rage, so with a little thought towards composition and some photoshop work this can be a fun lens. With a standard 18-55 lens, you'll get vignetting at around 35mm and a full circle at 18. With .18x, you can get the angle incredibly wide.
Summary: I use this lens on my Canon t3i/600D with the 18-55mm kit lens. My only complaint is that the fisheye lens is so heavy. It adds a lot of extra weight to the front and can drag your focus ring down if you hold the camera downward. This complaint is also a compliment though, because the weight of the lens makes it feel solid. Most, if not all, of the body is made of metal, which receives a big thumbs-up from me.
Summary: Love this lens/filter - Needs a lot of light, but the clarity is outstanding. Great for landscapes, and creative shots, very well built piece of equipment and it was shipped perfectly on time.
Summary: This screws on the end of a lens, like a filter. It is my first fisheye or super wide angle and I have had a lot of fun exploring the possibilities. The flat glass on the front allows the lens to actually touch a flower's edge in order to get to the center to take the picture. It even steadies the flower by touching it (with tripod)-just clean it with a proper lens cloth. It's fun taking round photographs.
Summary: Obviously not the lens you would buy if you're looking for great quality. But if you just want to mess around with a fish eye, it's good! I haven't used it a whole lot, and I did notice a little discrepancy in the construction quality, but all in all I think for what you're paying, it's a fun little lens!