"That particular fisheye is a zoom lens."
It seems like you and I have little to agree on so I generally don't (trying not to anyway) respond to you but this time we do.
The Canon EF 8-15mm f/4L Fisheye USM Lens is a special lens and it is more fun than most can realize. Just as a big tele is great to use so is an extreme UWA lens. One thing, however, it is only a full circle 180 degree on a FF. Keep in mind anything that runs directly through the center of the lens, horizontal or vertical is straight.
Over the years I have had the opportunity to own or use a couple hundred different lenses. Still own some forty+. All brands included. Some borrowed from work. Some I bought. Some I bought first and either kept or sold them on. All Canon lenses are good, likewise so are brand-N's. Some are better than others. Some are great and they are keepers. The Canon EF 8-15mm f/4L Fisheye USM Lens falls into that category. It has become a mainstay in my bag.
In this case, though, the Tokina AT-X 16-28mm f/2.8 Pro FX Lens for Canon is the lens the OP wants. The only quirky thing about it is the AF/MF switch but I rarely take a lens off AF so I don't care. It isn't in my main bag as I love the Canon EF 16-35mm f/2.8L II USM Lens. But for half the cost of the Canon the Tokina would do nicely.
EB
EOS 1DX and 1D Mk IV and less lenses then before!
Check out the sample photos at my favorite NYC online camera store. 
