The Canon 8-15mm f/4.0L fisheye lens is one of the most exciting lenses to be released in a long time for underwater photographers. It has some very cool features for both full-frame and cropped sensor shooters. It has a minimum focusing distance of only 6.2 in., making it a excellent choice for close focus wide angle.
The useable zoom range on a cropped body is 10-15mm. You can, of course, shoot at 9mm and 8mm, but you will start to see the curved corners of the lens. There is a lock on the lens to prevent you from going past 10mm when shooting on a crop sensor body. This lens is often compared to the Tokina 10-17mm, and on a cropped sensor camera the Tokina is the closest thing to it. The Tokina is about half the cost and produces very good results, but if you want the absolute best image quality then the Canon lens is for you. You will lose that little bit of extra reach that you would get at the 17mm end of the Tokina though.
Full Frame Bodies
For those shooting full-frame there is not much to compare the Canon 8-15mm to. At the 8mm end of the 8-15mm you get a full circular fisheye. I happen to really like the look of circular fisheyes, but not so much that I would invest in a lens that can only shoot circular or to spend a whole dive committed to that one style of shot.
Now I don’t have to worry about that anymore. I have the best 15mm lens on the market, and when I want a special effect full circular shot I just zoom into the 8mm end.
Most full-frame shooters are not really going to use the zoom range between the 8mm or 15mm ends. You can shoot at any zoom range, but you will get partially rounded corners that are not very useful. This lens does however, work well with the Kenko 1.4 teleconverter behind it. It turns the lens into an 11-21mm f/5.6 fisheye and still retains excellent image quality. It will give you a usable zoom range of 15mm to 21mm. You can shoot wider than 15mm but you will start to see the partly rounded corners. Nauticam and Xit 404 make zoom gears for this combination.
You’ll want to use a dome port with a removable dome port shade if you intend to shoot circular fisheye photos at 8mm. Small 4 inch domes ports, like the Zen DP100-CR, are perfect for close focus wide angle and the Zen features a removable shade as well.