After some delays the Tokina fisheye lens I ordered recently arrived today. At around 450 euros the lens itself wasn’t that pricy, but as the dome port (and port base) for underwater use were actually more expensive than that, the whole thing still ended up quite a big investment.
The lens is not really that useful for normal photography as fisheye distortion (straight lines becoming curved near image edges) is quite heavy especially on the wide end. Topside it’s only suitable for some special occasions and fun/joke shots. Technically you can remove the fisheye distortion in postprocessing, but as this will affect the photo framing it’s by no means a perfect replacement for (more expensive!) rectilinear wide-angle lenses.
Underwater it’s a whole different story. Tokina 10-17 is one of the most popular wide-angle lenses for underwater use. The focal length range makes it pretty optimal for underwater wide-angle shots (on cropped cameras) and the short minimum focus distance of 14 cm allows one to get really close to the target (almost always a big plus in water!). The fisheye effect is also much less pronounced underwater.
Well, that’s the theory anyway, I’m heading out tomorrow for some shore diving to test the lens in practice. Assuming the conditions are decent that is, if vis is too bad I’ll probably just focus on some macro work and test it later.