Fisheye problem

I have bought a 15mm Fisheye from Zenitar, Russia fabric. This works perfectly on land on my Canon Eos 300D. Full sharpness just perfect and fun to use. Underwater it has a big problem with focus everything is out of focus or has some kind of blur. Just to show you what I mean is this picture of a half/half moment. The diver getting out of the water is completly out of focus while the whole boat and boat deck is sharp. Anybody a clue???

It looks to me, like you focused on the boat, and the underwater scene was out of focus.

If you shoot purely underwater, does it focus ok?

What is the closest focus distance, of the lens, out of water? Can it focus on the virtual image, created by your dome port?

In general, you may want to shoot as high f-stop as possible, to get more DOF, to capture the curved virtual image.

Don