Optics seems to be the "next frontier" in the industry at the moment. The good news is that I know of one manufacturer who is currently developing a commercial product that is similar, in performance at least, to Alex's corrector port (although it will probably use the Nikkor 50mm lens). The project is still in the prototype phase, but I am very confident that there will be a product for sale in the near future. I should point out that it is likely to be expensive! Once it is out, Wetpixel will be testing and using it!
Seems strange choice of lens. Sure a wide angle would be better? Not convinced about stretching a 50mm to a wide angle for stills (with presumably a water contact front element) will be that great for high resolution shooting. Probably OK for sub 10MP applications, like 4K video.
Did this lens come from a movie camera housing or a stills camera and which housing was it designed for?.....if stills what film format? I am just fascinated to know where the adaptor originated from and how old it might be? If the design truly can be used with any lens (excluding fish eye) then it is a very interesting trial indeed!
My glass came from an old medium format, scientific photogrammetry survey camera. But all my tests so far show it should work on a very wide range of lenses.
I have probably done my last dives with the system now. So will pull together a selection of images.