You could try Nikonos lenses. They could be way off the mark from what you need. There are literally tons of Nikonos lenses at giveaway prices. Try a few of them and see. From my own experience these lenses are made for water contact and most will not focus topside but UW they are tack sharp and distortion free. The higher end Nikonos RS lenses are even more sophisticated. I have re-chipped a few of them and have added aperture rings and they are probably the best UW corrected lenses there is. They are again designed by Nikon just for underwater photography. I have done some experiments myself. Even made a port that could make the Nikon 14-24mm working without too much corner distortion. Let me know what camera and focal length I may be interested in studying this further.
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