This incredible beauty is an underwater fisheye. Made for the first underwater interchangeable lens reflex system, the Nikon RS.
This was intended with a glass-water surface in mind, so no land use, sorry. It would simply not be able to focus. As for the design, it is adapted from the Nikkor 16mm 2.8, and shares also the bayonet filters at the rear, but covers 170 degrees on the diagonal instead of 180.
a great THANKYOU to Marco Cavina for the infos, you can find far more on his NIKONOS PAGE.
As always MIR pages are a precious information source