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Hey Burt, if you happen to have a Nikonos RS 13mm fisheye in your collection, then you have a pretty valuable lens that can be converted to work with modern Sony bodies & housings. https://www.isaacszabo.com/13mm.html. I got one of these converted (I had to buy it off eBay – sadly I didn’t already have one) and it has been an awesome underwater fisheye lens for my Sony a7rV. Really good for close focus wide angle too.