I have the same lens S/N 3052 and it uses waterhouse stops. The glass is great and I use mine on my largest camera which is my 14x17. Not much room for movements and it covers. I believe it is a 20 inch 508mm lens. Great glass don't ever sell it. I have not used mine enough and will do some portraits and landscape with it soon. It is like a wide angle on my 14x17!