We believe this to be a copy lens, but looks like it could make a great spotting scope. The front elements clear diameter is 65mm and the rear elements clear diameter is 28mm. The rear elements clear diameter could be larger if you machine the back part of the mounting on a lathe. Front element mount outside diameter is 79mm. The rear element mount outside diameter is 69mm. The flange diameter is 88mm with a 50mm long flat side. Looks to have a pink anti-reflective coating.