This is a Zeiss 50mm multi-element eyepiece or projection lens. When I use this lens to view a flat sheet of paper, I can see over a 2" image field, which is flat, with the central 1.50"-1.75" being very crisp. It may work as a projection lens, I did not test it for that purpose.
What I am sure of, is that it is a geniune Zeiss lens, made in West Germany.
The first $75 plus $6 shipping can have it, and I would think that it originally sold for a lot more than this. The lens is free of sleeks and scratches, even the outside barrel is very clean and scratch free.
The lens measures 1.914" OD by 1.71" long, and 1.815" OD on the threaded flange side, with the threads measuring 1.845" OD.