This is a Wollensak 35mm focal length multi-element lens assembly. The front lens clear diameter is 11mm and the rear lens clear diameter is 8mm. The optics have a pinkish/purple anti-reflective coating. The housing is 37mm long by 28mm in diameter. The housing is marked: Wollensak 23 4X 165. There is a slight groove in the metal in the middle of the housing. May need some internal cleaning.