Made in Japan this 16mm projection lens has a 2" focal length f/1.2. The front lens clear diameter is 1-1/2" and the rear lens clear diameter is 5/8". Has at least 4 elements and all appear are multi-coated. The housing is 3-1/4" long by about 2-3/16" in diameter. Towards the rear of the housing is it is threaded 1-1/16" long with a diameter of 2. May make a nice 2" 51mm telescope eyepiece with some adapting.