This lens was manufactured by Diop USA for medium wave thermal imager use (3-5u). It has a large front element, the aperture is 100mm. The markings indicate it is F2, which would suggest a focal length of 200mm. It has a remote control connector which we would presume to be aperture and/or focus control.

The lens is in almost mint condition, there are a couple of small blemishes in the A/R coating which are barely visible in the images below. The housing is aluminium/plastic and does show slight signs of handling/use.

A beautiful lens.