Strange optic device that I have not had much luck in figuring out. The device itself has typical German feldgrau green paint. Marked R.F. 3x12.5 FENNEL KASSEL 141 with a large hand painted 25. There is a finger twist screw in nut to attach it to some sort of equipment. The optics are nice and clean and shows 6 lines forming a cross hair of sorts. The form fit case is typical German military with a belt loop and spring tightened closure strap. On the side is stamped FENNEL KASSEL 1937 with a waffenampt WaA380. I have found this company making survey equipment the images of which all appear to be postwar. Whatever this is for they did not make many of.