This is a M39 mount lens for the view lens of the Tokyo Kogaku (Topcon) "Primo Flex" twin-lens reflex camera. At the time, this company produced high-quality lenses that rivaled Nippon Kogaku. Even now, the "Primo Flex" is a popular model among twin-lens reflex cameras. I think the secret to its popularity is its stable and sharp image quality. Since it has an M39 (L39) screw thread, it can be attached to Leica cameras, but focus will not be achieved unless the flange back is adjusted. There are some scratches on the exterior, but the optics are mostly free of mold and dust. There is a very thin hairline on the front element, but I took a picture against a white background, and it produced a clear and crisp image without any flare. It is a 3-group, 3-element triplet lens, and it shoots in the center of the 6x6 format, thus eliminating the drawbacks of triplet lenses. Although there is no aperture and it is shot wide open, it still produces quite good images even in close-up shots, and I think you can enjoy the Topcon's image quality. Thank you for your consideration.