This is a YMMAR 50mm f/3.5 lens. I believe it's a Hungarian lens. I don't remember where I bought it, but I think it was about 10 years ago. The lens has some cleaning marks. I can't find any information about it, but I remember that it had a very soft rendering near the maximum aperture. It's an M42 mount, but the rear element hits the mirror box, making it difficult to use with a single-lens reflex camera. As a bonus, I'll include an M42 EF adapter. It should work without any problems on a mirrorless camera.