It's a Suntar Auto 135mm f/2.8 M42 mount. I just bought it, so I hope it's good. The only example images I could find where these. The pictures look nice and sharp and have good color, so I'm hopeful. I want to start getting into portraits and I've read repeatedly that 135mm f/2.8 lenses made very good portrait lenses. Does anyone have one of these? If you do, what do you think of it? Can you post some shots taken with it? I would have asked before purchasing, but I found it right before it ended. I didn't have much time to think, lol.