I have a 521/16 with the fast f/3.5 Novar. I don't think I would shoot it wide open unless as a last resort, because of both the optics and the difficulty of hitting focus with that depth of field. Nevertheless, from f/5.6 on down it's a pretty sweet performer. Certainly not as good as the Tessar versions, but at least as enlargeable as a nice 35mm lens. It's also extremely pocketable, and because it was so cheap I take it places I would not take an expensive setup.