Hello! I am looking for a nice, sharp and not too expensive medium telephoto in m42 mount (at less 135mm, as I already have a 85mm f/1.8 ). Any idea? For now, the best price/quality ratio seems to be with the Jupiter 37A-AM 135mm f/3.5; any experience? Even more important, does anybody knows if there is mirror issues for that lens with the 6D? Thanks for the help!