I have an Olympus E-PM2 and I'm interested in using a Helios-44M lens I have. I live in Europe so I thought I'd look at Amazon UK. There's a whole bunch of options there. Which one should I get? I know many people use this lens so I would like to hear from experience if there's any that works without having to grind it or other issues. I've read auto-aperture causes problems. The one I have has a manual-/auto-aperture switch.