EBC Fujinon 55mm f1.8
All I need to say is WOW. I've wanted an EBC Fujinon for years. It is all I hoped it would be.
It's tack sharp at 1.8 w/ a beautifully smooth bokeh. Color rendition is amazingly accurate. Almost no chroma w/ just a tad of green bokeh fringing which can be seen at 200%. Focus is well dampened. Flare is well controlled w/ a uniform loss of contrast across the frame.
The only issue I had is w/ the way the lens meets the m42 adapter. The aperture ring rubs against the adapter which means you have to loosen the lens to change the f-stop. It mounts upside down, too. Despite this annoyance I love this little gem already.