I've been walking around with my Konica TC with a fungal prism sporting a CZ Jena "Biotar" lens lately.
It's a funky lens. Quality control wasn't all the best. There are bubbles in the lens. But it is strangely super sharp. On my Nikon D40 it is a 87mm equivalent focal length. And it has done very well as a very tight portrait lens.
It was because of these digital lens test that I've decided to use it with film.
Well, the Konica+M42 adapter+CZ Jena lens has so far been an auspicious set-up. I used it to take a portrait of John Noble, the actor, who stars on the show, Fringe, and played Denethor in Lord of the Rings.
I also took it for a test run in Lynn Canyon. It's a regional park with a very nice suspension bridge and trail. Even in the rain, it makes for an excellent day out.