Last month I was in search for a long, wide-aperture lens. 77LTD was too slow, FA*85 too expensive, etc, etc. Then I found a Contax Planar MMJ on fleabay for cheap, and I also bought a Leitax conversion mount. The conversion was pretty painless: unscrewing the old mount and replacing a small lever within the lens. I also cut out a slot for the body's locking pin and made insulators so that the body would recognize it as a f/1.4 - f/16 lens. Furthermore I also unscrewed the lens mount on my K20D and stuck a piece of aluminum foil over the 'A' pin to allow matrix metering.
The bokeh is pretty smooth at close distances, but can get a little rough around the edges at f/1.4 and 50ft. out. You have to stop-down meter, but since the camera thinks it's at f/1.4 all the time, you can stop down to whatever you want and the exposure will be accurate. Things start to sharpen up really nicely at around f/2.8. I think I'm getting the hang of this LBA thing