Well, since I started this thread a little prematurely ( it seemed to work for me) I've experimented a bit more and have arrived at these conclusions.
a) The jupiter 12 will mount on all the bessa cameras.
b) The edge of the rear element of the lens will make physical contact with the shelf (just in front of the shutter) of the camera body when focused toward infinity ( or at infinity).
c) SO FAR, I see no deterioration or marks on the lens element due to this physical contact with the camera body. It rubs only the very outside edge of the element.
d)I would advise that in mounting the lens, always mount it focused close (out) as opposed to focused at infinity (in) to avoid making contact when mounting the lens. Or, never mount the lens when it is focused on infinity.
e) Because the rear element is so close to the shutter, where the meter takes its reading, the rear element blocks its view, especially when the lens is focused on infinity, and is physically closest to the shutter.
f) The meter will however become more accurate in its reading as the lens is focused close -- and physically farther away from the shutter.
g)The meter will approach an accurate, give or take a stop, reading when focused all the way out.
h)I've tried this tecnique on the bessa r3m, the t, and the r and the results are consistant.
Disclaimer: These lenses may have different physical characteristics and so may function somewhat differently in practice. All I'm saying is this works for me with my examples. These cameras and these lenses were not made for each other. The likely reason people say they are not compatable is that either the camera or the lens might become damaged from doing this, so my advise would be be well aware of the risks involved -- dont try this if the risk outweighs the potential benifit -- there are after all, lots of 35's that will work without possible complications.
For me though, the lens is a great preformer, and well worth the risk. And wish there were more non retro-focused lenses out there. Anyone tried the russian 28mm?