I have done a comparison shoot between the following lenses: Carl Zeiss G Planar 45/2, Carl Zeiss Planar ZM 50/2 and Konica Hexanon 50/2 lenses, all in Leica M Mount. Please have a look at this dedicated page for the results and feel free to comment on it.
For me the Hexanon looked the best. I just feel it produces smooth grey’s and a nice range. There is an obvious difference between the Planer 45 G and the Hex and Planer 50 ZM. How do these all compare to a Leica 50?
Unfortunately I do not own a Leica 50 to compare them to, otherwise I would have had it run alongside with the others.
As for grays and tonality, it is difficult to judge. I tweaked the levels in PS so that the images would all look similar enough to compare general rendering properties at various apertures. I don’t think this comparison and the process (scanning, adjustment etc.) can say much about the tonality or contrast of these lenses.