I seriously doubt that you can judge the quality of a 6x7-optic on a standard
computer screen.

I own a 50mm for the RB (Sekor C with FLE), a 50mm for the Mamiya 6 and a 43mm
for the Mamiya 7. The RB lens is clearly weaker than the other two lenses...
but this isn't astonishing, the Mamiya rangefinders have the best optics
money can buy, and this is like saying Rolls Royce is better than Mercedes.

Compared to a SL66 4/50 Zeiss Distagon, the Mamiya lens is better. I have a
100x120cm enlargement from a Delta 100 negative made with the 50mm RB lens
here on my office wall, and you can easily see tiny details (<1mm in the enlargement).
Ok, the extreme edges are going softer, but from 40cm distance this isn't
noticeable and this expected from a retrofocus lens.

All in all, an excellent lens, buy it.

Martin

I have the 50mmm and its sharp as a tack, however I am using it less
and less and using my old Super-23 more because of the format.  The RB
is not a true IDEAL FORMAT of 4x5 proportions, its a bit squarer.  I
fond myself using the 645 back more to same film and I also picked up
a Rollie SL66E (complete kit) for %28 at an estate auction but its
jammed.  When its fixed I'll be using it alot more.

THOM