I have the 75mm but unfortunately it suffers from doublet separation in the rear element as Precision Camera Works has deemed it. I just received a 50mm I suspect also has this problem. Should I simply keep on looking for a good copy or is this just the outcome of Mamiya 6 lenses down the road? Are Mamiya 7 lenses fairing any better? I might have to try that route but I much prefer the 6.