Actually the nominal focal length of lenses can vary quite a bit. And, if they are mounted in different shutters, their optical centers will be in different places relative to the lensboard. This is why Linhof cuts cams individually, matching them perfectly to their lens, then marking the cam with that lens' serial number. And believe me when I tell you Linhof cams are perfect.
Originally Posted by Tom1956
So unless your Optar and your Schneider are precisely the same focal length, mounted in precisely the same relationship to the lensboard, they never will interchange. It isn't the RF's fault.
As for getting cams perfect, I cammed a 6" Goerz Dagor for my Linhof. No sweat, just a bit of patience and skill with a #6 file. If there's any error, I can't find it.