Quote Originally Posted by Tom1956 View Post
I'm not looking for any "magic bullet". I am telling you that on 5different Crowns or Speeds I have calibrated--that I have successfully gotten the Kalarts to be so absolutely dead-on within less than 1/8 of an inch of in agreement with the groundglass from 4 feet to 50 feet. I've calibrated these things to where you don't need to use the GG and a magnifier. In other words--perfect. But when I remove the 135 Optar and put on the 135 Schneider, it's off by a good bit. Bothe 135's are marked 135, but they are not exactly. This means that since the top-mounted Graphic finders that use cams cannot possibly be so dead-perfect. The cams are for their marked focal-length lenses. Yes, I can make cams, and yes I am a very meticulous perfectionist worker, but you can sand, file, taper, and labor till you end up in an asylum on a cam and never get it just perfect. The only reason I leaned towards the top-mounted finders is the auto-parallax and the handy push-button beam light. Actually, the top-mounted finders are really plasticy-junky in construction.
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.
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.