Recently I upgraded from 4x5 to 5x7, and I am unconvinced that my first dozen or so shots are accurately focussed. In particular, 11x14 enlargements from the 5x7 are not as sharp as those from my 4x5. I do not believe that weather, technique, lens, or film differences are at fault.

Amongst the various other variables at play, the one that intrigues me today is, how do I know that the film in the filmholder, when inserted, is precisely where the ground glass was when I focussed on it? Were it not, how can I determine which is at fault, the camera back or the filmholder? (Hint: the camera is brand new and the filmholders are quite used ;-)). If it is the camera back, what can I do about it? And finally, how likely is this to be be the cause, or am I following a red herring here?

Not being a craftsman, and not owning a micrometer, I think my first step will be to buy a pair of brand new filmholders, maybe that will solve the problem...

Has anyone else encountered similar focus problems and successfully resolved them? How?

TIA,