Film Plane vs. Ground Glass Plant

[John Hartung]

An issue that I have seldom seen addressed is the potential discrepancy between the film plane and the ground glass plane. Discounting the possibility of a defective or worn film holder, are LF cameras rated for their integrity in this regard? I have read only one review which mentions this issue -- of a Zone VI that was, on average across the two planes, 0.02 inches discrepant. Given typical depth of focus in the area of 0.1 inches or less, is it an issue that careful focus with a loop on the GG will always be a bit off on the film plane? If so, do any field/technical cameras have a particularly good reputation in this regard . . . is metal likely to be better than wood? Thank you for sharing your knowledge. John Hartung (hartung@post.ha

[CW]

Yes, and no. Yes it is an issue, with some cameras being better than others. But, no there probably isn't much you can do about such slight variations. I find the old press cameras to actually be the best in this regard, probably due to their rigid metal bodies. I think what you will find first with cameras is actually a misalignment at the lens. Most field cameras, especially wooden ones, have quite sloppy zero indicators for the front standard. Some don't have any detents at all, just marks. That leads to unintentional tilts and swings, that even when slight, screw up the focus across the film plane. I find it ironic that I can achieve an excellent squareness with an old Crown Graphic that a Gondolfi can't even come close to. I have various cameras, but the Crown is the only one I will use at night anymore because of this. I suspect the modern metal technical cameras like Horseman and Linhof are very good as well.

[Glenn Kroeger]

John:

This issue is discussed repeatedly on this forum. Bottom line, you need to check the registration. This can be done mechanically with dial calipers and other contraptions, but the easiest and most reliable way is to check it optically.

Robert Zeichner (sp?) published an article in View Camera a few years ago on an excellent way to do this. Bob frequents this Q&A and I am sure he will chime in with the exact reference.

[John Hartung]

Thank you all for much help -- especially R.A.Z.

[Robert A. Zeichner]

Yes, indeedy! I do offer my two cents on this topic from time to time. My article, however is not posted as it was part of the Nov./Dec.'96 issue of ViewCamera and I've never asked Steve Simmons if posting it would be a problem with him. I am, however emailing a scan of it for you to examine and if you have any specific questions, I'll be happy to try an answer them for you.

BZ

[John Smith]

Concerning the zero position of the front and rear swings, it seems to me that for certain cameras, it's best not to rely on any markings to set to zero. Instead, insert a square piece of something and flush both standards up against it, then lock the standards down. This way you know the standards are at least parallel. This should solve the problem.

H

[Clark King]

I believe that article is posted on this forum actualy. It is an interesting read!

Clark