Roll Film backs have different set backs.

[Wayne Crider]

In comparing two rolfilm backs I have, a probably newer Graphic 6x7 24 exp (yellow handle) and a later model Wista 6x7, I can visually see a difference in the setback to the pressure plate. Have you encounted this and how are you compensating for it. My use is on a Crown Graphic camera, and I would prefer to use the newer Wista back which has larger rollers. I'm thinking the Graphic back has the correct setback for focus and if it does, I'll have to compensate the GG view for the Wista, yet I'll need to use film holders as well. Thoughts?

[Oren Grad]

There are differences in film plane register among different roll holders. Scroll down a bit on the following page and look for the table labeled "Roll Film Holder Availability":

medfmt.8k.com/mf/rollfilmback.html (http://medfmt.8k.com/mf/rollfilmback.html)

Unfortunately, the Graphic and the Mamiya RB backs are not included, but the data in the table do confirm that there are variations.

[jose angel]

And big variations. I´m on the same matter with different cameras and holders. I didn´t be worried about roll film holders because I scarcely use my Wista 6x9 holder. Now I have read on Oren´s link that mine could be 0.30mm off. Great.

For a long time I thought that LF was not as sharp as I expected... time later I found that my super-expensive and bright plastic screen was not absolutely flat. I replaced it with a simple&cheap GG, and sharpness arrived. I must say that since then, I am also more careful when focusing. The finer grain of my ordinary GG helps also.

If you like accuracy, I think the only way is to load the holders and to take precise real measurements of each component. The GG must be always in the same plane with the film´s emulsion. If not, you must add shims to your GG. If you enjoy a fresnel between the GG and the lens, things are not as easy.