Ground Glass holder from Film Pack Adapter Question on 9x12cm

OK, tired of procrastinating; need to get this done.

When you adapt a film pack holder for an AVUS 9x12cm camera to a ground glass focus viewer, must you shim the glass equal to the thickness of the film pack itself? By that, I mean the metal cartridge that fit into the holder...

It would seem that the thickness of the metal lip of the yellow holder has to be accounted for; correct?

There is a standard for large format film holders but the web page is gone, so here is a copy.


The ground surface of the ground glass must be at the same distance from the edge of the holder as the emulsion side of the film is in a holder.
Measure one or two existing holders with a caliper to find the Depth to film surface.

9x12= 3.54 inches X 4.72 inches so the Depth to film surface is likely .197 ± .007 inch.
4X5 sheet film is .007 inch thick.

To clarify what Charles wrote, you'll have to shim the GG back from the front of the FPA. His table tells you how far behind the front surface of the FPA the GG must be.

Thank you very much!