My camera (4x5) is a Graphic View II, for which I've just ordered a Satin Snow GG to replace the old scratched plastic screen.
Likely discrepancies between the GG plane and my film holder planes had been on my mind, and while anticipating the arrival of my first pack of film, I thought I'd check things out..
I began by checking the film plane to front mounting surface of my film holders, and found they are consistently .010" under the ANSI standard (0.197, +/- 0.007"). No matter, I thought, as long as I can shim out the new GG to match my film holders..
Removing the existing 'GG', I found it was made up of two parts -- a plastic Fresnel screen, and a plastic GG. The strange thing was that the Fresnel was in front of the GG!
Now, I think from what I've read that this is incorrect, that the image-gathering surface (i.e. GG) should be the first thing that the image photons encounter. That is, unless my old camera is strange in this regard. Maybe ideas about GG focusing and the position of Fresnel screens were different way back when..?
Anyway, as things stand, the locating plane for the GG in the glass-holder is a full 0.050" (1.27mm) closer than the film surface in my holders. It's a pain in the butt, but I can probably cut strips of gasket material and shim the new GG out by that amount, and all will be fine. I'm guessing 0.050" would make things quite a bit of out-of-focus. (I hate to think how many old cameras out there have no relationship between their GG and their film holders).
Apart from that, am I missing anything?
Oh yeah -- can you actually have the Fresnel in front of the GG? (Moot point in the case of my old camera, as this still doesn't bring the two surfaces to within tolerances!)
And after all this, of course, the film sits a thou or so above the holder plane -- or wherever it wants(!) Just add that to the +/- 0.007" manufacturing tolerances, and it's wonder anything is infocus!
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