Boy, that sure sounds easy doesn't it? I wondered about the gg thickness so I tried some substitute glass while I was having a piece of glass (satin glass) prepared which may give you other considerations to take into account in preparation of your gg.
In another thread I mentioned using a substitute glass #1 (s.g. #1 http://www.largeformatphotography.in...ad.php?t=37482) which was a piece of glass designed for framing. It was about the same thickness & was coated to protect the print (art) from adverse effects of the sun.
The second piece or substitute glass (s.g. #2) was much thicker, in fact it was so thick that when I put it into the frame, it actually extended above the frame by a height that was close to the original G.G.! I was using these as a means to do some shooting with the camera I am (was) building, to see how well the adaptations I was making worked as I went through the remodeling process. S.G. #2 was stock ground glass from a factory, a stock item. The first time I used it, I came to the crux of a real problem with the glass => grain size. I went down to the pier & they were preparing for an triathlon to be held about a week later so I wanted to make some test exposures of the participants as they made their preparations for the real deal.Swimmers would enter the water swim the length of the pier to a buoy, then turn & swim to the far shore where some steps had been placed in the water so they could get up the retaining wall. I set up along the entrance (drive out) to the pier intent of shooting those who were just swimming the first leg (foreground running parallel) but allowing for those in the lead (second leg running perpendicular) as a group shot. First problem even with the 500mm len, the swimmers offered little more than their heads to focus on so I tried focusing on the kayaks which were being used to escort. The grain in that area turned out to be as large as the kayak that I was trying to focus on!
So much for the substitute glass but how does the thickness of the glass (gg) itself effect the focus? See attached photos, note taped glass is s.g #1, the cracked glass si s.g #2 ( broke while mounting glass as I reversed the part which held glass in frame) & the mounted glass is Satin Glass via Dave.
Note the piece [part] used to secure glass, I certainly didn't want a repeat preformance which broke the substitute glass.
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