What did Hopf and Satin Snow do differently during ground glass production?

[c.d.ewen]

I don't see that anyone has yet mentioned it, but I've made GG's from diamond abrasives. Using diamond abrasives is way faster than any other abrasive, and not expensive. That was years ago, and I don't remember the supplier or the grit used.

I made a couple of 12x20 and several 4x5 glass plates by gluing the 4x5 plates to the bottom of an orbital sander and using them to grind the 12x20's.

Charley

[Colin Graham]

I was always curious about this too, so last year I finally just cut a screen blank in half and ground each half with progressively finer aluminum oxide grits up to 3 micron until I found the one I liked the most. I installed both halves in the camera at the same time to compare different grits, flipping the back 180° just to make sure there was no dominant eye bias skewing the results. I liked the 9 micron screen, but ground the other half through to 3 micron just to make sure. I didn't like the finer grits at all.

For what it's worth, I bought a Satin Snow screen from Dave back in 2006 or so, and can't tell much difference between it and the 9 micron screen viewed under a loupe on light box.

Most glass isn't very flat, so I usually lap it with 320 silicone carbide first. I use an flat-bottomed element from a cheap telephoto lens to grind with. It's kind of a slog, even on a small screen- I need try Charley's orbital sander/diamond grit trick.

[Peter De Smidt]

Generally, the coarser the ground glass, the less diffusion there will be, and the brighter the hot spot will be. Conversely the finer the grind, the more diffusion, the dimmer the hotspot will be, but there will be less brightness dropoff outside of the hotspot. As others have said, experimenting with different grits is useful to find what works best for you. This depends on the lenses you use. Longer lenses have less of a bright spot effect on the ground glass. Thus, a coarser screen/brighter screen might be best. Wide angle lenses have inherent fall off which can make the corners of the screen really dark. A screen with finer granularity might help. And all this depends on whether you are using a fresnel, as they allow a brighter screen while still keeping the corners bright. Finally, you can experiment with a coarser screen with a coating of something like Renaissance Wax.