Acrylic for ground glass

[Kirk Gittings]

Sooooo. We are thinking about going over to making some acrylic ground glass for our view cameras at the university I teach at as they come back in broken. You know the story. Students are REALLY hard on equipment. Are there any downsides to using acrylic for this purpose. I know some of the ULF guys use acrylic for theirs for obvious reasons.

[Drew Wiley]

It tends to bow with temp or humidity differential one side vs the other. You can pay a premium for a special type that is baked out first, but I doubt anyone will
actually go for that option. I wouldn't worry about deflection unless someone is trying to do very precise work or is using something bigger than 4x5. I'd never put
it on 8x10; but contact printers can get away with things I can't enlarging. The other problem is that it scratches and hazes easily, so the smooth side might get
beat up. It will obviously take a bit of practice to get an ideal grind pattern for focus.

[vinny]

Should be fine for 4x5 cameras. My 8x10 wehman came with one and it was thick enough to not flex when a loupe was applied.
Look into window frost material to stick to the acrylic as well. I've seen some very fine stuff used on sets but never got ahold of a piece to try myself.

[Mark Sawyer]

I made one for my 14x14 studio camera, using 1/4" thick and sanding with 320 grit using a DA sander. It works well as long as I don't push hard with the loupe. One big problem is scratching; I use a soft rubber barreled loupe and have no problems, but if your students are breaking the glass, they may just scratch up the acrylic.

[Erik Larsen]

I had one on my Ritter camera. It didn't flex and worked well enough, but it was about a stop less bright than the canham gg I replaced it with. I keep it as a backup.

[Drew Bedo]

What about the Fresnel magnifiers sold at book stores? Could something like that be incorporated into the project?

[jose angel]

In my experience, material bow could be of an issue here. I have experienced this even on a on a 4x5" screen (I stopped using them for this reason), so in larger ones it could be inusable.
But obviously, any possible bow could be noticeable or not depending on the desired CoC (aperture and enlargement). I have not calculated it, but on 4x5" and at a portrait distance, using something like f16 gives a -huge- marging for the focus error, if we plan to print 8x10".
I actually haven`t tested different materials. It could be interesting to find or make cheap "real" GG screens to have spares at a very low cost (say, $5); they could be even cheaper to make than acrylic ones. Students could be in charge of their gear; if someone get the screen broken, he/she should pay for a new one. Maybe this also will help to make them more responsible with that gear.

[vinny]

In my experience, material bow could be of an issue here. I have experienced this even on a on a 4x5" screen (I stopped using them for this reason), so in larger ones it could be inusable.
But obviously, any possible bow could be noticeable or not depending on the desired CoC (aperture and enlargement). I have not calculated it, but on 4x5" and at a portrait distance, using something like f16 gives a -huge- marging for the focus error, if we plan to print 8x10".
I actually haven`t tested different materials. It could be interesting to find or make cheap "real" GG screens to have spares at a very low cost (say, $5); they could be even cheaper to make than acrylic ones. Students could be in charge of their gear; if someone get the screen broken, he/she should pay for a new one. Maybe this also will help to make them more responsible with that gear.

making students more responsible? That's funny. Making them cost $5 would likely result in even getting broken.

[Jim Fitzgerald]

On my 14 x 17's I use acrylic covered with window frost that I got from Lowe's. It works fine. Now that is for 14 x 17's. All of my other cameras have ground glass. Also I'm careful.

[Tracy Storer]

I have used acrylic for decades on 20x24 and for shorter times on smaller formats. Use a thick-ish piece and it won't bow. Try to get cast rather than extruded acrylic, it machines better. FYI acrylic with clear plastic protective covering is extruded, paper covering is cast.

[Cor]

Kirk,

I guess you have already seen the thread on the Bohemia Acrylic Ground Glass (http://www.largeformatphotography.info/forum/showthread.php?120052-Review-Bohema-Studio-Poly-Acrylic-ground-quot-glass-quot). IMO it's quite coarse, but at 4*5 bending is a non issue since it's quite thick (but I do not use a loupe though, just take off my glasses..)

Best,

Cor