View Full Version : Ever made plexi ground glass?

Ty G
10-Apr-2010, 22:15
Has someone made a plexi or lexan ground glass viewing screen? Does it "grind" like real glass? How is the image quality?

10-Apr-2010, 22:35
Considering making one for a super light weight camera, if you still want to know in a month or two, I will report.

10-Apr-2010, 22:58
wehman cameras come with a plexi gg installed. image quality is good. I haven't made one myself.

Doremus Scudder
11-Apr-2010, 01:36
My Wista ground glass/Fresnel sandwich is plex and works just fine, so I would imagine a plain gg would as well. If I'm not wrong, lots of factory Fresnel sandwiches are plastic of some sort.

There might be issues with flatness on a thin, large piece of plex, but a 3/16 piece for 4x5 should stay flat. Maybe even 1/8 would be alright.

You've got me interested now... Being able to carry a lightweight, virtually unbreakable spare in the field seems a real advantage. Heck, it might shave an ounce or two off the camera weight as well.

I'm looking forward to other replies.


Doremus Scudder

11-Apr-2010, 02:00
Does it "grind" like real glass? ...

No. Much easier...:)

Bruce Barlow
11-Apr-2010, 05:03
Richard Ritter now used plexi for his ULFs. "Why have glass shatter and poke holes in expensive bellows?" he says. Alice, my 8x10, has plexi, and it's wonderful. No to mention lighter.

Richard showed me a comparison of his plexi and a famous-maker glass side-by-side. Richard's was brighter.

So it can be done, and it's a good idea, methinks.

11-Apr-2010, 05:09
I once fabricated a plexi gg for an emergency. Just coated one side with Scotch Tape. Worked fine. Kind of bright, actually.

Paul O
11-Apr-2010, 05:36
I'm 99.9% sure that Mike Walker uses acrylic/plexiglass for the screens in his cameras? They are very bright! I am speaking with him this week so I'll double check this fact!

11-Apr-2010, 06:09
I have one of RRs ULF cameras with an acrylic ground glass. Pexi is a very good choice IMO for ULF cameras. It is lighter than glass, and will not break. Just be careful what you use to clean it because some solvents, acetone for example, will ruin a plexi ground glass. Plexi will also scratch easily, but that is much better than breaking.

A plexi ground glass can be made to be just as bright as a glass ground glass. It is a matter of the technique use to make it, not the material.

Sandy King

David McNiven
11-Apr-2010, 07:51
I often had to make GG's for quick checks of focus on cameras & lenses in for repair and still have the remainder of a 6' x 3' sheet of 1/8 plexi.
I used a grit blaster at very low pressure and some fine sand hammered almost to dust. Nice even results, very effective & quick, quite bright but haven't measured this.
Always meant to try one as a user screen but haven't yet.

11-Apr-2010, 08:26
In the door and window trade a window that is 16 x 20 must have a sheet of glass that is 3/16 of inch thick or greater to prevent breakage. But we photographer insist on using glass that is 1/16 of inch thick. This size glass break very easy and is very sharp when broken. I have seem any a lager sheet of broken ground glass. Once I received a camera that the glass broke and went through the bellows. Just think if it was a new bellow and you just back packed the camera into a remote site reach in to pull the camera and end up slicing your hand open then finding out that the glass also went through the brand new $500 bellows and left it useless.

Optical grade acrylic plastic is the same type of material most glasses you wear to see with. It is about 2% brighter then the glass that is used to make ground glass.

Colin Graham
11-Apr-2010, 09:10
Does the plexi ever distort and throw off the focus plane? Whenever I use plexi for a simple picture frame, the glare angle reflections look distorted from the plexiglass buckling here and there, and that's in a stable indoor environment.

Ty G
11-Apr-2010, 09:10
These are great responses; as I am in the process of making a 20x24 collodion customer camera and was thinking of going this route to eliminate the breakage factor.

Ty G
12-Apr-2010, 23:04
I'll add a bit of info. I have been experimenting with various methods of producing a ground acrylic. Of course the best glass is "ground", there is no doubt there. On glass I use 5 micron and start with a small sander and finish by hand. This produces amazing ground glass. However, I have asked a lot of questions and emailed a few people and I really like the concept of the "unbreakable" acrylic.

So, for two days I have hand ground with various grits, and tried a sander with various grits. AND, acrylic is its own monster! With the hand grinding, I was getting swirl marks that were driving me nuts. Even when I could not see them just holding up light, when I put the glass/acrylic on my camera, I was FAR from impressed. Realizing that this stuff is behaving differently than regular glass, my last resort at 3:00 am last night was to try the sandblaster route. Using super fine abrasive and a small cheapo gun, the results I got were spectacular. My comparison was my own camera with the lens I use all the time, so I KNOW what the image looks like on my glass. I cannot tell the difference between the hand ground glass and the sandblasted acrylic.

The sandblasting was no faster than the hand grinding in all honesty. To produce the product that impressed me, I just took my time.

Carsten Wolff
13-Apr-2010, 01:34
I never seriously contemplated making one, but I do like the idea...Many years ago, I used ordinary paint thinner to give a frosted surface to one side of a sheet of clear acrylic [in an application not related to photography] and if applied only for brief periods, with care, it gave a wonderful surface....the trick seemed in the even application and drying....much easier than grinding I would think.

Nathan Potter
13-Apr-2010, 10:02
Acrylic, plexiglass, etc. is much softer than glass and will resist the fracture characteristics needed to frost it decently. It is as Ty G discovered, difficult to obtain a uniform scattering surface due to the fractured particles of acrylic being soft. So floating around in the abrasive solution they "gum" up the works by sticking to the grinding block while holding some of the abrasive. The far better solution is to use bead or sand blasting where the abrasive particles fall away immediately from the screen surface. It is possible to hand grind with some success but takes a very light hand and minimal grit in an abundant water solution with a hell of a lot of time, and even then it's difficult to end up with a uniform grind.

Nate Potter, Austin TX.

13-Apr-2010, 13:22
Surplusshed has various sizes of "ground plastic". I installed one in my Bahnhof 2A Poco and it seems quite adequate. The Bahnhof #3 will be 7x17 and, as the Surplusshed sizes are insufficiently wide I have two pieces to cut and will butt them in the center, similar to the way a Cirkut is fitted.

Drew Wiley
13-Apr-2010, 13:42
Colin - plexi inherently distorts or bows, usually toward the warmer side. Acrylic is not
a crystalline plastic like polycarbonate. You can buy it baked-out or coated to reduce
moisture activity internally (which affects dimensional stability), but this kind of material wouldn't work for a groundglass substitue anyway. Uncoated plexi also scratches easily and is electrostatic, attracting dust. Polycarb has about 8-10% less
light transmission but is a lot tougher and more dimensionally stable. I don't think I'd personally choose to use either of these except as a protective cover to a true groundglass, but it's cheap enough to test such materials except coated stock, which
will be quite expensive.