Graflex.org

[Scoop]

A recent acquisition for me has been a 4x5 Crown. Unhappily, the groundglass was broken.

I decided to make my own replacement part - the ones I've seen on ebay recently are going for more than 25% of what I paid for new jewel.

Starting with a piece or ordinary window glass that I had on hand, I began to grind the surface (it is a groundglass, after all) using 80 grit sandpaper in a random orbit power sander. This was doing the job, and I would hsave had quite a decent focussing screeen after about 30 minutes sanding.

I decided to accelerate things a bit and changed my grinding medium to 180 grit silicon carbide lapping compound (people my age might have some left over valve grinding compound stored somewhere). I merely smeared this on the glass then used the 80 grit paper in the power sander as a matrix to rub the lapping compound against the glass. After no more than two minutes, the glass was frosted to the same extent as the broken screen which I was replacing. The screen is in the camera now and so far as I can tell, will serve me well.

If you don't have all of the exotica which I used, there is no doubt in my mind that ordinary silicon carbide sandpaper (probably wet grade paper) rubbed against the glass surface by hand would produce a perfectly suitable groundglass with about 30 minutes effort.

I do suggest that you purchase the window glass already cut to size - about 3 7/8" x 4 7/8" for my Crown . This will probably set you back about the price of a Hershey Bar.

I ground a 12x12" piece then cut my screen out of it.

[R.H.]

You've got me thinking, maybe some thin plexi-glass could work also. I just know it would be easier to file.

[Les]

Ihad a plate camera that I wanted to use modern film holders with, but the new holders shifted the film plane.

By milling a rabbet in some plex and sandblasting the inner surface I was able to get the needed shift without modifying the camera.

The only difference is that even though I used a very fine silica sand, the surface is much rougher than acid etched ground glass. The image is there, but I can't use much more than a 4x loupe

[glennfromwy]

I make my own ground glass when needed by simply cutting plain glass to size and spraying it with several light, even coats of NO VUE window frosting spray.
Go easy, build it up very slowly until it's like you want it. NO VUE is available in the paint dept. of any good hardware store. I find it gives a much finer image than a lot of the ground glass you can buy.

_________________
Glenn

"Wyoming - Where everybody is somebody else's weirdo"

[Scoop]

Following up on Les's reply, the glass which I made with the 180 grit compound is indeed coarser than the one which it replaced. I use a 7x loupe and that's about all of the magnification which I would use at present.

The 180 grit is relatively coarse material for lapping compound - I used it because it cuts quickly. I imagine that the surface could easily be refined by following the initial "grind" with progressively finer lapping compound say 250 then 400 grit.

Plexiglass (Perspex (?) to the Brits I think) opens the possibility of etching the surface with a solvent, much as hydrofluoric acid is used to etch ordinarly glass. Has anyone tried this?

[Murray@uptowngallery.org]

I was going to eventually try Silicon Carbide grit on acrylic sheet, but haven't yet.

I have made a few pieces of ground glass up to 11"x14". I used a blend from a lapidary (rock-polishing) supplier. 220/200 blend was too coarse for me. The 400/500 with an overabundance of water was really easy. I sanded the edges of both pieces first to spare my fingers. I used dry SiC powder, not the grease suspension used for valve grinding.

A 5x7 piece took maybe 10 minutes including rework of 'bald spots'. Too little water and it gets muddy & 'binds'.

Murray

[dvonk]

in response to the use of plexiglass for ground glass- the glass of my top handle speed mustve been broken by the previous owner (among committing some other atrocities to the poor camera), and it was replaced with plexiglass.
now, the plexiglass idea should work, in theory, as long as it is the proper thickness. mine does an alright job, but the guy who made it must have taken 2 minutes to hand sand and 'eyeball' the size of the plexiglass. i had to cut it down to make it fit properly, but the shoddy hand sanding job leaves much to be desired and creates focusing difficulty. it is soon to be replaced by real, acid-etched glass.
i guess what im trying to say is that the plexiglass can work, given you actually care about focusing and take more than 2 minutes to sand it. its probably cheaper than real glass as well.

[t.r.sanford]

If you're going to use "Plexiglass" or some other transparent plastic, why not get a small plastic Fresnel lens and sand the smooth side? Sort of a built-in condenser.

I picked up a couple of 7x9" Fresnels with matte-finish backs from a surplus outfit, a decade or so ago. I've used them for lighting effects, but they might make dandy focusing screens, now that you mention it.