Does anyone know of or can recommend a reliable supplier of ground glass focusing screens. I have several mahogany cameras in the process of restoration but I need to acquire ground glass screens for them? Any suggestions gratefully received.
Simon, why not make your own? If you have the skill to restore wooden cameras, then you shouldn't have any difficulty making ground glass screens. All you need are sheets of 2mm picture glass and some silicon carbide powder, 500 or 600 grit. You can buy this off Amazon, and any local glass supplier will have picture glass.
Cut your glass to size, or have it cut for you by the supplier. Mix some powder with water into a slurry Put a small amount onto a glass screen, place another sheet of glass on top, and grind in a random circular motion. Wash it off to check your progress and the evenness of the abrasion. Replace with fresh slurry two or three times. Finally, clean with running water.
Alternately you can put the slurry on a pad made from a wet rag, and rub the glass with that. You are less likely to cut your fingers on a wet rag!
I did my first one, a 10 x 8 screen, with nothing more than a 900 grit Japanese Water Stone, used for sharpening wood chisels and plane irons. I got it good and wet, then just rubbed it around on the glass in a regular but random fashion, cleaning the glass off with water from time to time to check the evenness of the grinding.
It is worth putting a finished screen into a working camera to check how well it works and focusses. Then you can tailor the amount of grinding on future screens.
Alan's advice is good.
He's missed one small thing that I find important. You should grind off the sharp edges of the glass blank before you do anything else. This will protect your fingers but more importantly, it will avoid having razor-sharp edges damaging the most important surface of your camera. Your fingers will heal...
Choose a time to do it when there's something interesting on the radio.
If you search this forum, you might find more advice.
Yes, I should have mentioned that it is a good idea to first take the sharp edges off the glass. An oilstone, used for sharpening woodwork tools, is good for this.
There are a few other things I could have mentioned. Instead of grinding with a second piece of glass or a cloth pad, you could try using a small flat block of wood, which will be easier to hold.
Instead of using grinding powder you could try just using a small sheet of 600 grit "wet and dry" paper. Fold into three in the usual way, then wet it and rub in a completely random fashion.
David's reference to listening to the radio is a hint that should tell you that this is definitely not a five-minute job. You will have heard of the man who got a job drilling holes in a field and said it was well-boring.....Or the cobbler whose job was so boring he said it was "sole" destroying......Beware! Getting a nice even grind on glass is worse.
A tip that Ian G mentioned elsewhere on the forum was to get a smaller piece of thicker glass and use that as a grinding tool. I've generally used an oversized sheet of glass underneath and rubbed the actual screen on it. I've found that WD-40 is a better grinding medium than water, but it is more messy. Water works fine. You will need several layers of newspaper on your worktop.
I found that IKEA clip frames were a useful source of thinner glass, but you'd have to cut them yourself.
If you want markings on the screen, put them on afterwards with a fine pencil.
I make a lot of GG screens for MF cameras up to ULF, the largest so far is a 15"x12". I have to carry an assortment of different thickness glass. Technically the thinnest that can now be sold to the public for things like picture frames is 2mm. Old TLR's etc need 1.2mm and many German cameras 1.5mm.