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Ground Glass
Ground Glass construction is easy and cheap. I was pricing ground glass for my camera and found that it is pretty expensive compared to what I could do myself. If you have the equipment available you can cut it yourself and grind the edges. If you can't, go to your local glass shop, an auto glass place will do. They cut and ground the pieces for me for about a buck a piece. Not bad, eh! I used double thick glass so I wouldn't have to worry so much about it breaking in the field. I had four pieces cut for me 4"X5" with a 1/2" cut off the corners. I also got two more full sheets about foot or so square. One piece will provide me backup for the future and the other piece is what I used to grind with. I tried a couple of methods to frost the surface of the glass. I'll tell you what worked and what didn't. First, what didn't work. I got some Armour Etch, a glass etching cream, and tried that. It etched the glass alright but the frosting was dark and uneven and not at all acceptable for camera work. I tried it two ways, the first by spreading it on the grinding glass surface and then putting the focusing screen against that. No joy. I tried it again the same way but I thinned the concoction. Again, no joy. Two pieces of glass later I was not happy. Next, I tried some wet/dry 600 grit sandpaper with a sticky back. This created a useable focusing screen but it took along time and still wasn't quite satisfactory. In a pinch it will work. I peeled off the back paper and stuck the sandpaper onto the grinding glass surface (right in the middle to give you room). I put a little water on the surface of the sandpaper and put the glass I was grinding on top of that. Working in circular motions rub the focusing screen onto the sandpaper rather vigorously. Work on it about 15-20 minutes and the surface should be useable. One problem I found, besides wearing out your arm, is that the sticky back doesn't last too long and you have to trade out sheets of sandpaper fairly regularly. The most successful way I found to get the job done was to get a couple of ounces of 500 grit Aluminum Oxide power or an equivalent substance. There are many substances that are used to grind glass in industry and any will do as long as it is 500 grit or finer. I found a couple of places on the internet that carried Aluminum Oxide and the cost was pretty cheap. I got lucky and one of the places I called, after asking how many 55 gallon drums I needed, they sent me four ounces for free. Just check around, you'll find a good deal somewhere. I also understand that valve grinding compound will work as well (you can get it at any good auto parts place). Take a tablespoon of Aluminum Oxide powder and mix it with a bit of water to make a nice thick paste. Put the paste in the center of your grinding glass surface and put your focusing screen on top of that. Work it in so it is evenly spread over the surface of your focusing screen. Try not to get any on the top, unetched, surface of you focusing screen (if you get some on there just don't work it in, it will scratch the surface pretty quickly). Working in circular motions rub the focusing screen into the paste rather vigorously. Work on it about 10-15 minutes and the surface should be perfect. After the surface is ground to your satisfaction rinse it off and clean it up. From here you can paint on some lines if you wish (I chose not to). Here is what other people found worked for them:
If anyone has any other suggestions please let me know!
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