Making a Ground Glass Focus Screen

Valve grinding paste is far to coarse so isn't suitable.

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Ian

Is a new grinding blank required every time a new piece of ground glass is made? I gave it a go this weekend but because I was anxious to try it out, I had a large piece of glass with a smaller (but still large, maybe 5x5 inches) piece of glass on top. I put some grit in between, added a few drops of water, and started going at it. The piece that I was using as a grinding blank (the two pieces of glass were equal in thickness), got ground before the piece that I intended to grind got ground. This may just be because of the size of the bottom piece though that I was trying to grind. I need to get my hands on a thick 3x3 piece or just cut a piece myself. Does the thickness of the grinding blank matter or is the only reason for its thickness is to make it easier to handle?

Yes keep using the same grinding blank, and it will get ground faste as it's a smaller area that's one reason why I get blanks made from thicker glass, the other as you've realised is a thicker piece is far easier to work with.

Ian

I've made these for focus checking on 35mm and 6x6 but I did two at a time in those sizes and it worked fine.
I got the grit from an optical bloke, and a ground up to 1000 grit although that was maybe overkill...