I made a couple telescope about 40 years ago (ouch!), and still have some of the supplies. I've tried various grades for ground glass, and my opinion is that 400-600 is about right. The coarser grades will work fine but are distracting when using an 8x grain magnifier.
And remember, if you don't like the result with whatever grade you have chosen, just regrind it with something else. Until you run out of glass to grind you can always change it (although big jumps --- 80 to 400, for example --- should be done in steps, just like sandpapering). If you haven't ground glass before, try this procedure: Place the ground-glass-to-be on a flat, solid surface covered with several thicknesses of newspaper (I do it in the kitchen next to the sink). Sprinkle a bit of grinding grit near the center of the glass and drip a bit of water on it (you'll soon discover how much of each to use). Then use as thick a piece of flat glass as you can find as a grinding tool --- I have a piece of 4x5x1/2" glass, but anything will do as long as you can hang onto it. With moderate pressure grind back and forth, in circles, and randomly over the ground glass. When the grit begins drying out and sticking, add a bit of water. Soon you'll notice that it's not feeling and sounding gritty any longer. Rinse the "mud" off and start over. After two or three times, dry it off, hold it up to the light and look at what you've accomplished. Then go back to grinding, paying special attention to the areas that are still clear. The whole process can be done in 5 to 10 minutes. Myron _______________________________________________ Cameramakers mailing list [EMAIL PROTECTED] http://rmp.opusis.com/mailman/listinfo/cameramakers
