In yesterday's mail was a package for me containing some canada balsam and a few optical flats. The flats weren't originally made as flats and aren't as thick as the real thing. But the surfaces of the glass are still flat and the flats were cheap. To 1/10 wave and to 1/20 wave. I wanted to see the interference fringes but a monochromatic light source is needed for sharp lines and I don't have the typical sodium light source used for this purpose. But I do have a green laser pointer which is pretty monochromatic. So I shined the laser through a piece of frosted glass and onto the flats and it worked great. Now I'm gonna check me some surface plates to see just how flat they are, albeit in small areas. The largest flat is 3 1/8 diameter x 3/8 thick, another is 1 1/8 dia. x 1/4, and the last is 1 inch square x 1/4 thick. The canada balsam I bought so I could re-cement some older lenses. Eric
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8 years ago