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Strange Polarizer Test - Strain Or Not?

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Posted by on March 30, 2000 06:08:55 UTC

Steve Swayze is currently getting ready to grind a mirror for me. Before starting in, he had a look at the blank with a pair of polarizers to look for signs of strain in the glass. His observation was rather strange. I reproduce his message below:

"It looks like a nice piece of glass, but I have some concern. I put the polarizers on either side of it, and in places around the edge, the
darkening affect from the polarizers, doesn`t happen. As I turn the polarizers to each other, they darken, but the light still comes through
the mirror. It doesn`t darken like the polarizers do. On a good blank, the glass doesn`t normally change what the polarizers are doing. This is
all I know about what`s going on. The bad blanks I`ve seen, have real funny bands, or loops, or streaks showing up inside when the polarizers are
placed on either side of the glass. This one is different in that respect. What it`ll do, is unknown to me. We just have to grind and polish, and hope to God we don`t see any astigmatism. I`ve seen blanks with funny bands or stripes in them, and they perform great. Others, not so lucky. I don`t like seeing anything unusual. I`ll plan on just moving ahead with it, and we`ll find out I guess."

Anybody have any thoughts?


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