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Knife Edge Testing

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Posted by Joe/">Joe on May 3, 1999 12:51:07 UTC

I am now finishing and parabolizing my 8" f/8.1 mirror. I have a question about knife edge testing. I think I am doing it wrong.

I set the focal plane to the back of the knife edge test. I can move the knife towards the mirror and cut into the focal point and darken the left side of the mirror. However, I can not darken the right side of the mirror because I can not move the knife back any further. Therefore, it appeared to me that I had a perfect sphere because I was not able to properly cut the knife it to the focal point. Am I supposed to set the focal point of the mirror more towards the mirror so I have more range of movement for the knife edge?

Also, how long does it usually take to parabolize an 8" mirror?

Thanks, Joe

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