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Re: Knife Edge Testing

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Posted by Robert May on May 3, 1999 20:31:45 UTC

: I set the focal plane to the back of the knife edge test. The test is done at the Center of Curvature (radius of the mirror surface), not the Focal Length (1/2 of CofC). You should be able to see the entire mirror darken at the same time if the mirror is spherical. If you are doing a double pass test (light goes from source to mirror under test, to flat, to mirror under test and finally back to the tester where you see it. When setting up, insure that you can make the cut of light both ways before doing any measuring. I have occasionally not done so and have had to restart the test with the tester moved to a new location.

: Also, how long does it usually take to parabolize an 8" mirror? Did a 10" recently and it took about 2 hours total of polishing work and testing. The owner of the mirror was amazed that it took so little time.

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