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RE: Flexing A Sphere Into A Parabola

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Posted by Rick Crockett on September 22, 2000 17:15:42 UTC

Hi Pete.

No doubt the bolt would be removed when coated.

Know what? I believe the difficulty factor in producing a good sphere and a good paraboloid is mainly a myth perpetuated by those than have never figured a mirror. Note that I said "good". I have seen some people have a better feel for the work and I use a null test to do my work so the figure is like working for a sphere in a foucault test.

I polished to a paraboloid on my 22" in about 4 hrs. Prior I had polished a 16" to a sphere and then to a paraboloid and that took about twice as long for a much smaller mirror.

I used the same size tool for both (12.5")but a heavier one on the 22". The 22 is Pyrex the 16" is plate and I had to wait longer for testing. I used the foucalt test and mask for the 16" and a null test for the 22".

Try making some paraboloids even in cheap plate glass before going rinky-dink with a stress bolt and I believe you will be happier.

Have Fun,
-Rick

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