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RE: Missed Post

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Posted by Rick Crockett on March 22, 2000 06:06:16 UTC

Hi Boz:

I suspect that you meant to ask this of the general forum members but to them it probably looks like you are asking walt or myself.

Basically there are two test you can apply. The Foucault Test is a null test when performed with a star. No matter what the optical configuration is, if a knife edge cuts the focus and the image of the mirror dims uniformly across its entirity then th optic is figured correctly. Then there is the method of examining the Airy disk with its diffraction rings. Using a good eyepiece rack the focus in a 1/4 to 1/2 turn or so. If the seeing is good and the scope performs well, you should see a series of progressively dimmer concentric rings. If the rings are evenly spaced, nicely round and quite concentric, things are starting to look good. Now rack the same distance outside of focus and hope the image matches the same. The precise analysis of what one may see has been documented in this and other forums and extensively in various observing books. If your test doesn`t impress you as being good then you may want to dig further or invite an experienced observer to evaluate what you have.

Cheers,
Rick

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