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I probably wasnt very clear in the howto on the visual checking part.
In viewing a star the real test is what shape you see when focus is very close to, but not quite at focus.
One can focus in and out to see the rings in a startest, but these rings should become smaller and diminish down to a round dot or small blob as you approach focus. If seeing any other shape there may be a problem with astigmatism.
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