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Hmmm interesting....The 9mm SHOULD be ok to use for this purpose...How far each side of focus are you going John? The "seeing" conditions have to be pretty good for a star-test. Also the star you're testing with, has to be fairly high up in the sky. Is this a 12" mirror we're talking about here? If so, 1 hour is not enough time for the mirror to cool successfully...My 12.5" takes at least 3 hours..Sounds to me like you're taking it too far each side of focus....perhaps?.....John, the 4 spikes you are seeing is from your 4 vaned "spider" holding your diagonal mirror....this is normal.
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