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Old 02-04-2012, 02:07 PM
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alocky (Andrew lockwood)
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Join Date: Aug 2010
Location: perth australia
Posts: 1,289
They're Newton's rings. Caused by interference and the extremely monochromatic nature of an H-alpha scope. You can take 'flats' by defocussing when you're pointed at the sun and subtract them.
Cheers,
Andrew.
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