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[ATM] aperture mask /astigmatism

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Subject: [ATM] aperture mask /astigmatism
From: jeff newsom <triolian@earthlink.net>
Date: Sun, 23 Oct 2005 09:32:25 -0600 (GMT-06:00)
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Reply-To: jeff newsom <triolian@earthlink.net>
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My first mirror (a 14.5" porthole) ended up with a reasonable case of astigmatism. Not a big problem for deep sky viewing but an obvious problem for planetary viewing.The use of an aperture mask virtually eliminated this problem. I noticed on David Harbours page he talks about using an aperture mask for folks who  themselves suffer from astigmatism. It seems I've stumbled onto a nice solution, thoughI'm not sure what the mechanisms are for reducing the astigmatism. Any explanations?? Is it simply a reduction of that area that is astigmatic?
  Thanks--Jeff Newsom
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