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Subject: Re: [M]: focal planes
From: W. Miller
Reply To: mapug@shore.net
Date: Sat Dec 28 00:31:04 1996

Here is another possibility:
If you are using a filter and focus on the moon, you should have
to refocus when viewing a star or dim object without the filter.
This is because light travels slower through a glass filter (higher
index of refraction material) than in air. To avoid refocusing you
could use a clear filter of same thickness on those dim objects.
This is more common knowledge for those of us using CCD cameras.

Bill Miller, Los Gatos, CA