Astronomy Site: Meade Advanced Products Users Group Archive: [M]: Re: Focal length changes

 
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Subject: [M]: Re: Focal length changes
From: Michael A. Covington
Reply To: mapug@shore.net
Date: Sun May 06 06:15:45 2001

While you're here, how about checking out the Astronomy Book List ?

Someone asked about focal length changes...

The focal length of a Schmidt-Cassegrain changes as you focus it, because
you're varying the separation of the two mirrors. I don't have an equation
handy, but the changes can be substantial (several percent over just a few
centimeters). When you use a diagonal, you are putting the image in roughly
the place the telescope was designed for, as I understand it.




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