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Old 31-10-2007, 10:07 PM
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rogerg (Roger)
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rogerg is offline
Join Date: Feb 2006
Location: Perth, Western Australia
Posts: 4,542
I use a starfield and Astrometrica to calculate the exact focal length (and hence focal ratio) of my telescope. It takes a little work first time to work out how to do it, but then gets easier.

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