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Posted by Daniel Johnson on October 11, 2002 03:30:11 UTC

Meade and Celestron focal reducers are available from most vendors (,, etc ). Remember, the LOWEST power that you can use with any scope is about 4 times its aperture in inches--beyond that, your eye can't dilate to accept all the light, and it can seldom use that low power well. I find that 6 or 8 power per inch of aperture works better, for several reasons:
1)It puts most of the light in the more accurate, central part of your cornea/lens system, instead of at the periphery, which focuses poorly.
2)If you are under any but the darkest skies, or if you are near or past retirement age, your pupil won't dilate fully anyway (with age, you lose a lot of your eye's aperture because dilation stops working well, and city lights also block dilation).
3) If the exit pupil (the cylinder of light leaving the eyepiece from each star) is maxed out to your eye's full dilation, you can't move your eye a single millimeter without losing light. Higher powers give smaller exit pupils.
I own a 10-inch SCT and don't use powers below 50--usually not below 60--for dim objects.

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