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The Effect Of Aperture On Light Polution

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Posted by Pete P/">Pete P on July 22, 1999 21:47:13 UTC

Please consider the following two statements:

1. There is an astronomers old wives tale that you can't use a 'scope over 3" aperture in light polluted areas without loosing significant contrast. (This is supported by statements in the latest Orion catalog as well as throughout website comments.) 2. S&T's City Astronomy states that "No telescope can make an extended object appear any brighter: all it can do is provide magnification for you to see it better."

Since the two statements are contradictory, one is correct and one is incorrect.

I suspect that since "general seeing " conditions usually limit magnification, and since smaller 'scopes don't have extended magnification, they're by definition "unlimited." Maybe this is the basis for statement #1.

Since "extended objects include planets, the moon, and nebula, I expect they also include the atmosphere through which we are attempting to observe. Therefore, my particular belief is that larger apertures don't improve the contrast of planets, etc., but they don't hurt either. The f ratio of the 'scope seems to have no bearing on the outcome. Increased magnification will darken the sky as well as the extended objects, but will not darken stars. But going from 75X to 150X on a 10" scope will have the same effect as with a 3" scope.

Anyone out there care to agree or disagree?

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