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Old 18-09-2020, 06:24 AM
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Slawomir (Suavi)
Going visual

Slawomir is offline
 
Join Date: Sep 2014
Location: North Queensland
Posts: 3,217
Image brightness and focal ratios

Hi all,

I'm starting to explore visual astronomy and due to a lack of experience I'm wondering whether in visual astronomy slower focal ratios mean dimmer images, given the same aperture and the same magnification (and the same skies).

For example a 10" f/4 and a 10" f/15 at the same location, as long as eyepieces are matched so magnification remains the same in both telescopes, my gut feeling tells me that image brightness should remain the same
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