本帖最后由 z_g_yang 于 2015-2-19 08:22 编辑
这是公式: http://www.televue.com/engine/TV3b_page.asp?id=86#.VOXvhS44d8M
Exit pupil = Objective diameter / Magnification
= Eyepiece focal length / (Objective f/#)
所以,只和物镜口径和放大倍数有关,其余的因素是不起作用的。
看着段,和焦距也无关。
Myth #3: Faster telescopes show brighter images.
This is a misconception carried over from photographic use, where the fast f/ratios do mean brighter images and shorter exposures for extended objects. Telescopes with equal apertures and equal magnifications have the same visual image brightness, regardless of the objective's f/number.
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