Quote:
Originally Posted by N1
I might add that the lower power limit (i.e. upper exit pupil limit) only applies to obstructed optics. Unobstructed, there is no penalty for going as wide TFOV and low power as your eyepieee case permits.
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That's not so. The light from a distant point-like object enters the eye from the eyepiece as a beam of definite width = aperture / magnification. That beam width is what is called exit pupil. If the beam is wider than the pupil of the human eye, it will simply not fit in the eye. You still get an image but if you go wider you are throwing light away (using a smaller effective telescope aperture). That's got nothing to do with obstructions in the optical path. It's easy to show this diagrammatically using basic geometric optics.
Something like this:
http://www.jayandwanda.com/digiscope...asic_scope.gif