Quote:
Originally Posted by janoskiss
if you go wider you are throwing light away (using a smaller effective telescope aperture).
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Thankfully, not everybody seems to think so
http://www.vixenoptics.co.uk/Pages/sg_2.1x42.html
http://www.televue.com/engine/TV3b_page.asp?id=102
"Throwing light away" and "using a smaller effective telescope aperture" by stopping down the exit pupil with your own pupil is of approximately zero consequence
in unobstructed optics. In fact, stating it like that is misleading, because it suggests that the image will be darker. Wrong. The image simply stops getting brighter, and that is because it's the same brightness as what you see unaided, only magnified (for extended objects that is - point sources like stars do look brighter because their light is not being spread out over the magnified area). So if you want super widefiled, go for it. Unless of course your scope has a secondary mirror. You see, the exit pupil is just a small image of the entrance pupil - the telescope's objective. So enlarging it enlarges everthing in it as well, such as the secondary' image. And when its size gets close to your own pupil size, while the outside of the exit pupil is being cropped away by your own pupil, well you get the idea. "Lowest practical power" is strictly a problem of obstructed optics.
Apologies to the OP for moving off topic a bit here.