Quote:
Originally Posted by Wavytone
Then what matters is focal length (limiting magnitude) and focal ratio (time to image extended objects).
Focal length matters if image scale is an issue (e.g. trying to resolve planets or close binaries). For "pretty pics" it's irrelevant.
Exit pupil is irrelevant.
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I don't agree with the statement that limiting magnidude of stars is determined by focal length. If this was the case then a tiny refractor with a long focal length would show just as dim stars as a big light bucket of the same focal length. This is not true. The larger aperture collects more light and for point sources like stars it is the light collection that is important and this is determined by the aperture of the scope.