Quote:
Originally Posted by a-l-e-x
My question is, if it has nothing to do with the brightness of an image visually, why then do you need longer exposures when you hook a camera up to the scope with instruments that have a longer f ratio? Does this also include point and shoot digicams afocally held right in front of the eyepiece or just dslrs?
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The f ratio for photography through a scope is only relevant for extended sources. i.e. anything that isn't a star. It makes essentially no difference to the brightness of stars. It does make a difference to the size of the field on the camera.
To image very dim stars the aperture of the scope is the most important thing and not the f ratio.