How does "F" ratio affect imaging

[Starkler (Geoff)]

Originally Posted by Dennis

However, visually, at the same magnification, the bigger light bucket will make the galaxy appear brighter if your eye can accommodate the full exit pupil of the eyepiece.

To expand on this, if you have the same exit pupil size (aperture/mag) any size scope will show the galaxy at the same brightness (assuming transmission losses are equal), but at a bigger image scale (smaller fov) in the larger scope.

The limiting factor of course is the maximum size that your pupil can dilate to when dark adapted.

[astroboy]

Most this sounds fine for extended objects but back in the film days it was understood for stars aperture is the main thing , this is why I had to expose a 20 mm F5.6 shot for 90min on film to get enough stars for a good milky way shot.
I dont think CCD makes much differance but if you take the focal length too far the stars may behave like extended objects.

Zane