[cybereye (Mario)]

OK,

I'm still trying to decide which would be the next best scope to upgrade to and now I'm looking at an ED120 APO refractor, in particular the Skywatcher Black Diamond or the Megrez 120 f/7.5.

I guess my main question is: if I take a 5 minute image using my 8" f/5.9 newt do I need to take an image 4 times as long (double the exposure time for the roughly one f stop difference and double again for the roughly half decrease in aperture) to get the same image?

If so, what is the advantage of going to a refractor?

Cheers,
Mario