[Hoges (John)]

I'd setup last night to take 6 x 5 minute exposures on Centaurus A - I got one done and then the clouds rolled in. Looking at last night's photo made me wonder - more time = more signal = less noise. So, what practical limits are in place for DSLR (or astrocams) length of exposure. My Centaurus A photo is 330 seconds at iso 1600 and I can see the light pollution is starting to make it's presence felt there, so I feel I'm approaching the practical limit in this part of the sky. But, given a nice dark sky and if the autoguiding is good, why not 10 minutes? 15? 20? The one obvious thing that strikes me is that you wouldn't want to be 18 minutes into a 20 minute exposure and have Elon Musk's Sky Hoons turn up and party all over your exposure!