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Easy question for me...exposure times are determined by the mount and how well it is aligned as the first consideration.
Second in the city that pre determined exposue time is then tested at varying isos and a choice is made on how I feel...if I feel conservative I go 800 iso if I feel daring I go 1600 iso ..if I feel like experimenting I will try 400 iso or short shots at 6400 iso...fills the time...
ath the moment the 30 second trip works very well for me...firstly my polar is off because I move the mount for building this cube box...and irrespective of the mount etc the sky seems to say to my that 2 minutes will stop it ..so even if I could say do 30 at 5 minutes to fit the numbers the glow may kill it...
Up North its different..I have had a single wield field exposure of 1 hour 20 minutes...manually guided.
I would think the more exposures the better if for no other reason than percentage wise you should have more good ones...and you can always tell the stack program to select if you like to follow the 30 idea..limit its stack to 30.
I stacked hundreds of eta and it semmed better.
alex
alex
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