thanks Brian, i will explain, in my case i'm a traveller so i have to go far in search of a dark sky , that means I ususally can only go out once a month , so, I need to take what i think is the best for only one night. The point is: I use the Halpha as luminance so I need it to be in the best shape i can, Halpha has a lot more signal than o3 and s2 so 300seconds is enough for most DSOs , since o3 and s2 are very faint, in my experience 600 seconds get better result than 300 even with few subs. o3 and s2 puts color in the halpha only. And that's it, if you donยกt understand something please let me know and I will try to explain it, I hope my english is understable at least
greetings!