Originally posted by bricha ... I wish I had F2.8 so I wouldn't have had to go to ISO 6400 but all have is F4.
If you are going to combine multiple exposures, you can have it all. Both lower ISO and pinpoint stars baring any coma a lens may have. You just need exposures around 2 to 4 minutes depending on things.
Perhaps you can get the Pentax GPS Astrotracer or build yourself a
Barn Door Tracker. You can find plans online from simple to complicated. For 5 minutes or so you can get by with a simple tangent type. You don't have to constantly keep rotate these things ( like a motor would) if you have a wide angle lens on them. You can rotate them on increments of say 5, 10 or 15 seconds depending wide your lens is and how sharp you want your stars.