i tried some star shots over the weekend with limited results, see two pictures. These were taken with 5DMKIII, 24-105, tripod and 30 sec exposure, 100iso. My questions is how to focus in pitch black ..there is probably a really simple answer about this but i struggled to get any infocus. any advice, suggestions would be great as i want to try again...and hopefully get better pic's
The hyperfocal distance at 24mm f/4 is only 15.8 ft, so (greatly simplified) if you focus on anything farther than that, everything behind it will be in focus. If you have foreground elements you want in focus, as long as they are farther away than that, just focus on them and the stars will be fine.
If you're only worried about the stars, then what I'll usually do is set the lens to infinity, and then back it off just a tiny bit. Take a test shot, and check for sharpness at 100%.