To automate DSLRs, I use gPhoto as a library and as a CLI (simple as, apt-get install gphoto).
Getting crisp focus on stars with a DSLR is a pain in the neck! We need autofocus for long exposures. I don't care if it takes 20 min, as long as I can be kissing Tracey under the stars while the machines autonomously take care of the tedious setup.
Just like in robotics, the math never matches reality "Infinity" ≠ ∞. Heat/cold causes things to change. Cameras are made to go "to infinity, and beyond!" so that autofocus PID controller can overshoot, etc. It changes by a couple microsteps throughout the night even. Even once automated, it's not perfectly repeatable because of backlash in the motor - have to approach from same direction and completely reset if it overshoots. All the same stuff as in robotics.
Some manual suggestions include autofocusing on a distant street lamp or the moon if it's out, or to manually focus on a distant mountain during the day and then don't touch it until nighttime. Otherwise, you get is as close as possible by eye and then take many test shots.
I'm looking into algorithms to determine focus quality, but at the very least for now we can use this bash script to take test shots from which to choose the best setting. Then, use this script to experiment with ISO, aperture, shutter speed, ... Finally, capturing the sky with this one.
Notice that ∞ is indeed blurry and it's not until about ∞-14 that it becomes clear. These are in microsteps ("Near1", smallest allow by Canon):
- ∞
- ∞-1
- ∞-2
- ∞-3
- ∞-4
- ∞-5
- ∞-6
- ∞-7
- ∞-8
- ∞-9
- ∞-10
- ∞-11
- ∞-12
- ∞-13
- ∞-14
- ∞-15
- ∞-16
- ∞-17
- ∞-18
- ∞-19
- ∞-20
