Location: Big Sur, CA / Settings: (12 vertical images) F2.8, ISO 6400, 15 seconds
For this shot I just cranked the ISO about as far as I could take it without totally inundating my images with noise. I'd say about 6400 is as far you can take it with a Canon 6D.. Unless in colder conditions - it's funny that most cameras have a sweet spot with temperature and functionality, I'd imagine around 55 degrees is best for my little mechanical companion.
It took a bit of editing to get it to this point - I brought the highlights out, pushed the clarity quite a bit, and had to do a bit of warping to get all the vertical images lined up with a more realistic horizon.
If you were going to try and shoot an image like this for yourself you'll want a few key things:
1. Dark skies - check out this site to scope out dark skies in your location. Pay attention to the moon phase: (iphone app, android app).
2. The right camera gear - I've put together a list of recommended product here, it's not all-inclusive, but it'll give you an idea of what features you may want to look for in a camera.
4. Set your gear to something like F2.8, ISO 3200, for 15 seconds and see what happens (magic).