>>2613635Basically I do the focus on a bright star (like vega, sirius..). I use the "live view" function on my camera with the maximum digital zoom (x10 on my canon). The star should be big enough on your screen to find a good enough focus. Better if you can see this live view on a laptop or bigger screen. There are software like backyardEOS or Astro Photography tool to control the focus (and every other settings) from a computer.
With telescopes, the focus will slightly move with atmospheric and temperature changes. Not sure if it plays a role in wide field. I usually take all my gear outside 1 hour before the shooting, so it can adapt to outside temperature. And when I take a lot of frames, I have to check if my focus is still ok (like every 20 or 30 minutes)
