How to Focus on the Stars at Night for Astrophotography

Learning how to focus to infinity at night as one of the first great humps along the astrophotography learning curve. The infinity mark on the lens will almost always be close, but not quite. The optics will change very slightly as the lens adapts to nighttime temperatures. You'll need to find your focus at night to. 

STEP 1: Look directly into a bright light source. 

No, not really, that was just a test to filter out the visual astronomers. I'm sure they've all rage-closed the page now, but just in case: This guide is for astrophotographers only. None of this will work for visual astronomy because human eyes are weak and uninteresting. Once you have upgraded to cybernetic oculars, then you can revisit this guide for use in visual astronomy. 

Okay, let's start over:

STEP 1:  Focus to the infinity marker left by the manufacturer. 

Yeah, that one, the one I said didn't work earlier. Whatever, it's a starting line, not the finish, gosh!

STEP 2: Point your camera at a bright star
Don't use a planet for this one. It just complicates things. Something like Vega, or Spica, or even Alcyone will work nicely. If you don't know where any of those are, that's okay too, just nod and point your camera at a big, bright one before anyone notices.

STEP 3: Zoom in on the Live View

Can you see what you're doing? Zoom in more. Adjust the focus ring very slightly so that the star is at its smallest point. 

Get serious, you can't do this alone
Our weak, human eyes just kind of fail in the dark. Focusing this way is really hard, and you probably still don't have perfect focus. This is where we bring out the Bahtinov Mask to get precision focus.

Bahtinov Masks diffract the income starlight to create a clear focal point. As you adjust focus, the spikes will move into position. 

"WAIT, STOP! I DID ALL THAT AND MY CAMERA LOST FOCUS DURING THE NIGHT. MY PICS WENT FROM IN FOCUS TO OUT OF FOCUS," Karen fumed.  

Woah, first of all, uncapslock. Second, it sounds like Dew has formed on your lens. Don't wipe it off, just pack it up and try again tomorrow (you should probably toss a silica gel packet in your camera bag though). 
 
Dew Prevention is the name of the game. We'll get a blog on that going next time...