It’s dark. Your autofocus is not going to work the way you think it is. Unless you believe it’s not going to work. Then you are right.
For aurora photography, I am usually shooting at my lowest f-stop, so the depth-of-field is not great. Focus on the foreground will lead to blurry stars and blurry aurora. Typically, for night images, the goal is to have the stars crisply in focus. Unfortunately, for most lenses, simply cranking the focus ring to infinity will overdo it.
Step 1 – Use a Tripod
It would be best if you got a good tripod — not a rinky-dink plastic thing from Wal-Mart. If you are shooting the aurora, you are likely out in the cold. I’ve had a cheap plastic tripod snap on my at -10°F in Fairbanks. If you’re putting an expensive, fragile camera and lens on a cheap tripod, be ready to face the consequences. Additionally, they don’t work well in the cold.
I recommend using a ball-head for a tripod. Ball-heads are easy to adjust, and most do reasonably well in the cold. The system doesn’t need to break the bank. Here’s a base system from Mactrem on Amazon for $60 (I can’t personally vouch for this, but it looks like a sound, affordable system). Around $120-$150 will usually get a set-up that will last for life. Manfrotto, Feisol, and Oben have a lot of good options available. I’ve found them to be very trustworthy brands.
Step 2 – Star Focus – The Simple Method
- Switch to “Live View” mode to view on the LCD
- Zoom in to a bright star or the moon (much easier to find)
- Turn the focus ring until the object becomes sharp. Usually, a few back-and-forth turns of the ring to bring it into and out of focus will help you find the perfect spot
- Prevent the lens from being bumped out of focus turn auto-focus off on the camera
- If you have a focus lock on the lens, use it
- Turn auto-focus OFF on the camera
- Turn auto-focus ON on the lens (usually locks the focus ring)
- Put tape over the focus ring (gaffer or electrical tape work well)
If you prefer to focus on the foreground, this same method applies. Just use a headlamp, flashlight, or another light source to illuminate the subject.
Once you are set-up, it’s time to move on to your camera settings!