Star trails are the marathon of astrophotography. One shot of the Milky Way takes 20 seconds. A star trail takes 200 shots over three hours, and whatever focus you pick in shot one, you're living with for all 200. So pick on purpose.
Two places to focus, two different looks
Focus at infinity for sharp stars. The stars become crisp, thin lines, and you'll see more of the faint ones. This is the look most people picture when they think of star trails.
Focus on the foreground for soft stars. The stars go slightly out of focus, which spreads each one out and makes the trails thicker, bolder, and more painterly. Your foreground subject stays tack sharp. This is a perfectly good stylistic choice, not a mistake, as long as it's the one you meant to make.
Want both? If your foreground is far away (a mountain, a distant tree line), it'll be sharp at infinity focus anyway, especially with a wide-angle lens. If it's close (a tree 20 feet away, a tent, your buddy), shoot your star trail sequence at infinity, then shoot one extra frame focused on the foreground and blend the two. Sharp trails, sharp foreground.
The steps below are for infinity focus. Going for soft trails? Focus on your foreground subject instead, and skip to step 5.
STEP 1: Set up before it's fully dark.
Fumbling with a tripod in total darkness is how lens caps disappear forever.
STEP 2: Switch to manual focus and turn off image stabilization.
On a tripod, stabilization can actually add blur as it tries to correct movement that isn't there.
STEP 3: Find true infinity with a Bahtinov mask.
Point at a bright star, zoom in on live view, clip on your mask, and adjust until the middle spike is centered. Your lens's infinity mark won't get you there. Here's why.
STEP 4: Remove the mask.
STEP 5: Tape the focus ring.
You're about to spend three hours near this camera in the dark. You will bump it. Gaffer tape doesn't care.
STEP 6: Recompose without touching the focus ring.
Aim at your scene, frame it, and start your intervalometer.
STEP 7: Check focus at every battery swap.
Over a multi-hour session, the temperature drops and focus drifts. A battery swap is a natural pause, so take a test shot, zoom in, and if the stars look puffier than you intended, slap the mask back on and refocus. Fifteen seconds of gap in your trails won't show. Three hours of accidental softness will.
STEP 8: Watch for dew.
If your stars get hazy as the night goes on, it may be dew on your lens, not focus. A lens heater strap prevents it.
STEP 9: Repeat step 4.
Yes, again. The mask is not a creative filter.
Gear for this one
Most star trail shooters use a wide-angle lens, which fits our clip-on Bahtinov Mask or Carbon Fiber Bahtinov Mask. Not sure which size? See How to Choose the Right Bahtinov Mask Size. For the full shooting process, see our star trail step-by-step guide.
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