Search for aurora camera settings and you will be handed something like f/2.8, 5 seconds, ISO 1600. It is not wrong. It is the answer to a night that somebody else had, with a lens you may not own, pointed at a display that may have been four stops brighter or fainter than the one in front of you.
The aurora has an enormous brightness range. A faint arc low on the horizon and a substorm breaking overhead are separated by a factor of ten or more. No fixed recipe survives that.
The four numbers, and what each one costs
Aperture. Open it as far as the lens goes and leave it there. This is the only one of the four that is free - a wider aperture collects more light without adding noise or blur. If your lens is f/1.8, use f/1.8. Corner quality suffers slightly wide open, and on this subject that trade is worth making every time.
Shutter. Longer collects more light, and blurs anything that moves. Two things move: the stars, because the Earth turns, and the aurora itself, which during an active substorm changes faster than the stars do.
ISO. Amplifies what you collected, and amplifies the noise with it. Modern sensors handle 3200 and often 6400 well enough for this; there is no virtue in a clean, black, empty frame.
Focus. Not an exposure setting, but it ruins more aurora photographs than the other three combined.
Start from the lens, then adjust for the display
A practical way to arrive at a starting point:
- Open the aperture fully. That fixes one number.
- Pick a shutter from the movement you expect. Faint, slow arc: 8 to 15 seconds. Moving, structured display: 2 to 5 seconds. Fast substorm with rays: 1 to 2 seconds, and accept the noise.
- Set ISO to make that exposure work. This is the number that absorbs the difference between an f/1.4 lens and an f/4 kit zoom.
The order matters. Most people fix ISO first out of habit and then discover their shutter has to be twenty seconds, which turns a rayed curtain into a green smear.
Star trails: the ceiling on shutter speed
Stars move about 15 degrees an hour. How long before that becomes visible in your frame depends on focal length and on the sensor, and the traditional rule of thumb is to divide 500 by your full-frame-equivalent focal length to get seconds.
- 14 mm: about 35 seconds
- 24 mm: about 20 seconds
- 35 mm: about 14 seconds
- 50 mm: about 10 seconds
Treat these as generous. The rule dates from film and modern sensors resolve trailing sooner; halving the result is a safer target if you intend to look at the image at full size. In practice the aurora usually imposes a tighter limit than the stars do - if the display is moving, you will be at a few seconds regardless of what the arithmetic allows.
Focus, which is where nights are lost
Autofocus does not work on this subject. The reliable method:
- Switch to manual focus.
- Point at the brightest star or a distant light and magnify it on the live view as far as it goes.
- Turn the focus ring until the point of light is at its smallest. Not smallest-looking - actually smallest; go past it and come back.
- Tape the ring, or at least stop touching it. Zoom lenses shift focus when the zoom changes.
- Re-check after an hour. Cold changes lens dimensions enough to matter.
Infinity marked on the barrel is usually not infinity, particularly in the cold. Trust the magnified view, not the engraving.
Reading the histogram instead of the screen
A camera screen at night looks bright no matter what it is showing, and every underexposed aurora photograph in existence looked fine on the back of the camera.
Use the histogram. You want the data pushed towards the right without clipping - if the bulk of it is bunched against the left edge, the frame is underexposed regardless of how good it looks on the screen. Shadow noise recovered in editing is worse than noise from a higher ISO taken correctly.
Phones
A recent phone will photograph the aurora, and in some conditions it will photograph it better than your eyes see it. Three things make the difference:
Hold it still. Night mode exposures run for several seconds. Handheld gives you a smear. A small tripod, or the phone braced against a rock or a car roof, is the single biggest improvement available.
Use the longest night mode you can. On most phones the exposure length is adjustable once the phone is on a stable surface and knows it.
Turn off everything that lights up. Flash off, screen brightness down, and ideally a red interface - both to preserve your own dark adaptation and to avoid lighting the foreground for everyone around you.
What a phone will not do well is a fast substorm. The multi-second stacked exposures that make phone night mode work assume the scene is static; when the aurora is moving quickly the result is mush. That is the moment to accept a noisier, shorter frame if the phone lets you, or to put the phone down and watch.
Things worth doing before it starts
- Batteries. Cold roughly halves them. Carry spares in an inside pocket, not in the bag.
- Shoot raw. White balance under an aurora is genuinely ambiguous and you will want to set it afterwards.
- Turn off long-exposure noise reduction if it doubles your frame time. Missing a substorm to a dark-frame subtraction is a poor trade.
- Frame something in the foreground. A ridge, a building, water. A sky-only frame has no scale and every one of them looks the same.
- Set up before dark, or at least before the display starts. Doing it in a hurry in the cold is where mistakes come from.
Then stop taking pictures
The best part of a strong substorm lasts a few minutes. It is worth deciding in advance that at some point you will set the camera to shoot on an interval, or simply leave it, and watch the sky with your own eyes for a while. Photographs of it are common. Having actually seen it is the thing you came for.
Aurora Forecast works out a starting exposure for tonight's activity and for your lens - move the aperture and the ISO follows - and pairs it with a field checklist and a gallery of the forms worth aiming for. It also has a deep red night mode, which is the reason your eyes still work between frames.