3: Camera settings - exposure

You may already be familiar with the exposure triangle - ISO, aperture, and shutter speed. If not, don’t worry - this part is actually easier in night photography. The low light conditions mean you’re limited in your options, so choosing the right settings is a simpler task. To start with the easiest one:

APERTURE - This is the “iris” of the lens, the circular opening in the front that lets in all the light. If it’s wide open (a small f number like f/2.8 or f/4), it lets more light through. Conversely, the smaller the opening, the less light can fit through it (bigger f numbers, like f16, f32). Photos tend to be a little sharper at the middle values, like f/8 (the actual sharpest aperture depends on the lens). But tack sharp images aren't hugely important for aurora photography. The higher priority is getting enough light to the camera’s sensor. So my opinion is to pretty much always use the widest aperture (smallest f number) that your lens allows. If you look at my camera settings below the photos, you'll see that literally all of them were shot at f/2.8.

ISO - The light sensitivity of the camera. The higher the ISO (eg. 1600 and above), the more light the sensor will pick up. So the darker the environment and subject, the more reason you might have for increasing the ISO. Unfortunately with higher ISO comes more “noise”, the ugly graininess that plagues your cell phone or cheap old digital camera photos when shooting in any low light conditions. If ISO is low (100-200), the photo will be practically noise-free and higher quality. But at night a low ISO setting will likely end up too dark. So choosing the ISO is all about making compromises.

As a very general rule: If you have a cheaper or older camera, I would recommend ISO 800 or so. 1600 could start to be distractingly noisy, even after some post-processing. But if your camera is new or a more expensive model, you can use 1600 or even 3200 without too much of a problem. There are many exceptions to this rule, but it’s a good starting point. Ultimately you'll need to take some test shots in the dark and examine the results on a computer, to decide how high you’re comfortable pushing your ISO. Post processing makes a huge difference, so remember to use noise reduction in your preferred editing software before deciding what your maximum ISO is.

SHUTTER SPEED - As you already know, the longer the shutter takes, the more light ends up on the sensor and the resulting photo. When it’s very dark, it’s typically necessary to use shutters several seconds long. The downside is motion blur: things that move end up blurry with long shutters. Stars become lines instead of dots, and auroras become blurry and lose their definition. So once again you need to compromise. You have to let enough light in for the picture to not be too dark, but shouldn’t take so long that the northern lights end up looking like a large green blob all over the sky.

We chose a wide open aperture and high ISO, so that the shutter speed can be faster. 2sec is great if possible - faster than that can be difficult to attain with most cameras, unless the auroras are exceptionally bright. 10sec is starting to be pretty slow, and 30sec is usually too slow in my opinion, for most lenses and situations. Of course there are always exceptions. The thing that really ends up determining shutter speed is the brightness of the auroras themselves, as they can vary a lot from very bright, to hardly visible with the naked eye.