First of all, some of this may seem rudimentary; I don’t mean to insult anybody’s intelligence, I just don’t know what your skill level is going in so I’m including some basics.
Second, my bona fides: I’ve been doing nature photography for years, and doing a lot of nightscape photography for 5 or 6 years. I’ve had the opportunity to shoot the northern lights on two trips, one to Iceland and one to Lofoten, Norway. I’ll be going to Alaska in March to shoot them again. Here are a couple of samples.
Gear
Tripod: Use a sturdy tripod, either carbon fiber or aluminum. I prefer a tripod without center column because raising the column makes the whole thing much less stable. You’ll be doing relatively long exposures, so you want as much stability as possible.
If you use an aluminum tripod, I highly recommend you purchase some cheap pipe insulation from Home Depot and duct-tape it to the upper section of one of your trips legs. Aluminum will suck the heat out of your hand like nobody’s business. (https://www.homedepot.com/p/Everbilt-3-4-in-x-6-ft-Foam-Semi-Slit-Pipe-Insulation-K7PXE048078HD1/327682713)
Lens: Use a wide, fast lens. By wide, I’d recommend something in the 15mm to 24mm range. By fast, I mean a lens with a minimum f-stop of 2.8 or smaller. You’ll be doing everything manually, so don’t worry about image stabilization or anything else fancy. There are some really good, relatively cheap, third-party fully-manual lenses that are great for astrophotography. My main astro lens is a Rokinon 24mm 1.4 (https://www.bhphotovideo.com/c/product/819786-REG/Rokinon_24mm_f_1_4_ED_AS.html). If you don’t want to buy a lens, I’ve had good luck renting from Aperturent.com and LensRentals.com.
Remote Shutter Release: I’m partial to a wired remote release, but you can also use apps on your phone. Canon’s app is called “Canon Camera Connect” and is available for Android and iPhone. If you don’t to do either of these, use the 2-second delay feature on your camera’s shutter release setup. This will allow the camera to stop shaking after you press the shutter release before it takes the picture.
Technique
Shoot RAW: Shoot in RAW format. This will give you the greatest flexibility in post processing.
Shoot in Manual Mode: This will to allow you to completely control the exposure. I haven’t had much luck shooting in Aperture or Shutter Priority mode.
White Balance: Set your white balance to somewhere in the 3500-5500K range. If you’re shooting RAW, you can adjust this in post, but I like to get it close in-camera so things look right on the LCD screen when I’m reviewing my shots.
LCD brightness: Turn down the brightness of your LCD. Once your eyes get adjusted to the dark and you start reviewing your shots after you take them, if your LCD is at normal daytime brightness everything will look very bright on the screen. You can actually get fooled into under exposing images this way. So if it’s set to 6 or 7 during the day, turn it down to 2 or 3 at night.
Manually focus: If you’re using a zoom lens, set your zoom to where you want it for your composition. Then, point your camera at a bright star. On your LCD screen on the back of the camera (use live-view if you’re not using a mirrorless camera), magnify that star as much as possible (15x if your camera supports it). DO NOT ZOOM the lens, just magnify the image on the LCD. Now turn your focus ring until the star on the LCD is as small and sharp as possible. Don’t depend on the infinity marker on the zoom ring; your actual focus point will probably be near that but not on it. If you want, once you have focus set, you can tape your zoom ring in place using gaffer’s tape to prevent bumping it.
If you change the zoom level at any point, you should refocus your lens.
Also refocus during your shooting session, just to be sure.
Settings: This is going to depend quite a bit on the auroras and on the camera; you’ll need to play with it a bit to get the correct exposure.
Open up the aperture on the lens as wide as it will go; if your lens is a 2.8 lens, set it to 2.8. Go to a smaller f-stop if you can. If you’re using a fully-manual lens, this will involve turning a ring on the lens itself.
If the auroras you’re seeing are very active and moving quite a bit, you’ll want to use a relatively short exposure, between 1-5 seconds. If they’re relatively static, you can go up to 15 seconds or more. For the active ones, you want to use the shorter exposure to capture the detail; longer exposures will cause them to blur and smooth out, just like shooting a waterfall.
Use your camera’s ISO setting to control the exposure. Assuming you’re shooting in RAW and have access to noise reduction software (either Lightroom or something like Topaz DeNoise), don’t be afraid to go high on the ISO. I’ve shot auroras successfully at ISO 12800 (on a Canon R5). This works fine for shots with JUST the auroras. If you have a foreground element, I’d recommend you don’t go higher than ISO 6400. But remember, the lower ISO, the lower the noise in the image, so keep it as low as you can and still get a properly exposed shot.
Test Shots: Take a lot of test shots. Digital shots are free; take time to set your composition the way you want, using test shots and reviewing them to make sure your horizon is level, there’s nothing weird jutting into the frame edges, etc.
Composition: Personally, I prefer almost all of my nightscape shots to have some sort of foreground element. Whether it’s shooting the Milky Way or the Northern Lights, I prefer them to be a secondary – although interesting – addition to the shot, not the primary focus. That said, there are some great abstract shots of just the auroras to be had and I enjoy those, too.
Post-processing: Assuming you’re using Lightroom, take advantage of its noise reduction feature. This works really well with auroras. Also, boost the clarity of your aurora using a local selection of the sky.
Practice: Familiarize yourself with all these settings and functions at home, in the dark, before you go on your trip. There’s nothing worse then fumbling around in the cold dark snow trying to figure out how to do these things, and potentially missing a shot.
Red lights: Leave red lights at home. Yes, they help you maintain your night vision, but if you get red light polluting your shot, it’s virtually impossible to get it out.
Enjoy the night: This is important: Get out from behind the camera and take some time to just enjoy the amazing spectacle of what you’re seeing.
