Excellent advice above!
I'll re-iterate most of it with my experience and maybe offer a few more points.
I was fortunate enough to be in New Zealand last November and see/photograph the Southern Lights. Then, less than a month later, I was in Alaska to witness/photograph the Northern Lights.
I've been doing astrophotography for over 30 years, but Borealis was only something I dreamed of...not living in the right areas.
As mentioned, without a DSLR, don't bother too much. When in NZ, on a star gazing tour at the top of Queenstown, we could see the faint glow of a vertical light. Looked like a wide, very faint spotlight - with the slightest difference in contrast with the background sky. When I put my camera to it at ISO:16,000 at 5 seconds shutter with an f/4 lens, the sky exploded with color! Enough to stop the sky tour as everybody with a cell phone was taking photos of the back of my camera.
Alaska was similar, except as what you might experience in Iceland: the aurora was ALL around us...not just in one direction!
So here is a basic list of what you should have with you:
- Tripod: nothing fancy, just to hold camera still for longer exposure. Ideally, small, compact and light for trekking with. I used nothing more than a set of
monopod legs and
monopod tilt head or simply set it on the ground facing straight up...propping the camera with something for more angle. But ideally, a light tripod with ball head will get you more flexibility
- Wide, fast lens: my recommendation goes to the Zeiss 15mm Distagon. I rented this a few months ago for shooting the Milky Way in Washington state. VERY sharp lens, wide, f/2.8 for alot of light to let in and best of all, it locks at infinity. Most lenses go past infinity and will make your shots soft. Either way, make sure you use live view or test shots to get your manual focus set properly before committing to composure or exposure.
- Camera: Ideally a full frame body will get you the most field of view. The newer the body, the better ISO capability it'll have. Some newer ones have intervalometer built in, otherwise rent a pocket wizard or remote trigger with timer if you want to do time lapse.
- ISO: as high as you need to get the look you want based on shutter speed. Noise can be cleaned quite a bit, blur cannot.
- Shutter speed: This is your flexibility point. Long exposures get you more fluid, massive curtains. Shorter exposures get you tighter, threaded groups: great for time lapse. Both offer great photos, but your style may sway toward one or the other.
The key to ISO and shutter is to see where your limiting return is based on sky brightness. But keep in mind that contrast can be more tuned in after the shots are taken with some basic editing.
I'll be heading to Iceland next year, but unfortunately in the summer. Also planning a trip to Longyearbyen one of these winters to get 24 hours of darkness.
Be sure to check out SpaceWeather.com for the expected aurora forecast when you're there.
As mentioned: above all: look up and enjoy the show!