When I lived in Interior Alaska, where temperatures often fell below -30 degrees F, my manual NIKON FM2 35mm single lens reflex camera on a tripod with a cable release in hand was the only way to photograph the northern lights. While I am certainly am excited by the technological advances of digital cameras, there's something to be said about photographic film. Digital camera batteries cannot keep their charge very long in extreme cold. Many of these cameras also don't have the option of a bulb setting for on the fly custom time exposures. Also, the nature of digital CCD chips has a feel of one dimensionality while film has layers of emulsion that response to different light color and produces a non-linear transition from dark to light that mimics a truer appearance of the aurora as seen by the eye. Sure, film at low temperatures has the problem of being very brittle and during advancing or rewinding the film can tear and it can induce static sparking that appears as spider-like scratch patterns across the film. Film is also inherently grainy at higher sensitivity and far from uniform in structure. Film is expensive; if you make a mistake with a digital shot, it doesn't cost you anything.
While these comparisons seem large, the fundamentals for taking a great photo of the aurora apply to both mediums. Use a wide-angle 24 mm to 50 mm lens and set it to the largest or second largest aperture opening numerically, this will be the smallest or to avoid spherical aberration of star images, the second to smallest f-stop (i.e., f/1.4 to f/2.8). Exposures of 5 to 12 seconds work well unless the aurora is faint or mostly stationary, in which case the exposure time should be doubled. If the aurora is bright, moonlight and city lights should not interfere and can offer an interesting foreground:
Because the aurora is only visible under clear skies, photographers will often be shooting in temperatures below zero. They may be running inside and outside with their camera to keep themselves and the camera from freezing. Condensation will form on the lens in the warmer interior and fog-up or ice-up the lens. Therefore, always be prepared to wipe the lens clean in order to get the clearest picture. It is also a good idea to tape the lens to infinity focus so that it doesn't slip and cause your images to be out of focus. Never forget to take your lens cover off. Yes, this has happened to me on occasion to my great despair.
Whether using digital or film cameras, I recommend using an ISO (old ASA) setting of 400 or 800, which is a good compromise between detail and quality of the image. Bracket your exposures (i.e., one 5 seconds, 10 seconds, and 15 seconds). The good news is that with today's editing software such as Photo Shop, images can be corrected for exposure, color, graininess, and even imperfections or the removal of unwanted objects. My experience with aurora images is that they are recorded as too bright and too green as compared to what the eye sees. While these uncorrected images can appear dramatic, they are exaggerations of reality.