As far as I know (which isn't very far), you should try to keep the exposure time fairly short. The aurora "flickers", sometimes rapidly, sometimes slowly. I have seen some very good pictures taken at 30s, f:3.5 with 800 Iso film. And others at 15s, f:4, 100 Iso... So depending on film size I would go for a moderately fast film, wide aperture, and somewhere around 8 to 60 seconds... has some very basic hints - their conclusion seems to be "experiment".