Thanks, everyone, for your comments, but I'm sure that what Bjørn posts will wash these away. Still, it is interesting and fun to try to catch the aurora this far south. The sky goes green and purple and stays that way - quite stable - for longish periods, but the more interesting effects which are worth photographing, are very brief and elusive - perhaps 2 or 3 minutes in a whole hour. Last night I was out from 7pm until 1am and only got around a dozen worthwhile images. The best effects were early in the evening when tall, pale columns of green and purple shimmered across the sky, but the sky was much too bright and there was no contrast between the aurora and the rest of the sky. I tried, but those shots are a failure; my best images came between 11pm and midnight.
I'm shooting these with the 28mm f2 AIS - the hard infinity-stop is useful, and closed down to f4 it is very, very sharp with just a little vignetting in the corners.
