I tried capturing a few star trail images while we were out in Chaco Canyon last week. Not really crazy about any of the results, but here's the best one:
This was a 30 minute exposure at f4 with ISO set to 400
A few lessons from my first attempts at this genre:
1. It really does help if you compose your shot in the daylight before it becomes totally dark (doh!).
2. I discovered my D70 is limited to a 30 minute exposure. Obviously this limits the length of the trail I can capture without going to multiple exposures and combining images, but still long enough to get some interesting results IMO.
3. Fully charged and healthy batteries are important. I found a 30 minute exposure would take a battery showing fully charged on the camera down to about 25% charge. Ambient temps were probably 30-35* or so, which is probably cold enough to affect battery charge. Also, my batteries are kind of old, dating back to when the D70 was actually a camera that people wanted to buy. Finally, it should be noted I had noise reduction turned on which results in a lot of post exposure in camera number crunching.
4. I need more practice with light painting - I had a few flubbed shots due to over zealous attempts.
It was a lot of fun and I plan to try some more when I get a chance.