The in-camera NR feature has worked well for me on the d70 and now the d200, although it really cuts into your battery time, and thus exposure time. Sean
One way to avoid too much noise creeping in is to take a series of images, and stack them. http://www.tawbaware.com/is_help/imgstack_help.htm#stack Scroll down a bit and you'll see a star trails example.
The d70 was 30 min of course since it didn't have the 10 pin terminal. With the D200 (and 2 batteries in the vert. grip) I think I've done about 90 minutes without running out of juice. Chris (cgaengineer) and I talked about this awhile back and he was going to pursue the limits of this further, but I never heard what he came up with so you might pm him and see how far he was able to push the batteries.
Glad I can help out, Thom. I plan on doing a lot of star trail images up at the lake this summer. The city is far too bright for this stuff. We should have a time-lapse contest at the end of the summer!! :biggrin:
