I've shot star trails before, but always with film. I'll find myself with a 20D in the southern hemisphere (only slightly, in Tahiti at W149? and S 17?) and want to take star trail photos with the 20D, a Canon TC-80N3 timer remote control, and perhaps a 28/1.8, 50/1.4, or 17-40L/4.0. But I don't know what settings to use. I used 400 speed film in the past, should I set the 20D to 400? Perhaps it's best to use the 28 prime stopped down to 2.8? I also read that with digital it may be better to take several shots rather than keep the shutter open for 4-5 hours. (Could be my imagination but I read of CMOS censor warming up?) I have bits and pieces of information but nothing definitive, and am seeking the right way to do it with a digital SLR. Perhaps I can set the remote to take several one hour exposures (but won't that result in gaps?) or is one contiguous exposure of 3-5 hours possible without the battery dying? Please advise, thank you.