I recently tried to shoot star trails with my 40D but got a lot of noise. I shot at ISO100, f/16 and 45 minutes, long exposure noise reduction off. I did shoot in RAW, but I was so frustrated I deleted the photo before trying noise reduction in LR. I've heard that digis can't do long exposures like film. My questions are, is there any way to do a very long exposure (30 minutes+) without ridiculous noise? and what is the longest exposure I can get a good photo with on my 40D.