Andrew Carlson , Dec 16, 2004; 12:23 p.m.
I haven't tried exposures that long yet but I hope to try my hand at astrophotography with my 20D soon as I can counterbalance the weight on my telescope. I understand that long exposures increase the noise in the image over time. The 20D has a long exposure noise filter you can enable for that and I have read some other posts discussing combining multiple shorter exposures or subtracting in photoshop to clear up the image. The Rebel doesn't have such a filter.