I recently took an hour long exposure to get the star trail effect with my Canon XSi.?

Question

Small red dots show up in the background (noise) and I can't figure out why. I have the ISO set to 100 and I used a tripod with a remote. How can I avoid this in the future, or do I need to digitally take it out?

Answer 1

From what I've read, that kind of noise is just an artifact of the sensor.  You could digitally take it out.  You could also just take multiple shots and average them together.  You did everything right.  You're just hitting up against the limits of your camera.  

"Having said that..."

Noise is caused by heat.  You could come up with a creative way to keep you camera cool.  I've never been dumb enough to try it, but maybe a enclosing the camera with in a semi-airtight container with a few pounds of dry ice?

Answer 2

Next time, use the noise reduction feature in your camera. If that proves insufficient a program like Noise Ninja should help. Your Owner's Manual should have information on making long exposures. Read and heed.

Make your long exposures as soon as you turn the camera on. Then turn it off and allow the sensor to cool before your next long exposure.

I'd advise against trying the dry ice in a box idea. Cold has an adverse effect on batteries and you might just chill them enough to leave your camera inoperable.