Long exposure problems

Hi everyone.
I have encountered 2 problems with shooting long exposures of night sky while using EOS 20D and TC-80N3 remote. Not to run out of battery, I am using an AC-E2 for power.

1) the exposure time for the photo is never what I set the timer to keep the shutter open. a 4 hour exposure prodused a photo with exposure time of 1393 sec. (23 minutes) and a 5 hour setting made a 5019 sec. (83 min.)

2) the photos are very grainy even with the NR turned on. I have tried keeping the camera cool, turning off the NR, locking the mirror but none makes a lot of difference.

Any suggestions?

thanx
Vahid

Haven't tried anything like that kind of long exposure with my TC80, so I can't offer any comments there other than trial and error. Are the times consistently as you reported? is this based on a stopwatch reading or EXIF data (wwhich I wouldn't trust for that length exposure)?

Inevitably, long exposures will be noisy due to the sensor heating up as it is left on. Have you turned on automatic noise reduction? You might also want to use some noise-reduction post-processing software straight off.