Canon 5D MkII In-Camera Noise Reduction
Washigton-based night photographer Brian Chapman has posted an update to his long exposure tests of the Canon 5D MkII. In this update he repeated his earlier long exposure experiments, this time he shot for 15 minutes at base ISO of 100, and compared in-camera noise reduction both on and off.
Very interesting results. I think it's clear from his experiments that the Long Exposure Yucky Threshold for the 5D MkII is some point well beyond fifteen minutes.