One if the really great features of the Canon 40D for sunset and night photography is Long Exposure Noise Reduction. This is enabled by selecting C.Fn II:Image -1 and setting it to 1 (Auto) or 2 (On). This is an interesting feature and according to Canon it works as explained below.
Noise reduction will be automatically activated when noise is detected in any exposure over one second. Noise reduction is subtractive, so after the initial exposure, a second exposure of identical length is made with the shutter closed. Noise from the second exposure is subtracted from the first image leaving a pristine, noise-free image. The only downside is the exposure takes twice as long.
As you can see in the shot above, even the deep blue and totally black areas in the image are virtually noise free. Just to see how really noise-free this image was, I exported the raw file from Lightroom as a tiff and opened it in Noise Ninja. Even Noise Ninja’s superb engine could only find a few pixels in the entire image with any color noise at all. Very cool indeed!