Quote Originally Posted by canoli
I've never used the long-exp. NR on my 40D. Do you think it's worthwhile using it? According to David Busch's book it's good for shutter speeds slower than 1 second, although you'll trade off some detail if you use it.

That may be an okay rule-of-thumb, but thermal noise depends on a lot of factors other than shutter speed. It is much worse at higher temperatures (which is why the serious long exposure guys cool their cameras), and like all noise, is most noticeable when the signal is weak. I think your picture looks fine and does not need long exposure NR.


If you took a 5 minute or longer exposure of the night sky, thermal noise would be obvious. I find that in these cases, the camera's built-in long exposure NR works very well.