Like astronomical CCDs and unlike film, DSLRs make it easy to subtract a reasonable amount of sky fog from the picture. This is partly because their response is linear and partly because it is easy to stack multiple exposures. In the suburbs, a single 15-minute exposure might come out overexposed, but five 3-minute DSLR exposures are easy, and you can combine them and set the threshold so that the sky is relatively dark. The results are not quite equivalent to what you'd get under a dark country sky, but they are much better than what used to be possible in town.
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