Perhaps the single biggest difference between film and DSLR astrophotography is that DSLR images are usually combined (stacked). That is, instead of taking a single 30-minute exposure, you can take six 5-minute exposures and add them; the result is at least as good.
More importantly, if there is a brief problem, such as a tracking failure or a passing airplane, it only ruins part of your work, not the whole thing. Some image-combining algorithms will actually omit airplane trails or anything else that differs too drastically from the other images in the stack. For details of how to combine images, see p. 178.
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