1. Reciprocity - is there an equivalent with digital sensors or is this now completely irrelevant? Or is it compensated for by technology?
6. Speed - does digital handle low light better than film? I know film goes grainy and digital gets noisy, but how do they compare for low light hand held use?
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One thing that I haven't seen yet in the other answers.
Besides raising the ISO, the traditional method for dealing with low lights is long exposures.
Digital does indeed not suffer from reciprocity failures, but many cameras have noise appearing with long exposures (long being as short as 15 seconds).
This is the result of the dark current of the sensor that becomes visible together with actual image information if incoming light is very weak. This is integrated over time. Most DSLR deal with this by exposing a second frame the same lenght as the actual exposure and then substract the result electronically.
The facto, this doubles the actual exposure time of images, which can from a user standpoint been seen like a kind of digital reciprocity failure. It shows up in a stepwise matter for exposures as short as 2 seconds, and always doubles the exposure time.
When this is done, the noise issue disappears almost completely with top of the notch DSLR like the Nikon D2x and Canon 1ds2, but it is still very present with some of the medium format digital backs (Leaf, Mamiya ZD to some extend).
Even with DSLR, there is a bit of smearing that shows in very long exposures, but it is often not really a problem.
One problem that can occur with really long exposures is the appearance of an ugly green cast, but that also shows up with film.
Finally, even a D2x that probably has the best battery around will not be able to do an 8 hours star trails with one fresh battery. The technique used by most people doing these things with digital is to supposed 30 sec exposures taken one after the other. This has less effect on battery, and does also not induce green casts.
Regards,
Bernard