In short, each pixel is a material where when a photon hits it, an electron pops out (the photoelectric effect, and the only one of Einstein's three pivotal papers to actually win him the Nobel Prize). Put together a bunch of them and you get a CCD (astronomy) or CMOS (commercial digital cameras). Everything other than the sensor is identical in film and digital.
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http://en.wikipedia.org/wiki/Photoelectric_effect
http://en.wikipedia.org/wiki/Charge-coupled_device
In short, each pixel is a material where when a photon hits it, an electron pops out (the photoelectric effect, and the only one of Einstein's three pivotal papers to actually win him the Nobel Prize). Put together a bunch of them and you get a CCD (astronomy) or CMOS (commercial digital cameras). Everything other than the sensor is identical in film and digital.