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In Reply to: Can anyone explain me how the digital works at low light condition? posted by Romy on October 01, 2001 at 09:02:56:
But, basically, there's an error (noise) ever time the CCD is read out, due to the charge on the electron. this noise grows as square root of the number of reads. There's also a cumulitive noise effect due to thermal electrons from the CCD. There are also a couple of semiconductor effects due to surface crystal structure problems, etc, but I've not used CCD detectors now in about 20 years at the gut level, so I don't recall all the effects, but what it comes down to is that while film is "stable" to the tune of worrying about reciprocity, CCD's have noise that adds as a function of time.When photons are very scarce, this noise can be the primary "signal", which isn't very useful, I agree.
Now, SOME CCD's, used with liquid gases to cool them, do incredibly well in the 10-hour exposure department, but we're talking handheld cameras, right? :)
JJ
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