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The dynamic range is defined as the ratio between the largest 
detectable signal and the smallest detectable signal. For a small 
signal to be detectable,  it needs to be at least as big as the read 
noise (that's just the common definition, we're dealing with 
probabilities/uncertainties and not with binary true/false here). 
Thus the dynamic range is equal to the ratio between FWC (which 
obviously determines the largest detectable signal) and the read noise.

BTW, the dynamic range should not be confused with the maximum SNR or 
the number of gray levels, because for these, the photon noise (which 
is intrinsic to the signal) must be taken into account also.

Beat

At 16:46 23-07-2008, you wrote:
>Search the CONFOCAL archive at 
>http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal
>Hi everybody,
>
>I don't understand why the dynamic range of a CCD is defined as the 
>full-well capacity divided by the camera noise, and not minus the camera noise.
>
>Thanks a lot for your help,
>
>Laurent.
>
>___________________________________________
>Laurent Gelman, PhD
>Friedrich Miescher Institut
>Facility for Advanced Imaging and Microscopy
>WRO 1066.2.16
>Maulbeerstrasse 66
>CH-4058 Basel
>Tel.: 061 696 43 38 / Cell phone: 079 618 73 69
><http://www.fmi.ch/>www.fmi.ch
>
>