I think this is a good analogy, only small distinction is an anti-alias filter prevents higher frequency signals from folding into the sampled data and masquerading as an in band signal. If we sample at 20K samples / sec we must cut off all frequencies above 10KHz to prevent them from aliasing down into the in-band signals. That is, a 12KHz tone would end up being sampled as a 2KHz tone if not for the anti-alias filter. I am sure this is what you meant by the above, I simply am amplifying to it.
To continue the anti-alias filter concept, I suspect the camera lenses we are using act as such a filter. The really high frequency components that would cause alias problems are stopped by our camera lenses. At the scanner one can push the aperture down and down into the single micron range but the film (at least commercial film and not 'spy' film) has nothing more to give up other than the grain or grain clumps (or whatever the term). This is my theory on the subject feel free to take it with a grain of silver.
It should, that is the signal to noise ratio (SNR), should improve as bit depth increases otherwise the added bits are totally meaningless. PMT's do have some noise associated with their operation. The interested student is encouraged to check the Hamamatsu site for some interesting reading on PMTs. Including photon counting with PMTs.
Best,
Tim
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