[filmscanners] RE: Newish Digital Tech

["Austin Franklin" <austin@darkroom.com>]

Hi Paul,

> I thought I made it clear that the noise I was talking about was the noise
> intrinsic in the fact that the photons themselves don't arrive in
> nice neat
> streams,

Actually, I hadn’t taken that into consideration.  You may have made that
“clear”, but obviously, I failed to catch it.

> but rather arrive more like the droplets sprayed from a hose.
> Imagine a sensor that detects the impact of water droplets, placed out in
> the rain. If the sensor is a square inch, it will produce very erratic
> impulses. If it is a square foot, it will produce a much smoother
> stream of
> impulses. If it is an acre, it will produce an almost noise-free
> continuous
> output.

Hum.  I have to think about that, I like the example though.  I understand
it, and I need to see if it fits my model, and if not, why.  I think it
does, I just never thought of it that way.  Reason is, it’s not an area
issue for me, it’s an intensity issue.  The number of electrons you get is
dependant on intensity of light as well as area, and I always think in terms
of intensity, as with a sensor, the area is fixed.

> Naturally, a CCD has other sources of noise in the subsequent electronics.
> But it is my understanding that in real-world digicams and scanners the
> limiting factor is in the sensor itself,

You are correct.

> which is why the best
> digicams have
> the largest pixels (thus capturing more light)

Another reason for the better noise characteristics is the reduced
EMI/crosstalk due to the electronics/wires being spread out more within the
sensor.

> and the best scanners use
> photomultiplier tubes (which capture virtually all the photons,
> rather than
> only some fraction of them).

I am only somewhat familiar with how PMTs operate, but I do know the ones I’
ve seen use a beam splitter of some sort...but why would a PMT get “more”
light, or not be subject to the same issue you raise above about columnation
of “signal”?  It appears to me they would.  I’m not talking about sensor
noise, but simply photon noise.  If you could explain why you believe that I
’d appreciate it.

Additionally, one of the reasons the PMTs have less noise is the image is
scanned one pixel at a time, and therefore there is no crosstalk/EMI, or
other CCD characteristics like bloom and smear.

Regards,

Austin

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