[filmscanners] RE: scanner dmax discussion

["Clark Guy" <guy.clark@siemens.com>]

HI, Paul!

I agree that 9 decades (180 dB) is a WWWWWIIIIIIIDDDDDDDDEEEEEEEE range, but
maybe possible.

24bit (144dB) A/Ds are commercially available for digital Audio for a while,
so maybe 30bits A/Ds are being worked on in the lab?  One could sacrifice
speed for quality more easily in scanning than in audio!

I would expect something on the order of 14 bits  (84dB) or better from any
good scanner.

On further reflection, 30 bits (per channel) would be likely to be overkill
for any but the most demanding instrumentation applications.  A good solid
16 bits per channel is probably more than enough for my needs!

Later!!!

Guy



-----Original Message-----
From: Paul D. DeRocco [mailto:pderocco@ix.netcom.com]
Sent: Wednesday, July 16, 2003 3:12 PM
To: Clark Guy
Subject: [filmscanners] RE: scanner dmax discussion


> From: Clark Guy
>
> I think he means Decades...
>
> Octaves are usually used for frequency ranges (as they were
> originally used
> in music, where an octave is a the frequency range between one
> frequency and
> double that frequency (eg between 440 and 880Hz is an octave)
>
> Light levels are usually described in decades (if speaking in
> LINEAR terms)
> or in powers of 10.  Hence 9 Decades is a range of 1 to 1Thousand Million
> (10^9).....  (a linear photodiode might output 1picoAmp (1*10^-12Amp) of
> current at the low end of this 9 decade range, and 1miliAmp
> (1*10^-3 Amp) at
> the high end)

A decade is a factor of 10. An octave is a factor of 2. In a photodiode or
phototransistor, the current is proportional to the light level, so it would
take a measuring device with better than 180db of dynamic range to verify
linearity over nine decades of range. That's why I thought he meant octaves,
because that would be 54db of range, which is quite reasonable.

--

Ciao,               Paul D. DeRocco
Paul                mailto:pderocco@ix.netcom.com

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