[filmscanners] RE: scanner dmax discussion

["Paul D. DeRocco" <pderocco@ix.netcom.com>]

> 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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