[filmscanners] RE: scanner dmax discussion

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

HI, Paul!

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)

Hope this helps...

Guy Clark

-----Original Message-----
From: Paul D. DeRocco [mailto:pderocco@ix.netcom.com]
Sent: Wednesday, July 16, 2003 12:34 PM
To: Clark Guy
Subject: [filmscanners] RE: scanner dmax discussion


> From: filmscanners_owner@halftone.co.uk
>
> This is just not an accurate statement: silicon (and similar)
> photoconductive photosensors are about the most linear of all
> detectors, and
> little else is used these days.  One elegant variety of ccd-like sensor is
> strictly linear to within better than 0.1% over about 9 decades of light
> level.  Nearly all non-linearities and most noise effects are introduced
> after the detectors and are minimal effects.

You mean nine octaves, don't you?

--

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

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