Wayne Harridge wrote:
> Just how is ISO determined for a digital camera ? As I recall the ISO rating
> of a film is determined from the film's characteristic curve which is
> distinctly different to the curve (straight line !) of a digital sensor.
>
The rules are easy enough to find with a search. I don't recall the
details, but I recall deciding that there was no obvious problem with
measuring the ISO sensitivity of a digital camera using the same rules
as for film. I believe the film spec only uses the linear, central
portion of the curve.
From a practical standpoint, though, at least with current technology,
the correct speed to use is strongly affected by the highlight and
contrast situation. Avoiding clipped highlights is so much different
with digital than film.
I try always to put my cameras away in 'ready for anything' settings.
One of those is an EV adjustment of -2/3. When I've finished shooting
with a different exposure comp. setting, I try to remember to reset to
that. For me, it's been true from the original S110 to the 5D, for Canon
and Fuji, digicam P&S and DSLRs, that -2/3 gives the best chance of
correct histogram in bright, contrasty light.
So I could be cynical and guess the Panny marketing people fudged the
numbers. But it's possible that some engineers said something like "The
ISO standards just don't give the average user the best results with our
cameras. Let's just use settings that give the best practical results."
Just a thought ...
Moose
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