Hi Chuck and all,
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>
>Sorry, I didn't follow your logic about decreasing effective ISO. Can
>you first define "effective ISO"?
OK, I think I'm mixing two related, but not identical concepts here. By
'effective ISO' I understand the achieved exposure value for a certain
lighting conditions. _Overexposing_ with the intent of recovering the proper
tonal scale in post (be it on digital or film) means going to exposure
values 'just right' for a lower ISO, thus _decreasing_ that 'effective ISO'.
On the other hand, assuming that most sensors' native WB is close to
daylight (5500 K) the Tungsten setting is achieved by _cranking up_ the blue
channel gain, and possible decreasing the red gain... The blue channel with
its 'boosted ISO' is going to be the major contributor to noise in
Tungsten-WB shots -- it is in my current GF1 and was that way in the
EOS-300D.
Using a 80A filter instead of the WB setting means getting the blue channel
back to a reasonable gain, increasing picture quality as per my experiment.
But the exposure correction for the filter factor (x4) implies exposure
settings of a _quarter_ of the set ISO (e.g. 200 instead of 800).
It's likely that shooting at that reduced ISO without filter but on Tungsten
setting won't get the blue channel gain any higher than with the filter on
(and high ISO + daylight WB) but haven't actually tried.
Cheers,
--
Carlos J. Santisteban Salinas
IES Turaniana (Roquetas de Mar, Almeria)
<http://cjss.sytes.net/>
--
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