> Man, I hope that's not me! However, Ctein happens to have opined on the
> subject in what I find to be useful ways today
> on TOP.
> <http://theonlinephotographer.typepad.com/the_online_photographer/2012/09/why-iso-isnt-iso.html>
> Perhaps he will
> convince you that there is no "true" ISO. :-)
Ctein has brought up what I've been yelping about for some time. DxO
had come up with their own definition of ISO which essentially has no
meaning in the real world. Heaven forbid that you actually set studio
lighting up based on those ISO numbers.
Anybody who has ever spent quality time with a narrow
exposure-latitude film like Velvia knows exactly what ISO 50 or ISO
100 means. And it has nothing to do with the highlights or shadows.
It's all about the midtone. (Of course, we then into arguments about
is it 18% gray?)
For me, I find that accurate representation of ISO as a midtone
standard is important. Why? Well, because I use multiple formats,
multiple cameras, multiple sensor/film types. The only thing that all
of them have in common is the midtone. A midtone is a midtone is a
midtone. How many stops either way from the midtone is quite variable.
But when I am shooting and using more than one camera or film, having
a standard of exposure is critical. I want to use the same exposure
for my ISO 100 B&W film as I do for the ISO 100 transparency film as I
do for ISO 100 in the digital camera. It would be a pure disaster if I
set the exposure of a camera loaded with Fujichrome 100 based on what
one of these digital wonderbrick cameras is saying the exposure should
be for ISO 100.
So, back to that 18% thing...
AG
--
Ken Norton
ken@xxxxxxxxxxx
http://www.zone-10.com
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