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Re: [OM] iso-invariance - conceding

Subject: Re: [OM] iso-invariance - conceding
From: Wayne Shumaker <om3ti@xxxxxxxx>
Date: Sun, 13 Oct 2019 07:27:13 -0700
At 10/12/2019 11:12 PM, Ken wrote:
>I'm totally confused.
>
>Is flat good or is a slope good?

There are two curves of interest:

Dyanmic range vs ISO - called PDR or photographic dynamic range

Shadow improvement vs ISO - called PDR Shadow or Photographic
dynamic range Shadow Improvement

All with respect to ISO.

The Shadow Improvement vs ISO shows the improvement in shadow
performance as you increase ISO.  A flat line implies that there is no
gain in the shadow performance as ISO is increased. A bump up in that
curve implies that there was some improvement in the shadows with
an increase in ISO. Same with an upward slope in that curve.

The Dynamic Range vs ISO is showing where the highlights start clipping
relative to the shadows, so the number of stop from dark to light.
This curve is usually a nearly straight line decreasing with ISO. Loosing
almost 1 stop per 1 EV increase in ISO. Increasing ISO loose dynamic
range.

Having a nearly flat Shadow Improvement with ISO means that increasing
the ISO does not gain much in shadow noise performance. While at the same
time increasing the ISO decreases the dynamic range before clipping highlights.

So what Moose has been saying is that you get more dynamic range by
setting the ISO low and setting the EV compensation to -2/3. Then pull back
in the shadows in post processing - Because the Shadow Improvement
with ISO is nearly flat but the overall dynamic range decreases with ISO.

If your camera shadow curve slopes up, then you could get more shadow
performance by increasing ISO - but generally not much, especially compared
to how much you loose in overall dynamic range with higher ISO.

I have not thought about what the implications are for using auto-ISO,
other than you can probably shoot at -3EV and be able to pull back in
the shadows in post processing.

WayneS

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