rambling on iso-invariance...
Moose linked to a dpreview article on iso-invariance. I was reviewing what it
says and was questioning....
https://www.dpreview.com/reviews/panasonic-lumix-dmc-zs200-tz200/5
The article says "... we've used the same aperture and shutter speed at
different ISO settings to see how much difference there is between shooting at
a particular ISO setting (and using hardware amplification) vs. digitally
correcting the brightness, later. This has the advantage that all the shots
should exhibit the same shot noise and any differences must have been
contributed by the camera's circuitry."
This says that the iso-invariance has to do with added noise from circuitry and
nothing to do with sensor performance. Which implies using a lower ISO, under
exposed, can be pushed. This is because the sensor is essentially capturing the
same number of photons as it would at a higher ISO properly exposed, hence no
difference in sensor signal to noise. That is, the ISO setting doesn't matter
when the sensor, at same speed/aperture, captures the same number of photons.
To me this means I can under expose at lower ISO, but if over exposed at higher
ISO, it could blow out highlights - sensor saturation or clipping.
From a user point of view, I don't see the advantage of cranking the exposure
knob to -3 versus cranking the ISO knob +3 stops. Other than the exposure knob
is more accessible than the ISO knob? and the need to then post process the
exposure setting. Am I missing the point? Perhaps this changes the way auto-ISO
selects ISO when the exposure is at -3? Or changes the way the camera captures
highlights.
In conclusion, iso-invariance has nothing to do with sensor performance or
improvements. The only difference is what the camera might decide to do
internally with circuitry or post processing based on the ISO setting, or how
auto-ISO might behave. To me, iso-invariance is a moot point, in that it is not
related to sensor performance or improvements.
Hence, using iso-invariance, one is still shooting at the "same aperture and
speed" for a given sensor noise level. Lower sensor noise level is still a
desired feature and unrelated to iso-invariance.
One potential use of iso-invariance might be from the difference in how cameras
capture highlights. The sonies tend to preserver the highlights, say, compared
to a nikon which preserves shadows.
WayneS
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