Why bother changing base ISO?

Started Jul 18, 2007 | Discussions thread
kevm14 Senior Member • Posts: 2,253
Re: Why bother changing base ISO?

Muntz wrote:

Yeah but the sensor doesn't really have a concept of properly
exposed. I think people think that exposing to the right means
you're filling the photosites to full well capacity with photons.
The "right" is just a histogram calculated from a final image.

Say 1/500th, f/5.6 and ISO800 creates a JPEG that is exposed to the
right on the histogram. This will take X many photons, average, per
photosite, and X
at 1/500th and f/5.6, but at ISO100. You are 8 stops from being
"properly" exposed to the right. BUT, a key point is that your
sensor has received the same X photons per photosite, since the
exposure was the same, and we'll assume conditions didn't change.
Since DR and noise is all about the noise floor, how could the ISO800
picture end up looking better than the ISO100 one that was boosted 8
stops in PP?

That's exactly what I'm saying (but very well explained).

BTW, I should point out that going from iso 800 to iso 100 is only a
3 stop difference.

Whoops. You're right. I wasted my edit on something else already, too bad

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