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ISO on the R5

Started 10 months ago | Discussions thread
Quarkcharmed
Quarkcharmed Senior Member • Posts: 2,713
Re: ISO on the R5

John Sheehy wrote:

Quarkcharmed wrote:

bclaff wrote:

Right, that's very interesting. It's prominent before ISO 1600 although a bit debatable after 1600. But maybe it's just the small scale that hides it.

However the question is, why doesn't it show in the raw histogram? Say if ISO 500 is ISO 400 digitally multiplied by 5/4, we should see clear gaps every 5th bar.

Some cameras use analog gain in a second stage for 1/3-stop ISOs, which would prevent histogram gapping in any 1/3 or 2/3 stop pushes.

It could be that, but then it's not 'digital', and the Canon's representative from the OP said it was digital multiplication between the 1-stop ISOs.

When that is the case, RAW highlight headroom does not vary in a sawtooth, but read noise levels may vary the way they do with integer math pushes.

Some older Canons in the first wave of 1/3 stop ISOs used a second gain, but it was off-sensor, and amplified post-gain read noise, just like using integer math. The analog gains were +1/3 and +2/3, rather than +1/3 and -1/3, so with these cameras, 160, 320, etc had very elevated post-gain read noise.

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Beware of correct answers to wrong questions.
John
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 Quarkcharmed's gear list:Quarkcharmed's gear list
Canon EOS R5 Canon EF 70-200mm F2.8L IS II USM Canon EF 24-70mm F2.8L II USM Canon EF 16-35mm F4L IS USM Canon EF 50mm F1.8 STM
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