Canon EOS R3 Advanced User's Manual page 372

Shooting Settings
Manually setting the ISO speed to 100–640 will make the dynamic range narrower.
Canon Log offers a dynamic range of approx. 1600% at ISO 800 or higher.
The following are expanded ISO speeds: ISO 100, 125, 160, 200, 250, 320, 400, 500
and 640. [ ] is displayed when an ISO speed is set.
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