Canon EOS R3 read noise vs ISO

The Canon EOS R3 was measured at 33 ISO settings from ISO 50 to ISO 204800. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (100) read noise is 1.04 DN, or 6.6 electrons at the sensor. A second gain (dual gain) kicks in at ISO 1250, cutting input-referred read noise by about 1.3 stop. From ISO 1250 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise. Settings above ISO 51200 don't change analog gain (digital push). Full well at base ISO is about 102,073 electrons; unity gain is around ISO 650.