Canon EOS R6 Mark III (ES) read noise vs ISO

The Canon EOS R6 Mark III (ES) was measured at 31 ISO settings from ISO 50 to ISO 102400. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (100) read noise is 2.85 DN, or 13.8 electrons at the sensor. A second gain (dual gain) kicks in at ISO 800, cutting input-referred read noise by about 1.8 stop. From ISO 3200 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 77,289 electrons; unity gain is around ISO 490.