Canon EOS 1D C read noise vs ISO

The Canon EOS 1D C was measured at 31 ISO settings from ISO 50 to ISO 204800. This model has no measurement of its own; the Canon EOS 1D X, which uses the same sensor, is shown.

At base ISO (100) read noise is 5.31 DN, or 30.7 electrons at the sensor. From ISO 10000 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 82,802 electrons; unity gain is around ISO 580.