Canon EOS 1Ds vs Canon EOS 1Ds Mark II: read noise comparison

The Canon EOS 1Ds was measured at 5 ISO settings from ISO 100 to ISO 1250. Values were derived by Bill Claff from DxOMark lab data.

At base ISO (100) read noise is 2.27 DN. From ISO 400 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise.

The Canon EOS 1Ds Mark II was measured at 15 ISO settings from ISO 50 to ISO 3200. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (100) read noise is 2.00 DN, or 25.6 electrons at the sensor. From ISO 800 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise. Settings above ISO 1600 don't change analog gain (digital push). Full well at base ISO is about 50,866 electrons; unity gain is around ISO 1280.