Nikon D2Hs read noise vs ISO

The Nikon D2Hs was measured at 12 ISO settings from ISO 200 to ISO 6400. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (200) read noise is 2.19 DN, or 16.1 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 30,142 electrons; unity gain is around ISO 1470.