Nikon D750 read noise vs ISO

The Nikon D750 was measured at 29 ISO settings from ISO 50 to ISO 51200. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (100) read noise is 1.04 DN, or 5.2 electrons at the sensor. From ISO 3200 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise. Settings above ISO 8000 don't change analog gain (digital push). Full well at base ISO is about 78,478 electrons; unity gain is around ISO 500.