Nikon D850 (ES) read noise vs ISO

The Nikon D850 (ES) was measured at 30 ISO settings from ISO 32 to ISO 25600. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (64) read noise is 1.16 DN, or 4.3 electrons at the sensor. A second gain (dual gain) kicks in at ISO 400, cutting input-referred read noise by about 1.3 stop. From ISO 2500 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise. Full well at base ISO is about 59,127 electrons; unity gain is around ISO 230.