Sony a77 II read noise vs ISO

The Sony a77 II (ILCA-77M2) was measured at 28 ISO settings from ISO 50 to ISO 25600. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (100) read noise is 2.55 DN, or 4.6 electrons at the sensor. From ISO 1250 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise. Settings above ISO 5000 don't change analog gain (digital push). Full well at base ISO is about 28,645 electrons; unity gain is around ISO 180.