Sony a7R IIIA read noise vs ISO

The Sony a7R IIIA (ILCE-7RM3A) was measured at 34 ISO settings from ISO 50 to ISO 102400. This model has no measurement of its own; the Sony a7R III, which uses the same sensor, is shown.

At base ISO (100) read noise is 1.27 DN, or 4.2 electrons at the sensor. A second gain (dual gain) kicks in at ISO 640, cutting input-referred read noise by about 1.4 stop. From ISO 2500 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise. Settings above ISO 25600 don't change analog gain (digital push). Full well at base ISO is about 52,477 electrons; unity gain is around ISO 330.