Sony a7R IIIA vs Sony a7R IV: read noise comparison

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.

The Sony a7R IV (ILCE-7RM4) was measured at 34 ISO settings from ISO 50 to ISO 102400. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (100) read noise is 1.35 DN, or 2.9 electrons at the sensor. A second gain (dual gain) kicks in at ISO 320, cutting input-referred read noise by about 1.1 stop. From ISO 400 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise. Settings above ISO 12800 don't change analog gain (digital push). Full well at base ISO is about 34,452 electrons; unity gain is around ISO 220.