Sony a7R vs Sony a7R II (ES): read noise comparison

The Sony a7R (ILCE-7R) 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 1.15 DN, or 3.6 electrons at the sensor. From ISO 500 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise. Settings above ISO 20000 don't change analog gain (digital push). Full well at base ISO is about 49,091 electrons; unity gain is around ISO 310.

The Sony a7R II (ES) (ILCE-7RM2) was measured at 31 ISO settings from ISO 100 to ISO 102400. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (100) read noise is 3.25 DN, or 10.4 electrons at the sensor. A second gain (dual gain) kicks in at ISO 640, cutting input-referred read noise by about 1.3 stop. From ISO 4000 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 50,821 electrons; unity gain is around ISO 320.