Ricoh GR IV read noise vs ISO

The Ricoh GR IV was measured at 34 ISO settings from ISO 100 to ISO 204800. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (100) read noise is 2.01 DN, or 3.3 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 3200 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise. Full well at base ISO is about 27,054 electrons; unity gain is around ISO 170.