Ricoh GR IV Monochrome read noise vs ISO

The Ricoh GR IV Monochrome was measured at 35 ISO settings from ISO 160 to ISO 409600. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (160) read noise is 1.99 DN, or 3.5 electrons at the sensor. A second gain (dual gain) kicks in at ISO 800, cutting input-referred read noise by about 1.1 stop. From ISO 20000 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise. Full well at base ISO is about 28,746 electrons; unity gain is around ISO 280.