FujiFilm X-S1 read noise vs ISO

The FujiFilm X-S1 was measured at 14 ISO settings from ISO 100 to ISO 3200. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (100) read noise is 1.69 DN, or 3.4 electrons at the sensor. From ISO 320 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise. Full well at base ISO is about 7,773 electrons; unity gain is around ISO 200.