FujiFilm FinePix X100 vs FujiFilm GFX 100: read noise comparison

The FujiFilm FinePix X100 was measured at 4 ISO settings from ISO 200 to ISO 1600. Values were derived by Bill Claff from DxOMark lab data.

At base ISO (200) read noise is 0.88 DN. From ISO 400 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise.

The FujiFilm GFX 100 was measured at 26 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 1.42 DN, or 4 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 8000 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 45,323 electrons; unity gain is around ISO 280.