Leica SL (Typ 601) read noise vs ISO

The Leica SL (Typ 601) was measured at 11 ISO settings from ISO 50 to ISO 51200. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (50) read noise is 1.85 DN, or 9.8 electrons at the sensor. A second gain (dual gain) kicks in at ISO 200, cutting input-referred read noise by about 2.1 stop. From ISO 200 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise. Settings above ISO 6400 don't change analog gain (digital push). Full well at base ISO is about 83,599 electrons; unity gain is around ISO 260.