Leica C vs Leica M (Typ 240): read noise comparison

The Leica C was measured at 9 ISO settings from ISO 80 to ISO 12800. Values were derived by Bill Claff from DxOMark lab data.

At base ISO (80) read noise is 1.41 DN. Read noise keeps falling across the measured range, so the camera isn't fully ISO-invariant there.

The Leica M (Typ 240) was measured at 17 ISO settings from ISO 100 to ISO 6400. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (200) read noise is 3.61 DN, or 7.7 electrons at the sensor. From ISO 250 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise. Full well at base ISO is about 35,065 electrons; unity gain is around ISO 430.