Leica M9 vs Leica M9-P: read noise comparison

The Leica M9 was measured at 14 ISO settings from ISO 80 to ISO 2500. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (160) read noise is 7.62 DN, or 15.2 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 32,788 electrons; unity gain is around ISO 320.

The Leica M9-P was measured at 6 ISO settings from ISO 80 to ISO 2500. Values were derived by Bill Claff from DxOMark lab data.

At base ISO (80) read noise is 9.58 DN. Read noise keeps falling across the measured range, so the camera isn't fully ISO-invariant there.