Pentax K-5 vs Pentax K-5 II s: read noise comparison

The Pentax K-5 was measured at 11 ISO settings from ISO 80 to ISO 51200. Values were derived by Bill Claff from DxOMark lab data.

At base ISO (80) read noise is 1.13 DN. From ISO 25600 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise.

The Pentax K-5 II s was measured at 29 ISO settings from ISO 80 to ISO 51200. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (80) read noise is 1.13 DN, or 3.3 electrons at the sensor. From ISO 2000 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise. Full well at base ISO is about 47,442 electrons; unity gain is around ISO 230.