Pentax K-x vs Pentax K100D: read noise comparison

The Pentax K-x was measured at 8 ISO settings from ISO 100 to ISO 12800. Values were derived by Bill Claff from DxOMark lab data.

At base ISO (100) read noise is 0.80 DN. From ISO 6400 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise.

The Pentax K100D was measured at 5 ISO settings from ISO 200 to ISO 3200. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (200) read noise is 2.62 DN, or 15.7 electrons at the sensor. From ISO 400 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise. Full well at base ISO is about 23,788 electrons; unity gain is around ISO 1200.