Pentax K10D read noise vs ISO

The Pentax K10D was measured at 13 ISO settings from ISO 100 to ISO 1600. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (100) read noise is 1.77 DN, or 13 electrons at the sensor. From ISO 500 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise. Full well at base ISO is about 30,084 electrons; unity gain is around ISO 740.