Olympus E-520 read noise vs ISO

The Olympus E-520 was measured at 5 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 3.25 DN, or 17.2 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 21,393 electrons; unity gain is around ISO 530.