Olympus OM-D E-M5 read noise vs ISO

The Olympus OM-D E-M5 was measured at 22 ISO settings from ISO 200 to ISO 25600. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (200) read noise is 0.98 DN, or 5.9 electrons at the sensor. From ISO 640 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise. Settings above ISO 3200 don't change analog gain (digital push). Full well at base ISO is about 23,204 electrons; unity gain is around ISO 1200.