Sony a57 read noise vs ISO

The Sony a57 (SLT-A57) was measured at 9 ISO settings from ISO 100 to ISO 16000. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (100) read noise is 2.39 DN, or 4.5 electrons at the sensor. From ISO 6400 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise. Full well at base ISO is about 29,877 electrons; unity gain is around ISO 190.