Sony a700 read noise vs ISO

The Sony a700 (DSLR-A700) was measured at 19 ISO settings from ISO 100 to ISO 6400. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (200) read noise is 1.28 DN, or 6.3 electrons at the sensor. From ISO 250 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 19,384 electrons; unity gain is around ISO 980.