Canon PowerShot V1 read noise vs ISO

The Canon PowerShot V1 was measured at 27 ISO settings from ISO 100 to ISO 51200. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (100) read noise is 2.50 DN, or 4 electrons at the sensor. From ISO 20000 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise. Full well at base ISO is about 25,725 electrons; unity gain is around ISO 160.