Canon EOS 250D read noise vs ISO

The Canon EOS 250D was measured at 10 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 3.29 DN, or 7.1 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 34,103 electrons; unity gain is around ISO 210.