Canon EOS 20D vs Canon EOS 250D: read noise comparison

The Canon EOS 20D was measured at 6 ISO settings from ISO 100 to ISO 3200. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (100) read noise is 2.08 DN, or 24.9 electrons at the sensor. Read noise keeps falling across the measured range, so the camera isn't fully ISO-invariant there. Settings above ISO 1600 don't change analog gain (digital push). Full well at base ISO is about 47,537 electrons; unity gain is around ISO 1200.

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.