Canon EOS 5D vs Canon EOS 5D Mark II: read noise comparison

The Canon EOS 5D was measured at 15 ISO settings from ISO 50 to ISO 3200. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (100) read noise is 1.96 DN, or 27.1 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 54,794 electrons; unity gain is around ISO 1380.

The Canon EOS 5D Mark II was measured at 22 ISO settings from ISO 50 to ISO 25600. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (100) read noise is 6.77 DN, or 27.1 electrons at the sensor. From ISO 1250 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise. Settings above ISO 6400 don't change analog gain (digital push). Full well at base ISO is about 61,399 electrons; unity gain is around ISO 400.