Pentax K-70 read noise vs ISO

The Pentax K-70 was measured at 31 ISO settings from ISO 100 to ISO 102400. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (100) read noise is 1.88 DN, or 3.3 electrons at the sensor. From ISO 80000 up the camera is effectively ISO-invariant: raising ISO further doesn't meaningfully lower shadow noise. Full well at base ISO is about 28,895 electrons; unity gain is around ISO 180.