Nikon 1 J2 vs Nikon 1 J4: read noise comparison

The Nikon 1 J2 was measured at 7 ISO settings from ISO 100 to ISO 6400. Values were derived by Bill Claff from DxOMark lab data.

At base ISO (100) read noise is 2.43 DN. Read noise keeps falling across the measured range, so the camera isn't fully ISO-invariant there.

The Nikon 1 J4 was measured at 8 ISO settings from ISO 160 to ISO 12800. Values are Bill Claff's (Photons to Photos) direct measurements from raw files.

At base ISO (160) read noise is 3.53 DN, or 10.9 electrons at the sensor. From ISO 1600 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 11,952 electrons; unity gain is around ISO 490.