DxOMark review for the Nikon 24-120, the new constant f/4 aperture on DxOMark.

Vignetting at wide apertures

With respect to vignetting, when used on a full frame sensor, the new zoom suffers from a deeper loss of luminosity than its predecessor. The general vignetting score displays minus 1.9 EV for the new 24-120mm versus minus 1.4 for the old version.
If we look at this phenomenon in detail, we notice a pronounced loss of 2 EV at any focal length between f/4 and f/5.6, except at 24 and 28mm, where the loss is present until f/8, and at 85mm where it peaks again at approximately f/6.3.
This all said, between 35mm and 75mm, the lens is almost perfect at wide apertures (between f/4.5 and f/5.6).

24-120mm f/4 vignetting on a Full Frame sensor (D3x): Except between 35 and 75mm, strong vignetting is noticed under f/5.6, and sometimes at f/8.

24-120mm f/3.5-5.6 vignetting on a Full Frame sensor (D3x): the old version of the zoom suffered from significant vignetting only at the beginning and at the end of the zoom range, mostly at wider apertures.

When used with an APS-C sensor, however, the new 24-120 mm shows almost no signs of vignetting throughout the zoom range at any aperture.

24-120mm f/4 vignetting on an APS-C sensor (D300s): “full green”… meaning that everything is perfect!