Nikon D850 Menu Manual page 166

❚❚ Auto AF Fine-Tuning
Auto AF fine-tuning is performed as described below.
1
Ready the camera.
Mount the camera on a tripod and aim the camera at a flat,
high-contrast subject parallel to the camera focal plane. Note
that auto AF fine-tuning works best at maximum aperture
and may not function in dark surroundings.
2
Start live view.
Rotate the live view selector to C and
press the a button.
166 Menu Guide