Nikon D850 User Manual page 67

Mode
Subject-tracking AF: Position the focus point over your subject and
press the center of the multi selector. The focus point will track
the selected subject as it moves through the frame. To end
tracking, press the center of the multi selector again.
Alternatively, you can start tracking by touching your subject in
the monitor; to end tracking and take a photograph, lift your
finger from the screen. If tracking is already in progress,
&
touching the monitor anywhere will cause the camera to focus
on the current subject, and a photo will be taken when you lift
your finger from the screen. Note that the camera may be
unable to track subjects if they move quickly, leave the frame or
are obscured by other objects, change visibly in size, color, or
brightness, or are too small, too large, too bright, too dark, or
similar in color or brightness to the background.
To choose an AF-area mode, press the AF-mode button and
rotate the sub-command dial until the desired mode is displayed
in the monitor.
AF-mode button
Description
Sub-command
dial
43