Nikon AF-S NIKKOR 24-70mm f/2.8G ED Manuel D'utilisation page 19

2. Focusing
Set your camera's focus mode selector according to this chart.
■Autofocus with manual override (M/A mode)
1 Set the Focus mode switch " to [M/A].
Note: Be sure to set the switch so that the indicator
aligns with [M/A] precisely.
2 Autofocus is provided, but you can manually
override the focus by operating the separate Focus
ring 2 while lightly depressing the shutter release
button or the AF start (AF-ON) button on the camera.
3 To cancel manual override, again lightly depress the
shutter release button or the AF start button on the
camera. This will return the camera to autofocus mode.
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