Nikon D500 User Manual page 128

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See Also
For information on using focus priority in continuous-servo AF, see
Custom Setting a1 (AF-C priority selection, 0 292). For information
on using release priority in single-servo AF, see Custom Setting a2
(AF-S priority selection, 0 292). For information on preventing the
camera from focusing when the shutter-release button is pressed
halfway, see Custom Setting a8 (AF activation, 0 293). See Custom
Setting a10 (Autofocus mode restrictions, 0 294) for information on
limiting focus-mode selection to AF-S or AF-C and f4 (Customize
command dials) > Change main/sub (0 302) for information on
using the sub-command dial to choose the focus mode. See page 47
for information on the autofocus options available in live view or
during movie recording.
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The AF-ON Button
For the purpose of focusing the camera,
pressing the AF-ON button has the same
effect as pressing the shutter-release button
halfway.
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Predictive Focus Tracking
In AF-C mode, the camera will initiate predictive focus tracking if the
subject moves toward or away from the camera while the shutter-
release button is pressed halfway or the AF-ON button is pressed. This
allows the camera to track focus while attempting to predict where the
subject will be when the shutter is released.
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AF-ON button