Nikon D800E User Manual page 26

This option controls how autofocus adjusts to sudden large
changes in the distance to the subject when AF-C(_ 91) is selected
during viewfinder photography.
_-_!!!_O_ption -'_'_'I_ Description
AF- S (Long)
AF- 4
AF- 3 (Normal)
AF--- 2
AF_ 1 (Short)
Off
When the distance to the subject changes abruptly, the
camera waits for the specified period before adjusting
the distance to the subject. This prevents the camera
from refocusing when the subject is briefly obscured by
objects passing through the frame.
The camera immediately adjusts focus when the
distance to the subject changes. Use when
photographing a series of subjects at varying distances
in quick succession.
If Shutter/AF-ON is selected, both the
shutter-release button and the AF-ON button
can be used to initiate autofocus. If AF-ON
only is selected, autofocus is only initiated
when the AF-ON button is pressed.
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