Nikon D800E User Manual page 25

When AF-S(_ 91) is selected for viewfinder photography, this
option controls whether photographs can be taken only when the
camera is in focus (focus priority) or whenever the shutter-release
button is pressed (release priority)in single-servo AE
Regardless of the option selected, if the in-focus indicator (0) is
displayed when AF-Sis selected for autofocus mode, focus will lock
while the shutter-release button is pressed halfway. Focus lock
continues until the shutter is released.
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