Nikon D800 User Manual (en)

Recompose the photograph 
and shoot.
Focus will remain locked 
between shots if you keep the 
shutter-release button pressed 
halfway (AF-S) or keep the 
AE-L/AF-L button pressed, allowing 
several photographs in succession to be taken at the same 
focus setting. 
Do not change the distance between the camera and the subject 
while focus lock is in effect. If the subject moves, focus again at the 
new distance.
Locking Focus with the 
B Button
During viewfinder photography, focus can be locked using the 
button in place of the shutter-release button (
0 92). IAF-ON only is 
selected for Custom Setting a4 (AF activation
0 283), the camera will 
not focus when the shutter-release button is pressed halfway; instead, 
the camera will focus when the 
B button is pressed, at which point 
focus will lock and remain locked until the 
B button is pressed again. 
The shutter can be released at any time, regardless of the options 
selected for Custom Settings a1 (AF-C priority selection
a2 (AF-S priority selection
0 282), and the in-focus indicator will not 
be displayed in the viewfinder.
See Also
See Custom Setting c1 (Shutter-release button AE-L
information on using the shutter-release button to lock exposure, 
Custom Setting f6 (Assign AE-L/AF-L button
0 315) for information 
on choosing the role played by 
AE-L/AF-L button.