Nikon D3s Technical Manual page 57

Note
Most of the functions listed in the table on the previous
page can also be assigned to the Pv and AE-L/AF-L buttons
using Custom Settings f5 (Assign preview button) and
f6 (Assign AE-L/AF-L button). Additionally, the AE-L/AF-L
button can be assigned the AF-ON function. Note, how-
ever, that Focus point-selection can not be assigned to
either the Pv or the AE-L/AF-L button, and that 1 step spd/
aperture can not be assigned to the AE-L/AF-L button.
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