Nikon D810 - Manual (Page 384)

360
z
IDisable/
enable
If the flash is currently off, front-curtain sync will be
selected while a focus function button is pressed. If
the flash is currently enabled, it will instead be
disabled while a focus function button is pressed.
x
Disable
synchronized
release
Keep any of the focus function buttons pressed to
take photographs with the master camera only
when using a wireless remote controller for remote
synchronized release.
y
Remote
release only
Keep any of the focus function buttons pressed to
take photographs with the remote cameras only
when using a wireless remote controller for remote
synchronized release.
Option Description