Nikon D780 Reference Manual page 677

Option
[ c Disable/
h
enable]
q
[Preview]
[Preview (Lv
%
max.
aperture)]
[Matrix
L
metering]
[Center-
M
weighted
metering]
[Spot
N
metering]
[Highlight-
t
weighted
metering]
If the flash is currently enabled, it will be
disabled while the control is pressed. If the
flash is currently off, front-curtain sync will be
selected while the control is pressed.
Hold the control to stop aperture down and
preview depth of field during viewfinder
photography. During live view, pressing the
control stops aperture down to the selected
value.
Press the control to temporarily select
maximum aperture for an improved focus
preview during live view.
[Matrix metering] is activated while the
control is pressed.
[Center-weighted metering] is activated
while the control is pressed.
[Spot metering] is activated while the control
is pressed.
[Highlight-weighted metering] is activated
while the control is pressed.
Menu Guide > A Custom Settings
Description
631