Nikon D780 Reference Manual page 178

A
Choosing the Image Area via Buttons and Command Dials
If [Choose image area] has been assigned to a button using Custom
Setting f3 [Custom controls], the image area can be selected by pressing
the button and rotating a command dial.
• The selected crop is displayed in the viewfinder ( 0 130).
•
The option currently selected for image area
can be displayed in the control panel and
viewfinder by pressing the button to which
[Choose image area] is assigned.
[FX (36×24)]
[DX (24×16)]
[1 : 1 (24×24)]
[16 : 9 (36×20)]
•
Camera controls cannot be used to select image area when a DX lens is
attached and [Auto DX crop] is on.
A
Image Size
Image size varies with the option selected for image area.
132 Shooting Settings
Image area Display