Nikon D780 DSLR Camera (Body Only) - Manual (Page 667)

621 Menu Guide > A Custom Settings
Choose how the camera adjusts flash level when auto ISO
sensitivity control is enabled.
Select [ On ] to enable the modeling flash emitted if the Pv
button is pressed when the camera is used with an optional
flash unit that supports the Nikon Creative Lighting system.
e4: Auto c ISO Sensitivity Control
G button
U A Custom Settings menu
Option Description
e
[ Subject and
background ]
The camera takes both the main subject and
background lighting into account when adjusting
ISO sensitivity.
f [ Subject only ]
ISO sensitivity is adjusted only to ensure that the
main subject is correctly exposed.
e5: Modeling Flash
G button
U A Custom Settings menu