Nikon D780 DSLR Camera (Body Only) - Manual (Page 508)

462 On-Camera Flash Photography
D i-TTL Flash Control
When an optional flash unit that supports the Nikon Creative Lighting
System is attached and set to TTL, the camera uses monitor preflashes for
balanced or standard i-TTL fill-flash flash control. i-TTL flash control is not
available with flash units that do not support the Nikon Creative Lighting
System. The camera supports the following types of i-TTL flash control:
• Standard i-TTL fill-flash is activated automatically when [ Spot
metering ] is selected.
Flash
control
Description
i-TTL
balanced
fill-flash
The camera uses i-TTL balanced fill-flash flash control for
a natural balance between the main subject and ambient
background lighting. After the shutter-release button is
pressed and immediately before the main flash, the flash
unit emits a series of monitor preflashes which the
camera uses to optimize flash output for a balance
between the main subject and ambient background
lighting.
Standard
i-TTL
fill-flash
Flash output is adjusted to bring lighting in the frame to
standard level; the brightness of the background is not
taken into account. Recommended for shots in which the
main subject is emphasized at the expense of
background details, or when exposure compensation is
used.