Nikon Z 8 Reference Manual page 390

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 pre-flashes 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:
Flash control
i-TTL balanced
fill-flash
Standard i-TTL
fill-flash
Standard i-TTL fill-flash is activated automatically when [Spot metering] is selected.
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 pre-flashes which the camera uses to optimize
flash output for a balance between the main subject and ambient background
lighting.
Flash output is adjusted to bring lighting in the frame to a 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.
Description
390
Using an On-Camera Flash