Nikon D750 DSLR Camera (Body Only) - Manual (Page 212)

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A
Metering
Select matrix, center-weighted, or highlight-weighted metering to
activate i-TTL balanced fill-flash for digital SLR. Standard i-TTL flash for
digital SLR is activated automatically when spot metering is selected.
A
Lowering the Built-in Flash
To save power when the flash is not in use,
press it gently downward until the latch
clicks into place.
D
The Built-in Flash
Remove lens hoods to prevent shadows. The flash has a minimum
range of 0.6 m (2 ft) and can not be used in the macro range of zoom
lenses with a macro function. i-TTL flash control is available at ISO
sensitivities between 100 and 12800; at other sensitivities, the desired
results may not be achieved at some ranges or aperture values.
If the flash fires in continuous release modes ( 0 103), only one picture
will be taken each time the shutter-release button is pressed.
The shutter release may be briefly disabled to protect the flash after it
has been used for several consecutive shots. The flash can be used
again after a short pause.