Nikon D800 User Manual (en)

Notes on Optional Flash Units
Refer to the flash unit manual for detailed instructions. If the unit 
supports CLS, refer to the section on CLS-compatible digital SLR 
cameras. The D800 is not included in the “digital SLR” category in the 
SB-80DX, SB-28DX, and SB-50DX manuals.
i-TTL flash control can be used at ISO sensitivities between 100 and 6400. 
At values over 6400, the desired results may not be achieved at some 
ranges or aperture settings. If the flash-ready indicator blinks for about 
three seconds after a photograph is taken, the flash has fired at full 
power and the photograph may be underexposed. View the 
photograph in the monitor; if it is underexposed, adjust aperture, ISO 
sensitivity, or the distance to the subject and try again.
When an SC-series 17, 28, or 29 sync cable is used for off-camera flash 
photography, correct exposure may not be achieved in i-TTL mode. We 
recommend that you select standard i-TTL flash control. Take a test shot 
and view the results in the monitor.
In i-TTL, use the flash panel or bounce adapter provided with the flash 
unit. Do not use other panels such as diffusion panels, as this may 
produce incorrect exposure.