SYNC TERMINAL VIEWFINDER ILLUMINATOR SWITCHA separate sync terminal is provided on the F4. It accepts allstandard PC-type plug-in sync cords, and is threaded for usewith a Nikon screw-in sync cord. Use this terminal to attachflash units which do not have the standard ISO hot shoe.When it's dark, use the viewfinder illuminator to light up allviewfinder information. Turn the switch on, and lightly press theshutter release button to illuminate the display. The illuminatorautomatically switches off as the viewfinder display disappears;it also momentarily switches off during exposure. Although theilluminator is automatically switched off when the camera is setto the L (lock) position, switch it off, when no longer needed, toconserve power.