Only D-Flashes are compatible but, it is possible to use older flashes in manual mode.
For older flashes: Flash and camera should be switched to manual mode. There is no flash metering.
For D-7 Series: If the monitor is too dark, press PASM-Button and i+ button simultaneously in M-mode.
For A-Series: See shortcuts in Setup mode for automatic monitor amplification in M-mode.
See flash compatibility on this web page (\\\"compatibility information\\\")