Nikon Speedlight Instruction Manual page 13

To use the ringlight, attach the camera to the main
speedlight unit and screw the ringlight into the front
of the lens by turning the knurled ring in the center.
The synchro cord should be disconnected before vou
do this.
Connect the 4-pin plug at the end of the power cord
into the ringlight socket on the side of the flash head.
Plug the synchro cord into the synchro terminal
of
the Nikon F, or the X terminal of the Nikkormat.
Switch on the power switch on the back of the flash
Exposure Determination
For subjects at distances greater than 0.6m (2 feet),
use the guide numbers given in the table below
Divide the guide number by the flash-to-subject
distance to find the correct aperture.
ponds to the measured distance. Nikon and Nikkor_
mat cameras have a film plane indicator which shows
the exact position of the film.