Nikon D300 Complete Manual page 565

If you set Commander mode, you're telling the camera that
want to use the internal flash for wireless flash control. You
then need to set the flash mode and flash exposure
compensation for each and every flash group, including the
internal flash (I'll have more to say about this in the section on
wireless flash on page <627>):
Recommendations:
1. If you're going to use Repeating flash, start by first
establishing a shutter speed you're going to use. Let's say
your shutter speed will be 1/60. Next, use Interval to
determine how many flashes will be fired a second. An
interval of 1Hz means 1 times a second, so we need to
divide the lower value of our shutter speed (60) into this,
which tells us that we could have as many as 1 flash while
the shutter is open, which obviously isn't going to
generate a "repeating" flash effect. By contrast, if your
shutter speed was 1/2 and your Interval was 10hz, you
could get as many as 5 flashes into your shot. You'll need
to jigger your shutter speed and Interval until you get a
meaningful potential set of repetitions. Finally, set Times
to a value less than or equal to what you just calculated.
Thom Hogan's Complete Guide to the Nikon D300
V1.02
Page 565