Testfiring/Openflash - Nikon Speedlight Unit SB-4 Instruction Manual

Test
f
iring/open
flash
Depress
the
test
firing button
if
necessary.
The
test
firing
button
also serves
as
the
open
flash button
for firing
several
times
with
the
shutter
held
open at the
B
setting
for
strobe
and
other
like effects.