Nikon SB-25 Instruction Manual page 47

5 Press until a number (flash speed per second)
starts blinking beside .
Use or to set a desired flash speed.
See "Determining shutter speed with number/speed of
flashes" on page 93.
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6 Press again until a number (flashes per frame)
starts blinking beside center hyphen .
Use or to set the desired number.
The maximum number of flashes per frame depends on
light-output amount and flash speed. If two hyphens
blink, the available number of flashes is fixed (no other
choice). For details, see the chart below.
Number of repeating flashes per frame (shown with blinking
hyphens ) : Figures indicate use with External Power Source
SD-7 or SD-8
Light output amount
Flash speed
per second
1 — 7 Hz 20 40 80
8 — 10 Hz 10 20 40
20 — 50 Hz 8 16 20
F90-Series/N90's LCD panel
7 Set desired shutter speed and aperture on the camera.
Choose B (bulb) setting or a shutter speed long enough to
accommodate the flash you will fire. For calculations, see at
right, "Determining shutter speed with number/speed of
flashes."
Use a tripod to minimize camera shake.
160
80
40
Chapter
Repeating Flash Mode
Determining shutter speed with number/speed of
flash
Frequency (Hz) represents the number of flash fired
per second. For example, 10Hz will fire 10 times in one
second. Or, because firing the flash five times takes
1/2 sec. at 10Hz, the shutter speed must be adjusted
to at least as slow as 1/2 sec.
For another example, firing six times at 8Hz takes
6/8 sec. to occur. However, because your camera
does not have a shutter speed of 6/8 (0.75) sec., you
should set it to the closest slower shutter speed,
which is one second.
The following equation can be applied to calculate
an appropriate shutter speed:
[Number of flash per frame]
[Shutter speed]
[Speed of flash (Hz)]
where the result (shutter speed) must be rounded off to
the closest slower shutter speed available with your
camera.
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