Using
High Speed Strobes
The Shutter-Beam
interfaces with any set of studio or camera mounted strobe units via
an standard PC jack output. When triggered the Shutter-Beam can
directly fire your strobes hooked up to this output.
Benefits:
- Strobes have negligible
propagation delay. .
(<
1/1,000,000 second, thats less than one Millionth of a second)
-
Strobes can have much faster effective shutter speed
THE
TRICK:
Camera is placed in a darkened studio with the shutter held open on
BULB. When the Shutter-Beam detects the subject it fires the strobes
directly. The cameras film is exposed by the flash and then the
shutter is closed and film advanced for the next shot.
|

|
Strobes as a Shutter:
When in a
darkened studio your strobe becomes the shutter. Strobes can be
fired at a much faster shutter speed than your cameras shutter.
High Speed strobes can achieve speeds as short as 1 millionth of a
second (1/1,000,000 s) or better.
VERY EXPENSIVE!!
The average every day
camera mounted and studio strobes are not as fast as a millionth of
a second. But they can achieve satisfactory results. Turning the
power down on these strobes shortens the flash duration. The rule of
thumb is the lower the power the faster the strobe flash. Consult
your flash manufacturer for exact numbers. My SB-24 at 1/16 power
puts out about a 1/12,000 of a second flash. Turning the power down
reduces the flashes output. Multiple flash units will help get more
light on the subject.
Tricking your flash
unit for faster flash:
To achieve even
faster strobe outputs you can fool your flash unit into thinking
there is plenty of light and use it's automatic features to turn the
flash off even quicker. To do this you set your flash on automatic
and take a piece of white paper and fold a portion of the flashes
output directly back into its sensor. I have been told, that you can
use a small piece of fiber optic cable to do the same thing,
although I personally have not tried it. On the SB-24 this can
produce a flash somewhere around 1/40,000 of a second or better.
Aesthetic preference:
The faster shutter
speeds, freeze more of the action. This is purely an aesthetic
preference. Some people like the image to be frozen in space, others
like a little movement (blur) in the picture. Frozen pictures tend
to look fake, a little blur adds some realism to the shot. Again,
this is an individual thing and you have to play with what you got
and find out if it gives you satisfactory results for your tastes.
Strobes have no
propagation delay:
The second reason to
do this type of photography is that strobes have little to no
propagation delay. They do not have mechanical things to move like a
shutter and their reaction times are typical less than a millionth
of a second.
|
Examples:
A bullet traveling at 1,200
feet/second:
Shutter-Beam propagation delay
(1/1,000,000 second)
Bullet Moves: 0.01
inches
Strobes propagation delay (1/1,000,000 second)
Bullet Moves: 0.01 inches
You focus your
camera downrange:
A total of: 0.02 inches
If using an 8008 camera:
Shutter-Beam
propagation delay (1/1,000,000 second)
Bullet Moves: 0.0012 feet
Cameras shutter propagation delay 85mS:
Bullet Moves: 102 feet
You focus your
camera downrange:
A total of: 102.0012 feet
|
FORGET the Shutter-Beam's
delay
|
Image Blur:
The same bullet
traveling 1,200 ft/s will be moving while the shutter is open or even
while the strobe is flashing. This will be recorded on the film as
image blur.
Camera at 1/1000 second shutter
speed:
Image Blur: 14.4 inches
Camera at 1/8000 second shutter speed:
Image Blur: 1.8 inches
Strobe at 1/40,000 second flash duration:
Image Blur: 0.36 inches
Strobe at 1/1,000,000 second flash duration:
Image Blur: 0.01 inches
When dealing with ballistics you can see how critical both the
reaction time of your equipment and the effective shutter speed is. A
22 bullet is one of the faster ballistic subjects around and it is
about 1/4 inch wide. To have it travel 14.4 inches across your picture
while the shutter is open will not return desirable results. You have
to use strobes to freeze this kind of action. And the faster the
strobes the better.
|
Questions about
using strobes? Email
me.
Return to How To
|