Handbook of High Speed Photography - IET Labs, Inc.

The versatility of this photographic system is considerably in
creased if the camera is equipped with a contactor which synchronizes
the shutter with the stroboscope's flashes (see Figure 6-1). The ef
fective high shutter speed of a strobe triggered directly by the con
tactor produces images devoid of the blur one gets when the camera's
relatively slower shutter is used with conventional photo lighting. This
REPETITION/^* "X I
RATE / \ I (TYPE 1536)
I SUBJECT 1 P-» »
STROBOTAC
D 0«" p»rvT
FLASHING
RATE
OPTIONAL
Figure 6-1.
Synchronization of a movie camera's shutter to a stroboscope.
improved clarity is important where there is to be a detailed frame-byframe
analysis as in the model-airplane vibration study in Figure 6-2.
The determination of exposure for the synchronized system with its
single-flash per frame is simpler than for the unsynchronized system.
If the framing rate is variable, the frames-per-second control on the
camera (instead of the strobe internal oscillator) may be adjusted to
produce synchronization of the subject and stroboscope. The framing
and flash rates need not be at the subject frequency; identical pictures
result if the subject frequency is an intergral number of times the fram
ing rate, as in Figure 6-3. A slower framing (and flash) rate permits a
higher strobe-intensity setting.
If slow-motion sequences are to appear to "slip" at a specific
rate when projected, the following correction must be made during
filming:
Apparent
"slip rate" _ Camera frame rate x apparent "slip rate" while projecting
while
Projector frame rate
filming
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