Handbook of High Speed Photography - IET Labs, Inc.

chronization. For instance, the motion of a device powered by a syn
chronous motor may be "stopped" with stroboscopic light by triggering
the flash with the ac line voltage. The practicality of this method is
determined by the triggering characteristics of the particular strobe
used. If electrical noise is present in the form of spikes or transients,
false triggering may occur, but harmonic distortion is usually not a
problem if relatively high levels of input signal are employed. A small
coupling capacitor (about 0.1/laF) in series with the strobe input ter
minal is necessary if the strobe units will not trigger properly when dc
is present on the input signal. The same capacitor may be used when
the small dc component at the strobe input interferes with the operation
of the signal source.
Figure 5-5. Typical photographic setup illustrating the use
of the photoelectric pickup.
5.2.5 PROXIMITY PICKUP TRIGGERING. Devices which generate
an electrical signal when an object passes close by may be built or
bought by the photographer of high-speed machinery. These devices,
called proximity pickups, are usually magnetic and require the trig
gering object to be a magnet (when a magnetic pickup consisting sim
ply of a coil of several thousand turns of wire is used) or to be a ferro
magnetic material such as iron or steel (when a "variable reluctance"
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