Handbook of High Speed Photography - IET Labs, Inc.

5.2.3 OPTICAL PICKUP. The optical pickup, which generates an
electrical signal when a change in illumination occurs, has become a
popular synchronizing device with the advent of fast, relatively inex
pensive solid state photosensors. Such devices may be used over ex
tremely wide speed ranges, have no bounce problems, cause no physi
cal loading, and may be very sensitive, so that they can be located at
relatively large distances from the subject. Examples of commercially
available optical pickup systems are the GR 1536 Photoelectric Pickup
in combination with either a Strobolume and 1540-P4 Oscillator Delay
Unit or the 1531-P2 Flash Delay (used with the 1531, or 1538 Strobo
tac or 1539 Stroboslave), and the 1537 Photoelectric Pickoff (used
with the 1538 Strobotac or the 1539 Stroboslave). The 1536 Photo
electric Pickoff contains a light source, a concentrating lens, and
a photocell all in a small cylinder that is mounted on an adjustable
stand. The 1537 Photoelectric Pickoff has no internal light source,
and its photosensitive element is a light activated silicon controlled
rectifier. Both devices operate to 2500 pulses per second. The Pickoff-Flash-Delay
combination mentioned has the advantage of a built-in
time delay between light pulse and trigger signal. This system shown
in Figure 5-3, will be described more fully in paragraph 5.3.1.
Figure 5-3. Strobotac/Flash Delay/Photopickoff combination.
The two common techniques for optical triggering are illustrated
in Figure 5-4. A lens may be required in front of the cell to increase
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