Handbook of High Speed Photography - IET Labs, Inc.

BLADE HAS JUST
CLEARED WINDOW
TO
STROBOSCOPE
SHUTTER BLADE
Figure 6-5. In a movie camera the synchronizing contact should be in
stalled so that it operated once per revolution of the shutter blade, and
just as the film window is fully uncovered.
the shutter is fully open. For a conventional movie camera, either
mechanical contacts, a reed relay, or a photoelectric device may be a
satisfactory synchronizer. With a photoelectric device, care should be
exercised to eliminate internal light paths to the film chamber. A fur
ther disadvantage of photoelectric devices is the need for external
power for the lamp and an amplifier for the photocell output. Cam-oper
ated contacts are usually easiest to install, but may exhibit consider
able bounce. The reed relay operated by a permanent magnet is a com
mon compromise, though it lacks the desirable phase accuracy.
In high-speed cameras, the bounce problem tends to rule out the
use of contact-type synchronizers. Reluctance pickups become useful,
on the other hand, because their output voltage increases with increas
ing speed. A common technique is to place the reluctance pickup near
the sprocket-wheel teeth (the sprocket must be a ferrous metal) to gen
erate one sync pulse per frame. The phasing of the sync pulse with
respect to the frame is adjusted by moving the pickup around the
sprocket axis. If greater phase accuracy is required, a larger, external
gear with appropriate number of teeth may be employed. Fast, minia
ture photoelectric devices which produce precise synchronization at
the highest camera speeds are becoming popular. Internal installation
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