Handbook of High Speed Photography - IET Labs, Inc.

section 6
MOTION-PICTURE
PHOTOGRAPHY
6.1 USE OF A MOVIE CAMERA.
It is often desirable to have more information about the subject
than can be obtained from a single or multiflash exposure, particularly
when the subject "doesn't get out of the way of itself" for successive
exposures, as described in Section 1.3. In such cases, a motion picture
of the event may supply this information. A movie is merely a series of
still pictures taken at different instants in time. The movie camera
just allows these still pictures to be taken in succession, more rapidly
than is possible with a roll or cut-film camera. The advantages of
stroboscopic illumination for motion pictures are similar to those for
photography, and most of the techniques and considerations discussed
in the foregoing sections apply equally to both photographic methods.
The type of camera to be employed will depend upon the nature
of the event. In general, a conventional movie camera may be used to
photograph repetitive subjects, such as rotating or vibrating parts, re
gardless of the subject speed. A high-speed movie camera must be
used to photograph transient events, such as projectiles in flight or
destructive processes.
6.2 CONVENTIONAL MOVIE CAMERAS.
The ability of the stroboscope to act as an electrically operated
high-speed shutter makes it useful with any full-shutter movie camera
including the least expensive amateur models, even where there is no
camera-strobe synchronization. Best results are obtained when the
stroboscope's flash rate is many times the camera framing rate (six
times the framing rate or more). Lower flash rates will result in inten
sity flicker or blank or partically masked frames. A disadvantage of
the unsynchronized technique is that exposure can only be determined
by trial and error.
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