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Explosive.
Ul
Initiated end
SIDE VIEW
Lens
Rotating mirror
Fig. 1. Schematic diagram of the formation of the streak image in the rotating-mirror camera.
by replacing or supplementing the standard mechanical shutters by electronic shutters which have no moving parts. The equipment most widely used to obtain submicrosecond single exposures involves the interference of polarized light. This type of shutter is generally expensive, and competent electronics personnel are required to design, build and operate it. The major shortcoming of this equipment is that only a single exposure can be obtained with each shutter. To obtain data in the study of explosives, it is therefore necessary to have a whole battery of cameras or to fire large quantities of like charges and get a single exposure from each, timed at a different instant after firing.
The most desirable, but by far the most complex and costly of the cameras employed in the study of explosives are motion picture cameras which can be used at rates from 100,000 to 100,000,000 frames/sec with the exposure times of the fastest cameras approaching 10"9 sec. Cameras operating in this speed range are usually designed for specific
performance characteristics at the expense of other desirable, but less essential, characteristics.
Table I is a summary of the equipment discussed above and includes the specific cameras now in use at the Terminal Ballistic Laboratory, described in the following paragraphs.
Streak-Camera (Bowen RC-3 Rotating Mirror}. The earliest type of camera used successfully in the study of highspeed transient phenomena,3 and perhaps the most widely used today in the study of detonation and shock rates, is the streak-camera. The photographs obtained with this camera are records of distance as a function of time, and therefore differ from standard photographs, which are essentially records of space taken at a fixed time.
The essential feature of the streakcamera is a method of producing relative motion of a slit along the film plane. Rotating-drums and rotatingmirrors have been used to produce the relative motion of the slit along the film, and the rotating-mirror has proved to be the
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February 1953 Journal of the SMPTE VoL 60