Journal of the Society of Motion Picture and Television Engineers (1950-1954)

superior of these two methods. The discussion which follows describes the formation and motion of the image in the Bowen RC-3 rotating-mirror streakcamera.4 In all streak-cameras the event (or an optical image of the event) takes place at the slit. In Fig. 1 an image of the slit is formed on the film plane by the lens after reflection from the rotating mirror. A cylindrical stick of explosive, located on the slit and initiated at the end as shown in Fig. 1, will light the slit at the detonation front I0, and an image of the lighted portion will be formed by the ray RO on the film plane at IV At some later time the detonation front will have moved along the slit and reached a position in the charge indicated by Ii. In this period of time the rotating mirror will have moved through an angle a, and by a simple geometric construction it can be seen that the position of the lighted portion of the image of the slit will fall at I'i. By similar construction a continuous series of points can be located along the film plane, and the streak "S" will be formed. Since the axis of the motion along the film represents time and the motion along the slit represents distance, the slope of "S" is velocity when the proper scale-distance and scale-time are employed in the measurement of that slope. By the same type of geometrical construction it can be shown that if velocity varies along the slit the streak will be curved (Fig. 2a). These velocity recordings are commonly referred to as "rate" records. If the axis of a stick of explosive is perpendicular to the slit, and the stick is initiated at one end, the "profile" of the front will be recorded as shown for the curved front in Fig. 2c. End-view emergence records are also obtainable with the rotating-mirror streak-camera with the slit oriented as shown in Fig. 2b. The choice of which of these two types of recordings is best suited to a particular "profile" study depends on the waveshape and data required. This simplified explanation of the operation of the Bowen RC-3 rotatingmirror streak-camera does not include a discussion of such details as the actual shape of the focal plane which is generated by reflection from the octagonal mirror which is not rotating around its face. That analysis has previously been published.4 Synchronization of the event with the position of the mirror, although not essential in the Bowen RC-3 camera, was accomplished as shown in Fig. 3 and as previously described.1'* This synchronization was found to be extremely effective in improving the quality of the records of detonating charges. The rotating-mirror streak-camera is a powerful tool for the determination of velocity in explosive research, but caution must be taken in extrapolating information from the slit to other portions of the charge to which the camera is blind. For most explosive studies the low effective aperture of this type of camera is no handicap. High writing speeds are obtained with simple mechanical systems by employing a long optical arm. In the Bowen camera the image speed along the film will resolve time to the accuracy required in the study of explosive velocities. However, the actual instantaneous shape of the detonation front, the air shock associated with it, and the change in shape of the detonation and shock fronts as the explosion progresses are not recorded by the streak-camera. Single-Exposure High-Speed Shutter (Rapatronic). A 4-/xsec Rapatronic Shutter,* which embodies the Faraday magnetooptic effect, was successfully perfected by the firm of Edgerton, Germeshausen and Grier of Boston. Dr. H. E. Edgerton, in his many visits to our laboratory, expressed interest in the problems associated with the study of explosive Morton Sultanoff: Study of Explosives 151