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1949
BOWEN RIBBON-FRAME CAMERA
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that the camera can be given a solid footing on the ground independent of the tires.
The angles needed to make the optic axis perpendicular to the trajectory are "set in" at the camera by means of a small sighting telescope mounted on top of the camera and a gunner's quadrant which is set parallel to the proposed trajectory. The quadrant is mounted on the camera and the bubble balanced at the angle of the expected trajectory, as shown in Fig. 4.
In the CZR-1, it is intended to mount the camera in a system of gimbals around the axes of which are fastened precise scales capable of being read to =*=15 seconds of arc. The vernier on the telescope shown in Fig. 4 can be read to ± 1 minute of arc.
AUXILIARY EQUIPMENT ON CAMERAS
In determining a trajectory, it is necessary to know the time at which each picture was exposed in respect to some instant called "zero time" presumably that moment at which the missile began its flight. In the Bowen ribbon-frame cameras currently used, the timing consists of small marks impressed upon the edge of the film every Viooo second by a flashing neon bulb, in the manner shown at the edge of Fig. 5.
The timing light is so arranged that it is opposite the center of the frame when the frame is exposed, so the number of thousand-cycle marks on the edge of the frame between centers of adjacent pictures is the elapsed time between frames. At the present time, the timing marks are counted over a group of frames and divided by the group to increase interframe accuracy. This gives rise, of course, to certain errors. On the CZR-1, a system is being employed which remedies this situation, making accurate time difference measurable for adjacent frames. It consists of a binary counting system in which the light from a series of flashing neon bulbs is projected through the shutter itself and thereby impressed upon the film to give the time of exposure to an accuracy of 20 microseconds. A great advantage in the system is that the pattern of lighted bulbs impressed on each frame gives the additive time measured from "zero time" so that each frame has within itself an independent temporal record relating that frame in a definite manner to all preceding and succeeding pictures, and to zero time.
An assessment aid on both cameras consists of three reticles projected through the shutters and on to the film. These reticles appear on each frame as three small crosses, not shown however in Fig. 5. The reticle projectors are constructed so as always to project the