Journal of the Society of Motion Picture Engineers (1930-1949)

the film may not be the true tracking error at the time of exposure of the dials from which the azimuth and elevation angles of the camera are determined. If the angular error in tracking is greater than 3° per sec, timing errors appreciably affect the accuracy of the data. A study of Table II indicates that in some cases the time of exposure can be determined very precisely. Often this cannot be done without studying the camera design and measuring some of its components. For a camera such as the Bowen it is necessary to obtain the dimensions of the shutter drum, shutter slit, and film drum and to measure the revolution rate of the shutter drum, the film speed, and the position of the missile in the film. This and other corrections to Bowen Cameras have been investigated previously.3 These, then, are the tools available for recording photographic data of missile flights. The Bowen and Askania cameras are used to obtain the greater part of metric data. The higher speed cameras are relegated to uses such as determining flame characteristics, for which they are better fitted. Data describing high frequency changes in missile behavior can be obtained only through use of metric electronic equipment. Since electronic equipment cannot be used under many conditions, it is essential that each camera be used in such a way that the utmost accuracy from that camera is obtained and the highest significant frame rates can be used. Instrument Usage The problem of using each camera at its maximum efficiency by making use of its good points and minimizing its weak points has been met at NOTS in the following ways: 1. Determine the sources of errors in each camera. 2. Modify cameras where possible to eliminate errors. 3. Determine the magnitude of those errors that cannot be eliminated conveniently by modification. 4. Use the camera in a location and manner which minimize the effects of remaining errors. 5. Have sufficient records to make it possible to overdetermine each trajectory point. 6. Apply statistics to obtain a satisfactory approximation of the trajectory point in question. 7. In terms of the solution obtained in item 6 above check the determination of errors from each camera (item 3) and also obtain an evaluation of the test data. 8. On a long term basis, design cameras which will have the characteristics required. The development and use of Askania Cinetheodolite cameras exemplify the method of accounting for camera errors. The cameras were built and used by the Germans to obtain aeroplane flight data. For this use neither high frame speeds, high shutter speeds, high tracking rates nor good synchronization between the dials and the picture was needed. In planning to use these cameras for missile flight data it was immediately obvious that the tracking rates would have to be increased. This was accomplished by eliminating the gear-drive making them free-sliding on their bearings. Since exposure of the dials indicating camera orientation was not well synchronized with the main shutter, better synchronization was achieved by illuminating the dials with Edgerton flashlamps whose discharge was timed to coincide as far as possible (±3 msec) with the opening of the main shutter. The high illumination and short exposure of the Edgerton flashlamps also effectively stopped the apparent motion on film of the azimuth and elevation dial readings. With these modifications Askanias were installed as an integral part of the range instrumentation system. To minimize reading errors, the cameras were 490 December 1952 Journal of the SMPTE Vol. 59