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C-R-TuBE APPLICATIONS 65
their description will be on interest and help to anyone concerned with a precise electronic approach to a measurement problem.
SHUTTER, FLASHBULB, AND SYNCHRONIZER TESTING
One of the basic problems in photography as in many other industries is that of accurate short-interval timing. Photographic shutters are called upon to operate reliably and reproducibly over a wide range of speeds. Synchronizers and flashbulbs must be timed to operate within milliseconds of one another. This problem of proper adjustment is becoming more important with the increasing use of color films whose latitude does not tolerate the careless operation to which photographers using monochrome emulsions have become accustomed.
SHUTTER TESTING
The obvious way to study and make these adjustments is by picking up the opening of the shutter by means of a phototube and light and displaying its output on an oscillograph. This procedure, was, in fact, tried many years ago using a string or mirror oscillograph with fairly satisfactory results.1
There are a number of advantages to be gained by the use of a cathode-ray oscillograph :
1. There is no practical limit on the shortest time that can be measured so that high-speed mechanical shutters or electrooptical shutters can readily be studied.
2. The image of the shutter characteristic appears instantaneously on the face of the cathode-ray tube, so that no waiting is necessary to view the record.
3. The shutter may be operated rapidly any number of times in succession, synchronized with the single sweep on the oscillograph, and any erratic operation easily observed by comparing each pattern with the previous one by means of a long-persistence cathode-raytube screen; by operating the shutter a few times and then observing the persistent image, an average value for the shutter speed may be obtained. This is of value in the case of simple shutters whose reproducibility is not such that a single reading suffices for calibration.
6. Various other electronic methods of testing camera shutters have been devised. These generally involve integrating the total light transmitted during the operation of the shutter, and expressing the result as a single reading on a meter. Such a reading fails to show any erratic operation of the shutter such as bouncing or slow opening