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1949 HIGH-SPEED PHOTOGRAPHY 449
method for the time of exposure is reduced to about 1 microsecond. Furthermore, the high-speed motion picture camera, either Kodak or Fastax, provides the necessary shutter action so that the unit can be used under fully lighted conditions. Prismatic aberrations caused by the angle of rotation in a rotating prism are eliminated, only those aberrations existing which are caused by the glass block itself remaining. These new lighting units which can be synchronized quite easily with the Fastax or Kodak camera are available from Edgerton, Germeshausen, and Grier, Cambridge, Massachusetts.
JBoth the Kodak and Fastax cameras can be used as ultrahighspeed oscilloscopic recording cameras and frequencies up to one million cycles can be recorded as a continuous-wave trace and considerably above this if only the envelopes are required. In the case of the Fastax camera, the prism assembly is removed from the camera for this procedure. This can be done by removing the aperture plate and the four screws which hold the split plates. The prism shaft is then pulled out very carefully and the split plates removed as soon as they are clear. The prism shaft can then be completely removed. It is suggested that split-plate assembly be replaced by a single plate with four holes drilled in it so that film chips will not get down into the main drive assembly. It will be necessary to refocus the camera and use the visual focusing only on the ground glass and disregard the lens-focusing scale. In reassembling the camera the prism faces should be lined up so that the picture will be framed correctly and not out either y6, 2/5> 3/5> or 4/5 of a frame because of mismatching gear teeth.
The Eastman Kodak Company does not recommend that owners of the Kodak high-speed camera attempt to modify their cameras for oscillographic work. It is recommended that such modification be made at the factory in Rochester.
A Pll coating is used on the cathode-ray tube and additional intensifying voltages supplied. In the case of a 5-inch tube it is best to use voltages in the neighborhood of 6000 in order to get 350 kilocycles. A 2-inch-tube oscilloscope which is designed for this particular unit when operating at 2000 volts will supply the necessary frequencies up to a million. Very fine relay chatter, blast fronts, velocities of projectiles, and many other subjects can easily be studied by this new method.
There is a control unit now being made for the Fastax camera known as the J410 or "Goose." This unit is manufactured by the