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1949 CATHODE-RAY OSCILLOGRAPHY 573
oscillography, the Type 271-A camera, a 35-mm camera which fits directly on most standard oscillographs; and the Type 314 camera designed for a wide range of relatively slow speeds. Fig. 25 shows an Avimo drum camera which has a 3-foot drum resulting in a complete loop of about 10 feet, and is capable of being used at speeds up to 250 feet per second.
When recording low-speed phenomena, the resolution obtained from the usual photographic objectives is more than adequate to avoid degrading the cathode-ray-tube image. In attempting to record the highest writing speeds, one must try the highest aperture lenses obtainable. For oscillographic use the highest rated aperture lenses (either / or T) are not necessarily the fastest. The lens resolution is at least as important in obtaining the highest writing rates. The lens preferably should be designed for the object: image ratio r.sed. Not enough attention has been given to the design of highaperture objectives, particularly for oscillography. Our experience to date has indicated that the Wray //I cathode-ray-tube copying lens designed for a 4 : 1 reduction is the most suitable.
PROCESSING
Most electronic laboratories now have some darkroom photographic facilities. For the purposes of developing oscillograms, however, one can usually dispense with a darkroom by the use of the proper daylight processing equipment. The processing procedure used should be that which gives the maximum writing rate. This will not usually be the film manufacturer's recommended technique, but rather one which gives the maximum threshold density above fog, regardless of actual fog level. We have found so far, that Linagraph Pan film with prolonged development in D-19, gives the best results. Because of the extremely short exposure times obtained in oscillography causing reciprocity-law failure, there is no evident relation between the Weston or Schemer film speeds and the speeds for oscillography. With recent improvements in Kerr cells and flashlamps, some basic emulsion research is indicated in order to determine those factors which contribute high sensitivity to short exposures.
After the film is developed there are a number of chemical processes which may be used for after-treatment in order to obtain improved results. The process of intensification is one which in ordinary photography results in an improvement in the printing density of the negative and therefore in the improvement of the print or