Journal of the Society of Motion Picture and Television Engineers (1950-1954)

taken under these adverse conditions. In one instance in particular the light reading was approximately 50 Weston, the camera was operated at a rate of 1000 frames/sec, and we still secured a picture from which usable information could be had. This should not be construed as recommending that one make a habit of taking pictures under such conditions, but merely to indicate that it can be done. In general, with phenomena of the type under investigation in this program, it is desirable to set the camera for the maximum possible frame rate obtainable with the light that is available. This is particularly true in rock where the phenomena occur so rapidly that a rate of less than 2000 frames/sec results in pictures which are almost useless from the standpoint of analysis. A rate of 4000 frames/sec is the minimum, and it would be better if one could obtain pictures at rates more closely approximating 8000 frames/sec. However, this does not seem possible at the present, even with the illumination provided by the sun on a bright day in the desert. It would be worthwhile to experiment with various types of artificial light sources to supplement the illumination from sunlight. Some means of providing a fill light to control contrast would make the problem of securing a good high-speed picture much easier. In this connection it may be well to point out that use of Linagraph Pan Film in an attempt to secure a higher frame speed through the greater emulsion speed of this film resulted in quite unsatisfactory pictures. We therefore carried out a short investigation of the suitability of the various types of film that we could readily secure (see Fig. 4). Unfortunately, the halftone reproduction does not convey the differences visible in the original films, particularly with respect to grain. A camera was set up to photograph a typical charge area and several different types of film were run through in the space of some 15 min. During thi time the light did not change and t camera settings were left the same. Therefore, to at least a first approximation, the only variable involved was that of the film type. This film was all processed through the Houston machine in D-16 developer at approximately 80°F at about 4 fpm, which would correspond to approximately 7^-min development time. The film found most satisfactory as a result of this test was Ansco Gun Film. The rest, jl in order of decreasing merit, were: » Background X, Linagraph Shellburst, ,. Linagraph Ortho, Super XX, and Linagraph Pan. Of course, one is j never satisfied, and it would still be < desirable to have film possessing a higher emulsion speed than the Ansco Gun j Film while retaining the present grain and resolution. We are now planning an investigation of film plus developer combinations that may enable us to secure better definition with a reasonable film speed. As experience was gained in predicting the area which could be expected i to move following the detonation of the charge, it became possible to establish a field of view which included only that I portion of the ground about the charge that would be essential to the analysis. This procedure had the obvious advantage of giving one the maximum amount of information that could be obtained from a given picture, but since no extraneous elements were permitted to appear, the resulting pictures are not particularly interesting to one who is not endeavoring to make an analysis (see Fig. 3). For the purpose of making pictures that would provide an interesting display, it would be better to have the cameras set to include the entire explosion in the field of view. Although our major interest lay in the investigation of details of the movement of the ground around the charge immediately following the detonation, some incidental pictures 410 April 1953 Journal of the SMPTE Vol. 60