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484 MILLER November
through the four objective lenses. The two objective lenses forming the upper (lower) two images as seen on the rotor in Fig. 5 have three times the angular spacing between them as have any two adjacent refocusing lenses on a given level. Consequently, secondary images formed by light from these two objective lenses are exposed on the film strips simultaneously. When the line of intersection of two rotor faces cuts across one of the upper (lower) images on the rotor, part of this image is refocused on one film strip and part on another. At all such tunes, however, the other upper (lower) image is falling full on one of the rotor faces and is consequently refocused entirely on one film strip. It is therefore possible to secure a continuous, uniformly timed series of whole images on the film for a complete turn of the rotor.
Four objective lenses were provided instead of two in order to double the picture-taking frequency and the number of. frames exposed in a single series. The objective lenses forming the upper images in Fig. 5 are offset from those forming the lower images by 1 1/% times the angular spacing between two adjacent refocusing lenses. Consequently, images corresponding to one of these pairs of objective lenses are formed on the film while the reflected beams corresponding to the other pair are falling on the spherical wall between
two adjacent refocusing lenses. One of the pairs Fig. 5— Camera J .....
rotor with positions of objective lenses is thus responsible for a uni
of four stationary fOrmlv timed series of exposures, 102 in number, primary images. /
during a single turn of the rotor, and these exposures are interspersed with a similar series exposed by the other pair. The two sets can be combined to give 204 successive exposures.
At many times during a turn of the rotor, two whole images are formed on different film strips at the same time. In such cases, the better image is used and the other discarded. In general, this procedure results in use of more images on the central film strips than the outer ones.
Re-exposure of images on continued turns of the rotor is avoided by timing the light flash for the duration of only one turn. Gas-filled flash tubes receive the early part of the discharge from a condenser whose capacity is sufficient to produce nearly uniform light intensity for the period of one rotor turn. At the end of one turn, an electronic delay system short-circuits the flash tubes through a grid-controlled arc tube.