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BELL SYSTEM TECHNICAL JOURNAL 



formed by the camera lens results from change in refraction of light 

 rays at opposite faces of the cube as the cube rotates. When the 

 cube is in the position shown at "^" an upward displacement of the 

 image to the point "a" results. Rotation of the cube in the clockwise 

 direction diminishes the amount of displacement with the result that 

 a downward image movement takes place which is synchronized with 



Fig. 1 — Schematic arrangement of high speed camera. 



the film movement. With the compensator cube in position as shown 

 at "5," that is, its entrant and emergent faces perpendicular to the 

 optical axis, no vertical deviation or displacement of the image results 

 and the image falls at the point "6" on the film sprocket. Further 

 rotation of the cube causes the image to move downward to the point 

 "c" where the exposure is terminated and the next adjacent face of 

 the cube comes into play. In this manner a succession of images is 

 laid down frame by frame at a high rate of speed, each elemental 

 area of the film having received exposure during a substantial part of 

 the rotation cycle. The duration of each exposure is controlled by the 

 film speed and by the angular height of a fixed aperture in front of 

 each of the four faces of the cube. The film sprocket is directly driven 

 from the motor shaft. Spur gears are employed to drive the optical 

 compensator. A separate motor is employed to drive the take-up 

 reel. 16 millimeter film in hundred foot lengths is used. 



A finder is provided which permits viewing the image on the film 

 as projected upon a ground glass screen mounted on the hinged door 

 of the camera. Lenses of various focal lengths are interchangeable 

 on the front of the camera. The camera is mounted upon a sub- 

 stantial tripod and is readily portable. Figure 2 shows the exterior 

 of the Bell Telephone Laboratories high speed camera. Figure 3 

 shows the interior of this camera where the location of the film spools 

 and main drive sprocket are shown. Figure 4 shows the camera with 

 its two motors and portable lighting units of the type developed for 



