682 



HANDBOOK OF PHOTOGRAPHY 



shutter, shown between the lens and the gate, to cut off the light during the period of 

 motion and admit it again during the "dwell time " when the film is at rest and exposed 

 to the light. As pictured in the diagram, the shutter is cutting off the light, its opaque 

 sector being between the lens and the film. 



The sprocket, the intermittent mechanism, and the take-up are driven through 

 suitable gears by a motor, usually of the synchronous a.-c. type to permit interlocking 

 with the sound recorder and the accurate maintenance of synchronism at the required 

 90-in. per min. speed. 



The operating elements of the camera being understood, reference to Fig. 23 will 

 identify the principal parts of an actual professional camera. This happens to be a 

 Bell and Howell model, this company and the Mitchell Camera Corporation being the 

 principal manufacturers of such equipment in the United States. The lens mount and 



Fig. 27.— External ^new of Twentieth Century-Fox silent camera. 



motor are absent from the photograph, a hand crank being in place of the latter. The 

 shutter assembly is at the extreme left, the gate, the intermittent mechanism, and the 

 driving sprocket with the various guide rollers being shown successively to the right. 

 The magazine is mounted above. The path of the film may readily be followed. 



In Fig. 24 parts of the camera mechanism are shown in more detail — these include 

 the shutter, some of the gearing, the sprocket, and the intermittent. It may be men- 

 tioned at this point that, partly owing to the requirements of process photography, 

 modern cameras are built with pilot-pin registration movements which keep the film 

 accurately registered even at speeds up to 128 pictures per second. 



Figure 25 shows the camera complete, with magazine, motor, and lens mount, in 

 an external view from the operating side. The take-up belt shows in this figure. 

 From this view it is clear that there is much more to a professional motion-picture 

 camera than the basic parts so far described. Instead of a single lens, four lenses 

 are mounted on a turret (right) in order to be easily interchangeable. A footage 

 counter will be noted at the left of the crank. Exposure being controlled both by the 

 aperture of the lens and the adjustment of the shutter opening (0 to 170° in the model 



