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70 KNAPP Vol 49, No. ]
which all the light rays will pass through the interface at an angle oi 90 deg and therefore suffer no refraction. This possibility was referred for analysis to Dr. Leonard M. Ross, consultant for Mt Wilson Observatory.
A series of careful calculations showed that spherical windows were feasible and that the optical distortion would be no worse than in air if a satisfactory radius of curvature were employed and if the camera lens were mounted so that its front nodal point was at the center of curvature of the window. This combination results in a slight decrease in the field of view of the lens, since the addition oi the spherical window is equivalent to adding another element to the lens system. Its effect is to decrease the apparent distance between the original lens and the object. Thus, for example, if the distance from the lens to the object is actually 12 ft, the lens must be set foi a focal distance of about 2 ft when used with the spherical window For a one-inch lens, this decreases the field of view about 4 per cent, which is not very serious.
Film-Magazine Requirements. — The normal type of film magazine for a motion picture camera is, of course, one which uses twc spools, a supply spool for the unexposed film and a take-up spool foi the exposed film. However, this system is not well adapted tc film speeds as high as 35 ft per sec. To obtain such a speed starting with the film at rest requires a leader many feet long, even though the spools are accelerated as rapidly as is possible without film breakage. Decelerating the film at the end of the exposure is also a problem if fraying of the film and the consequent filling of the camera with small film fragments is to be avoided.
The installation contemplated here offers the unique feature that the cameras are looking into a completely dark tank until the flash illumination is started. This makes possible the use of an endlessbelt type of magazine into which the required amount of film for one run can be loaded and cemented into a continuous strip. With such an arrangement the film can be run through the camera over and over again, thus making it possible to accelerate the film at a completely safe rate until the desired speed is reached. This speed can be set exactly and held without variation during the time of the exposure, after which the film can be decelerated and brought to a stop with no danger of damage. Such a system appeared particularly desirable for use with a bank of cameras, since it would not only reduce the film consumption, but also the danger of film breakage and