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Fig. 8. Finished block of 60 reflecting prisms.
were fabricated in blocks of 60, as illustrated in Fig. 8. From plates of an air-hardening alloy steel, 44 blocks were cut, each approximately 2^ in. square and §-in. thick. The blocks were then divided into 22 pairs and next were heat-treated to 50 Rockwell G and ground all over. One entire surface of each block of a pair was then covered, by grinding, with V-grooves. The grooved surfaces of the two blocks were then cemented together, the grooves interlocking. This assembly was then placed on a magnetic chuck, and the upper plate was removed by grinding until nothing was left of it except prisms of the desired cross section, but more than three times the desired length. Finally, four grinding cuts were made across the face of the block and the imbedded prisms, to cut three prisms of the correct length from each long prism.
After completion of the grinding operations, the entire surface of the block with the imbedded prisms was polished optically. A vacuum-deposited layer of aluminum was then applied, and, finally, a protective layer of quartz. The finished prisms were then pried out of the matrix, with some aid by a solvent to loosen the adhesive.
Assembly of the reflectors in the
periphery of the spinning disk involved.] laying 50 of them in place at a time, then inserting an aluminum retaining sector at each end and securing with I screws.
Tests have shown, for the Isotran. ca^nera at Battelle, a resolution in the projected motion pictures of 20 lines/mmij lengthwise of the film and 15 lines/mm i crosswise. The resolution in individualframes viewed as stills is slightly less.
In the earlier form of the Isotran camera, the two mutually perpendicular* reflecting surfaces used for image transi port were two faces of a single glass) prism. Reflection was internal, and! the light rays travelled a distance of] about 0.15 in. through glass.
A difficulty was always encountered^ in obtaining glass prisms of this miniature type with a 90° angle between the reflecting surfaces accurate to within i ±15 min. If this angle is not exactly 90°, the Isotran camera produces not one image on a film frame but two| superposed images. The displacement j between the superposed images is pro-' portional to the error in the 90° angle, and to the distance between the focal; plane of the primary image and the line i of intersection of the two reflecting! faces. Hence, if the focal plane could be made to contain the line of intersection of the reflecting faces, the two superposed images would be identical on the film regardless of any small error in the 90° angle. However, as the reflected light beam passing to the first refocusing lens must be separated from the incident light beam proceeding from the objective lens, it is only possible to form the primary image in a focal plane that is pierced by the line of intersection of the two reflecting faces. Hence, the two superposed images on the film can be made identical over their entire area only if the 90° angle between reflecting faces is exact.
With the arrangement in the new Isotran camera, in which the two reflecting faces are surfaces of inde
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February 1953 Journal of the SMPTE Vol. 60