Journal of the Society of Motion Picture Engineers (1930-1949)

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Fig. 4. 10,000-rps turbine with rotating mirror. without any noticeable deformation of the piece. The ^-in. round optical aperture is near the center of the shutter. Circular pieces of transparent plastic are fitted in these holes to prevent glass fragments from entering the camera. The block of ^-in. plate glass fits in the long groove. The electric detonator (not shown) is pressed against the end of the glass block by means of the hollow screw which fits in the shutter cap. A chamber is formed around the detonator so that the explosive gas pressure will not be too high before exhausting to the outside through the ports in the cap. The detonator is loaded after the shutter has been assembled and fitted to the camera. The 10,000-rps rotating mirror and air turbine drive4 is shown in Fig. 4. The mirror has faces 1 5^ X 1 1^ mm and is 8 mm thick. The air and oil lines for driving and lubricating the unit are at the left. The compact construction was achieved by combining the mirror and turbine into a unit. There is a turbine and sleeve' bearing at each end of the mirror. Dural bucket wheels are press-fitted on the mirror shaft. Ordinary No. 10 grade lubricating oil at 100 psi in a circulating system is used for lubricating and cooling of the bearings. The bucket-wheel manifolds are so arranged that the exhaust air sweeps the bearing-oil leakage out the exhaust pipe so that it will not deposit on the mirror and optics inside the camera. A 19 X 17 J mm drive has also been constructed so that image cutoff is avoided when the mirror is at 45° to the optic axis. This larger size mirror operates with very little strength safety factor at 10,000 rps, and its use is avoided when the highest speed of operation is required. The camera has an effective aperture of f/26 and the final image size is 12 X 14 mm. Dynamic resolution tests with Shell Burst Panchromatic film give 30 lines/mm over the entire picture area. Diamond shaped stops5 are used for the lenses as it has been found that there is no practical loss of resolution relative to a circular or rectangular stop of the same linear dimensions. The diamond stop has the advantage that the effective time of exposure is about two-thirds of that obtained by a rectangular stop. The design of the camera is such that it is adaptable for a wide range of operating speeds. Another model almost identical in appearance to the one illustrated was made for operation at 100,000 frames/sec to give 90 20-mm diameter images. It uses an electric motor drive to give a mirror speed of 550 rps. Berlyn Brixner: Rotating-Mirror Camera 507