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Discussion
Dave Miller (Chairman of the Session; Battelle Memorial Inst.} : I would like to congratulate the author, Berlyn Brixner, on making some progress toward a name for this camera, which it needs rather badly. It has often been called the "Rotating-Mirror Camera." There is a good deal of ambiguity there because the term "Rotating-Mirror Camera" might apply to a camera which simply causes an image to move continuously on a film and might not necessarily refer to this type of camera in which a reflected beam of light rotates about a focused image as a center. I have invented my own name for this type of camera which I shall describe at the next session of this symposium.
Jean St. Thomas (Civil Aeronautics Admin.) : How do you eliminate schlieren patterns of the air surrounding the mirror, or does the mirror run in a vacuum?
[Mr. Buck, who read the paper, replied. The following more tightly knit answer has been supplied by the author.] Schlieren patterns in air are made visible by means of collimated light beams or an equivalent system using a point light source and a restricting field stop in a suitable optical system. The image on the camera's rotating mirror is formed by //32 beams and these are sufficiently large so that no schlieren pat
terns are visible. The optical disturbances in the air surrounding the mirror could easily deteriorate the final image resolution were it not for the fact that they occur adjacent to the image on the mirror and hence have only a short optical lever arm with which to operate. If there were trouble of this kind, it could be greatly reduced by using some gas with a high sound velocity for the mirror atmosphere, for example helium or hydrogen. The latter is dangerous to use because of its highly inflammable and explosive nature.
Mr. Miller: I can't recommend rotation in a vacuum as a solution to the problem of these high-speed rotating mirrors. That caused us no end of grief at NAG A; because of the absence of air, oil spattered without limit and the very negligible amount of oil that came through the bearing came up onto the rotor and spattered off onto the optics. It presented a problem without any solution. We tried for months every conceivable sort of trap to eliminate this spattered oil, but we were not successful. And because of that fact we had to resort to an electromagnetic suspension and an electromagnetic drive for the rotor, as long as we spun it in the vacuum. With the electromagnetic drive I understand this rotor, weighing twothirds of a pound, eventually reached a speed of 4,000 rps, corresponding to 800,000 frames a second for that camera.
Berlyn Brixner: Rotating-Mirror Camera
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