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

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1950 TV CAMERA TUBES 239 even diametrically opposed to each other, that our attitudes and methods in the two fields must need be quite different. We shall indicate some ways in which television methods may find application in the field of astronomy. An obvious use is to let the television camera substitute for the observer at the eyepiece of the telescope, making possible remote control of the instrument with a minimum of thermal and other disturbances. Even if the astronomer himself might not deem it advisable to separate himself to that extent from his telescope, he might readily appreciate the advantages of letting visitors view his equipment and the stars with television eyes instead of with their own. An electronic technique derived from television development may also be employed to flatten the image field of the Schmidt Camera and, eventually, increase its sensitivity. To this end the curved cathode of an image tube is made to coincide with the focal surface of the Schmidt Camera. This photocathode is imaged electronically on a flat fluorescent screen. In order to photograph the sidereal image, a photographic plate is placed in contact with the screen. Since the number of quanta ejected from the fluorescent screen by each accelerated electron may be made to exceed considerably the average number of quanta required to free a photoelectron from the photocathode, a shorter exposure time will be needed to leave a visible star record on the photographic plate. It is true that, though the image produced at the fluorescent screen is brighter than that at the photocathode, it is also "noisier," that is, contains less intrinsic information. Television techniques may, furthermore, be employed to advantage for stabilizing star images. Whitford and Kron at Washburn Observatory many years ago installed a photoelectric guiding mechanism on a telescope to correct the clock drive (Fig. 12) . A selected fixed star is imaged on the edge of a roof prism, which directs the split beams through opposite sides of a rotating 180° sector disk onto a multiplier phototube. If the intensity of the two beams is unequal an alternating current is generated which is employed to correct the clock drive so that the star image remains centered on the edge of the roof prism. Some time ago the author proposed an allelectronic system with the corresponding almost complete absence of inertia for compensating fluctuations in atmospheric refraction (Fig. 13). In the figure, the sidereal image is formed on the photocathode of an image iconoscope, the electron image of a particularfixed Star being centered on a small aperture in the middle of the mosaic. The electrons forming this image fall on the vertex of a