[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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The beam current density distribution of 1 inch M-M type vidicon is investigated. A portion of the beam current passing through a fine pinhole in a metallic target with slight beam scanning is detected by an electron-multiplier and three-dimensionally displayed as a current density distribution on an oscilloscope screen. As a result, it becomes clear that the beam spot size of a 1 inch vidicon using a conventional magnetic focus and deflection coil assembly is to 20 to 30μm in diameter, and the current density distribution is very similar to the Gaussian shape. The actual crossover is about 40μm in diameter, but the size of the image at the target is reduced to 20μm due to anode 62 aperture interception.

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This paper describes a new focusing and deflecting method, called the 2-loop CMF (Concentrated Magnetic Flux) method, which improves the resolution of the 1 inch vidicon type M-M camera tube. Beam electrons in this method revolve through two loops to cross the axis at the target. In the first loop, only the CMF focusing field which reduces the magnification by half is applied. In the second loop, the uniform focusing and Gaussian deflecting fields are applied so that minimum beam spreading and deflection aberration are achieved. As a result, the beam spot half-width is reduced to 10μm in diameter and the AR value at 400 TV lines is 92% below the 1400V mesh and 1000V wall electrode voltages. Further, the resolution uniformity over the target is so good that an 85% AR value is retained at the corners as compared with that of the center when dynamic focusing is used.

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Readability of Japanese characters (Kanji and Katakana) and visual fatigue caused by the reading task were measured. Readability was determined by quickness and accuracy of character reading, while visual fatigue was presumed from measurements of lowering CFF and accommodation abilities. The results indicate that Kanji is read more quickly and accurately than Katakana, and further, that a lesser degree of visual fatigue is induced with Kanji.

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