| 摘要 |
PROBLEM TO BE SOLVED: To improve astigmatism of a focus lens by adding a slot to a wall body of a focus electrode for vertically limiting a central green aperture, and more weakening influence of an electric field exerted on a green electron beam passing through the aperture than influence of an electric field exerted on red and blue electron beams. SOLUTION: Electron beams passing through a prefocus lens are more strongly focused and diverged by a main focus lens composed of a fifth electrode 45 and a sixth electrode 46. At this time, a central side green electron beam is selectively weakly focused by a slot 80 added to a second cup-shaped member 45b of the fifth electrode 45. That is, an electric field weakened by the slot 80 is generated only on the outlet end of a central aperture 68, and since this acts in the vertical direction of the central aperture 68, the green electron beam passing through this is more weakly focused in the vertical direction than peripheral red and blue electron beams, and astigmatism is corrected, so that red, green and blue picture elements composed of a uniform vertical diameter are formed on an screen.
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