| 摘要 |
A color display device (19) is disclosed with an improved focus performance. In present-day color display tubes with DAF, the electron gun is provided with a second focusing electrode (25) driven with a dynamic voltage which is varied synchronously with the deflection field. The dynamic quadrupole lens formed between the first focusing electrode (23) and the second focusing electrode (25) is designed in such a way that the horizontal lens action, which arises when the voltage on the second focusing electrode is increased, should be compensated by the main lens which becomes weaker when the voltage on the second focusing electrode (25) is increased. In practice, it is not possible to achieve this in the required range of the dynamic voltage on the second focusing electrode (25), leading to a deterioration of the focus performance of the color display device (19). This problem is solved by the present invention. By applying a dynamic voltage to the first focusing electrode (23), it becomes possible to focus the electron spots on the display window (3) in the horizontal and vertical directions, resulting in an optimally focused picture.
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