Leydig, Voit & Mayer
Electron gun with dynamic focus
 An electron gun for a color cathode ray tube includes a triode having a cathode, a control electrode and a screen electrode for producing an electron beam, and first, second, third and fourth focus electrodes and a final accelerating electrode for accelerating and focusing the electron beam. A predetermined static focus voltage is supplied to the first and third focus electrodes, a dynamic focus voltage synchronized with a deflection signal is supplied to the second and fourth focus electrodes, and an anode voltage higher than the highest dynamic focus voltage is supplied to the final accelerating electrode. Thus, by means of a dynamic and axially symmetrical lens, astigmatism of the electron beam spot on the periphery of the screen is improved, thereby forming an almost circular beam spot. Due to the dynamic variation of intensity of the main lens, the spot size on the periphery of the screen approaches is the spot size on the center of the screen through adjustment of the focusing distance of the electron beam. 
Samsung Electron Devices
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inventional additional inventional inventional
Wan-Jae Yu-Seon
Son Kim