lens 133 between the third focusing electrode and the fourth focusing electrode has a converging action in a horizontal direction and a diverging action in a vertical direction this is because the fourth cap 441 has the electron beam pass through holes 441 a each with a width greater than a length and the third cup 431 has the electron beam pass through holes 432 a each with a width greater than a length that is the third dynamic quadrupole lens 133 acts opposite to the first dynamic quadrupole lens 131 and the lens actions of the center electron beam pass through holes and the lens actions of the side electron beam pass through holes in the respective electrodes of the third dynamic quadrupole lens differ as shown in fig9 b the appropriate deflection of the electron beams made available by the quadrupole lenses between the focusing electrodes according to the aforementioned actions permits to form a clear image even at the center of the screen for dropping the dynamic voltages provided to respective focusing electrodes forms of the electron beam pass through holes between the second focusing electrode and the third focusing electrode which form the second dynamic quadrupole.