that they are communicated with the circular center 34 the extended sides 33 can instead take on other shapes such as rectangular semi circular or oval when the pitch s and shape of the beam passage apertures 31 of the first focusing electrode 32 are designed as above the result is the electron beams of fig6 and 7 in fig6 and 7 the electron beams corresponding to the red color at the center of the screen is increased in the left image spreading and the electron beam corresponding to the blue color is increased in the right image spreading by contrast as known from the comparison between the structures shown in fig7 and 9 with the electron beams in the first quadrant the right upper side of the screen the electron beam corresponding to the red color is decreased in the left image spreading and the electron beam corresponding to the blue color is decreased in the right image spreading thus reducing the difference between the red and the blue colors with the usage of the electron guns 20 where the pitch s of the beam passage apertures 31 of the first focusing electrode 32 was varied to be 5 57 mm 5 58 mm 5 60 mm 5 63 mm and 5 65 mm the image spreading of the electron beams corresponding to the red color at the center and in the first and second quadrants of the screen was measured on the left and right sides thereof around the central point and listed in table 1 as illustrated in table 1 as the pitch s of the beam passage apertures 31 of the first focusing electrode 32 is decreased the left and right difference in the first and the.