Electron gun for color picture tubes having uniquely formed lens apertures

An electron gun for a color picture tube, having at least a cathode, a control grid, an accelerating grid, a focus grid and an anode, each of which has three apertures aligned in line, said focus grid and said anode made of elongated plates serving as main lens electrodes, and said apertures of said focus grid and said anode constituting a main lens assembly, wherein said three apertures of each of said elongated plates comprise

• a central aperture defined by two first arcuate curves each having a first radius of curvature, and
• two side apertures each of which is defined by a second arcuate curve having a second radius of curvature and a third arcuate curve having a third radius of curvature, said first and second radii of curvature being greater than said third radius of curvature, said three apertures being aligned such that the major axes thereof are parallel to a shorter axis of said elongated plate and such that said three apertures are spaced apart at equal intervals from each other through corresponding bridge portions, and said third curve of each of said two side apertures being spaced apart from the corresponding edge of said elongated plate along a longitudinal direction thereof:
• and further including
• at least one elongated ring bonded to one of the elongated plates of said main lens electrodes adjacent the elongated plate of the other of said main lens electrodes and formed so that said elongated ring surrounds said central aperture and said two side apertures, thereby obtaining three electron beams whose cross sections are circular, said elongated ring thereby reducing astigmatism caused by the passage of said electron beams through said apertures.