To achieve excellent picture quality at low cost using electron guns in large-screen color TV tubes, an improved E4 main lens has been developed by generating a negative astigmatism at the entrance of the main lens while maintaining a strong positive astigmatism at the exit of the main lens. Enlarging the main lens diameter by 67% in the horizontal direction improved the focus performance of the guns even though a cheaper oxide cathode was used instead of an expensive impregnated cathode in a large-screen color TV tube (in which a high luminance is required). And the guns of both dynamic focus and non-dynamic (or static) focus types use the same design for each electrode, except for G3, which helps further cost reduction of the electron guns.
