Abstract: Electron gun for colour cathode ray tube comprising two successive electrodes to form a focusing lens, both electrodes each comprising three in-line apertures. The extremity of the electrode brought to the focusing voltage comprises a plate, drilled with in-line apertures. This plate is folded in such a manner that the lateral apertures are arranged in a plane different from the plane of the central aperture. The extremity edge of the electrode comprises an internal peripheral lip that extends according to a longitudinal direction Z, following a width at the level of the central aperture different from its width at the level of the lateral apertures. This structure enables the two main functions of a focusing lens to be controlled independently: the difference in focusing between the lateral beams and the central beam the difference in astigmatism of the central beam with respect to the lateral beams.