To prevent the formation of a corona (2) in a known in-line color picture tube with an automatic-focusing deflection system and four grids (G1-G4), a rectangular opening is provided on the side of the second grid (G2) facing the first grid (G1). As a result, the luminous spot (1) formed by the electron beam at the center of the screen is converted to a vertical ellipse and the ratio of the axes of the lateral ellipses on the edge of the image is reduced, thus improving the sharpness of the edges. The openings (5) in the first grid (G1) are elongated in the in-line direction, in particular rectangular, the adjacent openings of the second grid (G2) are also rectangular and all the other openings in the other grids (G2, G3, G4) are circular. In this way, the ratio of the axes of the luminous elliptical spot (11) produced by the electron beam at the center of the screen is reduced without adversely affecting the sharpness of the edges.