Abstract: A display device comprising a deflection unit and a cathode ray tube having an in-line electron gun. The electron gun comprises a main lens portion having means for generating a main lens field and a quadrupole field. During operation, the intensity of said fields is dynamically varied. The electron gun comprises a prefocusing lens portion having means for generating a prefocusing lens field and a further quadrupole field. During operation, the intensity of said fields is controlled in such a way that, in operation, the first quadrupole field and the main lens cause a dynamically converging effect in a direction parallel to the in-line plane, and the second quadrupole field and the prefocusing lens cause a dynamically diverging effect in a direction parallel to the in-line plane, the dynamically converging effect compensating the dynamically diverging effect in the direction parallel to the in-line plane. By virtue thereof, an improved picture reproduction can be obtained.

Abstract: A color display device comprises an electron gun, a display screen and a flat color selection electrode as well as a deflection means. The distance between the electron beams is dynamically varied, whereby the distance in the deflection space decreases as the beams are deflected in at least one direction. The reduction of the distance enables the distance between the color selection electrode and the display screen to be increased in that direction. As a result, the curvature of the inner surface of the color selection electrode may be increased, which has a positive effect on the strength and doming behavior of the color selection electrode.

Abstract: A device for optically scanning an information plane (2) having tracks (5). Radiation supplied by a radiation source (7) is focused on the information plane by an objective system (8). The beam reflected by the information plane is incident on a dividing element, for example, a grating (12), which divides the beam into two halves along a dividing line (17). Two sub-gratings (15, 16) at both sides of the dividing line, respectively, each form a sub-beam from one half of the beam, which sub-beams are detected by a detection system (10), which produces detection signals therefrom. A focus error signal is generated from the detector signals. According to the invention, modulation of the focus error signal by the track structure will be minimal if the dividing line (17) is located at an angle between 15.degree. and 80.degree. to the direction of the tracks.