| 摘要 |
PURPOSE:To increase the quality of pictue over a entire surface of a screen, by performing a focus control of lens in accordance with the position of the electronic beams that form a TV image on a projection tube. CONSTITUTION:The screen of the projection tube 1 has a curvature in the horizontal direction, and a linear image face exists in the vertical direction. Accordingly, the projected image face goes further away from the screen 3 toward the horizontal periphery as long as the refractive index of the projection lens 4 is constant. In this respect, the lens 4 is formed with the material having an electrooptical effect such as DP(KH2PO4), LiTaO3 or the like. Then the horizontal synchronous pulse is applied to the lens driving circuit 8 from the deflecting circuit 10 that drives the deflecting coil 9 of the tube 1. The circuit 8 applies the parabola voltage of 1H-cycle to the electrode of the lens 4. In this way, an in-focus picture can be obtained over the entire surface of a screen by varying the focus of the lens 4 in accordance with the position of electron beam of the tube 1. |
