| 摘要 |
PURPOSE:To effectively increase an aperture of a main lens which is restricted by an external shape and to improve forcusing performance of an electron gun by selecting a structure and dimension of a pair of electrodes plate facing a wide gap type main lens and of a short cylinder, to obtain a focusing electron lens which has less non-axially symmetric component. CONSTITUTION:A large lens is formed between edges 112 and 122 of an outer electrode and a small lens is formed in a round opening installed in electrode plates 116 and 126. The large lens is a non-axially symmetric lens in a longitudinal direction. The small lens is almost axially symmetric when a short cylinder is high, but is a non-axially symmetric lens in longitudinal direction by effect of the outer electrode when the short cylinder is low. When electrode plate recession distances d1 and d2, and short cylinder height h1 and h2 are selected in consideration of strength of each lens, axially symmetric electron lens is formed to each of three electron beams passing through this parts. A main lens having an effectively large aperture is formed within a restriction of external shape. |
