| 摘要 |
PURPOSE:To obtain a projection lens for video projector which has the distortion of higher order compensated well and has a large aperture and a wide field angle, by specifying shapes and refracting powers of the first-fourth lenses. CONSTITUTION:The first lens L1 having a positive refracting power, the second double convex lens L2 having a positive refracting power, the third meniscus lens L3 whose concave is directed to the CRT side, the fourth lens L4 which has a negative refracting power and has the concave of high curvature directed to the screen side, a silicone rubber S which can be handled optically as an approximately parallel plane plate for the purpose of coupling the lens and the CRT, a CRT front glass G having approximately parallel planes, and a fluorescent surface P as the object surface are arranged in order from the screen side. Screen-side surfaces r1 and r7 of the first and fourth lenses L1 and L4 and the CRT-side surface r6 of the third lens L3 are made aspherical. The first lens L1, the third lens L3, and the fourth lens L4 which have aspherical surfaces consist of an acryl, and only the second lens consists of glass materials.
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