| 摘要 |
PURPOSE:To obtain a large-aperture-ratio projection lens with high optical performance while increasing the aberration compensating ability by adding a 5th lens with positive refracting power and a 6th lens with negative refracting power to 1st-4th lenses which form an Eronstar type, and specifying the composite and individual focal lengths of those lenses. CONSTITUTION:The 1st lens L1 which has positive refracting power and has its convex surface on the screen side of a projection device for a TV image and the 2nd meniscus lens L2 which has positive refracting power are provided in order from the screen side. Further, the 3rd biconcave lens L3 which has negative refracting power and the 4th lens L4 which has positive refracting power are provided, and the 5th biconvex lens L5 with the refracting power and the 6th lens L6 which has a large-curvature surface on the screen side and also has the negative refracting power are added to those lens groups. Then inequalities hold for the focal length (f) of the entire lens system, the composite focal length fa of the lenses L1, L2, and L3, the Abbe numbers V2 and V3 of the lenses L2 and L3, the air gap d8 between the lenses L4 and L5, and the air gap d10 between the lenses L5 and L6.
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