| 摘要 |
PURPOSE: To obtain a bright and wide-angle projecting lens by composing this lens of first to fifth lens groups and forming the lens so as to satisfy specific conditions. CONSTITUTION: This lens consists of the first lens group U1 having an aspherical face, the second lens group U2 consisting of positive and negative lenses, the third lens group U3 consisting of biconcave positive and negative lenses, the fourth lens group U4 of a positive lens having an aspherical face and the negative fifth lens group U5. The lens is so constituted as to satisfy the conditions|f1/f2|>12,|f1/f0|>4.8, 1.0<f3/f0<1.8, 1.9<f4/f0<5, -1.9<f5/f0<-1.2, d12/f0< 0.2, 0.12<d23/f0<0.16, fB1<=0 when f0 is defined as the focal length of the entire system of the projecting lens, f1 to f3, f5 are defined as the focal lengths of the first to third and fifth lens group, d12, d23 as the air spacings on the optical axes between the first and the second lens groups and between the second and the third lens groups and fB1 is defined as the focal length of the first lens calculated by best fitting the aspherical lens face shape of the first lens group to a spherical face within the effective diameter and using the curvature of this spherical face.
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