| 摘要 |
PURPOSE:To obtain a relatively wide angle or a 22 deg. half field angle and to hold 100% aperture efficiency up to an outermost peripheral part by constituting a modified Gaussian lens of five-group, six-element constitution and satisfying specific conditions. CONSTITUTION:This lens consists of the front group of three elements, i.e. a positive meniscus lens L1, a positive meniscus lens L2, and a negative meniscus lens L3 having a large-curvature concave surface at the image side successively from the object side and a lens group of three elements, i.e. the cemented lens of a negative meniscus lens L4 having a large-curvature concave surface at the object side and a positive meniscus lens L5 and a positive lens L6. This lens of five-group, six-element constitution meets requirements shown by inequali ties (I)-(X) [where (f) is the composite focal length of the whole system, f1,2,3 the composite focal length of the front group, Ri the radius of curvature of the (i)th surface, di the gap from the object side to the (i)th refracting surface, SIGMAd the composite thickness of the 1st - final surfaces, ni the refractive index of the line (e) of the (i)th lens Li, and nu1 the Abbe number of the 1st lens L1].
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