JPS6455512A - Zoom lens - Google Patents

Abstract

PURPOSE:To compensate aberrations and to obtain excellent optical performance over the entire power variation range, by arranging lens groups for focusing, power variation, compensation, luminous flux collimation, and image formation, using a cemented lens for a group II and a single lens for a group III, and making respective lenses meet specific requirements. CONSTITUTION:A group I for focusing which has positive refracting power, the negative cemented lens group II for power variation, the negative single lens group III for image plane compensation which varies as the power varies, a group IV for divergent luminous flux collimation, and a group V for image formation consisting of five elements are arranged. The convex surfaces of the respective lenses are directed to an image plane as specified, and inequalities I hold for the refractive index of a (j)th lens in an (i)th group, Abbe numbers Nij and upsilonij, focal length Fi, the focal length FT of the whole system, image forming power values beta2T and beta3T of the groups II and III at the telephoto end, and the power variation ratio Z. Further, the group I consists of three specific lenses, two lens elements on the object side are cemented lens elements, and an inequality II holds. At this time, the small-sized zoom lens is obtained which has about F1.4, an about 10 power variation ratio, a large diameter, and a fast power variation ratio.