| 摘要 |
PURPOSE:To perform continuous power variation by moving the whole lens system in an optical-axis direction while holding the aberration state excellent. CONSTITUTION:The lens system consists of the 1st lens group L1 having an large-curvature concave surface on an image side, the 2nd lens group L2, the 3rd lens L3 which has a concave surface on the object side and a convex surface on the image side, the 4th lens group L4, and the 5th lens group L5 consisting of a cemented lens having positive refracting power on the whole successively from the object side. In this case, (1) 0.25<¦rII.phic¦<0.60 and (2) 1.00<rIV/ rII<1.50, where phic is the refracting power of a rear conversion system (c), rII is the radius of curvature of the surface closest to the image side in the 3rd lens group L3, and r4 is the radius of curvature of the surface closest in the object side in the 4th lens group L4. Namely, a successive negative-positive refracting power arrangement from the object side is employed basically, a front principal point is positioned as closely to the object side as possible, and the refracting power of the whole rear conversion lens system is reduced to facilitate aberration compensation; and the conditions (1) and (2) are satisfied to hold the aberration state excellent. |
