| 摘要 |
A variable magnification optical system consists of a first lens-group having negative refractive-power, a stop and a second lens-group having positive refractive-power in this order from an object-side. The first lens-group includes an L11 negative meniscus lens, an L12 negative lens and a C11 cemented lens, in which a biconcave lens and a positive lens are cemented together in this order from the object-side, in this order from the object-side. The second lens-group includes an L21 positive lens that is arranged closest to the object-side and includes at least one aspheric surface, and an object-side surface of which is convex, and only two cemented lenses toward an image-side of the L21 positive lens, and each of which consists of a negative lens and a positive lens cemented together in this order from the object-side. The following conditional expressions (1) and (2) are satisfied:;−1.0<Rf11/Rf12<0.7 (1); and;55.0<νdave1 (2). |
| 主权项 |
1. A variable magnification optical system consisting of:
a first lens group having negative refractive power: a stop; and a second lens group having positive refractive power in this order from an object side, and the variable magnification optical system being configured to change magnification by changing a distance between the first lens group and the second lens group in an optical axis direction and to perform correction of the position of an image plane necessitated by the change in magnification by moving the first lens group in the optical axis direction, wherein the first lens group comprises an L11 negative meniscus lens, an L12 negative lens and a C11 cemented lens, in which a biconcave lens and a positive lens are cemented together in this order from the object side, in this order from the object side, and wherein the second lens group comprises an L21 positive lens that is arranged closest to the object side and includes at least one aspheric surface, and an object-side surface of which is convex, and only two cemented lenses toward an image side of the L21 positive lens, and each of which consists of a negative lens and a positive lens cemented together in this order from the object side, and one of the cemented lenses closer to the object side being a C21 cemented lens and the other one of the cemented lenses closer to the image side being a C22 cemented lens, and wherein the following conditional expressions (1) and (2) are satisfied:
−1.0<Rf11/Rf12<0.7 (1); and55.0<νdave1 (2), where Rf11: a curvature radius of an object-side surface of the L11 negative meniscus lens, Rf12: a curvature radius of an object-side surface of the L12 negative lens, and νdave1: an average of Abbe numbers for d-line of negative lenses arranged toward the object side of the positive lens constituting the C11 cemented lens. |
