| 摘要 |
A variable magnification optical system includes, in order from the object side, a negative first lens group and a positive second lens group, wherein the interval between these lens groups in the optical axis direction is changed during magnification change. The most image-side lens and the second most image-side lens of the first lens group are a negative single lens with a concave surface facing the object side and a positive single lens, respectively. The second lens group includes, in order from the object side, a positive lens disposed at the most object-side position with at least one surface thereof being an aspherical surface, a first cemented lens formed by a negative lens and a positive lens, and a second cemented lens formed by a negative lens and a positive lens. |
| 主权项 |
1. A variable magnification optical system comprising, in order from an object side, a first lens group having a negative refractive power, a stop and a second lens group having a positive refractive power, the variable magnification optical system being configured such that magnification change is achieved by changing an interval between the first lens group and the second lens group in an optical axis direction, and correction of an image plane position along with the magnification change is achieved by moving the first lens group in the optical axis direction, wherein
a most image-side lens in the first lens group is a single lens having a negative refractive power with a concave surface facing the object side and a second most image-side lens in the first lens group is a single lens having a positive refractive power, the second lens group includes, in order from the object side, a positive lens disposed at a most object-side position with at least one surface thereof being an aspherical surface, a first cemented lens formed by a negative lens and a positive lens that are cemented together in this order from the object side, and a second cemented lens formed by a negative lens and a positive lens that are cemented together in this order from the object side, an image-side surface of the negative lens forming the first cemented lens and an image-side surface of the negative lens forming the second cemented lens are concave surfaces, and conditional expression (1) below is satisfied:
−0.5<(R23f+R23r)/(R23f−R23r)<0.5 (1),where R23f is a radius of curvature of an object-side surface of the positive lens forming the first cemented lens, and R23r is a radius of curvature of an image-side surface of the positive lens forming the first cemented lens. |
