| 摘要 |
A variable magnification optical system consists of a positive first lens-group, a negative second lens-group, a positive third lens-group and a positive fourth lens-group in this order from an object side. The first lens-group and the third lens-group are fixed when magnification is changed from a wide-angle end to a telephoto end, and the magnification is changed from the wide-angle end to the telephoto end by moving the second lens-group toward an image side, and correction of an image plane and focusing, which have been necessitated by magnification change, are performed by moving the fourth lens-group. The first lens-group consists of two positive lenses and a negative lens in this order from the object side. The second lens-group consists of a negative 21st lens, a positive 22nd lens, a negative 23rd lens and a negative 24th lens in this order from the object side. |
| 主权项 |
1. A variable magnification optical system substantially consisting of four lens groups of a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power and a fourth lens group having positive refractive power in this order from an object side,
wherein the first lens group and the third lens group are fixed with respect to the direction of an optical axis when magnification is changed from a wide-angle end to a telephoto end, and the magnification is changed from the wide-angle end to the telephoto end by moving the second lens group along the optical axis toward an image side, and correction of an image plane and focusing, which have been necessitated by magnification change, are performed by moving the fourth lens group along the optical axis, and wherein the first lens group substantially consists of three lenses of a lens having positive refractive power, a lens having positive refractive power and a lens having negative refractive power in this order from the object side, and wherein the second lens group substantially consists of four lenses of a 21st lens having negative refractive power, a 22nd lens having positive refractive power, a 23rd lens having negative refractive power and a 24th lens having negative refractive power in this order from the object side. |
