| 摘要 |
A variable-power eyepiece optical system, which is used in combination with an objective optical system, includes a negative first lens group, a second lens group having a positive first sub lens group and a positive second sub lens group, and a positive third lens group, in this order from the objective optical system. The first lens group, and the first and second sub lens groups of the second lens group are made moveable along the optical axis upon variable power, while the third lens group is made immoveable. At the time of variable power, the first sub lens group and the second sub lens group move independently of each other in a direction opposite to the direction along which the first lens group moves, and thereby the resultant power of the first and second sub lens groups is varied.
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