Patent ID: 7933075

Claim:
A variable-power optical system comprising: a first lens group having a negative refractive power; a stop; and a second lens group having a positive refractive power, wherein the first lens group, the stop, and the second lens group are arranged in this order from an object side, a gap between the first lens group and the second lens group on an optical axis is changed to vary power, the first lens group is moved along the optical axis to correct the position of an imaging surface due to the variation in power, the first lens group includes a first sub lens group having three negative meniscus lenses and a second sub lens group having a biconcave lens and a positive lens arranged in this order from the object side, the second lens group includes a first positive lens that is arranged closest to the object side and has at least one aspheric surface and a second positive lens that is arranged immediately after the image side of the first positive lens, and when the absolute value of the focal length of the first lens group is |f 1 | and the focal length of the entire system at a wide angle end is fw, the variable-power optical system satisfies Conditional expression 1 given below: 1.9<| f 1|/ fw< 3.6. [Conditional expression 1]