Patent ID: 7586691
Filing Date: 2009-09-08
Classification: G02B

Abstract:
1. A variable-power imaging optical system comprising: in order from an object side thereof, a first lens group having a negative refractive power, the first lens group comprising a first lens of a negative lens, and a second lens of a positive lens, in this order from the object side; a second lens group having a positive refractive power, the second lens group comprising a third lens of a positive lens, a fourth lens of a negative lens, and a fifth lens for correcting aberration, the fifth lens having an aspheric surface, in this order from the object side; and a third lens group comprising a sixth lens for correcting aberration, wherein the first lens is a glass lens, the second lens is a plastic lens having an aspheric convex surface on the object side, the third lens is a double-convex glass lens, both surfaces of the double-convex glass lens being spherical, the fifth lens is a plastic lens in a meniscus form having at least one aspheric surface, and the sixth lens is a positive lens; zooming is performed by moving at least the first and second lens groups along an optical axis independently from each other, and the variable-power imaging optical system satisfies Conditional Expressions (6) and(7): wherein fg 2 represents a focal length of the second lens, f1g represent a combined focal length of the first lens group, and Xp represents a value of Np2×Np2×Vp2, provided that a plastic material of the second lens has a refractive index Np2 and an Abbe number νp2.