Patent ID: 7872811

Claim:
An imaging optical system consisting of, in order from its object side, a front lens group of negative refracting power, and a rear lens group of positive refracting power, wherein: when a lens component is defined by a lens body having only two surfaces: an object side surface and an image side surface in contact with air on an optical axis, said front lens group comprises, in order from its object side, a first lens component concave on its image side and having negative refracting power, and a second lens component concave on its image side and having negative refracting power, said rear lens group comprises, in order from its object side, a third lens component convex on its object side and having positive refracting power, and a fourth lens component having positive refracting power, a sum of the total number of lens components in said front lens group and the total number of lens components in said rear lens group is 4, and said third component comprises a plastic positive lens that includes an aspheric surface and satisfies the following conditions (1-1) and (1-2): 19<ν3<29 (1-1) 1.59<n3<1.80 (1-2) where ν 3 is an Abbe constant of said plastic positive lens in said third lens component, and n 3 is a d-line refractive index of said plastic positive lens in said third lens component.