Patent attributes
An imaging optical system includes an aperture stop, a positive first lens group, and a positive or negative second lens group. The first lens group includes a positive first lens element and a negative second lens element. The first lens element is provided with an aspherical surface on the object-side surface thereof. The aspherical surface is formed so that the higher a height from the optical axis in a radial direction becomes the more an aspherical surface at the height is displaced toward the object, compared with a paraxial spherical surface. The second lens group includes a meniscus third lens element. The meniscus third lens element is provided with an aspherical surface on each lens surface thereof, and has the convex surface facing toward the object in the vicinity of the optical axis.
