Patent ID: 7307799
Filing Date: 2007-12-11
Classification: G02B

Abstract:
1. An imaging optical system comprises an aperture stop, a positive first lens group, and a positive or negative second lens group, in this order from an object, wherein said positive first lens group comprises a positive first lens element and a negative second lens element, in this order from the object, said positive first lens element having its most image-side surface as a convex surface facing toward an image side, and said negative second lens element having its most image-side surface as a concave surface facing toward the image side; wherein said second lens group comprises a meniscus third lens element; wherein said meniscus third lens element comprises an aspherical surface on an object-side surface and an image-side surface thereof, and has the convex surface facing toward the object in the vicinity of the optical axis; wherein said positive first lens element of said positive first lens group is provided with an aspherical surface on at least the object-side surface thereof; wherein said aspherical surface of said positive first lens element 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; and wherein said imaging optical system satisfies the following conditions: wherein f designates the focal length of said entire imaging optical system; f f f R