Patent ID: 8422150
Filing Date: 2013-04-16
Classification: G02B

Abstract:
1. An objective optical system having a field angle of 140° or larger and comprising a front group, an aperture stop, and a positive rear group arranged in order from an object side, wherein the front group has at least one aspherical surface and includes a negative first lens disposed closest to the object side and satisfying the following conditional expression (1), (4), and (8): where r 1 denotes a radius of curvature of the object side of the first lens, r 2 denotes a radius of curvature of an image side of the first lens, g 1 denotes the focal length of the front group, g 2 denotes the focal length of the rear group, f 1 denotes a focal length of the first lens, and fl denotes the focal length of the entire system.