| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an objective optical system which simultaneously realizes correction of distortion and expansion of observation depth while having a wide field angle of 140° or larger, and can be preferably applied to a high-pixel imaging element. <P>SOLUTION: An objective optical system (1) includes a front group (FG), an aperture diaphragm (S), and a positive back group (BG) arranged in this order from an object side. The front group (FG) includes a negative first lens (L1) having at least one aspherical surface, disposed closest to the object side, satisfying the following conditional expression (1): 0≤r2/r1<0.24, where r1 denotes the radius of curvature of the object side of the first lens (L1), and r2 denotes the radius of curvature of an image side of the first lens (L1), and having a field angle of 140° or larger. <P>COPYRIGHT: (C)2013,JPO&INPIT |
