| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a wide-angle optical system having fewer constituting lenses, in which: particularly aberrations such as curvature of field are excellently corrected; and variations in curvature of field is less even when focusing on a close-range object, keeping telecentricity, although the system has a wide angle. <P>SOLUTION: A wide-angle optical system comprises: a first lens group having negative refractive power; and a second lens group having positive refractive power, in the order starting from an object side. The second lens group includes: a first cemented doublet; an aperture diaphragm; a second cemented doublet; and a first biconvex lens, in the order starting from the object side, the largest ones of air spaces on an axis are the front and rear spaces of the aperture diaphragm except a back focus. The wide angle optical system is divided into the first lens group and the second lens group with the second largest air space as a boundary. The whole optical system is fed to perform focusing, while satisfying the following conditional expression: 1.4≤n<SB POS="POST">d</SB>≤1.8, where n<SB POS="POST">d</SB>is the refractive index at d-line of the first biconvex lens. <P>COPYRIGHT: (C)2012,JPO&INPIT |
