Patent ID: 10782511

Abstract:
An objective optical system includes in order from an object side to an image side, a first lens having a negative refractive power, an aperture stop, and a second lens having a positive refractive power. An image-side surface of the first lens is a surface which is concave toward the image side, and an image-side surface of the second lens is a surface which is convex toward the image side, and following conditional expressions (1), (2), (3), (4), (5), (6), and (7) are satisfied: 0.6<LL1is/LsL2i<1.25  (1)−3<(LL1is/RL1i)×(LsL2i/RL2i)<−1.25  (2)−2<fL22/(f×fL1)<−1.35  (3)2<(nd1−1.63)×(νd1−31)  (4)5<(n2−1.45)×(νd2−31)  (5)1.63<nd1, and, 31<νd1  (6)1.45<nd2, and, 31<νd2  (7).