Objective optical system
An objective optical system consists of, from an object side to an image side: a first lens group having positive optical power; a second lens group having negative optical power; and a third lens group having positive optical power, wherein the first lens group includes, from the object side to the image side, a first lens having negative optical power and a second lens having positive optical power, and the second lens group is moved according to a change in an object distance to perform focusing, and the following conditional expressions are satisfied: −19< f 2/ f 1<−3.5 0.5< v/f <1.1 where f2 is a focal length of the second lens, f1 is a focal length of the first lens, v is an amount of movement of the second lens group, and f is a focal length of an entire system during the most distant view observation.
1. An objective optical system consists of, in order from an object side to an image side: a first lens group having positive optical power; a second lens group having negative optical power; and a third lens group having positive optical power,
wherein the first lens group includes, in order from the object side to the image side, a first lens having negative optical power and a second lens having positive optical power, and
the second lens group is moved according to a change in an object distance to perform focusing, and conditional expressions below are satisfied:
−19< f 2/ f 1≦−3.69
0.5< v/f< 1.1
0.3<| g 1/ g 2|<0.5
where f2 is a focal length of the second lens, and f1 is a focal length of the first lens;
v is an amount of movement of the second lens group, and f is a focal length of an entire system during a most distant view observation; and
g1 is a focal length of the first lens group, g2 is a focal length of the second lens group.
2. The objective optical system according to claim 1 , wherein the second lens is a positive meniscus lens in which the object side is a concave surface.