Endoscope objective optical system

摘要

The diameter of an endoscope insertion portion is reduced, and a wide field angle of an endoscope insertion portion is obtained. An endoscope objective optical system includes, from an object side, a first lens formed of a plano-concave lens having a concave surface facing an image side, a second lens formed of a plano-concave lens having a concave surface facing the object side, an aperture stop, and a third lens formed of a plano-convex lens having a plane surface facing the object side, and satisfies
0.7≦|fab/f|0.91.7≦|fe/fab|≦22≦fb/fa≦4where f: focal length of the entire system; fa: focal length of the first lens; fb: focal length of the second lens; fe: represents focal length of the third lens; fab: combined focal length from the first lens to the second lens.

主权项

1. An endoscope objective optical system comprising in order from an object side:
a first lens formed of a plano-concave lens having a concave surface facing an image side; a second lens formed of a plano-concave lens having a concave surface facing the object side; an aperture stop; and a third lens formed of a plano-convex lens having a plane surface facing the object side, the endoscope objective optical system satisfying the following conditional expressions (1) to (3):
0.7≦|fab/f|≦0.9   (1)1.7≦|fe/fab|≦2   (2)2≦fb/fa≦4   (3) where f represents a focal length of the entire system, fa represents a focal length of the first lens, fb represents a focal length of the second lens, fe represents a focal length of the third lens, and fab represents a combined focal length from the first lens to the second lens.