Patent ID: 9454062
Filing Date: 2016-09-27
CPC Classification: G02B,G03B,Y10T

Claim Text:
1. An optical system, the optical system being configured as an observation optical system for observing an object and comprising, in order from the object side: a first lens having positive refractive power; a second lens having negative refractive power and a concave surface facing the object side; and a third lens having positive refractive power and a convex surface on an optical axis and facing an eyepoint side, an aspherical surface being included on at least one lens surface, and the following conditional expressions being satisfied: where R21 denotes a radius of curvature of the object side lens surface of the second lens, R22 denotes a radius of curvature of the eyepoint side lens surface of the second lens, f1 denotes a focal length of the first lens, and f2 denotes a focal length of the second lens.