Observation optical system, viewfinder equipped with observation optical system and method for manufacturing observation optical system

摘要

An observation optical system for observing an object includes, 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 facing an eyepoint side. An aspherical surface is included on at least one lens surface, and given conditional expressions are satisfied, thereby providing a compact observation optical system having excellent optical performance, a viewfinder equipped with the observation optical system, and a method for manufacturing the observation optical system.

主权项

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:
0.80<(R22+R21)/(R22−R21)<2.001.534≦f1/(−f2)<2.00 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.