Eyepiece optical system, optical apparatus and method for manufacturing the eyepiece optical system

An eyepiece optical system comprising, in order from an observation object along an optical axis:

• a first lens having positive refractive power;
• a second lens which has negative refractive power, and of which an observation object side lens surface is concave;
• and
• a third lens which has positive refractive power and of which an eye point side lens surface is convex,
• at least one lens surface, out of lens surfaces constituting the first lens, the second lens and the third lens, being aspherical, and
• the following conditional expressions being satisfied:
• 0.40<f3/f1<2.50 (5)
• 1.40<(R12+R11)/(R12−R11)<−0.75 (6A)
• 1.35<(R22+R21)/(R22−R21)<2.40 (7)
• where f1 denotes a focal length of the first lens, f3 denotes a focal length of the third lens, R11 denotes a radius of curvature of an observation object side lens surface of the first lens, R12 denotes a radius of curvature of an eye point side lens surface of the first lens, R21 denotes a radius of curvature of the observation object side lens surface of the second lens, and R22 denotes a radius of curvature of an eye point side lens surface of the second lens.

A method for manufacturing an eyepiece optical system including, in order from an observation object side:

• a first lens having positive refractive power;
• a second lens which has negative refractive power and of which an observation object side lens surface is concave;
• and
• a third lens which has positive refractive power and of which an eye point side lens surface is convex, the third lens being fixed on an optical axis with respect to the observation object when adjusting a diopter,
• the method comprising:
• disposing each lens in a lens barrel so as to satisfy the following conditional expressions:
• 0.65<R31/fe<1.30 (1)
• −0.80<(R32+R31)/(R32−R31)<−0.10 (2)
• 1.00<fe/f3<1.60 (3A)
• where fe denotes a focal length of the eyepiece optical system, R31 denotes a radius of curvature of an observation object side lens surface of the third lens, R32 denotes a radius of curvature of the eye point side lens surface of the third lens, and
• f3 denotes a focal length of the third lens.

A method for manufacturing an eyepiece optical system including in order from an observation object side along an optical axis:

• a first lens having positive refractive power;
• a second lens which has negative refractive power and of which an observation object side lens surface is concave;
• and
• a third lens which has positive refractive power and of which an eye point side lens surface is convex,
• at least one lens surface, out of lens surfaces constituting the first lens, the second lens and the third lens, being aspherical,
• the method comprising:
• disposing each lens in a lens barrel so as to satisfy the following conditional expression:
• 0.40<f3/f1<2.50 (5)
• 1.40<(R12+R11)/(R12−R11)<−0.75 (6A)
• 1.35<(R22+R21)/(R22−R21)<2.40 (7)
• where f1 denotes a focal length of the first lens, f3 denotes a focal length of the third lens, R11 denotes a radius of curvature of an observation object side lens surface of the first lens, R12 denotes a radius of curvature of an eye point side lens surface of the first lens, R21 denotes a radius of curvature of the observation object side lens surface of the second lens, and R22 denotes a radius of curvature of an eye point side lens surface of the second lens.