Eyepiece lens and optical instrument comprising same

An optical instrument, comprising:

• an objective lens for forming an image of an object on a predetermined surface;
• and
• an eyepiece lens for observing an image formed by the objective lens via an erecting optical system,
• the eyepiece lens consisting of a first lens being a negative lens, a second lens being a positive lens, and a third lens being a negative lens, which are arranged in this order from an eyepoint side along the optical axis, in such a way that diopter adjustment can be carried out by moving at least one among the first lens, the second lens and the third lens along the optical axis,
• the first lens and the third lens having a biconcave shape, and
• a concave surface of the third lens on the eyepoint side having a curvature greater than that of a concave surface of the third lens on the object side;
• satisfying:
• 0.5<f1/f3<0.8
• wherein, f1 is a focal distance of the first lens and f3 is a focal distance of the third lens.

A diopter adjustment method for an eyepiece lens for observing an image formed by an objective lens via an erecting optical system,

• the eyepiece lens consisting of a first lens being a negative lens, a second lens being a positive lens, and a third lens being a negative lens, which are arranged in this order from an eyepoint side along an optical axis,
• the first lens and the third lens having a biconcave shape, and
• a concave surface of the third lens on the eyepoint side having a curvature greater than that of a concave surface of the third lens on the object side, wherein
• the diopter adjustment method comprises a step of carrying out diopter adjustment by moving at least one among the first lens, the second lens and the third lens along the optical axis;
• satisfying:
• 0.5<f1/f3<0.8
• wherein, f1 is a focal distance of the first lens and f3 is a focal distance of the third lens.

An eyepiece lens for observing all image formed by an objective lens via an erecting optical system,

• consisting of a first lens being a negative lens, a second lens being a positive lens, and a third lens being a negative lens, which are arranged in this order from an eyepoint side along the optical axis, in such a way that diopter adjustment can be carried out by moving at least one among the first lens, the second lens and the third lens along the optical axis,
• the first lens and the third lens having a biconcave shape, and
• a concave surface of the third lens on the eyepoint side having a curvature greater than that of a concave surface of the third lens on the object side;
• satisfying:
• 0.3<Rs1/Rs3<1.0
• wherein, Rs1 is the radius of curvature of a concave surface of the first lens on the object side, and Rs3 is the radius of curvature of a concave surface of the third lens on the object side.

An eyepiece lens for observing an image formed by an objective lens via an erecting optical system,

• consisting of a first lens being a negative lens, a second lens being a positive lens, and a third lens being a negative lens, which are arranged in this order from an eyepoint side along the optical axis, in such a way that diopter adjustment can be carried out by moving at least one among the first lens, the second lens and the third lens along the optical axis,
• the first lens and the third lens having a biconcave shape, and
• a concave surface of the third lens on the eyepoint side having a curvature greater than that of a concave surface of the third lens on the object side,
• wherein a convex surface of the second lens on the eyepoint side and a convex surface of the second lens on the image side are configured as aspherical surfaces having positive refractive power that decreases away from the optical axis,
• the eyepiece lens satisfying a condition:
• −1.0<AS1/AS2<−0.2
• wherein, AS1 is the amount of asphericity of a convex surface of the second lens on the eyepoint side and AS2 is the amount of asphericity of a convex surface of the second lens on the object side, and the height from the optical axis is y=0.3×re2, where re2 is a paraxial radius of curvature of a convex surface of the second lens on the eyepoint side,
• the amount of asphericity AS of both convex surfaces of the second lens being given by a conditional equation
• AS=(y2/r)/{1+(1−K×y2/r2)1/2}+C4×y4+C6×y6+C8×y8+C10×y10−(y2/r)/{1+(1−y2/r2)1/2}
• in which y is a height from the optical axis, r is a paraxial curvature radius, K is a conic constant, C4 is a fourth-order aspherical surface coefficient, C6 is a sixth-order aspherical surface coefficient, C8 is an eighth-order aspherical surface coefficient, and C10 is a tenth-order aspherical surface coefficient.

A diopter adjustment method for an eyepiece lens for observing an image formed by an objective lens via an erecting optical system, the eyepiece lens consisting of a first lens being a negative lens, a second lens being a positive lens, and a third lens being a negative lens, which are arranged in this order from an eyepoint side along an optical axis,

• the first lens and the third lens having a biconcave shape, and
• a concave surface of the third lens on the eyepoint side having a curvature greater than that of a concave surface of the third lens on the object side, wherein
• the diopter adjustment method comprises a step of carrying out diopter adjustment by moving at least one among the first lens, the second lens and the third lens along the optical axis;
• and satisfying:
• 0.3<Rs1/Rs3<1.0
• wherein, Rs1 is the radius of curvature of a concave surface of the first lens on the object side, and Rs3 is the radius of curvature of a concave surface of the third lens on the object side.

A diopter adjustment method for an eyepiece lens for observing an image formed by an objective lens via an erecting optical system, the eyepiece lens consisting of a first lens being a negative lens, a second lens being a positive lens, and a third lens being a negative lens, which are arranged in this order from an eyepoint side along an optical axis,

• the first lens and the third lens having a biconcave shape, and
• a concave surface of the third lens on the eyepoint side having a curvature greater than that of a concave surface of the third lens on the object side, wherein
• the diopter adjustment method comprises a step of carrying out diopter adjustment by moving at least one among the first lens, the second lens and the third lens along the optical axis,
• wherein a convex surface of the second lens on the eyepoint side and a convex surface of the second lens on the image side are configured as aspherical surfaces having positive refractive power that decreases away from the optical axis,
• the eyepiece lens satisfying a condition:
• −1.0<AS1/AS2<−0.2
• wherein, AS1 is the amount of asphericity of a convex surface of the second lens on the eyepoint side and AS2 is the amount of asphericity of a convex surface of the second lens on the object side, and the height from the optical axis is y=0.3×re2, where re2 is a paraxial radius of curvature of a convex surface of the second lens on the eyepoint side,
• the amount of asphericity AS of both convex surfaces of the second lens being given by a conditional equation
• AS=(y2/r)/{1+(1−K×y2/r2)1/2}+C4×y4+C6×y6+C8×y8+C10×y10−(y2/r)/{1+(1−y2/r2)1/2}
• in which y is a height from the optical axis, r is a paraxial curvature radius, K is a conic constant, C4 is a fourth-order aspherical surface coefficient, C6 is a sixth-order aspherical surface coefficient, C8 is an eighth-order aspherical surface coefficient, and C10 is a tenth-order aspherical surface coefficient.