JP2013105102A - Eyepiece - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an eyepiece whose visibility can be adjusted and in which various aberrations such as a spherical aberration and a coma aberration are satisfactorily corrected.SOLUTION: An eyepiece comprises, in the order from an observation object side: a first lens group G1 having negative refractive power; a second lens group G2 having positive refractive power: and a third lens group G3 having negative refractive power. The second lens group G2 includes at least one aspherical surface, and by moving the second lens group G2 along an optical axis, visibility can be adjusted. The eyepiece satisfies conditional expressions (1): 0.25<d2/TL<0.50 and (2): 0.3<f2/f<0.6, where d2 is a movement distance of the second lens group G2 on the optical axis during the visibility adjustment, TL is a total thickness of the eyepiece (a distance on the optical axis from an optical surface of the first lens group G1 nearest to the observation object side to an optical surface of the third lens group G3 nearest to an eye point side), f2 is a focal distance of the second lens group G2, and f is a focal distance of the eyepiece at -1 [m].

Description

  The present invention relates to an eyepiece lens that is observed through an erecting system.

  In recent years, eyepiece lenses capable of diopter adjustment have been proposed (see, for example, Patent Document 1).

Japanese Patent No. 3850421

However, it has been desired to secure better aberrations within the diopter adjustment range compared to conventional eyepieces.

The present invention has been made in view of such a problem, and an object thereof is to provide an eyepiece in which various aberrations are favorably corrected within a diopter adjustment range.

In order to achieve such an object, an eyepiece according to the present invention includes a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a negative lens arrayed in order from the observation object side. A third lens group having a refractive power of at least one, and the second lens group has at least one aspheric surface,
Diopter adjustment is possible by moving the second lens group along the optical axis, and the following conditional expression is satisfied.

0.25 <d2 / TL <0.50
0.3 <f2 / f <0.6
However,
d2: a movement distance on the optical axis at the time of diopter adjustment of the second lens group,
TL: total thickness of the eyepiece lens (distance on the optical axis from the optical surface closest to the observation object of the first lens group to the optical surface closest to the eye point of the third lens group),
f2: focal length of the second lens group,
f: Focal length of the eyepiece at -1 [m ^-1 ].

In the eyepiece according to the present invention, it is preferable that the first lens group and the second lens group are each composed of a single lens and satisfy the following conditional expression.

20.00 <ν2-ν1
However,
ν1: Abbe number based on the d-line of the single lens constituting the first lens group,
ν2: Abbe number based on the d-line of the single lens constituting the second lens group.

The eyepiece according to the present invention preferably satisfies the following conditional expression when the shape factor of the lens located closest to the eye point in the third lens group is S3.

3.00 <S3 <6.00
However,
S3 = (Rs + Re) / (Rs−Re)
Rs: radius of curvature of the surface of the third lens group located closest to the eye point on the observation object side surface;
Re: The radius of curvature of the eye point side surface of the lens located closest to the eye point side of the third lens group.

  The eyepiece according to the present invention preferably satisfies the following conditional expression.

0.00 <d3 / TL <0.25
However,
d3: the thickness of the third lens group on the optical axis.

According to the present invention, it is possible to provide an eyepiece in which various aberrations are favorably corrected within the diopter adjustment range.

It is a block diagram of the eyepiece which concerns on 1st Example. FIG. 6 is a diagram illustrating various aberrations (spherical aberration, astigmatism, coma aberration, and distortion aberration) of the eyepiece according to the first example, and (a) is a diagram illustrating various aberrations at a diopter −1.0 [m ⁻¹ ]; (B) shows various aberrations when the diopter is −4.0 [m ⁻¹ ], and (c) shows various aberrations when the diopter is +7.9 [m ⁻¹ ]. It is a block diagram of the eyepiece which concerns on 2nd Example. FIG. 6 is various aberration diagrams (spherical aberration, astigmatism, coma aberration and distortion aberration) of the eyepiece according to the second example, and (a) is various aberration diagrams at a diopter −1.0 [m ⁻¹ ]; (B) shows various aberration diagrams when the diopter is -3.4 [m ^-1 ], and (c) shows various aberration diagrams when the diopter is +3.0 [m ^-1 ]. It is a block diagram of the eyepiece which concerns on 3rd Example. FIG. 6 is various aberration diagrams (spherical aberration, astigmatism, coma aberration and distortion aberration) of the eyepiece according to the third example, and (a) is various aberration diagrams at a diopter −1.0 [m ⁻¹ ]; (B) shows various aberration diagrams when the diopter is −4.3 [m ⁻¹ ], and (c) shows various aberration diagrams when the diopter is +3.9 [m ⁻¹ ].

Hereinafter, the present embodiment will be described with reference to the drawings. As shown in FIG. 1, the eyepiece according to this embodiment includes a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, arranged in order from the observation object side, Third lens group G3 having negative refractive power
The second lens group G2 has at least one aspheric surface, and diopter adjustment is possible by moving the second lens group G2 along the optical axis. The following conditional expression (1) , (2) is satisfied.

0.25 <d2 / TL <0.50 (1)
0.3 <f2 / f <0.6 (2)
However,
d2: movement distance on the optical axis at the time of diopter adjustment of the second lens group G2,
TL: total thickness of the eyepiece lens (distance on the optical axis from the optical surface closest to the observation object of the first lens group G1 to the optical surface closest to the eye point of the third lens group G3),
f2: focal length of the second lens group G2,
f: The focal length of the eyepiece when -1 [m ^-1 ].

Conditional expression (1) prescribes the ratio of the total movement distance on the optical axis of the second lens group G2 accompanying diopter adjustment to the total thickness of the eyepiece. If the movement amount of the second lens group G2 at the time of diopter adjustment is set so as to satisfy the conditional expression (1), it becomes possible to weaken the refractive power of the second lens group G2, which is accompanied by diopter adjustment. It is possible to reduce aberration fluctuation, particularly fluctuation of spherical aberration and coma aberration. If the lower limit of conditional expression (1) is not reached, it is necessary to increase the refractive power of the second lens group G2 in order to adjust the diopter, and the spherical aberration and coma change due to the movement of the second lens group G2. growing. If the upper limit of conditional expression (1) is exceeded, fluctuations in aberration due to movement of the second lens group G2 can be suppressed, but in order to perform diopter adjustment, it is necessary to increase the amount of movement of the second lens group G2.
The eyepiece becomes larger and its practicality is impaired.

In order to secure the above effect, it is preferable to set the upper limit of conditional expression (1) to 0.45.

Conditional expression (2) defines the refractive power of the second lens group G2. Satisfying conditional expression (2) while satisfying conditional expression (1) makes it possible to obtain good aberrations (particularly spherical aberration and coma aberration) within the diopter adjustment range. If the lower limit value of conditional expression (2) is not reached, the refractive power of the second lens group G2 becomes too strong, and the first lens group G1 and the second lens group G2 are accompanied by diopter adjustment.
When the distance between the two is widened, particularly the spherical aberration is overcorrected. If the upper limit value of conditional expression (2) is exceeded, fluctuations in aberration due to movement of the second lens group G2 can be suppressed, but the required movement amount of the second lens group G2 accompanying diopter adjustment increases, impairing practicality. .

In order to secure the above effect, it is more preferable to set the lower limit of conditional expression (2) to 0.34.

Then, by satisfying the conditional expressions (1) and (2) and disposing an aspheric surface in the second lens group G2, fluctuations in spherical aberration and coma during diopter adjustment can be reduced. In particular, it is desirable that the aspherical surface is disposed on the most observation object side of the second lens group G2. With this configuration, it is possible to most effectively correct aberration fluctuations (spherical aberration, coma aberration, etc.) when the lens interval between the first lens group G1 and the second lens group G2 changes with diopter adjustment.

In the eyepiece according to the present embodiment, it is desirable that the first lens group G1 and the second lens group G2 are each composed of a single lens and satisfy the following conditional expression (3).

20.00 <ν2-ν1 (3)
However,
ν1: Abbe number based on the d-line (wavelength 587.56 nm) of the single lens constituting the first lens group G1,
ν2: Abbe number based on the d-line (wavelength 587.56 nm) of the single lens constituting the second lens group G2.

Conditional expression (3) is for ensuring good aberration performance within the diopter adjustment range. If the lower limit value of conditional expression (3) is not reached, lateral chromatic aberration in the diopter adjustment range becomes large and color blurring occurs.

In order to secure the above effect, it is more preferable to set the lower limit of conditional expression (3) to 25.00.

The eyepiece according to the present embodiment preferably satisfies the following conditional expression (4), where S3 is the shape factor of the lens located closest to the eye point in the third lens group G3.

3.00 <S3 <6.00 (4)
However,
S3 = (Rs + Re) / (Rs−Re)
Rs: radius of curvature of the surface on the observation object side of the lens located closest to the eye point of the third lens group G3,
Re: the radius of curvature of the eye point side surface of the lens located closest to the eye point side of the third lens group G3.

Conditional expression (4) defines the shape of the lens located closest to the eye point of the third lens group G3. By satisfying conditional expression (4), it is possible to ensure good spherical aberration and coma aberration within the diopter adjustment range when diopter adjustment is performed using the second lens group G2, while ensuring a long eye relief. Can do. If the lower limit value of the condition value (4) is not reached, it is difficult to secure a long eye relief, and the spherical aberration and coma variation within the diopter adjustment range become large, and the aberration performance deteriorates. If the value is below the upper limit of the condition value (4), the radius of curvature of the lens located closest to the eye point in the third lens group G3 becomes so tight that external light is reflected and easily enters the eye, which is not preferable.

  The eyepiece according to this embodiment desirably satisfies the following conditional expression (5).

0.00 <d3 / TL <0.25 (5)
However,
d3: Thickness on the optical axis of the third lens group G3.

Conditional expression (5) defines the thickness of the third lens group G3 on the optical axis. The variation in the incident angle of the peripheral light beam incident on the third lens group G3 from the first lens group G1 and the second lens group G2 with the diopter adjustment is very large. Therefore, if the thickness of the third lens group G3 is increased so as to exceed the upper limit value of the conditional expression (5), the change in lateral chromatic aberration due to the change in incident angle increases, which is not preferable. By satisfying conditional expression (5), the lateral chromatic aberration can be satisfactorily corrected.

In order to secure the above effect, it is more preferable to set the lower limit of conditional expression (5) to 0.05.

In the eyepiece according to this embodiment, it is desirable to introduce aspherical surfaces into the first lens group G1 and the third lens group G3. By introducing an aspherical surface to the first lens group G1, it becomes easy to correct distortion. Further, by introducing an aspherical surface into the third lens group G3, it is possible to easily correct effects similar to those introduced into the second lens group G2, that is, correction of spherical aberration and coma in the diopter adjustment range.

Hereinafter, each example according to the present embodiment will be described with reference to the drawings. Below, Table 1
Table 3 is shown, and these are tables of specifications in the first to third embodiments.

  In [Overall specifications] in the table, Y represents the observation object height, and TL represents the total lens length.

In [Lens Specifications] in the table, the surface number indicates the order of the optical surfaces from the observation object side along the light traveling direction, R indicates the radius of curvature of each optical surface, D indicates the following from each optical surface: The distance between the surfaces on the optical axis to the optical surface (or image surface), nd is the refractive index with respect to the d-line (wavelength 587.56 nm) of the lens material, and νd is the d-line (wavelength 587.56 nm) of the lens material. ) To the Abbe number based on (
(Variable) is a variable surface interval, “∞” in the field of curvature radius R is a plane, P indicates an eye point. When the lens surface is an aspherical surface, the surface number is marked with *, and the column of curvature radius R indicates the paraxial curvature radius.

[Aspherical data] in the table shows the shape of the aspherical surface shown in [Lens Specification] by the following equation (a). X (y) is the distance along the optical axis direction from the tangential plane at the apex of the aspheric surface to the position on the aspheric surface at height y, R is the radius of curvature of the reference sphere (paraxial radius of curvature), and κ is Ai represents the i-th aspherical coefficient. “E-n” indicates “× 10 ⁻ⁿ ”. For example, 1.234E-05 = 1.234 × 10 ⁻⁵ .

X (y) = y ² / [R × {1+ (1−κ × y ² / R ² ) ^1/2 }]
+ A4 × y ⁴ + A6 × y ⁶ + A8 × y ⁸ (a)

In [Variable surface interval data] in the table, f indicates the focal length of the eyepiece, and Di indicates the variable surface interval of the i-th surface.

In [Lens Group Data] in the table, G represents the group number, the first group surface represents the surface number of each group closest to the observation object, and the group focal length represents the focal length of each group.

  In [Conditional Expression] in the table, values corresponding to the conditional expressions (1) to (5) are shown.

Hereinafter, in all the specification values, “mm” is generally used for the focal length f, curvature radius R, surface distance D, and other lengths, etc. unless otherwise specified, but the optical system is proportionally enlarged. Alternatively, the same optical performance can be obtained even by proportional reduction, and the present invention is not limited to this. Unit is `` mm ''
Without being limited to, other suitable units can be used.

The unit of diopter is “m ⁻¹ ”. Diopter X “m ⁻¹ ” indicates a state in which an image by the eyepiece can be formed at a position of 1 / X [m (meter)] on the optical axis from the eye point (however, the sign is the image from the eyepiece. The time when it is made on the observer side is positive).

  The description of the table so far is common to all the embodiments, and the description below is omitted.

(First embodiment)
A first embodiment will be described with reference to FIGS. 1 and 2 and Table 1. FIG. FIG. 1 is a lens configuration diagram (when the diopter is −1 [m ⁻¹ ]) according to the eyepiece of the first example. Although the erecting system P is shown in a developed state in the drawing, an erecting system such as a pentaprism is actually assumed.

As shown in FIG. 1, the eyepiece according to the first example includes a first lens group G1 having negative refractive power and a second lens group G2 having positive refractive power, which are arranged in order from the observation object side. And the third lens group G3 having negative refractive power, the second lens group G2 has an aspherical surface (fifth surface, sixth surface), and moves the second lens group G2 along the optical axis. Thus, the diopter adjustment is performed.

The first lens group G1 includes a negative meniscus lens L1 having a convex surface directed toward the observation object side. The second lens group G2 has a biconvex lens L2. The third lens group G3 includes a negative meniscus lens L3 having a convex surface directed toward the observation object side.

In the present embodiment, as shown in FIG. 1, the eyepiece of the first embodiment is configured by three lens groups G1 to G3 after the image on the focal plane F is converted into an erect image through the erect system P. And the observer moves the eyepoint E.E. Observe with P. The diopter can be adjusted by moving the second lens group G2 along the optical axis.

Table 1 below shows the values of each item in the first example. The surface numbers 1 to 9 in Table 1 are
This corresponds to each optical surface having the curvature radii R1 to R9 shown in FIG. In the first embodiment, the fifth surface and the sixth surface are formed in an aspherical shape.

(Table 1)
[Overall specifications]
Y 14.5
TL 19.5

[Lens specifications]
Surface number R D nd νd
1 ∞ 5.0 1.00000
2 ∞ 71.5 1.51680 64.20
3 ∞ 1.0 1.00000
4 163.85834 1.5 1.58518 30.24
* 5 18.32862 D5 (variable) 1.00000
* 6 13.33611 6.5 1.53460 56.27
7 -42.01906 D7 (variable) 1.00000
8 26.10282 3.0 1.49108 57.57
9 14.55433 D9 (variable) EP

[Aspherical data]
5th surface κ = 0.2198, A4 = -3.72746E-06, A6 = 1.36623E-08, A8 = -2.26420E-10
6th surface κ = -0.1796, A4 = -4.51921E-06, A6 = -1.60155E-08, A8 = -9.92454E-11

[Variable surface interval data]
f 61.64 56.06 45.52
Diopter -4.03 -1.00 7.98
D5 1.00 2.50 7.50
D7 7.50 6.00 1.00
D9 20.00 20.00 20.00

[Lens group data]
Group number Group first surface Group focal length G1 4 -35.40
G2 6 19.74
G3 8 -73.25

[Conditional expression]
Conditional expression (1) d2 / TL = 0.33
Conditional expression (2) f2 / f = 0.35
Conditional expression (3) ν2-ν1 = 26.03
Conditional expression (4) S3 = 3.52
Conditional expression (5) d3 / TL = 0.15

From the table of specifications shown in Table 1, it can be seen that the eyepiece according to the first example satisfies the conditional expressions (1) to (5).

FIG. 2 is a diagram showing various aberrations (spherical aberration, astigmatism, coma aberration, and distortion aberration) of the eyepiece according to the first example, and (a) shows a diopter of −1.0 [m ⁻¹ ]. Various aberration diagrams, (b) Diopter -4.0
Various aberration diagrams at [m ⁻¹ ], (c) shows various aberration diagrams at a diopter +7.9 [m ⁻¹ ].

In each aberration diagram, Y1 represents the incident height of the light beam to the erecting system P, and Y0 represents the object height on the focal plane F. In the astigmatism diagram, the solid line indicates the sagittal image plane, and the broken line indicates the meridional image plane. In the coma aberration diagram, “min” indicates “minute” in angular units. In the spherical aberration diagram and the astigmatism diagram, the unit of the horizontal axis is [m ⁻¹ ], and is represented by “D” in the drawing. C is C line (wavelength 656.28 nm), D is d line (wavelength 587.56 nm), F is F line (wavelength 486.13 nm), G is G line (wavelength)
An aberration curve at 435.84 nm) is shown. In the aberration diagrams of each example described later, the same symbols as those in this example are used.

As is apparent from the aberration diagrams shown in FIGS. 2A to 2C, the eyepiece according to the first example has various aberrations corrected well within the diopter adjustment range, and excellent optical performance is ensured. You can see that.

(Second embodiment)
The second embodiment will be described with reference to FIGS. 3 and 4 and Table 2. FIG. FIG. 3 is a lens configuration diagram (when the diopter is −1 [m ⁻¹ ]) according to the eyepiece of the second example. Although the erecting system P is shown in a developed state in the drawing, an erecting system such as a pentaprism is actually assumed.

As shown in FIG. 3, the eyepiece according to the second example includes a first lens group G1 having negative refractive power and a second lens group G2 having positive refractive power, which are arranged in order from the observation object side. And the third lens group G3 having negative refractive power, the second lens group G2 has an aspherical surface (fifth surface, sixth surface), and moves the second lens group G2 along the optical axis. Thus, the diopter adjustment is performed.

The first lens group G1 has a biconcave lens L1. The second lens group G2 includes a biconvex lens L2.
Have The third lens group G3 includes a negative meniscus lens L3 having a convex surface directed toward the observation object side.

In the present embodiment, as shown in FIG. 3, the eyepiece of the second embodiment is configured by three lens groups G1 to G3 after the image on the focal plane F is converted into an erect image through the erect system P. And the observer moves the eyepoint E.E. Observe with P. The diopter can be adjusted by moving the second lens group G2 along the optical axis.

Table 2 below shows the values of each item in the second embodiment. The surface numbers 1 to 9 in Table 2 are
This corresponds to each optical surface having the curvature radii R1 to R9 shown in FIG. In the second embodiment, the fifth surface and the sixth surface are formed in an aspherical shape.

(Table 2)
[Overall specifications]
Y 14.5
TL 19.5

[Lens specifications]
Surface number R D nd νd
1 ∞ 5.0 1.00000
2 ∞ 71.5 1.51680 64.20
3 ∞ 1.0 1.00000
4 -174.05687 1.5 1.58518 30.24
* 5 38.04339 D5 (variable) 1.00000
* 6 18.82955 6.5 1.53460 56.27
7 -50.40237 D7 (variable) 1.00000
8 22.42965 4.0 1.49108 57.57
9 15.87495 D9 (variable) EP

[Aspherical data]
5th surface κ = 1.4580, A4 = 3.29859E-06, A6 = -4.06074E-08, A8 = 1.34991E-10
6th surface κ = -0.0600, A4 = -1.78130E-06, A6 = -2.44444E-08, A8 = 1.61192E-11

[Variable surface interval data]
f 61.68 58.12 52.66
Diopter -3.40 -1.00 3.00
D5 1.0 2.9 6.5
D7 6.5 4.6 1.0
D9 20.0 20.0 20.0

[Lens group data]
Group number Group first surface Group focal length G1 4 -53.21
G2 6 26.50
G3 8 -138.44

[Conditional expression]
Conditional expression (1) d2 / TL = 0.28
Conditional expression (2) f2 / f = 0.45
Conditional expression (3) ν2-ν1 = 26.03
Conditional expression (4) S3 = 5.84
Conditional expression (5) d3 / TL = 0.20

From the table of specifications shown in Table 2, it can be seen that the eyepiece according to the second example satisfies the conditional expressions (1) to (5).

FIG. 4 is a diagram showing various aberrations (spherical aberration, astigmatism, coma aberration, and distortion aberration) of the eyepiece according to the second example, and (a) shows a diopter of −1.0 [m ⁻¹ ]. Various aberration diagrams, (b) is diopter-3.4.
Various aberration diagrams at [m ⁻¹ ], (c) shows various aberration diagrams at diopter +3.0 [m ⁻¹ ].

As is apparent from the aberration diagrams shown in FIGS. 4A to 4C, the eyepiece according to the second example has various aberrations well corrected within the diopter adjustment range, and excellent optical performance is ensured. You can see that.

(Third embodiment)
A third embodiment will be described with reference to FIGS. 5 and 6 and Table 3. FIG. FIG. 5 is a lens configuration diagram (when the diopter is −1 [m ⁻¹ ]) according to the eyepiece of the third example. Although the erecting system P is shown in a developed state in the drawing, an erecting system such as a pentaprism is actually assumed.

As shown in FIG. 5, the eyepiece according to the third example includes a first lens group G1 having negative refractive power and a second lens group G2 having positive refractive power, which are arranged in order from the observation object side. And the third lens group G3 having negative refractive power, the second lens group G2 has an aspherical surface (fifth surface, sixth surface), and moves the second lens group G2 along the optical axis. Thus, the diopter adjustment is performed.

The first lens group G1 has a biconcave lens L1. The second lens group G2 includes a biconvex lens L2.
Have The third lens group G3 includes a negative meniscus lens L3 having a convex surface directed toward the observation object side.

In the present embodiment, as shown in FIG. 5, the eyepiece of the third embodiment configured by three lens groups G <b> 1 to G <b> 3 after the image on the focal plane F is converted into an erect image through the erect system P. And the observer moves the eyepoint E.E. Observe with P. The diopter can be adjusted by moving the second lens group G2 along the optical axis.

Table 3 below shows values of various specifications in the third example. The surface numbers 1 to 9 in Table 3 are
This corresponds to each optical surface having the radii of curvature R1 to R9 shown in FIG. In the third embodiment, the fifth surface and the sixth surface are formed in an aspherical shape.

(Table 3)
[Overall specifications]
Y 14.5
TL 19.5

[Lens specifications]
Surface number R D nd νd
1 ∞ 5.0 1.00000
2 ∞ 71.5 1.51680 64.20
3 ∞ 1.0 1.00000
4 -120.00000 1.5 1.84666 23.78
* 5 78.52696 D5 (variable) 1.00000
* 6 19.00000 6.5 1.53460 56.27
7 -44.02515 D7 (variable) 1.00000
8 30.00000 2.0 1.49108 57.57
9 18.18745 D9 (variable) EP

[Aspherical data]
5th surface κ = 1.0000, A4 = 7.57095E-06, A6 = -6.55407E-08, A8 = 2.11444E-10
6th surface κ = 1.4573, A4 = -3.24370E-05, A6 = -7.60700E-08, A8 = -2.81338E-10

[Variable surface interval data]
f 64.39 60.00 54.28
Diopter -4.32 -1.03 3.98
D5 0.5 3.5 9.0
D7 9.0 6.0 0.5
D9 20.0 20.0 20.0

[Lens group data]
Group number Group first surface Group focal length G1 4 -55.86
G2 6 25.75
G3 8 -99.61

[Conditional expression]
Conditional expression (1) d2 / TL = 0.43
Conditional expression (2) f2 / f = 0.43
Conditional expression (3) ν2-ν1 = 32.49
Conditional expression (4) S3 = 4.07
Conditional expression (5) d3 / TL = 0.10

From the table of specifications shown in Table 3, it can be seen that the eyepiece according to the third example satisfies the conditional expressions (1) to (5).

FIG. 6 is a diagram illustrating various aberrations (spherical aberration, astigmatism, coma aberration, and distortion aberration) of the eyepiece according to the third example. FIG. 6A illustrates a diopter of −1.0 [m ⁻¹ ]. Various aberration diagrams, (b) is diopter-4.3.
Various aberration diagrams at [m ^-1 ], (c) shows various aberration diagrams at a diopter +3.9 [m ^-1 ].

As is apparent from the aberration diagrams shown in FIGS. 6A to 6C, the eyepiece according to the third example has various aberrations corrected well within the diopter adjustment range, and excellent optical performance is ensured. You can see that.

According to the present invention as described above, it is possible to provide an eyepiece in which various aberrations such as spherical aberration and coma are corrected well within a diopter adjustment range.

In order to make the present invention easier to understand, the configuration requirements of the embodiment have been described, but it goes without saying that the present invention is not limited to this.

G1 First lens group G2 Second lens group G3 Third lens group

Claims (4)

A first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a negative refractive power, arranged in order from the observation object side;
The second lens group has at least one aspheric surface;
Diopter adjustment is possible by moving the second lens group along the optical axis,
An eyepiece that satisfies the following conditional expression:
0.25 <d2 / TL <0.50
0.3 <f2 / f <0.6
However,
d2: a movement distance on the optical axis at the time of diopter adjustment of the second lens group,
TL: the total thickness of the eyepiece lens (distance on the optical axis from the lens surface closest to the observation object of the first lens group to the lens surface closest to the eye point of the third lens group),
f2: focal length of the second lens group,
f: Focal length of the eyepiece at -1 [m ^-1 ]. The first lens group and the second lens group are each composed of a single lens,
The eyepiece according to claim 1, wherein the following conditional expression is satisfied.
20.00 <ν2-ν1
However,
ν1: Abbe number based on the d-line of the single lens constituting the first lens group,
ν2: Abbe number based on the d-line of the single lens constituting the second lens group. 3. The eyepiece according to claim 1, wherein the following conditional expression is satisfied when a shape factor of a lens located closest to the eye point in the third lens group is S <b> 3.
3 <S3 <6
However,
S3 = (Rs + Re) / (Rs−Re)
Rs: radius of curvature of the surface of the third lens group located closest to the eye point on the observation object side surface;
Re: The radius of curvature of the eye point side surface of the lens located closest to the eye point side of the third lens group. The eyepiece according to claim 1, wherein the following conditional expression is satisfied.
0.00 <d3 / TL <0.25
However,
d3: the thickness of the third lens group on the optical axis.

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