JP7726160B2 - Eyepiece, optical instrument having eyepiece, and method for manufacturing eyepiece - Google Patents

Description

The present invention relates to an eyepiece, an optical instrument having an eyepiece, and a method for manufacturing an eyepiece.

Eyepieces for use in electronic viewfinders have been proposed in the past (see, for example, Patent Document 1). However, the problem with such conventional eyepieces is that it is difficult to achieve good optical performance when high magnification is required.

Japanese Patent Application Laid-Open No. 2007-225835

The present invention comprises, in order from the observation object side, a first lens having positive refractive power, a second lens having a meniscus shape and negative refractive power, a third lens having positive refractive power, and a fourth lens having positive refractive power,
the first lens, the second lens, the third lens, and the fourth lens do not include a diffractive optical surface;
The eyepiece must satisfy the following conditions:
-13.00<(R2a+R1b)/(R2a-R1b)<-2.75
0.78<TL/fe<1.60
0.7<f3/f4<1.5
however,
R2a: radius of curvature of the lens surface of the second lens facing the object of observation R1b: radius of curvature of the lens surface of the first lens facing the eyepoint TL: distance on the optical axis from the surface of the object of observation to the lens surface of the eyepiece closest to the eyepoint when the diopter of the eyepiece is -1 [1/m] fe: focal length of the eyepiece when the diopter of the eyepiece is -1 [1/m] f3: focal length of the third lens f4: focal length of the fourth lens Furthermore, the present invention provides an optical system comprising, in order from the object of observation side, a first lens having positive refractive power, a second lens having a meniscus shape and negative refractive power, a third lens having a meniscus shape and positive refractive power, and a fourth lens having positive refractive power,
the first lens, the second lens, the third lens, and the fourth lens do not include a diffractive optical surface;
The eyepiece must satisfy the following conditions:
0.39459≦ (-f2)/f3< 0.45
however,
f2: focal length of the second lens f3: focal length of the third lens

FIG. 1 is a cross-sectional view of the eyepiece according to the first embodiment when the diopter is −1 [1/m]. 2(a), 2(b), and 2(c) are diagrams showing various aberrations of the eyepiece of Example 1 when the diopters are −1 [1/m], −3 [1/m], and +3 [1/m], respectively. FIG. 3 is a cross-sectional view of the eyepiece according to the second embodiment when the diopter is −1 [1/m]. 4(a), 4(b), and 4(c) are diagrams showing various aberrations of the eyepiece of Example 2 when the diopters are −1 [1/m], −3 [1/m], and +3 [1/m], respectively. FIG. 5 is a cross-sectional view of the eyepiece according to the third embodiment when the diopter is −1 [1/m]. 6(a), 6(b), and 6(c) are diagrams showing various aberrations of the eyepiece of Example 3 when the diopters are −1 [1/m], −3 [1/m], and +3 [1/m], respectively. FIG. 7 is a cross-sectional view of the eyepiece according to the fourth embodiment when the diopter is −1 [1/m]. 8(a), 8(b), and 8(c) are diagrams showing various aberrations of the eyepiece of Example 4 when the diopters are −1 [1/m], −5 [1/m], and +5 [1/m], respectively. FIG. 9 is a cross-sectional view of the eyepiece according to the fifth embodiment when the diopter is −1 [1/m]. 10(a), 10(b), and 10(c) are diagrams showing various aberrations of the eyepiece of Example 5 when the diopters are −1 [1/m], −3 [1/m], and +3 [1/m], respectively. 1 is a cross-sectional view of an optical device having an eyepiece according to an embodiment. FIG. 1 is a flow chart showing an outline of a method for manufacturing an eyepiece according to an embodiment. FIG. 10 is a flow chart showing an outline of another method for manufacturing an eyepiece according to an embodiment.

The following describes the eyepiece lens, optical device, and eyepiece lens manufacturing method according to the present embodiment. First, the eyepiece lens according to the embodiment will be described.

The eyepiece according to this embodiment is an eyepiece for magnifying and observing an object. Here, the object being observed is an intermediate image formed by an objective lens, or the display surface of an image display element such as a liquid crystal display element or an organic EL (Electroluminescence) display, and is preferably the display surface of an LCD display element. Therefore, the eyepiece according to this embodiment is suitable for use in an electronic viewfinder for observing an image displayed on the display surface of an image display element. In the following description, the object being observed will also be referred to as the "object surface being observed."

In the following explanations of the embodiments and numerical examples, the diopter, which is the unit of diopter, is [1/m]. For example, diopter X [1/m] indicates that the image formed by the eyepiece is located 1/X [m (meter)] away from the eyepoint on the optical axis. Note that the sign is positive when the image is formed closer to the eyepoint than the eyepiece.

The eyepiece lens of this embodiment has, in order from the observation object side along the optical axis, a first lens with positive refractive power, a second lens with negative refractive power, a third lens with positive refractive power, and a fourth lens with positive refractive power.

As such, the eyepiece of this embodiment is provided with a first lens having positive refractive power for magnifying and observing the object being observed. Furthermore, the eyepiece of this embodiment is provided with a second lens having negative refractive power for correcting chromatic aberration, field curvature, and astigmatism that occur in the first lens having positive refractive power. Furthermore, the eyepiece of this embodiment is provided with a third lens having positive refractive power and a fourth lens having positive refractive power for effectively correcting coma and distortion.

The eyepiece of this embodiment, with its configuration, can effectively correct various aberrations and achieve high magnification. For example, to magnify and observe an object with a diagonal length of approximately 10 mm, it is possible to achieve high magnification with an apparent field of view of 30° or more.

With this configuration, the eyepiece according to this embodiment satisfies the following conditional expression (1).
(1) -13.00<(R2a+R1b)/(R2a-R1b)<-2.75
however,
R2a: radius of curvature of the lens surface of the second lens on the observation object side R1b: radius of curvature of the lens surface of the first lens on the eye point side

Conditional formula (1) defines the shape of the air lens formed by the lens surface of the first lens on the eyepoint side and the lens surface of the second lens on the object side. By satisfying conditional formula (1), good aberration correction can be achieved.

If the corresponding value of conditional formula (1) falls below the lower limit, it becomes difficult to correct various aberrations, particularly field curvature and coma, which is undesirable. It is also undesirable because the edge thickness of the first lens becomes thin, making manufacturing difficult. To ensure the effects of this embodiment, it is preferable to set the lower limit of conditional formula (1) to -12.00. To further ensure the effects of this embodiment, it is preferable to set the lower limit of conditional formula (1) to -11.65. To further ensure the effects of this embodiment, it is preferable to set the lower limit of conditional formula (1) to -11.30.

On the other hand, if the corresponding value of conditional expression (1) exceeds the upper limit, it becomes difficult to correct various aberrations, particularly field curvature and coma, and this is undesirable. To ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (1) to -3.50. To further ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (1) to -4.25. To further ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (1) to -5.00.

With this configuration, the eyepiece according to this embodiment satisfies the following conditional expression (2).
(2) 0.78<TL/fe<1.60
however,
TL: Distance on the optical axis from the observation object surface to the lens surface of the eyepiece closest to the eyepoint when the diopter of the eyepiece is -1 [1/m] fe: Focal length of the eyepiece when the diopter of the eyepiece is -1 [1/m]

Conditional formula (2) defines the appropriate range for the ratio of the axial distance from the observation object surface to the lens surface of the eyepiece closest to the eyepoint when the diopter of the eyepiece is -1 [1/m], i.e., the total optical length of the eyepiece, to the focal length of the eyepiece when the diopter of the eyepiece is -1 [1/m]. Satisfying conditional formula (2) enables compactness and high magnification to be achieved, while also providing good aberration correction.

If the corresponding value of conditional expression (2) falls below the lower limit, it becomes difficult to correct various aberrations, particularly field curvature and coma, and this is undesirable. To ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (2) to 1.00. To further ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (2) to 1.15. To further ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (2) to 1.30.

On the other hand, if the corresponding value of conditional expression (2) exceeds the upper limit, the overall optical length of the eyepiece will increase. Furthermore, achieving higher magnification is undesirable because it makes it difficult to correct various aberrations, particularly field curvature and coma. Note that in conditional expression (2), TL is the air-equivalent length when a parallel plate is inserted between the observation object surface and the lens surface of the eyepiece closest to the eyepoint. To ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (2) to 1.45. Furthermore, to further ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (2) to 1.43. Furthermore, to further ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (2) to 1.40.

The eyepiece according to this embodiment also has, in order from the observation object side along the optical axis, a first lens with positive refractive power, a second lens with negative refractive power, a third lens with positive refractive power, and a fourth lens with positive refractive power.

As such, the eyepiece of this embodiment is provided with a first lens having positive refractive power for magnifying and observing the object being observed. Furthermore, the eyepiece of this embodiment is provided with a second lens having negative refractive power for correcting chromatic aberration, field curvature, and astigmatism that occur in the first lens having positive refractive power. Furthermore, the eyepiece of this embodiment is provided with a third lens having positive refractive power and a fourth lens having positive refractive power for effectively correcting coma and distortion.

The eyepiece of this embodiment, with its configuration, can effectively correct various aberrations and achieve high magnification. For example, to magnify and observe an object with a diagonal length of approximately 10 mm, it is possible to achieve high magnification with an apparent field of view of 30° or more.

With this configuration, the eyepiece according to this embodiment satisfies the following conditional expression (3).
(3) 0.25<(-f2)/f3<0.53
however,
f2: focal length of the second lens f3: focal length of the third lens

Conditional formula (3) defines an appropriate range for the ratio between the refractive power of the second lens and the refractive power of the third lens. By satisfying conditional formula (1), good aberration correction can be achieved.

If the corresponding value of conditional expression (3) falls below the lower limit, it becomes difficult to correct coma and distortion, which is undesirable. To ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (3) to 0.29. To further ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (3) to 0.31. To further ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (3) to 0.33.

On the other hand, if the corresponding value of conditional expression (3) exceeds the upper limit, the refractive power of the second lens relative to the third lens decreases, the Petzval sum increases, and it becomes difficult to simultaneously correct field curvature and astigmatism, which is undesirable. It also becomes difficult to correct coma, which is undesirable. To ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (3) to 0.48. To further ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (3) to 0.45. To further ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (3) to 0.42.

With this configuration, the eyepiece according to this embodiment satisfies the following conditional expression (4).
(4) 0.34<d1/fe<0.60
however,
d1: the distance on the optical axis from the observation object surface to the lens surface of the first lens on the observation object side when the diopter of the eyepiece is −1 [1/m] fe: the focal length of the eyepiece when the diopter of the eyepiece is −1 [1/m]

Conditional formula (4) defines the appropriate range for the ratio of the distance on the optical axis from the observation object surface to the lens surface of the first lens facing the observation object when the diopter of the eyepiece is -1 [1/m] to the focal length of the eyepiece when the diopter of the eyepiece is -1 [1/m]. Satisfying conditional formula (4) enables compactness and good aberration correction.

If the corresponding value of conditional expression (4) falls below the lower limit, it becomes difficult to correct various aberrations, particularly coma and distortion, which is undesirable. Furthermore, the distance from the observation object surface to the lens surface of the first lens facing the observation object becomes short, which undesirably results in the focus being on foreign matter adhering to the lens surface of the first lens facing the eyepoint. To ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (4) to 0.35. To further ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (4) to 0.355. To further ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (4) to 0.36.

On the other hand, if the corresponding value of conditional expression (4) exceeds the upper limit, it becomes difficult to correct various aberrations, particularly coma and distortion, which is undesirable. It is also undesirable because it increases the overall optical length of the eyepiece. Note that, in conditional expression (4), d1 is the air-equivalent length when a parallel plate is inserted between the observation object surface and the lens surface of the first lens facing the observation object. To ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (4) to 0.52. To further ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (4) to 0.49. To further ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (4) to 0.45.

Moreover, it is desirable that the eyepiece according to this embodiment satisfy the following conditional expression (5).
(5) 0.5<(R2b+R2a)/(R2b-R2a)<2.4
however,
R2b: radius of curvature of the lens surface of the second lens on the eyepoint side R2a: radius of curvature of the lens surface of the second lens on the observation object side

Conditional expression (5) defines the shape of the second lens. By satisfying conditional expression (5), good aberration correction can be achieved.

If the corresponding value of conditional expression (5) falls below the lower limit, it becomes difficult to correct field curvature, coma, and distortion, which is undesirable. To ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (5) to 0.8. To further ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (5) to 1.0. To further ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (5) to 1.2.

On the other hand, if the corresponding value of conditional expression (5) exceeds the upper limit, it becomes difficult to correct field curvature, coma, and distortion, which is undesirable. To ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (5) to 2.1. To further ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (5) to 2.0. To further ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (5) to 1.9.

Moreover, it is desirable that the eyepiece according to this embodiment satisfy the following conditional expression (6).
(6) 0.7<f3/f4<1.5
however,
f3: focal length of the third lens f4: focal length of the fourth lens

Conditional expression (6) defines an appropriate range for the ratio between the refractive power of the third lens and the refractive power of the fourth lens. By satisfying conditional expression (6), good aberration correction can be achieved.

If the corresponding value of conditional expression (6) falls below the lower limit, it becomes difficult to correct coma and distortion, which is undesirable. To ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (6) to 0.80. To further ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (6) to 0.88. To further ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (6) to 0.95.

On the other hand, if the corresponding value of conditional expression (6) exceeds the upper limit, it becomes difficult to correct coma and distortion, which is undesirable. To ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (6) to 1.42. To further ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (6) to 1.39. To further ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (6) to 1.35.

Moreover, it is desirable that the eyepiece according to this embodiment satisfy the following conditional expression (7).
(7) 0.97<f34/(-f2)<1.5
however,
f34: composite focal length of the third lens and the fourth lens when the diopter of the eyepiece is −1 [1/m] f2: focal length of the second lens

Conditional expression (7) defines the appropriate range for the ratio of the combined focal length of the third and fourth lenses to the focal length of the second lens when the diopter of the eyepiece is -1 [1/m]. By satisfying conditional expression (7), good aberration correction can be achieved.

If the corresponding value of conditional expression (7) falls below the lower limit, the combined refractive power of the third and fourth lenses relative to the second lens will increase, the Petzval sum will increase, and it will become difficult to simultaneously correct curvature of field and astigmatism, which is undesirable. It will also become difficult to correct coma, which is undesirable. To ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (7) to 1.07. To further ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (7) to 1.14. To further ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (7) to 1.21.

On the other hand, if the corresponding value of conditional expression (7) exceeds the upper limit, it becomes difficult to correct coma and distortion, which is undesirable. To ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (7) to 1.45. To further ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (7) to 1.40. To further ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (7) to 1.37. To further ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (7) to 1.34. To further ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (7) to 1.30.

Moreover, it is desirable that the eyepiece according to this embodiment satisfy the following conditional expression (8).
(8) 0.4<(-f2)/fe<1.0
however,
f2: focal length of the second lens fe: focal length of the eyepiece when the diopter of the eyepiece is −1 [1/m]

Conditional formula (8) defines the appropriate range for the ratio between the focal length of the second lens and the focal length of the eyepiece when the diopter of the eyepiece is -1 [1/m]. By satisfying conditional formula (8), good aberration correction can be achieved.

If the corresponding value of conditional expression (8) falls below the lower limit, the refractive power of the second lens will increase, making it difficult to correct coma aberration, which is undesirable. To ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (8) to 0.45. To further ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (8) to 0.50. To further ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (8) to 0.55. To further ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (8) to 0.65. To further ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (8) to 0.70.

On the other hand, if the corresponding value of conditional expression (8) exceeds the upper limit, the Petzval sum increases, making it difficult to simultaneously correct field curvature and astigmatism, which is undesirable. It also makes it difficult to correct coma, which is undesirable. To ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (8) to 0.90. To further ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (8) to 0.84. To further ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (8) to 0.77.

Moreover, it is desirable that the eyepiece according to this embodiment satisfy the following conditional expression (9).
(9) 0.50<ΣD/fe<1.24
however,
ΣD: The distance on the optical axis from the lens surface of the eyepiece closest to the observation object to the lens surface closest to the eyepoint when the diopter of the eyepiece is −1 [1/m] fe: The focal length of the eyepiece when the diopter of the eyepiece is −1 [1/m]

Conditional formula (9) defines the appropriate range for the ratio of the axial distance from the lens surface of the eyepiece closest to the observation object to the lens surface closest to the eyepoint when the diopter of the eyepiece is -1 [1/m] to the focal length of the eyepiece when the diopter of the eyepiece is -1 [1/m]. Satisfying conditional formula (9) allows the axial thickness of the eyepiece to be reduced and good aberration correction to be achieved.

If the corresponding value of conditional expression (9) falls below the lower limit, it becomes difficult to correct field curvature, coma, and distortion, which is undesirable. To ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (9) to 0.70. To further ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (9) to 0.82. To further ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (9) to 0.93.

On the other hand, if the corresponding value of conditional expression (9) exceeds the upper limit, it becomes difficult to correct field curvature, coma, and distortion, which is undesirable. It is also undesirable because the axial thickness of the eyepiece increases. To ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (9) to 1.15. To further ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (9) to 1.08. To further ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (9) to 1.00.

Moreover, it is desirable that the eyepiece according to this embodiment satisfy the following conditional expression (10).
(10) 1.2<f4/fe<2.2
however,
f4: focal length of the fourth lens fe: focal length of the eyepiece when the diopter of the eyepiece is −1 [1/m]

Conditional formula (10) defines the appropriate range for the ratio between the focal length of the fourth lens and the focal length of the eyepiece when the diopter of the eyepiece is -1 [1/m]. By satisfying conditional formula (10), good aberration correction can be achieved.

If the corresponding value of conditional expression (10) falls below the lower limit, the refractive power of the fourth lens increases, the Petzval sum increases, and it becomes difficult to simultaneously correct curvature of field and astigmatism, which is undesirable. It also becomes difficult to correct coma, which is undesirable. To ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (10) to 1.35. To further ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (10) to 1.43. To further ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (10) to 1.50.

On the other hand, if the corresponding value of conditional expression (10) exceeds the upper limit, it becomes difficult to correct various aberrations, particularly coma, and this is undesirable. To ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (10) to 2.00. To further ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (10) to 1.90. To further ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (10) to 1.80.

Moreover, it is desirable that the eyepiece according to this embodiment satisfy the following conditional expression (11).
(11) 0.15<D1/fe<0.40
however,
D1: thickness of the first lens on the optical axis fe: focal length of the eyepiece when the diopter of the eyepiece is −1 [1/m]

Conditional formula (11) defines the appropriate range for the ratio between the axial thickness of the first lens and the focal length of the eyepiece when the diopter of the eyepiece is -1 [1/m]. By satisfying conditional formula (11), the axial thickness of the eyepiece can be reduced and good aberration correction can be achieved.

If the corresponding value of conditional expression (11) falls below the lower limit, it becomes difficult to correct field curvature and coma, which is undesirable. It is also undesirable because the edge thickness of the first lens becomes thin, making manufacturing difficult. To ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (11) to 0.20. To further ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (11) to 0.23. To further ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (11) to 0.25.

On the other hand, if the corresponding value of conditional expression (11) exceeds the upper limit, it becomes difficult to correct field curvature and coma, which is undesirable. It is also undesirable because it increases the thickness of the eyepiece in the optical axis direction. To ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (11) to 0.34. To further ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (11) to 0.32. To further ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (11) to 0.29.

Moreover, it is desirable that the eyepiece according to this embodiment satisfy the following conditional expression (12).
(12) 0.05<D2/fe<0.20
however,
D2: Thickness of the second lens on the optical axis fe: Focal length of the eyepiece when the diopter of the eyepiece is −1 [1/m]

Conditional formula (12) defines the appropriate range for the ratio between the axial thickness of the second lens and the focal length of the eyepiece when the diopter of the eyepiece is -1 [1/m]. By satisfying conditional formula (12), the axial thickness of the eyepiece can be reduced and good aberration correction can be achieved.

If the corresponding value of conditional expression (12) falls below the lower limit, it becomes difficult to correct field curvature and coma, which is undesirable. To ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (12) to 0.07. To further ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (12) to 0.08. To further ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (12) to 0.09.

On the other hand, if the corresponding value of conditional expression (12) exceeds the upper limit, it becomes difficult to correct field curvature and coma, which is undesirable. It is also undesirable because the thickness of the eyepiece on the optical axis increases. To ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (12) to 0.17. To further ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (12) to 0.16. To further ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (12) to 0.15.

Furthermore, in the eyepiece according to this embodiment, it is desirable that at least one surface of the first lens is aspherical. This configuration allows for excellent correction of field curvature, astigmatism, and coma.

Furthermore, it is preferable that all of the lenses constituting the eyepiece according to this embodiment have at least one aspherical surface. This configuration allows for excellent correction of field curvature, astigmatism, and coma.

Furthermore, in the eyepiece lens according to this embodiment, it is desirable that the first lens, the second lens, the third lens, and the fourth lens are plastic lenses. This configuration allows for lighter weight and lower costs. Furthermore, since aspherical shapes can be easily formed, spherical aberration, field curvature, astigmatism, coma, and distortion can be effectively corrected.

Furthermore, in the eyepiece according to this embodiment, it is desirable that the distance between the first lens and the second lens, the distance between the second lens and the third lens, and the distance between the third lens and the fourth lens are all constant. This configuration can reduce fluctuations in field curvature, coma, and distortion compared to when the distance between adjacent lenses varies.

Furthermore, with the eyepiece according to this embodiment, it is desirable to adjust the diopter by moving the first lens, the second lens, the third lens, and the fourth lens along the optical axis. This configuration makes it possible to reduce fluctuations in aberrations, particularly field curvature, coma, and distortion, during diopter adjustment.

Furthermore, with the eyepiece according to this embodiment, it is desirable to adjust the diopter by moving all of the lenses that make up the eyepiece as a whole. This configuration makes it possible to reduce fluctuations in aberrations, particularly field curvature, coma, and distortion, during diopter adjustment.

The optical device according to the embodiment of the present application has an eyepiece lens with the above-described configuration. This makes it possible to realize an optical device with high magnification, compact size, and high optical performance.

A manufacturing method for an eyepiece according to an embodiment of the present application is a manufacturing method for an eyepiece for observing an observation object, in which the eyepiece is configured to have, in order from the observation object side, a first lens having positive refractive power, a second lens having negative refractive power, a third lens having positive refractive power, and a fourth lens having positive refractive power, and is configured to satisfy the following conditional expressions (1) and (2):
(1) -13.00<(R2a+R1b)/(R2a-R1b)<-2.75
(2) 0.78<TL/fe<1.60
however,
R2a: Radius of curvature of the lens surface of the second lens on the observation object side R1b: Radius of curvature of the lens surface of the first lens on the eyepoint side TL: Distance on the optical axis from the observation object surface to the lens surface of the eyepiece closest to the eyepoint when the diopter of the eyepiece is -1 [1/m] fe: Focal length of the eyepiece when the diopter of the eyepiece is -1 [1/m]

This method of manufacturing eyepieces makes it possible to produce eyepieces that are high-magnification, compact, and have excellent optical performance.

Another method for manufacturing an eyepiece according to an embodiment of the present application is a method for manufacturing an eyepiece for observing an object, in which the eyepiece is configured to have, in order from the side of the object being observed, a first lens having positive refractive power, a second lens having negative refractive power, a third lens having positive refractive power, and a fourth lens having positive refractive power, and is configured to satisfy the following conditional expressions (3) and (4):
(3) 0.25<(-f2)/f3<0.53
(4) 0.34<d1/fe<0.60
however,
f2: focal length of the second lens f3: focal length of the third lens d1: distance on the optical axis from the observation object surface to the lens surface of the first lens on the observation object side when the diopter of the eyepiece is −1 [1/m] fe: focal length of the eyepiece when the diopter of the eyepiece is −1 [1/m]

This other manufacturing method for eyepieces makes it possible to produce eyepieces that are high magnification, compact, and have high optical performance.

(Numerical Example)
An eyepiece according to a numerical example of this embodiment will be described below with reference to the accompanying drawings.

(First Example)
FIG. 1 is a cross-sectional view of the eyepiece according to the first embodiment when the diopter is −1 [1/m]. In FIG. 1, EP denotes the eyepoint, and Ob denotes the object being observed. These symbols will be used in the same manner in the drawings of each embodiment described later. In this embodiment, the object being observed Ob is the display surface of a liquid crystal display element of an electronic viewfinder, and an image displayed on the display surface of the liquid crystal display element is observed at eyepoint EP. In each embodiment described later, the object being observed Ob is the display surface of a liquid crystal display element of an electronic viewfinder.

As shown in Figure 1, the eyepiece lens of this embodiment is composed of, in order from the observation object Ob side, a first lens L1 which is a biconvex lens, a second lens L2 which is a negative meniscus lens with its convex surface facing the eyepoint EP side, a third lens L3 which is a positive meniscus lens with its convex surface facing the eyepoint EP side, and a fourth lens L4 which is a positive meniscus lens with its convex surface facing the eyepoint EP side.

In the eyepiece of this embodiment, the lens surface of the first lens L1 facing the observation object Ob and the lens surface facing the eyepoint EP are aspherical lenses, the lens surface of the second lens L2 facing the observation object Ob and the lens surface facing the eyepoint EP are aspherical lenses, the lens surface of the third lens L3 facing the observation object Ob and the lens surface facing the eyepoint EP are aspherical lenses, and the lens surface of the fourth lens L4 facing the observation object Ob and the lens surface facing the eyepoint EP are aspherical lenses.

The eyepiece of this embodiment adjusts the diopter by moving the first lens L1, second lens L2, third lens L3, and fourth lens L4 together along the optical axis.

Table 1 below lists the specifications of the photographic lens according to this example.
In the [Overall Specifications], Y0 indicates the height of the observed object, and TL indicates the distance on the optical axis from the surface of the observed object to the lens surface of the eyepiece closest to the eyepoint EP when the diopter is −1 [1/m].

In [Surface Data], the surface number indicates the order of the optical surface counted from the object side, r indicates the radius of curvature, d indicates the surface spacing (the spacing between the nth surface (n is an integer) and the (n+1)th surface), nd indicates the refractive index for the d-line (wavelength 587.6 nm), and νd indicates the Abbe number for the d-line (wavelength 587.6 nm). Surface 0 indicates the object surface, i.e., the display surface of the LCD display element, which is the object Ob. Variable indicates the variable surface spacing, and EP indicates the eyepoint EP. A radius of curvature r = ∞ indicates a flat surface. The refractive index of air, nd = 1.0000, is omitted. If the lens surface is aspherical, an * is added to the surface number, and the paraxial radius of curvature is shown in the radius of curvature r column.

[Aspherical surface data] shows the conical coefficients and aspherical surface coefficients for the aspherical surface shown in [Surface data] when the shape is expressed by the following equations.
X(y)=(y ² /r)/[1+{1-κ(y ² /r ² )} ^1/2 ]+A4y ⁴ +A6y ⁶ +A8y ⁸ +A10y ¹⁰
Here, the height in the direction perpendicular to the optical axis is y, the amount of displacement in the optical axis direction at height y is X(y), the radius of curvature (paraxial radius of curvature) of the reference spherical surface is r, the conic coefficient is κ, and the n-th order aspherical coefficient is An. The second order aspherical coefficient A2 is 0 (zero) and is omitted. Furthermore, "E-n" represents "×10 ^-n ", and for example, "1.234E-05" represents "1.234×10 ^-5 ".

In the [Variable Distance Data], fe indicates the focal length of the eyepiece at each diopter, and di (i is an integer) indicates the surface distance between the ith surface and the (i+1)th surface.

[Data for each lens] indicates the first surface number and focal length of each lens.
[Conditional Expression Corresponding Value] indicates the corresponding value of each conditional expression.

Here, the focal length fe, radius of curvature r, and other length units listed in Table 1 are generally in millimeters. However, this is not limited to this because the optical system can achieve the same optical performance even when proportionally enlarged or reduced.
The symbols in Table 1 described above will be used in the tables of the respective examples described later.

(Table 1) First Example [Overall Specifications]
Y0 5
TL 22.97080

[Face data]
Surface number r d nd νd
0) ∞ Variable *1) 38.5000 4.7000 1.5311 55.91
*2) -7.9324 1.9500
*3) -5.9015 1.6000 1.6349 23.96
*4) -31.3532 0.4000
*5) -81.3698 3.6000 1.5311 55.91
*6) -13.4312 0.3000
*7) -86.6666 3.8000 1.5311 55.91
*8) -12.5836 Variable EP ∞

[Aspherical data]
Surface number κ A4 A6 A8 A10
1) 1.0000 -1.07830E-04 3.90090E-07 -8.84450E-09 0.00000E+00
2) 0.2300 1.46600E-04 -2.00600E-06 1.12720E-08 -1.76010E-10
3) 0.2000 6.32360E-06 -7.08210E-07 9.97080E-09 6.05370E-12
4) 2.4698 -4.51520E-05 3.34100E-07 5.44460E-09 -3.19170E-12
5) 1.0000 2.87140E-05 -4.06830E-07 8.06580E-09 -1.05880E-10
6) 0.4764 3.15160E-05 6.77160E-07 4.22120E-09 -1.12500E-10
7) 1.0000 1.61050E-05 -1.27860E-07 -6.30500E-10 1.97650E-11
8) -1.3000 -6.03300E-05 -2.60140E-07 5.18670E-10 1.33770E-11

[Variable Interval Data]
Diopter -1 -3 +3
fe 16.69882 16.69882 16.69882
d0 6.62 6.04 7.72
d8 22.00 22.58 20.90

[Data for each lens]
Starting surface f
L1 1 12.83484
L2 3 -11.73613
L3 5 29.74230
L4 7 27.23347

[Conditional expression value]
fe = 16.69882
-f2 = 11.73613
f3 = 29.74230
f4 = 27.23347
f34 = 14.92250
ΣD＝16.35000

(1) (R2a+R1b)/(R2a-R1b)=-6.81171
(2) TL/fe=1.37559
(3) (-f2)/f3=0.39459
(4) d1/fe=0.39648
(5) (R2b+R2a)/(R2b-R2a)=1.46374
(6) f3/f4=1.09212
(7) f34/(-f2)=1.27150
(8) (-f2)/fe=0.70281
(9) ΣD/fe=0.97911
(10) f4/fe=1.63086
(11) D1/fe=0.28146
(12) D2/fe=0.09582

Figures 2(a), 2(b), and 2(c) are diagrams showing various aberrations for the eyepiece of Example 1 when the diopter is -1 [1/m], -3 [1/m], and +3 [1/m], respectively.

In each aberration diagram, Y1 indicates the height at which light emitted from the optical axial center of the observed object is incident on the tangent plane of the first lens L1 on the observed object side, and Y0 indicates the height of the observed object. Also, in the diagram, d indicates the aberration curve for the d-line (wavelength λ = 587.6 nm), g indicates the aberration curve for the g-line (wavelength λ = 435.8 nm), and values without a notation indicate the aberration curve for the d-line. In aberration diagrams showing astigmatism, the solid line indicates the sagittal image plane, and the dashed line indicates the meridional image plane. The unit D on the horizontal axis of the spherical aberration diagram and astigmatism diagram is [1/m] (diopter). The same symbols as in this embodiment are used in the aberration diagrams of each embodiment shown below.

From each aberration diagram, it can be seen that the eyepiece according to Example 1 has excellent optical performance, with various aberrations being well corrected within the diopter adjustment range.

(Second Example)
FIG. 3 is a cross-sectional view of the eyepiece according to the second embodiment when the diopter is −1 [1/m].
As shown in FIG. 3, the eyepiece lens of this embodiment is composed of, in order from the observation object Ob side, a first lens L1 which is a biconvex lens, a second lens L2 which is a negative meniscus lens with its convex surface facing the eye point EP side, a third lens L3 which is a positive meniscus lens with its convex surface facing the eye point EP side, and a fourth lens L4 which is a biconvex lens.

In the eyepiece of this embodiment, the lens surface of the first lens L1 facing the observation object Ob and the lens surface facing the eyepoint EP are aspherical lenses, the lens surface of the second lens L2 facing the observation object Ob and the lens surface facing the eyepoint EP are aspherical lenses, the lens surface of the third lens L3 facing the observation object Ob and the lens surface facing the eyepoint EP are aspherical lenses, and the lens surface of the fourth lens L4 facing the observation object Ob and the lens surface facing the eyepoint EP are aspherical lenses.

In addition, the eyepiece of this embodiment adjusts the diopter by moving the first lens L1, second lens L2, third lens L3, and fourth lens L4 together along the optical axis. The observation object Ob is the display surface of the liquid crystal display element of the electronic viewfinder, and the image displayed on the display surface of the liquid crystal display element is observed at eyepoint EP.

Table 2 below lists the specifications of the photographic lens used in this example.

(Table 2) Second Example [Overall Specifications]
Y0 5
TL 22.44140

[Face data]
Surface number r d nd νd
0) ∞ Variable *1) 54.1310 4.6000 1.5311 55.91
*2) -7.1966 1.9000
*3) -5.1089 1.5000 1.6392 23.41
*4) -19.3192 0.4000
*5) -102.7678 3.7000 1.5311 55.91
*6) -15.0883 0.2000
*7) 10238.8333 3.7000 1.5311 55.91
*8) -13.2729 Variable EP ∞

[Aspherical data]
Surface number κ A4 A6 A8 A10
1) 3.0000 -1.08886E-04 9.45037E-07 -3.04555E-08 6.36072E-10
2) 0.5371 2.59662E-04 4.45097E-07 -7.58586E-09 1.52063E-10
3) -0.0106 -6.11178E-05 1.09499E-06 -4.80532E-08 -1.41908E-11
4) 0.9777 -6.22815E-05 1.22908E-06 -6.71364E-09 6.40334E-11
5) 1.0000 4.50000E-05 -3.08295E-08 1.00000E-09 -1.68575E-11
6) 1.0000 1.23962E-04 -1.63662E-06 1.82978E-08 -1.04522E-10
7) 1.0000 6.03686E-05 -1.05695E-06 3.14589E-09 5.91446E-11
8) -0.4502 6.02914E-05 4.18032E-07 -1.69597E-08 1.55783E-10

[Variable Interval Data]
Diopter -1 -3 +3
fe 16.26559 16.26559 16.26559
d0 6.44 5.89 7.48
d8 20.00 20.55 18.96

[Data for each lens]
Starting surface f
L1 1 12.27984
L2 3 -11.33254
L3 5 32.81807
L4 7 24.96209

[Conditional expression value]
fe = 16.26559
-f2 = 11.33254
f3 = 32.81807
f4 = 24.96209
f34 = 14.74024
ΣD＝16.00000

(1) (R2a+R1b)/(R2a-R1b)=-5.89429
(2) TL/fe=1.37969
(3) (-f2)/f3=0.34531
(4) d1/fe=0.39601
(5) (R2b+R2a)/(R2b-R2a)=1.71904
(6) f3/f4=1.31472
(7) f34/(-f2)=1.30070
(8) (-f2)/fe=0.69672
(9) ΣD/fe=0.98367
(10) f4/fe=1.53466
(11) D1/fe=0.28281
(12) D2/fe=0.09222

4(a), 4(b), and 4(c) are diagrams showing various aberrations of the eyepiece of Example 2 when the diopters are −1 [1/m], −3 [1/m], and +3 [1/m], respectively.
From the aberration diagrams, it can be seen that the eyepiece according to Example 2 has excellent optical performance, with various aberrations being well corrected within the diopter adjustment range.

(Third Example)
FIG. 5 is a cross-sectional view of the eyepiece according to the third embodiment when the diopter is −1 [1/m].
As shown in FIG. 5, the eyepiece lens of this embodiment is composed of, in order from the observation object Ob side, a first lens L1 which is a biconvex lens, a second lens L2 which is a negative meniscus lens with its convex surface facing the eye point EP side, a third lens L3 which is a biconvex lens, and a fourth lens L4 which is a positive meniscus lens with its convex surface facing the eye point EP side.

In the eyepiece of this embodiment, the lens surface of the first lens L1 facing the observation object Ob and the lens surface facing the eyepoint EP are aspherical lenses, the lens surface of the second lens L2 facing the observation object Ob and the lens surface facing the eyepoint EP are aspherical lenses, the lens surface of the third lens L3 facing the observation object Ob and the lens surface facing the eyepoint EP are aspherical lenses, and the lens surface of the fourth lens L4 facing the observation object Ob and the lens surface facing the eyepoint EP are aspherical lenses.

In addition, the eyepiece of this embodiment adjusts the diopter by moving the first lens L1, second lens L2, third lens L3, and fourth lens L4 together along the optical axis. The observation object Ob is the display surface of the liquid crystal display element of the electronic viewfinder, and the image displayed on the display surface of the liquid crystal display element is observed at eyepoint EP.

Table 3 below lists the specifications of the photographic lens used in this example.

(Table 3) Third Example [Overall Specifications]
Y0 5
TL 22.69130

[Face data]
Surface number r d nd νd
0) ∞ Variable *1) 36.8718 4.7000 1.5311 55.91
*2) -7.2203 1.7000
*3) -6.0441 1.5000 1.6392 23.41
*4) -58.5446 0.3000
*5) 2088.0633 4.0000 1.5311 55.91
*6) -16.6991 0.2000
*7) -294.5173 3.3500 1.5311 55.91
*8) -12.6937 Variable EP ∞

[Aspherical data]
Surface number κ A4 A6 A8 A10
1) 1.0000 -2.77100E-04 3.28531E-06 -5.95866E-08 5.56135E-10
2) -0.1834 3.98963E-05 3.59354E-07 -5.44538E-08 7.79143E-10
3) 0.0254 -4.50556E-05 -2.01226E-06 3.28413E-09 5.79187E-11
4) 11.4670 -1.64243E-04 4.99568E-07 2.72460E-09 3.97790E-11
5) 1.0000 1.99028E-06 -9.39927E-08 -6.16687E-10 1.30958E-11
6) 1.0000 -9.14500E-05 2.76509E-07 -2.08324E-10 -2.24194E-11
7) 1.0000 3.31997E-05 -9.70440E-07 9.59206E-09 -1.59816E-11
8) -1.9398 3.92293E-05 1.49940E-08 1.09811E-09 1.45671E-12

[Variable Interval Data]
Diopter -1 -3 +3
fe 16.25648 16.25648 16.25648
d0 6.94 6.39 7.98
d8 20.00 20.55 18.96

[Data for each lens]
Starting surface f
L1 1 11.80525
L2 3 -10.66309
L3 5 31.21356
L4 7 24.87468

[Conditional expression value]
fe = 16.25648
-f2 = 10.66309
f3 = 31.21356
f4 = 24.87468
f34 = 14.48819
ΣD＝15.75000

(1) (R2a+R1b)/(R2a-R1b)=-11.27733
(2) TL/fe=1.39583
(3) (-f2)/f3=0.34162
(4) d1/fe=0.42699
(5) (R2b+R2a)/(R2b-R2a)=1.23025
(6) f3/f4=1.25483
(7) f34/(-f2)=1.35872
(8) (-f2)/fe=0.65593
(9) ΣD/fe=0.96884
(10) f4/fe=1.53014
(11) D1/fe=0.28912
(12) D2/fe=0.09227

6(a), 6(b), and 6(c) are diagrams showing various aberrations of the eyepiece of Example 3 when the diopters are −1 [1/m], −3 [1/m], and +3 [1/m], respectively.
From the aberration diagrams, it can be seen that the eyepiece according to Example 3 has excellent optical performance, with various aberrations being well corrected within the diopter adjustment range.

(Fourth Example)
FIG. 7 is a cross-sectional view of the eyepiece according to the fourth embodiment when the diopter is −1 [1/m].
As shown in FIG. 7, the eyepiece lens of this embodiment is composed of, in order from the observation object Ob side, a first lens L1 which is a biconvex lens, a second lens L2 which is a negative meniscus lens with its convex surface facing the eye point EP, a third lens L3 which is a positive meniscus lens with its convex surface facing the eye point EP, and a fourth lens L4 which is a positive meniscus lens with its convex surface facing the eye point EP.

In the eyepiece of this embodiment, the lens surface of the first lens L1 facing the observation object Ob and the lens surface facing the eyepoint EP are aspherical lenses, the lens surface of the second lens L2 facing the observation object Ob and the lens surface facing the eyepoint EP are aspherical lenses, the lens surface of the third lens L3 facing the observation object Ob and the lens surface facing the eyepoint EP are aspherical lenses, and the lens surface of the fourth lens L4 facing the observation object Ob and the lens surface facing the eyepoint EP are aspherical lenses.

In addition, the eyepiece of this embodiment adjusts the diopter by moving the first lens L1, second lens L2, third lens L3, and fourth lens L4 together along the optical axis. The observation object Ob is the display surface of the liquid crystal display element of the electronic viewfinder, and the image displayed on the display surface of the liquid crystal display element is observed at eyepoint EP.

Table 4 below lists the specifications of the photographic lens used in this example.

(Table 4) Fourth Example [Overall Specifications]
Y0 5
TL 23.17110

[Face data]
Surface number r d nd νd
0) ∞ Variable *1) 45.0000 4.7000 1.5311 55.91
*2) -7.7479 2.0000
*3) -6.1500 1.6000 1.6349 23.96
*4) -31.9899 0.4500
*5) -72.0000 3.6000 1.5311 55.91
*6) -13.5279 0.3000
*7) -70.8540 3.9000 1.5311 55.91
*8) -12.6502 Variable EP ∞

[Aspherical data]
Surface number κ A4 A6 A8 A10
1) 1.0000 -1.07831E-04 3.90090E-07 -8.84455E-09 -1.00000E-11
2) 0.0556 1.36830E-04 -1.76475E-06 -1.38657E-09 -7.67919E-11
3) 0.2000 4.81429E-05 -9.80409E-07 -8.91375E-09 2.08310E-11
4) 1.2082 -5.40750E-05 5.44833E-07 1.22407E-09 -2.28888E-11
5) 1.0000 2.00599E-05 -3.00041E-07 5.73160E-09 -7.15876E-11
6) 1.0000 6.47050E-05 2.82244E-07 8.66025E-10 -3.63247E-11
7) 1.0000 5.59470E-05 -2.82099E-07 -3.84079E-09 3.66963E-11
8) -0.6000 1.20751E-06 -3.65237E-07 -3.60726E-10 1.20918E-11

[Variable Interval Data]
Diopter -1 -5 +5
fe 16.70093 16.70093 16.70093
d0 6.62 5.44 8.25
d8 20.00 21.18 18.37

[Data for each lens]
Starting surface f
L1 1 12.84253
L2 3 -12.28670
L3 5 30.70855
L4 7 28.33712

[Conditional expression value]
fe = 16.70093
-f2 = 12.28670
f3 = 30.70855
f4 = 28.33712
f34 = 15.47065
ΣD＝16.55000

(1) (R2a+R1b)/(R2a-R1b)=-8.69760
(2) TL/fe=1.38741
(3) (-f2)/f3=0.40011
(4) d1/fe=0.39645
(5) (R2b+R2a)/(R2b-R2a)=1.47601
(6) f3/f4=1.08369
(7) f34/(-f2)=1.25914
(8) (-f2)/fe=0.73569
(9) ΣD/fe=0.99096
(10) f4/fe=1.69674
(11) D1/fe=0.28142
(12) D2/fe=0.09580

8(a), 8(b), and 8(c) are diagrams showing various aberrations of the eyepiece of Example 4 when the diopters are −1 [1/m], −5 [1/m], and +5 [1/m], respectively.
From the aberration diagrams, it can be seen that the eyepiece according to Example 4 has excellent optical performance, with various aberrations being well corrected within the diopter adjustment range.

(Fifth Example)
FIG. 9 is a cross-sectional view of the eyepiece according to the fifth embodiment when the diopter is −1 [1/m].
As shown in FIG. 9, the eyepiece lens of this embodiment is composed of, in order from the observation object Ob side, a first lens L1 which is a biconvex lens, a second lens L2 which is a negative meniscus lens with its convex surface facing the eye point EP, a third lens L3 which is a positive meniscus lens with its convex surface facing the eye point EP, and a fourth lens L4 which is a positive meniscus lens with its convex surface facing the eye point EP.

In the eyepiece of this embodiment, the lens surface of the first lens L1 facing the observation object Ob and the lens surface facing the eyepoint EP are aspherical lenses, the lens surface of the second lens L2 facing the observation object Ob and the lens surface facing the eyepoint EP are aspherical lenses, the lens surface of the third lens L3 facing the observation object Ob and the lens surface facing the eyepoint EP are aspherical lenses, and the lens surface of the fourth lens L4 facing the observation object Ob and the lens surface facing the eyepoint EP are aspherical lenses.

In addition, the eyepiece of this embodiment adjusts the diopter by moving the first lens L1, second lens L2, third lens L3, and fourth lens L4 together along the optical axis. The observation object Ob is the display surface of the liquid crystal display element of the electronic viewfinder, and the image displayed on the display surface of the liquid crystal display element is observed at eyepoint EP.

Table 5 below lists the specifications of the photographic lens used in this example.

(Table 5) Fifth Example [Overall Specifications]
Y0 5
TL 23.58660

[Face data]
Surface number r d nd νd
0) ∞ Variable *1) 35.4135 4.5000 1.5311 55.91
*2) -8.6762 1.8000
*3) -7.0000 1.7000 1.6392 23.41
*4) -45.0000 0.3000
*5) -62.6687 3.7000 1.5311 55.91
*6) -13.8064 0.3000
*7) -63.9198 3.9000 1.5311 55.91
*8) -12.7708 Variable EP ∞

[Aspherical data]
Surface number κ A4 A6 A8 A10
1) 1.0000 -1.07831E-04 3.90090E-07 -8.84455E-09 -1.00000E-11
2) 0.0556 1.17846E-04 -2.11624E-06 3.16358E-08 -5.76944E-10
3) 0.2000 -1.38822E-04 -2.32251E-07 -3.48817E-08 1.02138E-10
4) 1.2082 -1.31713E-04 -1.87116E-08 5.54969E-10 -1.00641E-11
5) 1.0000 2.00599E-05 -3.00041E-07 5.73160E-09 -7.15876E-11
6) 1.0000 1.48790E-05 4.25697E-07 2.40718E-09 -2.65452E-11
7) 1.0000 5.63031E-05 -3.41994E-07 -4.83096E-09 2.44539E-11
8) -0.6000 1.67664E-05 -9.47558E-08 -1.86866E-09 -6.88487E-12

[Variable Interval Data]
Diopter -1 -3 +3
fe 17.16747 17.16747 17.16747
d0 7.38 6.77 8.55
d8 21.00 21.61 19.83

[Data for each lens]
Starting surface f
L1 1 13.60313
L2 3 -13.19877
L3 5 32.48781
L4 7 29.27539

[Conditional expression value]
fe = 17.16747
-f2 = 13.19877
f3 = 32.48781
f4 = 29.27539
f34 = 16.11274
ΣD＝16.20000

(1) (R2a+R1b)/(R2a-R1b)=-9.35223
(2) TL/fe=1.37391
(3) (-f2)/f3=0.40627
(4) d1/fe=0.43027
(5) (R2b+R2a)/(R2b-R2a)=1.36842
(6) f3/f4=1.10973
(7) f34/(-f2)=1.22078
(8) (-f2)/fe=0.76882
(9) ΣD/fe=0.94365
(10) f4/fe=1.70528
(11) D1/fe=0.26212
(12) D2/fe=0.09902

10(a), 10(b), and 10(c) are diagrams showing various aberrations of the eyepiece of Example 5 when the diopters are −1 [1/m], −3 [1/m], and +3 [1/m], respectively.
From the aberration diagrams, it can be seen that the eyepiece of Example 5 has excellent optical performance, with various aberrations being well corrected within the diopter adjustment range.

As described above, the above embodiments provide a high-magnification, compact eyepiece with excellent optical performance, and are particularly suitable for use in an electronic viewfinder for observing an image displayed on an image display device.
It should be noted that the above examples are merely examples of this embodiment, and the present embodiment is not limited to these. The following content can be adopted as appropriate within the scope that does not impair the optical performance of the eyepiece of this embodiment.

While a four-lens configuration has been shown as a numerical example of the eyepiece of this embodiment, other lens configurations, such as five lenses, are also possible. Furthermore, a configuration in which a lens is added closest to the observation object, or closest to the eyepoint, may also be used.

The lens surfaces of the lenses constituting the eyepiece of this embodiment may be spherical, flat, or aspherical. Spherical or flat lens surfaces are preferred because they facilitate lens processing and assembly adjustment, and can prevent degradation of optical performance due to errors in lens processing and assembly adjustment. They are also preferred because they minimize degradation of imaging performance even when the image plane is misaligned. If the lens surface is aspherical, it may be an aspherical surface formed by grinding, a glass-molded aspherical surface in which glass is molded into an aspherical shape using a mold, or a hybrid aspherical surface in which resin applied to the surface of glass is formed into an aspherical shape. The lens surface may also be a diffractive surface, and the lens may be a gradient index lens (GRIN lens) or a plastic lens.

In addition, the lens surfaces of the lenses that make up the eyepiece of this embodiment may be coated with an anti-reflection coating that has high transmittance over a wide wavelength range in order to reduce flare and ghosting and achieve high-contrast optical performance.

In addition, the eyepiece of this embodiment is configured so that the first lens L1, second lens L2, third lens L3, and fourth lens L4 move as a single unit, or the entire eyepiece moves as a single unit, to adjust the diopter. However, it is also possible to fix the lens closest to the eyepoint and move the entire lens closer to the observation object as a single unit, or to move at least some of the first lens L1, second lens L2, third lens L3, and fourth lens L4.

Next, an optical device equipped with the eyepiece according to this embodiment will be described.
11 shows a camera 1 as an optical device equipped with the eyepiece lens according to this embodiment. The camera 1 is a digital camera equipped with an objective lens OL, an image sensor C such as a CCD or CMOS, and an electronic viewfinder EVF. The electronic viewfinder EVF is configured with an image display element such as a liquid crystal display element, which is the observation object Ob, and an eyepiece optical system EL for magnifying and observing the image displayed on the image display element. Here, the camera 1 is equipped with the eyepiece lens according to the first example described above as the eyepiece optical system EL.

In a camera 1 configured as described above, light from an object (subject) (not shown) is collected by the objective lens OL and focused on the image sensor C to form an image of the subject. The image of the subject focused on the image sensor C is then captured by the image sensor C, and the image of the subject captured by the image sensor C is displayed on an image display element, which is the observation object Ob. By positioning the photographer's eye at the eyepoint EP, the photographer can observe a magnified image of the object (subject) formed by the objective lens OL via the eyepiece optical system EL.

In addition, when the photographer presses the release button (not shown), the image captured by the image sensor C at this time, i.e., the image corresponding to the image displayed on the image display element observed through the eyepiece optical system EL, is stored in memory (not shown) as an image of the object (subject). In this way, the photographer can photograph the object (subject) using the camera 1.

With the camera 1 described above, by using the eyepiece lens according to the first example as the eyepiece optical system EL, it is possible to realize a camera with a high magnification, compact, and high-performance eyepiece optical system. Note that a camera equipped with the eyepiece lenses according to the second to fifth examples can also achieve the same effects as the camera 1. Furthermore, even if a variable magnification optical system according to each of the above examples is installed in a camera with a quick-return mirror, the same effects as the camera 1 can be achieved. Furthermore, the eyepiece lenses according to the first to fifth examples can be installed as the eyepiece optical system EL of a viewfinder device that is detachable from the camera body. A camera equipped with such a viewfinder device can also achieve the same effects as the camera 1.

Next, we will explain the manufacturing method of the eyepiece lens according to this embodiment. Figure 12 is a diagram showing an outline of the manufacturing method of the eyepiece lens according to this embodiment.

The method for manufacturing an eyepiece according to this embodiment is a method for manufacturing an eyepiece for observing an object, and includes the following steps S1 and S2, as shown in FIG.
Step S1: The eyepiece is configured to have, in order from the observation object side, a first lens having positive refractive power, a second lens having negative refractive power, a third lens having positive refractive power, and a fourth lens having positive refractive power.
Step S2: The following conditional expressions (1) and (2) are satisfied.
(1) -13.00<(R2a+R1b)/(R2a-R1b)<-2.75
(2) 0.78<TL/fe<1.60
however,
R2a: Radius of curvature of the lens surface of the second lens on the observation object side R1b: Radius of curvature of the lens surface of the first lens on the eyepoint side TL: Distance on the optical axis from the observation object surface to the lens surface of the eyepiece closest to the eyepoint when the diopter of the eyepiece is -1 [1/m] fe: Focal length of the eyepiece when the diopter of the eyepiece is -1 [1/m]

The method for manufacturing an eyepiece according to this embodiment makes it possible to produce an eyepiece that is high-magnification, compact, and has excellent optical performance. It is particularly possible to produce an eyepiece that is suitable for use in an electronic viewfinder for observing images displayed on an image display element.

Next, we will explain another method for manufacturing the eyepiece lens according to this embodiment. Figure 13 is a diagram showing an outline of another method for manufacturing the eyepiece lens according to this embodiment.

Another method for manufacturing an eyepiece according to this embodiment is a method for manufacturing an eyepiece for observing an object, and includes the following steps S1 and S2, as shown in FIG.
Step S1: The eyepiece is configured to have, in order from the observation object side, a first lens having positive refractive power, a second lens having negative refractive power, a third lens having positive refractive power, and a fourth lens having positive refractive power.
Step S2: The following conditional expressions (3) and (4) are satisfied.
(3) 0.25<(-f2)/f3<0.53
(4) 0.34<d1/fe<0.60
however,
f2: focal length of the second lens f3: focal length of the third lens d1: distance on the optical axis from the observation object surface to the lens surface of the first lens on the observation object side when the diopter of the eyepiece is −1 [1/m] fe: focal length of the eyepiece when the diopter of the eyepiece is −1 [1/m]

This alternative manufacturing method for the eyepiece of this embodiment makes it possible to realize an eyepiece that is high-magnification, compact, and has excellent optical performance. It is particularly possible to realize an eyepiece that is suitable for use in an electronic viewfinder for observing images displayed on an image display element.

L1 First lens L2 Second lens L3 Third lens L4 Fourth lens Op Observation object EP Eye point 1 Camera OL Objective lens C Image sensor EVF Electronic viewfinder EL Eyepiece optical system

Claims (4)

The optical system comprises, in order from the observation object side, a first lens having positive refractive power, a second lens having a meniscus shape and negative refractive power, a third lens having positive refractive power, and a fourth lens having positive refractive power;
the first lens, the second lens, the third lens, and the fourth lens do not include a diffractive optical surface;
An eyepiece that satisfies the following conditions:
-13.00<(R2a+R1b)/(R2a-R1b)<-2.75
0.78<TL/fe<1.60
0.7<f3/f4<1.5
however,
R2a: radius of curvature of the lens surface of the second lens on the observation object side; R1b: radius of curvature of the lens surface of the first lens on the eyepoint side; TL: distance on the optical axis from the observation object surface to the lens surface of the eyepiece closest to the eyepoint when the diopter of the eyepiece is -1 [1/m]; fe: focal length of the eyepiece when the diopter of the eyepiece is -1 [1/m]; f3: focal length of the third lens; f4: focal length of the fourth lens The optical system comprises, in order from the observation object side, a first lens having positive refractive power, a second lens having a meniscus shape and negative refractive power, a third lens having a meniscus shape and positive refractive power, and a fourth lens having positive refractive power,
the first lens, the second lens, the third lens, and the fourth lens do not include a diffractive optical surface;
An eyepiece that satisfies the following conditions:
0.39459≦ (-f2)/f3< 0.45
however,
f2: focal length of the second lens f3: focal length of the third lens 3. The eyepiece according to claim 1, wherein the following condition is satisfied:
0.15<D1/fe<0.40
however,
D1: thickness of the first lens on the optical axis fe: focal length of the eyepiece when the diopter of the eyepiece is −1 [1/m] An optical instrument comprising an eyepiece according to any one of claims 1 to 3 .