Eyepiece, optical instrument having eyepiece, and method for manufacturing eyepiece

Abstract

With conventional eyepieces, it is difficult to achieve good optical performance when high magnification is required. [Solution] An eyepiece lens having, 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 satisfying the following conditional expressions: -13.00<(R2a+R1b) / (R2a-R1b)<-2.75 0.78 <TL / fe<1.60 where R2a is the radius of curvature of the lens surface of the second lens on the object side, R1b is the radius of curvature of the lens surface of the first lens on the eyepoint side, TL is the distance on the optical axis from the object surface to the lens surface of the eyepiece closest to the eyepoint when the diopter of the eyepiece is -1 [1 / m], and fe is the focal length of the eyepiece when the diopter of the eyepiece is -1 [1 / m].

Description

[Technical Field]

[0001] The present invention relates to an eyepiece, an optical instrument having an eyepiece, and a method for manufacturing an eyepiece. [Background technology]

[0002] Conventionally, eyepieces for use in electronic viewfinders have been proposed (see, for example, Patent Document 1). However, the above-described conventional eyepieces have a problem in that it is difficult to achieve good optical performance when high magnification is required. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-225835 Summary of the Invention

[0004] 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 R1b: radius of curvature of the lens surface on the eyepoint side of the first lens TL: The 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 Furthermore, the present invention provides an optical system comprising, 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; 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 [Brief explanation of the drawings]

[0005] [Figure 1] FIG. 1 is a cross-sectional view of the eyepiece according to the first embodiment when the diopter is −1 [1 / m]. [Figure 2] 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. [Figure 3] FIG. 3 is a cross-sectional view of the eyepiece according to the second embodiment when the diopter is −1 [1 / m]. [Figure 4] Figures 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. [Figure 5] FIG. 5 is a cross-sectional view of the eyepiece according to the third embodiment when the diopter is −1 [1 / m]. [Figure 6]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. [Figure 7] FIG. 7 is a cross-sectional view of the eyepiece according to the fourth embodiment when the diopter is −1 [1 / m]. [Figure 8] 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. [Figure 9] FIG. 9 is a cross-sectional view of the eyepiece according to the fifth embodiment when the diopter is −1 [1 / m]. [Figure 10] 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. [Figure 11] 1 is a cross-sectional view of an optical device having an eyepiece according to an embodiment. [Figure 12] FIG. 1 is a flow chart showing an outline of a method for manufacturing an eyepiece according to an embodiment. [Figure 13] FIG. 10 is a flow chart showing an outline of another method for manufacturing an eyepiece according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0006] An eyepiece lens, an optical device, and a method for manufacturing an eyepiece lens according to an embodiment of the present invention will be described below. First, an eyepiece lens according to an embodiment will be described.

[0007] The eyepiece according to this embodiment is an eyepiece for magnifying and observing an object. Here, the object is an intermediate image formed by an objective lens, or the display surface of an image display device such as a liquid crystal display device or an organic electroluminescence (EL) display, and preferably the display surface of a liquid crystal display device. 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 device. In the following description, the object is also referred to as the "object surface."

[0008] In the following description 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 (meters)] 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.

[0009] The eyepiece 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.

[0010] As described above, the eyepiece of this embodiment includes a first lens with positive refractive power for magnifying and observing an object. Furthermore, the eyepiece of this embodiment includes a second lens with negative refractive power for correcting chromatic aberration, curvature of field, and astigmatism that occur in the first lens with positive refractive power. Furthermore, the eyepiece of this embodiment includes a third lens with positive refractive power and a fourth lens with positive refractive power for effectively correcting coma and distortion.

[0011] 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 can achieve a high magnification with an apparent field of view of 30° or more.

[0012] 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 facing the object R1b: radius of curvature of the lens surface on the eyepoint side of the first lens

[0013] Conditional expression (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 expression (1), good aberration correction can be achieved.

[0014] If the corresponding value of conditional expression (1) falls below the lower limit, it becomes difficult to correct various aberrations, particularly field curvature and coma, which is undesirable. Furthermore, the edge thickness of the first lens becomes thin, which makes manufacturing difficult, which is also undesirable. To ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (1) to -12.00. To further ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (1) to -11.65. To further ensure the effects of this embodiment, it is preferable to set the lower limit of conditional expression (1) to -11.30.

[0015] 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.

[0016] With this configuration, the eyepiece according to this embodiment satisfies the following conditional expression (2). (2) 0.78 <TL / fe<1.60 however, TL: The 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: the focal length of the eyepiece when the diopter of the eyepiece is -1 [1 / m]

[0017] 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) makes it possible to achieve compactness, high magnification, and good aberration correction.

[0018] 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.

[0019] On the other hand, if the corresponding value of conditional expression (2) exceeds the upper limit, the total optical length of the eyepiece lens will increase. Furthermore, achieving high 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. To further ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (2) to 1.43. To further ensure the effects of this embodiment, it is preferable to set the upper limit of conditional expression (2) to 1.40.

[0020] In addition, 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.

[0021] As described above, the eyepiece of this embodiment includes a first lens with positive refractive power for magnifying and observing an object. Furthermore, the eyepiece of this embodiment includes a second lens with negative refractive power for correcting chromatic aberration, curvature of field, and astigmatism that occur in the first lens with positive refractive power. Furthermore, the eyepiece of this embodiment includes a third lens with positive refractive power and a fourth lens with positive refractive power for effectively correcting coma and distortion.

[0022] 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 can achieve a high magnification with an apparent field of view of 30° or more.

[0023] 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

[0024] Conditional expression (3) is a conditional expression for defining an appropriate range for the ratio of the refractive power of the second lens to the refractive power of the third lens. By satisfying conditional expression (1), good aberration correction can be achieved.

[0025] 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.

[0026] 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 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 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.

[0027] 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: focal length of the eyepiece when the diopter of the eyepiece is -1 [1 / m]

[0028] Conditional expression (4) defines an 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 on the observation object side 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 expression (4) allows for compactness and good aberration correction.

[0029] 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 causes the focus to be 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.

[0030] 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. Furthermore, it is 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.

[0031] 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 on the eyepoint side of the second lens R2a: radius of curvature of the lens surface of the second lens facing the object

[0032] Conditional expression (5) defines the shape of the second lens. By satisfying conditional expression (5), good aberration correction can be achieved.

[0033] If the corresponding value of conditional expression (5) falls below the lower limit, it becomes difficult to correct curvature of field, 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.

[0034] 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.

[0035] 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

[0036] Conditional expression (6) is a conditional expression for defining 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.

[0037] 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.

[0038] 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.

[0039] 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: the 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

[0040] Condition (7) defines an 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 condition (7), good aberration correction can be achieved.

[0041] 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 be large, increasing the Petzval sum and making it difficult to simultaneously correct curvature of field and astigmatism, which is undesirable. It is also undesirable because it makes it difficult to correct coma aberration. 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.

[0042] 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.

[0043] 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: the focal length of the eyepiece when the diopter of the eyepiece is -1 [1 / m]

[0044] Conditional expression (8) defines an 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 expression (8), good aberration correction can be achieved.

[0045] If the corresponding value of conditional expression (8) falls below the lower limit, the refractive power of the second lens becomes large, making it 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 (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.

[0046] 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 curvature of field and astigmatism, which is undesirable. It is also undesirable because it makes it difficult to correct coma. 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.

[0047] 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]

[0048] Conditional expression (9) defines an appropriate range for the ratio of the axial distance from the lens surface of the eyepiece closest to the 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]. By satisfying conditional expression (9), the axial thickness of the eyepiece can be reduced and good aberration correction can be achieved.

[0049] 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.

[0050] 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.

[0051] 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]

[0052] Condition (10) defines an 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 condition (10), good aberration correction can be achieved.

[0053] 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.

[0054] 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.

[0055] It is also desirable that the eyepiece according to this embodiment satisfy the following conditional expression (11). (11)0.15 <D1 / fe<0.40 however, D1: The thickness of the first lens on the optical axis fe: the focal length of the eyepiece when the diopter of the eyepiece is -1 [1 / m]

[0056] Conditional expression (11) defines an 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 expression (11), the axial thickness of the eyepiece can be reduced and good aberration correction can be achieved.

[0057] 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. Furthermore, the edge thickness of the first lens becomes thin, which makes manufacturing difficult, which is also undesirable. 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.

[0058] 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. Furthermore, the thickness of the eyepiece in the optical axis direction increases, which is also undesirable. 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.

[0059] 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: The 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]

[0060] Conditional expression (12) defines an 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 expression (12), the axial thickness of the eyepiece can be reduced and good aberration correction can be achieved.

[0061] 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.

[0062] 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 axial thickness of the eyepiece 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.

[0063] In the eyepiece according to this embodiment, it is desirable that at least one surface of the first lens is aspherical, which allows for excellent correction of field curvature, astigmatism, and coma.

[0064] In addition, it is preferable that all of the lenses constituting the eyepiece according to this embodiment have at least one aspherical surface, which allows for excellent correction of field curvature, astigmatism, and coma.

[0065] In the eyepiece according to this embodiment, the first lens, the second lens, the third lens, and the fourth lens are preferably plastic lenses. This configuration allows for weight reduction and cost reduction. Furthermore, since aspherical shapes can be easily formed, spherical aberration, field curvature, astigmatism, coma, and distortion can be effectively corrected.

[0066] In addition, 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.

[0067] Furthermore, in 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 various aberrations, particularly field curvature, coma, and distortion, during diopter adjustment.

[0068] Furthermore, in 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, which makes it possible to reduce fluctuations in aberrations, particularly field curvature, coma, and distortion, during diopter adjustment.

[0069] The optical device according to the embodiment of the present application has an eyepiece having the above-described configuration, which makes it possible to realize an optical device that has high magnification, is small in size, and has high optical performance.

[0070] A manufacturing method for an eyepiece according to an embodiment of the present application is a manufacturing method for 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 (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 facing the object R1b: radius of curvature of the lens surface on the eyepoint side of the first lens TL: The 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: the focal length of the eyepiece when the diopter of the eyepiece is -1 [1 / m]

[0071] This method of manufacturing an eyepiece lens makes it possible to manufacture a high-magnification, compact eyepiece lens with high optical performance.

[0072] 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: 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]

[0073] By using this other method for manufacturing an eyepiece, it is possible to manufacture an eyepiece that is high in magnification, compact, and has high optical performance.

[0074] (Numerical example) An eyepiece according to a numerical example of this embodiment will be described below with reference to the accompanying drawings.

[0075] (First Example) FIG. 1 is a cross-sectional view of the eyepiece of the first embodiment when the diopter is −1 [1 / m]. In FIG. 1, EP denotes the eyepoint, and Ob denotes the observation object. These symbols will be used in the same way in the drawings of each embodiment described later. In this embodiment, the observation object 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 observation object Ob is also the display surface of a liquid crystal display element of an electronic viewfinder.

[0076] 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.

[0077] In the eyepiece of this embodiment, the lens surfaces of the first lens L1 facing the observation object Ob and the eyepoint EP are aspherical lenses, the lens surfaces of the second lens L2 facing the observation object Ob and the eyepoint EP are aspherical lenses, the lens surfaces of the third lens L3 facing the observation object Ob and the eyepoint EP are aspherical lenses, and the lens surfaces of the fourth lens L4 facing the observation object Ob and the eyepoint EP are aspherical lenses.

[0078] The eyepiece according to this embodiment adjusts the diopter by moving the first lens L1, the second lens L2, the third lens L3, and the fourth lens L4 together along the optical axis.

[0079] 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].

[0080] In the [Surface Data] section, 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.

[0081] [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 displacement amount 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 aspheric coefficient is An. The second order aspheric coefficient A2 is 0 (zero) and is omitted. Also, "En" is "×10 -n ", for example, "1.234E-05" indicates "1.234×10 -5 " indicates.

[0082] 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.

[0083] [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.

[0084] 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 a limitation, as the same optical performance can be obtained even when proportional enlargement or reduction is performed on the optical system. The symbols in Table 1 described above will be used in the same manner in the tables of the respective examples described later.

[0085] (Table 1) First Example [Overall specifications] Y0 5 TL 22.97080 [Face Data] Surface number rd 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 corresponding 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

[0086] 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.

[0087] In each aberration diagram, Y1 indicates the height at which light emitted from the optical axial center of the observation object is incident on the tangent plane of the first lens L1 on the observation object side, and Y0 indicates the height of the observation 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 the 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.

[0088] 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.

[0089] (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 Figure 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 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 biconvex lens.

[0090] In the eyepiece of this embodiment, the lens surfaces of the first lens L1 facing the observation object Ob and the eyepoint EP are aspherical lenses, the lens surfaces of the second lens L2 facing the observation object Ob and the eyepoint EP are aspherical lenses, the lens surfaces of the third lens L3 facing the observation object Ob and the eyepoint EP are aspherical lenses, and the lens surfaces of the fourth lens L4 facing the observation object Ob and the eyepoint EP are aspherical lenses.

[0091] In addition, the eyepiece according to this embodiment adjusts the diopter by moving the first lens L1, the second lens L2, the third lens L3, and the 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.

[0092] Table 2 below lists the specifications of the photographic lens according to this example.

[0093] (Table 2) Second Example [Overall specifications] Y0 5 TL 22.44140 [Face Data] Surface number rd 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 corresponding 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

[0094] Figures 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 each aberration diagram, 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.

[0095] (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 Figure 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 eyepoint 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 eyepoint EP side.

[0096] In the eyepiece of this embodiment, the lens surfaces of the first lens L1 facing the observation object Ob and the eyepoint EP are aspherical lenses, the lens surfaces of the second lens L2 facing the observation object Ob and the eyepoint EP are aspherical lenses, the lens surfaces of the third lens L3 facing the observation object Ob and the eyepoint EP are aspherical lenses, and the lens surfaces of the fourth lens L4 facing the observation object Ob and the eyepoint EP are aspherical lenses.

[0097] In addition, the eyepiece according to this embodiment adjusts the diopter by moving the first lens L1, the second lens L2, the third lens L3, and the 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.

[0098] Table 3 below lists the specifications of the photographic lens according to this example.

[0099] (Table 3) Third Example [Overall specifications] Y0 5 TL 22.69130 [Face Data] Surface number rd 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 corresponding 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

[0100] 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.

[0101] (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 Figure 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 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.

[0102] In the eyepiece of this embodiment, the lens surfaces of the first lens L1 facing the observation object Ob and the eyepoint EP are aspherical lenses, the lens surfaces of the second lens L2 facing the observation object Ob and the eyepoint EP are aspherical lenses, the lens surfaces of the third lens L3 facing the observation object Ob and the eyepoint EP are aspherical lenses, and the lens surfaces of the fourth lens L4 facing the observation object Ob and the eyepoint EP are aspherical lenses.

[0103] In addition, the eyepiece according to this embodiment adjusts the diopter by moving the first lens L1, the second lens L2, the third lens L3, and the 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.

[0104] Table 4 below lists the specifications of the photographic lens according to this example.

[0105] (Table 4) Fourth Example [Overall specifications] Y0 5 TL 23.17110 [Face Data] Surface number rd 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 corresponding 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

[0106] 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 of Example 4 has excellent optical performance, with various aberrations being well corrected within the diopter adjustment range.

[0107] (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 Figure 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 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.

[0108] In the eyepiece of this embodiment, the lens surfaces of the first lens L1 facing the observation object Ob and the eyepoint EP are aspherical lenses, the lens surfaces of the second lens L2 facing the observation object Ob and the eyepoint EP are aspherical lenses, the lens surfaces of the third lens L3 facing the observation object Ob and the eyepoint EP are aspherical lenses, and the lens surfaces of the fourth lens L4 facing the observation object Ob and the eyepoint EP are aspherical lenses.

[0109] In addition, the eyepiece according to this embodiment adjusts the diopter by moving the first lens L1, the second lens L2, the third lens L3, and the 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.

[0110] Table 5 below lists the specifications of the photographing lens according to this example.

[0111] (Table 5) Fifth Example [Overall specifications] Y0 5 TL 23.58660 [Face Data] Surface number rd 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 corresponding 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

[0112] 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.

[0113] 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.

[0114] Although 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. Also, a configuration in which a lens is added closest to the observation object or closest to the eyepoint may be used.

[0115] The lens surfaces of the lenses constituting the eyepiece lens of this embodiment may be spherical, flat, or aspherical. Spherical or flat lens surfaces are preferred because they facilitate lens processing and assembly adjustment, preventing degradation of optical performance due to errors in lens processing and assembly adjustment. Furthermore, they are 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 obtained by grinding, a glass-molded aspherical surface in which glass is molded into an aspherical shape, or a hybrid aspherical surface in which a resin applied to a glass surface is formed into an aspherical shape. Furthermore, the lens surface may be a diffractive surface, and the lens may be a gradient index lens (GRIN lens) or a plastic lens.

[0116] 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.

[0117] 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, but it is also possible to fix the lens closest to the eyepoint and move all of the lenses closer to the observation object than that lens 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.

[0118] Next, an optical device equipped with the eyepiece according to this embodiment will be described. FIG. 11 shows a camera 1 as an optical device equipped with an eyepiece according to this embodiment. 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, camera 1 is equipped with the eyepiece according to the first example described above as the eyepiece optical system EL.

[0119] In camera 1 configured as described above, light from an object (subject) (not shown) is collected by objective lens OL and focused on image sensor C to form an image of the subject. The image of the subject focused on image sensor C is captured by image sensor C, and the image of the subject captured by image sensor C is displayed on an image display element, which is an observation object Ob. By positioning his or her eye at eyepoint EP, the photographer can observe a magnified image of the object (subject) formed by objective lens OL via eyepiece optical system EL.

[0120] Furthermore, 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 device observed through the eyepiece optical system EL, is stored in a memory (not shown) as an image of the object (subject). In this way, the photographer can photograph the object (subject) using the camera 1.

[0121] According to the camera 1 described above, by using the eyepiece lens according to the first embodiment as the eyepiece optical system EL, it is possible to realize a camera having a high magnification, compact eyepiece optical system with high optical performance. It should be noted that a camera incorporating the eyepiece lenses according to the second to fifth embodiments can also achieve the same effects as the camera 1. Furthermore, even if a variable magnification optical system according to any of the above embodiments is incorporated into a camera of the type having a quick-return mirror, the same effects as the camera 1 can be achieved. Furthermore, the eyepiece lenses according to the first to fifth embodiments may be incorporated as the eyepiece optical system EL of a viewfinder device detachable from the camera body. A camera incorporating such a viewfinder device can also achieve the same effects as the camera 1.

[0122] Next, a method for manufacturing the eyepiece according to this embodiment will be described. Figure 12 is a diagram showing an outline of the method for manufacturing the eyepiece according to this embodiment.

[0123] 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 facing the object R1b: radius of curvature of the lens surface on the eyepoint side of the first lens TL: The 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]

[0124] The method for manufacturing an eyepiece according to this embodiment makes it possible to realize a high-magnification, compact eyepiece with excellent optical performance, particularly an eyepiece suitable for use in an electronic viewfinder for observing an image displayed on an image display device.

[0125] Next, another method for manufacturing the eyepiece according to this embodiment will be described. Figure 13 is a diagram showing an outline of another method for manufacturing the eyepiece according to this embodiment.

[0126] 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: 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]

[0127] According to this method for manufacturing the eyepiece of this embodiment, it is possible to realize a high-magnification, compact eyepiece with excellent optical performance, particularly an eyepiece suitable for use in an electronic viewfinder for observing an image displayed on an image display device. [Explanation of symbols]

[0128] L1 First lens L2 Second lens L3 Third lens L4 4th lens Op Observation object EP Eyepoint 1 camera OL Objective Lens C Image sensor EVF Electronic Viewfinder EL eyepiece optical system

Claims

1. 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 object side R1b: radius of curvature of the lens surface on the eyepoint side of the first lens TL: the 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

2. 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. 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]

4. An optical instrument comprising an eyepiece according to any one of claims 1 to 3.

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