Ocular lens, optical device having the same, and method of fabricating ocular lens

Abstract

To provide an ocular lens which offers both a high magnification and good optical performance.SOLUTION: An ocular lens comprises 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, arranged in order from the observation object side, and satisfies the following conditional expressions: 0.25<(-f2) / f3<0.53, 0.34<d1 / fe<0.60, where f2 represents a focal length of the second lens, f3 represents a focal length of the third lens, d1 represents an optical axial distance between a surface of an observation object to an observation object-side lens surface of the first lens when diopter of the ocular lens is -1 [1 / m], and fe represents a focal length of the ocular lens when diopter of the ocular lens is -1 [1 / m].SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an eyepiece lens, an optical device having the eyepiece lens, and a method for manufacturing the eyepiece lens.

Background Art

[0002] Conventionally, an eyepiece lens used for an electronic viewfinder has been proposed (see, for example, Patent Document 1). However, such a conventional eyepiece lens has a problem that it is difficult to achieve good optical performance when a higher magnification is required.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

[0004] The present invention has, in order from the observation object side, a first lens having a positive refractive power, a second lens having a negative refractive power, a third lens having a positive refractive power, and a fourth lens having a positive refractive power, and is an eyepiece lens that satisfies the following conditional expressions. 0.25 < (-f2) / f3 < 0.53 0.34 < d1 / fe < 0.60 However, f2: the focal length of the second lens f3: the focal length of the third lens d1: the distance on the optical axis from the observation object surface to the lens surface on the observation object side of the first lens when the diopter of the eyepiece lens is -1 [1 / m] fe: the focal length of the eyepiece lens when the diopter of the eyepiece lens is -1 [1 / m]

Brief Description of the Drawings

[0005]

Figure 1

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Figure 13

Mode for Carrying Out the Invention

[0006] Hereinafter, the eyepiece lens, the optical device, and the manufacturing method of the eyepiece lens according to the embodiment of the present application will be described. First, the eyepiece lens according to the embodiment will be described.

[0007] The eyepiece lens according to the present embodiment is an eyepiece lens for magnifying and observing an observation object. Here, the observation object is an intermediate image formed by an objective lens, or a display surface of an image display element such as a liquid crystal display element or an organic EL (Electroluminescence) display, and particularly preferably the display surface of a liquid crystal display element. Therefore, the eyepiece lens according to the present 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 observation object is also referred to as an "observation object surface".

[0008] In the following description of the embodiments and numerical examples, the diopter, which is the unit of visual acuity, uses [1 / m]. For example, the visual acuity X [1 / m] indicates a state in which an image formed by the eyepiece lens can be formed at a position of 1 / X [m (meter)] on the optical axis from the eye point. The sign is positive when the image is formed on the eye point side of the eyepiece lens.

[0009] The eyepiece lens according to the present embodiment has, in order from the observation object side along the optical axis, a first lens having a positive refractive power, a second lens having a negative refractive power, a third lens having a positive refractive power, and a fourth lens having a positive refractive power.

[0010] Thus, the eyepiece according to this embodiment arranges a first lens having a positive refractive power to magnify and observe an observation object. Further, the eyepiece according to this embodiment arranges a second lens having a negative refractive power to correct chromatic aberration, field curvature, and astigmatism generated by the first lens with a positive refractive power. Further, the eyepiece according to this embodiment arranges a third lens having a positive refractive power and a fourth lens having a positive refractive power to correct coma aberration and distortion aberration well.

[0011] By adopting such a configuration, the eyepiece according to this embodiment can correct various aberrations well and achieve high magnification. For example, in order to magnify and observe an observation object with a diagonal length of about 10 mm, it is possible to achieve a high magnification with an apparent field of view angle of 30° or more.

[0012] The eyepiece according to this embodiment satisfies the following conditional expression (1) under such a configuration. (1) -13.00 < (R2a + R1b) / (R2a - R1b) < -2.75 However, R2a: The radius of curvature of the lens surface on the observation object side of the second lens R1b: The radius of curvature of the lens surface on the eye point side of the first lens

[0013] The conditional expression (1) is a conditional expression for defining the shape of the air lens formed by the lens surface on the eye point side of the first lens and the lens surface on the observation object side of the second lens. By satisfying the conditional expression (1), good aberration correction can be performed.

[0014] When the corresponding value of conditional expression (1) is less than the lower limit value, it is not preferable because it becomes difficult to correct various aberrations, particularly field curvature and coma. Also, the edge thickness of the first lens becomes thin, making manufacturing difficult, so it is not preferable. In order to ensure the effects of the present embodiment, it is preferable to set the lower limit value of conditional expression (1) to -12.00. Also, in order to more surely ensure the effects of the present embodiment, it is preferable to set the lower limit value of conditional expression (1) to -11.65. Further, in order to more surely ensure the effects of the present embodiment, it is preferable to set the lower limit value of conditional expression (1) to -11.30.

[0015] On the other hand, when the corresponding value of conditional expression (1) exceeds the upper limit value, it is not preferable because it becomes difficult to correct various aberrations, particularly field curvature and coma. In order to ensure the effects of the present embodiment, it is preferable to set the upper limit value of conditional expression (1) to -3.50. Also, in order to more surely ensure the effects of the present embodiment, it is preferable to set the upper limit value of conditional expression (1) to -4.25. Further, in order to more surely ensure the effects of the present embodiment, it is preferable to set the upper limit value of conditional expression (1) to -5.00.

[0016] The eyepiece lens according to the present embodiment satisfies the following conditional expression (2) under such a configuration. (2) 0.78 < TL / fe < 1.60 However, TL: The distance on the optical axis from the observation object plane when the diopter of the eyepiece lens is -1 [1 / m] to the lens surface on the most eye point side of the eyepiece lens fe: The focal length of the eyepiece lens when the diopter of the eyepiece lens is -1 [1 / m]

[0017] Conditional expression (2) is a conditional expression for defining an appropriate range of the ratio between the distance on the optical axis from the observation object plane when the diopter of the eyepiece lens is -1 [1 / m] to the lens surface on the most eye point side of the eyepiece lens, that is, the overall optical length of the eyepiece lens, and the focal length of the eyepiece lens when the diopter of the eyepiece lens is -1 [1 / m]. By satisfying conditional expression (2), miniaturization and high magnification can be achieved, and good aberration correction can be performed.

[0018] When the corresponding value of conditional expression (2) is less than the lower limit value, it is not preferable because it becomes difficult to correct various aberrations, particularly field curvature and coma aberration. In order to ensure the effects of the present embodiment, it is preferable to set the lower limit value of conditional expression (2) to 1.00. Further, in order to more surely ensure the effects of the present embodiment, it is preferable to set the lower limit value of conditional expression (2) to 1.15. Further, in order to more surely ensure the effects of the present embodiment, it is preferable to set the lower limit value of conditional expression (2) to 1.30.

[0019] On the other hand, when the corresponding value of conditional expression (2) exceeds the upper limit value, the overall optical length of the eyepiece lens becomes large. Further, when attempting to achieve high magnification, it is not preferable because it becomes difficult to correct various aberrations, particularly field curvature and coma aberration. In conditional expression (2), TL is the air-equivalent length when a parallel plate is inserted between the observation object plane and the lens surface on the most eye-point side of the eyepiece lens. In order to ensure the effects of the present embodiment, it is preferable to set the upper limit value of conditional expression (2) to 1.45. Further, in order to more surely ensure the effects of the present embodiment, it is preferable to set the upper limit value of conditional expression (2) to 1.43. Further, in order to more surely ensure the effects of the present embodiment, it is preferable to set the upper limit value of conditional expression (2) to 1.40.

[0020] Further, the eyepiece lens according to the present embodiment includes a first lens having a positive refractive power, a second lens having a negative refractive power, a third lens having a positive refractive power, and a fourth lens having a positive refractive power in order from the observation object side along the optical axis.

[0021] Thus, the eyepiece lens according to the present embodiment arranges the first lens having a positive refractive power in order to magnify and observe an observation object. Further, the eyepiece lens according to the present embodiment arranges the second lens having a negative refractive power in order to correct chromatic aberration, field curvature, and astigmatism generated by the first lens having a positive refractive power. Further, the eyepiece lens according to the present embodiment arranges the third lens having a positive refractive power and the fourth lens having a positive refractive power in order to favorably correct coma aberration and distortion aberration.

[0022] The eyepiece according to this embodiment can correct various aberrations well and achieve high magnification by adopting such a configuration. For example, in order to magnify and observe an observation object with a diagonal length of about 10 mm, a high magnification with an apparent field angle of 30° or more can be achieved.

[0023] The eyepiece according to this embodiment satisfies the following conditional expression (3) under such a configuration. (3) 0.25 < (-f2) / f3 < 0.53 However, f2: The focal length of the second lens f3: The focal length of the third lens

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

[0025] When the corresponding value of the conditional expression (3) is lower than the lower limit value, it becomes difficult to correct coma aberration and distortion aberration, which is not preferable. In order to ensure the effect of this embodiment, it is preferable to set the lower limit value of the conditional expression (3) to 0.29. Further, in order to more surely ensure the effect of this embodiment, it is preferable to set the lower limit value of the conditional expression (3) to 0.31. Further, in order to more surely ensure the effect of this embodiment, it is preferable to set the lower limit value of the conditional expression (3) to 0.33.

[0026] On the other hand, when the corresponding value of the conditional expression (3) exceeds the upper limit value, the refractive power of the second lens with respect to the third lens becomes small, the Petzval sum increases, and it becomes difficult to correct field curvature and spherical aberration simultaneously, which is not preferable. Also, since it becomes difficult to correct coma aberration, it is not preferable. In order to ensure the effect of this embodiment, it is preferable to set the upper limit value of the conditional expression (3) to 0.48. Further, in order to more surely ensure the effect of this embodiment, it is preferable to set the upper limit value of the conditional expression (3) to 0.45. Further, in order to more surely ensure the effect of this embodiment, it is preferable to set the upper limit value of the conditional expression (3) to 0.42.

[0027] Under such a 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 plane to the lens surface on the observation object side of the first lens 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]

[0028] The conditional expression (4) is a conditional expression for defining an appropriate range of the ratio between the distance on the optical axis from the observation object plane to the lens surface on the observation object side of the first lens when the diopter of the eyepiece is -1 [1 / m] and the focal length of the eyepiece when the diopter of the eyepiece is -1 [1 / m]. By satisfying the conditional expression (4), miniaturization can be achieved and good aberration correction can be performed.

[0029] When the corresponding value of the conditional expression (4) is below the lower limit value, it becomes difficult to correct various aberrations, particularly coma aberration and distortion aberration, which is not preferable. In addition, since the distance from the observation object plane to the lens surface on the observation object side of the first lens becomes short, the foreign matter or the like attached to the lens surface on the eye point side of the first lens is in focus, which is not preferable. In order to ensure the effects of this embodiment, it is preferable to set the lower limit value of the conditional expression (4) to 0.35. Further, in order to more surely ensure the effects of this embodiment, it is preferable to set the lower limit value of the conditional expression (4) to 0.355. Further, in order to more surely ensure the effects of this embodiment, it is preferable to set the lower limit value of the conditional expression (4) to 0.36.

[0030] On the other hand, if the corresponding value of conditional expression (4) exceeds the upper limit value, it is not preferable because it becomes difficult to correct various aberrations, particularly coma aberration and distortion aberration. Also, it is not preferable because the overall optical length of the eyepiece lens increases. In conditional expression (4), when a parallel plate is inserted between the observation object surface and the lens surface on the observation object side of the first lens, d1 is the air-equivalent length. In order to ensure the effects of the present embodiment, it is preferable to set the upper limit value of conditional expression (4) to 0.52. Further, in order to more surely ensure the effects of the present embodiment, it is preferable to set the upper limit value of conditional expression (4) to 0.49. Further, in order to more surely ensure the effects of the present embodiment, it is preferable to set the upper limit value of conditional expression (4) to 0.45.

[0031] Also, it is desirable that the eyepiece lens according to the present embodiment satisfies the following conditional expression (5). (5) 0.5 < (R2b + R2a) / (R2b - R2a) < 2.4 However, R2b: The radius of curvature of the lens surface on the eye point side of the second lens R2a: The radius of curvature of the lens surface on the observation object side of the second lens

[0032] Conditional expression (5) is a conditional expression for defining the shape of the second lens. By satisfying conditional expression (5), good aberration correction can be performed.

[0033] If the corresponding value of conditional expression (5) is below the lower limit value, it is not preferable because it becomes difficult to correct field curvature, coma aberration, and distortion aberration. In order to ensure the effects of the present embodiment, it is preferable to set the lower limit value of conditional expression (5) to 0.8. Further, in order to more surely ensure the effects of the present embodiment, it is preferable to set the lower limit value of conditional expression (5) to 1.0. Further, in order to more surely ensure the effects of the present embodiment, it is preferable to set the lower limit value of conditional expression (5) to 1.2.

[0034] On the other hand, if the corresponding value of conditional expression (5) exceeds the upper limit value, it becomes difficult to correct field curvature, coma aberration, and distortion aberration, which is not preferable. In order to ensure the effects of the present embodiment, it is preferable to set the upper limit value of conditional expression (5) to 2.1. Further, in order to more surely ensure the effects of the present embodiment, it is preferable to set the upper limit value of conditional expression (5) to 2.0. Further, in order to more surely ensure the effects of the present embodiment, it is preferable to set the upper limit value of conditional expression (5) to 1.9.

[0035] In addition, the eyepiece lens according to the present embodiment preferably satisfies 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 of the ratio of the refractive power of the third lens to the refractive power of the fourth lens. By satisfying conditional expression (6), good aberration correction can be performed.

[0037] If the corresponding value of conditional expression (6) is less than the lower limit value, it becomes difficult to correct coma aberration and distortion aberration, which is not preferable. In order to ensure the effects of the present embodiment, it is preferable to set the lower limit value of conditional expression (6) to 0.80. Further, in order to more surely ensure the effects of the present embodiment, it is preferable to set the lower limit value of conditional expression (6) to 0.88. Further, in order to more surely ensure the effects of the present embodiment, it is preferable to set the lower limit value of conditional expression (6) to 0.95.

[0038] On the other hand, if the corresponding value of conditional expression (6) exceeds the upper limit value, it becomes difficult to correct coma aberration and distortion aberration, which is not preferable. In order to ensure the effects of the present embodiment, it is preferable to set the upper limit value of conditional expression (6) to 1.42. Further, in order to more surely ensure the effects of the present embodiment, it is preferable to set the upper limit value of conditional expression (6) to 1.39. Further, in order to more surely ensure the effects of the present embodiment, it is preferable to set the upper limit value of conditional expression (6) to 1.35.

[0039] In addition, it is desirable that the eyepiece according to the present embodiment satisfies the following conditional expression (7). (7) 0.97 < f34 / (-f2) < 1.5 However, f34: The combined focal length of the third lens and the fourth lens when the diopter of the eyepiece is -1 [1 / m] f2: The focal length of the second lens

[0040] The conditional expression (7) is a conditional expression for defining an appropriate range of the ratio between the combined focal length of the third lens and the fourth lens and the focal length of the second lens when the diopter of the eyepiece is -1 [1 / m]. By satisfying the conditional expression (7), good aberration correction can be performed.

[0041] When the corresponding value of the conditional expression (7) is lower than the lower limit value, the refractive power of the combination of the third lens and the fourth lens with respect to the second lens increases, the Petzval sum increases, and it becomes difficult to correct the field curvature and the astigmatism simultaneously, which is not preferable. In addition, since it becomes difficult to correct the coma aberration, it is not preferable. In order to ensure the effects of the present embodiment, it is preferable to set the lower limit value of the conditional expression (7) to 1.07. In order to more surely ensure the effects of the present embodiment, it is preferable to set the lower limit value of the conditional expression (7) to 1.14. In order to further surely ensure the effects of the present embodiment, it is preferable to set the lower limit value of the conditional expression (7) to 1.21.

[0042] On the other hand, if the corresponding value of conditional expression (7) exceeds the upper limit value, it becomes difficult to correct coma aberration and distortion aberration, which is not preferable. In order to ensure the effects of this embodiment, it is preferable to set the upper limit value of conditional expression (7) to 1.45. Further, in order to more surely ensure the effects of this embodiment, it is preferable to set the upper limit value of conditional expression (7) to 1.40. Further, in order to more surely ensure the effects of this embodiment, it is preferable to set the upper limit value of conditional expression (7) to 1.37. Further, in order to more surely ensure the effects of this embodiment, it is preferable to set the upper limit value of conditional expression (7) to 1.34. Further, in order to more surely ensure the effects of this embodiment, it is preferable to set the upper limit value of conditional expression (7) to 1.30.

[0043] Further, the eyepiece lens according to this embodiment preferably satisfies 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 lens when the diopter of the eyepiece lens is -1 [1 / m]

[0044] Conditional expression (8) is a conditional expression for defining an appropriate range of the ratio between the focal length of the second lens and the focal length of the eyepiece lens when the diopter of the eyepiece lens is -1 [1 / m]. By satisfying conditional expression (8), good aberration correction can be performed.

[0045] If the corresponding value of conditional expression (8) is less than the lower limit value, the refractive power of the second lens increases, making it difficult to correct coma aberration, which is not preferable. In order to ensure the effects of this embodiment, it is preferable to set the lower limit value of conditional expression (8) to 0.45. Further, in order to more surely ensure the effects of this embodiment, it is preferable to set the lower limit value of conditional expression (8) to 0.50. Further, in order to more surely ensure the effects of this embodiment, it is preferable to set the lower limit value of conditional expression (8) to 0.55. Further, in order to more surely ensure the effects of this embodiment, it is preferable to set the lower limit value of conditional expression (8) to 0.65. Further, in order to more surely ensure the effects of this embodiment, it is preferable to set the lower limit value of conditional expression (8) to 0.70.

[0046] On the other hand, when the corresponding value of the conditional expression (8) exceeds the upper limit value, the Petzval sum increases, making it difficult to correct the field curvature and the astigmatism simultaneously, which is not preferable. Also, since it becomes difficult to correct the coma aberration, it is not preferable. In order to ensure the effects of the present embodiment, it is preferable to set the upper limit value of the conditional expression (8) to 0.90. Further, in order to more surely ensure the effects of the present embodiment, it is preferable to set the upper limit value of the conditional expression (8) to 0.84. Further, in order to more surely ensure the effects of the present embodiment, it is preferable to set the upper limit value of the conditional expression (8) to 0.77.

[0047] Also, it is desirable that the eyepiece lens according to the present embodiment satisfies the following conditional expression (9). (9) 0.50 < ΣD / fe < 1.24 However, ΣD: The distance on the optical axis from the lens surface on the most observation object side to the lens surface on the most eye point side of the eyepiece lens when the diopter of the eyepiece lens is -1 [1 / m] fe: The focal length of the eyepiece lens when the diopter of the eyepiece lens is -1 [1 / m]

[0048] The conditional expression (9) is a conditional expression for defining an appropriate range of the ratio of the distance on the optical axis from the lens surface on the most observation object side to the lens surface on the most eye point side of the eyepiece lens when the diopter of the eyepiece lens is -1 [1 / m] to the focal length of the eyepiece lens when the diopter of the eyepiece lens is -1 [1 / m]. By satisfying the conditional expression (9), the thickness on the optical axis of the eyepiece lens can be reduced, and good aberration correction can be performed.

[0049] When the corresponding value of conditional expression (9) is less than the lower limit value, it is not preferable because it becomes difficult to correct field curvature, coma aberration, and distortion aberration. In order to ensure the effects of the present embodiment, it is preferable to set the lower limit value of conditional expression (9) to 0.70. Further, in order to more surely ensure the effects of the present embodiment, it is preferable to set the lower limit value of conditional expression (9) to 0.82. Further, in order to more surely ensure the effects of the present embodiment, it is preferable to set the lower limit value of conditional expression (9) to 0.93.

[0050] On the other hand, when the corresponding value of conditional expression (9) exceeds the upper limit value, it is not preferable because it becomes difficult to correct field curvature, coma aberration, and distortion aberration. Further, since the thickness on the optical axis of the eyepiece lens increases, it is not preferable. In order to ensure the effects of the present embodiment, it is preferable to set the upper limit value of conditional expression (9) to 1.15. Further, in order to more surely ensure the effects of the present embodiment, it is preferable to set the upper limit value of conditional expression (9) to 1.08. Further, in order to more surely ensure the effects of the present embodiment, it is preferable to set the upper limit value of conditional expression (9) to 1.00.

[0051] Further, it is desirable that the eyepiece lens according to the present embodiment satisfies the following conditional expression (10). (10) 1.2 < f4 / fe < 2.2 However, f4: The focal length of the fourth lens fe: The focal length of the eyepiece lens when the diopter of the eyepiece lens is -1 [1 / m]

[0052] Conditional expression (10) is a conditional expression for defining an appropriate range of the ratio between the focal length of the fourth lens and the focal length of the eyepiece lens when the diopter of the eyepiece lens is -1 [1 / m]. By satisfying conditional expression (10), good aberration correction can be performed.

[0053] When the corresponding value of conditional expression (10) is less than the lower limit value, the refractive power of the fourth lens increases, the Petzval sum increases, and it becomes difficult to correct the field curvature and the astigmatism simultaneously, which is not preferable. Further, since it becomes difficult to correct the coma aberration, it is not preferable. In order to ensure the effects of the present embodiment, it is preferable to set the lower limit value of conditional expression (10) to 1.35. Further, in order to more surely ensure the effects of the present embodiment, it is preferable to set the lower limit value of conditional expression (10) to 1.43. Further, in order to more surely ensure the effects of the present embodiment, it is preferable to set the lower limit value of conditional expression (10) to 1.50.

[0054] On the other hand, when the corresponding value of conditional expression (10) exceeds the upper limit value, it becomes difficult to correct various aberrations, particularly the coma aberration, which is not preferable. In order to ensure the effects of the present embodiment, it is preferable to set the upper limit value of conditional expression (10) to 2.00. Further, in order to more surely ensure the effects of the present embodiment, it is preferable to set the upper limit value of conditional expression (10) to 1.90. Further, in order to more surely ensure the effects of the present embodiment, it is preferable to set the upper limit value of conditional expression (10) to 1.80.

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

[0056] Conditional expression (11) is a conditional expression for defining an appropriate range of the ratio between the thickness on the optical axis of the first lens and the focal length of the eyepiece lens when the diopter of the eyepiece lens is -1 [1 / m]. By satisfying conditional expression (11), the thickness on the optical axis of the eyepiece lens can be reduced, and good aberration correction can be performed.

[0057] If the corresponding value of conditional expression (11) is less than the lower limit value, it becomes difficult to correct field curvature and coma aberration, which is not preferable. Also, the edge thickness of the first lens becomes thin, making manufacturing difficult, which is not preferable. In order to ensure the effects of the present embodiment, it is preferable to set the lower limit value of conditional expression (11) to 0.20. Also, in order to more surely ensure the effects of the present embodiment, it is preferable to set the lower limit value of conditional expression (11) to 0.23. Also, in order to more surely ensure the effects of the present embodiment, it is preferable to set the lower limit value of conditional expression (11) to 0.25.

[0058] On the other hand, if the corresponding value of conditional expression (11) exceeds the upper limit value, it becomes difficult to correct field curvature and coma aberration, which is not preferable. Also, the thickness of the eyepiece lens in the optical axis direction becomes large, which is not preferable. In order to ensure the effects of the present embodiment, it is preferable to set the upper limit value of conditional expression (11) to 0.34. Also, in order to more surely ensure the effects of the present embodiment, it is preferable to set the upper limit value of conditional expression (11) to 0.32. Also, in order to more surely ensure the effects of the present embodiment, it is preferable to set the upper limit value of conditional expression (11) to 0.29.

[0059] Also, it is desirable that the eyepiece lens according to the present embodiment satisfies 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 lens when the diopter of the eyepiece lens is -1 [1 / m]

[0060] Conditional expression (12) is a conditional expression for defining an appropriate range of the ratio between the thickness of the second lens on the optical axis and the focal length of the eyepiece lens when the diopter of the eyepiece lens is -1 [1 / m]. By satisfying conditional expression (12), the thickness of the eyepiece lens on the optical axis can be made small, and good aberration correction can be performed.

[0061] When the corresponding value of conditional expression (12) is less than the lower limit value, it becomes difficult to correct field curvature and coma aberration, which is not preferable. In order to ensure the effects of the present embodiment, it is preferable to set the lower limit value of conditional expression (12) to 0.07. Further, in order to more surely ensure the effects of the present embodiment, it is preferable to set the lower limit value of conditional expression (12) to 0.08. Further, in order to more surely ensure the effects of the present embodiment, it is preferable to set the lower limit value of conditional expression (12) to 0.09.

[0062] On the other hand, when the corresponding value of conditional expression (12) exceeds the upper limit value, it becomes difficult to correct field curvature and coma aberration, which is not preferable. Further, since the thickness on the optical axis of the eyepiece lens increases, it is not preferable. In order to ensure the effects of the present embodiment, it is preferable to set the upper limit value of conditional expression (12) to 0.17. Further, in order to more surely ensure the effects of the present embodiment, it is preferable to set the upper limit value of conditional expression (12) to 0.16. Further, in order to more surely ensure the effects of the present embodiment, it is preferable to set the upper limit value of conditional expression (12) to 0.15.

[0063] Further, in the eyepiece lens according to the present embodiment, it is desirable that at least one surface of the first lens is an aspherical surface. With this configuration, field curvature, astigmatism, and coma aberration can be corrected well.

[0064] Further, in the eyepiece lens according to the present embodiment, it is preferable that at least one surface of each of all the lenses constituting the eyepiece lens is an aspherical surface. With this configuration, field curvature, astigmatism, and coma aberration can be corrected well.

[0065] Further, in the eyepiece lens according to the present embodiment, it is desirable that the first lens, the second lens, the third lens, and the fourth lens are plastic lenses. With this configuration, weight reduction and cost reduction can be achieved. Further, since an aspherical shape can be easily formed, spherical aberration, field curvature, astigmatism, coma aberration, and distortion aberration can be corrected well.

[0066] Also, for the eyepiece according to this embodiment, it is desirable that the intervals between the first lens and the second lens, between the second lens and the third lens, and between the third lens and the fourth lens are each constant. With this configuration, compared with the case where the intervals between adjacent lenses change, fluctuations in field curvature, coma aberration, and distortion aberration can be reduced.

[0067] Also, for the eyepiece according to this embodiment, it is desirable that the diopter adjustment is performed by moving the first lens, the second lens, the third lens, and the fourth lens along the optical axis. With this configuration, fluctuations in various aberrations during diopter adjustment, particularly fluctuations in field curvature, coma aberration, and distortion aberration, can be reduced.

[0068] Also, for the eyepiece according to this embodiment, it is desirable that the diopter adjustment is performed by moving all the lenses constituting the eyepiece integrally. With this configuration, fluctuations in various aberrations during diopter adjustment, particularly fluctuations in field curvature, coma aberration, and distortion aberration, can be reduced.

[0069] The optical device according to the embodiment of the present application has an eyepiece with the above configuration. Thereby, an optical device with high magnification, small size, and high optical performance can be realized.

[0070] The method for manufacturing an eyepiece according to the embodiment of the present application is a method for manufacturing an eyepiece for observing an observation object, wherein the eyepiece is configured to have, in order from the observation object side, a first lens having a positive refractive power, a second lens having a negative refractive power, a third lens having a positive refractive power, and a fourth lens having a 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: The radius of curvature of the lens surface of the second lens on the observation object side R1b: The radius of curvature of the lens surface of the first lens on the eye point side TL: The distance on the optical axis from the observed object plane to the lens surface closest to the eye point of the eyepiece lens when the diopter of the eyepiece lens is -1 [1 / m]. fe: The focal length of the eyepiece lens when the diopter of the eyepiece lens is -1 [1 / m].

[0071] By such a method for manufacturing an eyepiece lens, an eyepiece lens having a high magnification, a small size, and high optical performance can be manufactured.

[0072] Another method for manufacturing an eyepiece lens according to an embodiment of the present application is a method for manufacturing an eyepiece lens for observing an observed object, wherein the eyepiece lens is configured to include, in order from the observed object side, a first lens having a positive refractive power, a second lens having a negative refractive power, a third lens having a positive refractive power, and a fourth lens having a 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: The focal length of the second lens. f3: The focal length of the third lens. d1: The distance on the optical axis from the observed object plane to the lens surface on the observed object side of the first lens when the diopter of the eyepiece lens is -1 [1 / m]. fe: The focal length of the eyepiece lens when the diopter of the eyepiece lens is -1 [1 / m].

[0073] By such another method for manufacturing an eyepiece lens, an eyepiece lens having a high magnification, a small size, and high optical performance can be manufactured.

[0074] (Numerical Example) Hereinafter, an eyepiece lens according to a numerical example of the present embodiment will be described with reference to the accompanying drawings.

[0075] (First Example) FIG. 1 is a cross-sectional view of the eyepiece at a diopter of -1 [1 / m] according to the first embodiment. In FIG. 1, EP indicates the eye point, and Ob indicates the observed object. Note that these reference numerals shall be used in the same manner in the figures of each of the embodiments described below. In this embodiment, the observed 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 the eye point EP. In each of the embodiments described below, the observed object Ob is also the display surface of the liquid crystal display element of the electronic viewfinder.

[0076] As shown in FIG. 1, the eyepiece according to this embodiment includes, in order from the observed object Ob side, a first lens L1 which is a biconvex lens, a second lens L2 which is a negative meniscus lens with a convex surface facing the eye point EP side, a third lens L3 which is a positive meniscus lens with a convex surface facing the eye point EP side, and a fourth lens L4 which is a positive meniscus lens with a convex surface facing the eye point EP side.

[0077] In the eyepiece according to this embodiment, the lens surface on the observed object Ob side and the lens surface on the eye point EP side of the first lens L1 are aspherical lenses, the lens surface on the observed object Ob side and the lens surface on the eye point EP side of the second lens L2 are aspherical lenses, the lens surface on the observed object Ob side and the lens surface on the eye point EP side of the third lens L3 are aspherical lenses, and the lens surface on the observed object Ob side and the lens surface on the eye point EP side of the fourth lens L4 are aspherical lenses.

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

[0079] The following Table 1 lists the specifications of the photographing lens according to this embodiment. In [Overall specifications], Y0 represents the height of the observed object, and TL represents the distance on the optical axis from the observed object surface to the lens surface on the most eye point EP side of the eyepiece when the diopter is -1 [1 / m].

[0080] In [Surface Data], the surface number indicates the order of the optical surfaces counted from the observation object side, r is the radius of curvature, d is the surface interval (the interval between the n-th surface (n is an integer) and the (n + 1)-th surface), nd is the refractive index for the d-line (wavelength 587.6 nm), and νd is the Abbe number for the d-line (wavelength 587.6 nm). Also, the 0-th surface indicates the observation object surface, that is, the display surface of the liquid crystal display element which is the observation object Ob. Further, "Variable" indicates the variable surface interval, and "EP" indicates the eye point EP. Note that a curvature radius r = ∞ indicates a plane. The description of the refractive index of air nd = 1.0000 is omitted. Also, when the lens surface is an aspherical surface, an asterisk is attached to the surface number and the paraxial radius of curvature is shown in the column of the radius of curvature r.

[0081] [Aspherical Data] shows the conic coefficient and the aspherical coefficient when the shape of the aspherical surface shown in [Surface Data] is expressed by the following formula. X(y)=(y 2 / r) / [1+{1-κ(y 2 / r 2 )} 1 / 2 +A4y 4 +A6y 6 +A8y 8 +A10y 10 Here, let the height in the direction perpendicular to the optical axis be y, the displacement amount in the optical axis direction at the height y be X(y), the radius of curvature of the reference spherical surface (paraxial radius of curvature) be r, the conic coefficient be κ, and the aspherical coefficient of the n-th order be An. The second-order aspherical coefficient A2 is 0 (zero) and the description is omitted. Also, "E-n" indicates "×10 -n ", for example, "1.234E-05" indicates "1.234×10 -5 ".

[0082] In [Variable Interval Data], fe indicates the focal length of the eyepiece lens at each viewing angle, and di (i is an integer) indicates the surface interval between the i-th surface and the (i + 1)-th surface.

[0083] [Data of Each Lens] shows the starting surface number and the focal length of each lens. [Condition Formula Corresponding Values] shows the corresponding values of each condition formula.

[0084] Here, the unit of the focal length fe, the radius of curvature r, and other lengths described in Table 1 is generally "mm". However, since the optical system can obtain the same optical performance even when proportionally enlarged or reduced, it is not limited to this. Note that the symbols in Table 1 described above shall be used in the same manner in the tables of each of the following embodiments.

[0085] (Table 1) First Embodiment [Overall Specifications] Y0 5 TL 22.97080 [Surface 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] Visibility -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 of each lens] Initial surface f L1 1 12.83484 L2 3 -11.73613 L3 5 29.74230 L4 7 27.23347 [Condition formula 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] Figures 2(a), 2(b), and 2(c) are aberration diagrams at -1 [1 / m], -3 [1 / m], and +3 [1 / m] of the diopter of the eyepiece according to the first embodiment, respectively.

[0087] In each aberration diagram, Y1 represents the height at which the light emitted from the optical axis center of the observed object enters the tangent plane on the observed object side of the first lens L1, and Y0 represents the height of the observed object. Also, in the figure, d represents the aberration curve at the d-line (wavelength λ = 587.6 nm), g represents the aberration curve at the g-line (wavelength λ = 435.8 nm), and those without description represent the aberration curve at the d-line. In the aberration diagram showing the astigmatism, the solid line represents the sagittal image plane, and the dashed line represents the meridional image plane. The unit D on the horizontal axis of the spherical aberration diagram and the astigmatism diagram is [1 / m] (diopter). In addition, the same reference numerals as in this embodiment are used in the aberration diagrams of each of the following embodiments.

[0088] From each aberration diagram, it can be seen that the eyepiece according to the first embodiment has good correction of various aberrations within the diopter adjustment range and has excellent optical performance.

[0089] (Second Embodiment) Figure 3 is a cross-sectional view of the eyepiece according to the second embodiment at a diopter of -1 [1 / m]. As shown in FIG. 3, the eyepiece according to this embodiment includes, 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 the convex surface facing the eye point EP side, a third lens L3 which is a positive meniscus lens with the convex surface facing the eye point EP side, and a fourth lens L4 which is a biconvex lens.

[0090] For the eyepiece according to this embodiment, the lens surfaces on the observation object Ob side and the eye point EP side of the first lens L1 are aspherical lenses, the lens surfaces on the observation object Ob side and the eye point EP side of the second lens L2 are aspherical lenses, the lens surfaces on the observation object Ob side and the eye point EP side of the third lens L3 are aspherical lenses, and the lens surfaces on the observation object Ob side and the eye point EP side of the fourth lens L4 are aspherical lenses.

[0091] Also, for the eyepiece according to this embodiment, diopter adjustment is performed by moving the first lens L1, the second lens L2, the third lens L3, and the fourth lens L4 integrally 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 the eye point EP.

[0092] The following Table 2 lists the specifications of the photographing lens according to this embodiment.

[0093] (Table 2) Second Embodiment [Overall Specifications] Y0 5 TL 22.44140 [Surface 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] Visibility -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 of Each Lens] Initial surface f L1 1 12.27984 L2 3 -11.33254 L3 5 32.81807 L4 7 24.96209 [Conditional 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 aberration diagrams at -1 [1 / m], -3 [1 / m], and +3 [1 / m] of the diopter of the eyepiece according to the second embodiment, respectively. From each aberration diagram, it can be seen that the eyepiece according to the second embodiment has good correction of various aberrations within the diopter adjustment range and has excellent optical performance.

[0095] (Third Embodiment) Figure 5 is a cross-sectional view of the eyepiece at a diopter of -1 [1 / m] according to the third embodiment. As shown in Figure 5, the eyepiece according to this embodiment includes, 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 the 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 the convex surface facing the eye point EP side.

[0096] In the eyepiece according to this embodiment, the lens surfaces on the observation object Ob side and the eye point EP side of the first lens L1 are aspherical lenses, the lens surfaces on the observation object Ob side and the eye point EP side of the second lens L2 are aspherical lenses, the lens surfaces on the observation object Ob side and the eye point EP side of the third lens L3 are aspherical lenses, and the lens surfaces on the observation object Ob side and the eye point EP side of the fourth lens L4 are aspherical lenses.

[0097] Also, the eyepiece according to this embodiment performs diopter adjustment by moving the first lens L1, the second lens L2, the third lens L3, and the fourth lens L4 integrally 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 the eye point EP.

[0098] The following Table 3 lists the specifications of the photographing lens according to this embodiment.

[0099] (Table 3) Third embodiment [Overall specifications] Y0 5 TL 22.69130 [Surface 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] Visibility -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 of each lens] Initial surface f L1 1 11.80525 L2 3 -10.66309 L3 5 31.21356 L4 7 24.87468 [Condition formula corresponding values] 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] Figures 6(a), 6(b), and 6(c) are aberration diagrams at a diopter of -1 [1 / m], -3 [1 / m], and +3 [1 / m] of the eyepiece according to the third embodiment, respectively. From each aberration diagram, it can be seen that the eyepiece according to the third embodiment has good correction of various aberrations within the diopter adjustment range and has excellent optical performance.

[0101] (Example 4) Figure 7 is a cross-sectional view of the eyepiece lens according to the fourth embodiment at a diopter of -1 [1 / m]. As shown in Figure 7, the eyepiece lens according to this embodiment includes, 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 a convex surface facing the eye point EP side, a third lens L3 which is a positive meniscus lens with a convex surface facing the eye point EP side, and a fourth lens L4 which is a positive meniscus lens with a convex surface facing the eye point EP side.

[0102] In the eyepiece lens according to this embodiment, the lens surfaces on the observation object Ob side and the eye point EP side of the first lens L1 are aspherical lenses, the lens surfaces on the observation object Ob side and the eye point EP side of the second lens L2 are aspherical lenses, the lens surfaces on the observation object Ob side and the eye point EP side of the third lens L3 are aspherical lenses, and the lens surfaces on the observation object Ob side and the eye point EP side of the fourth lens L4 are aspherical lenses.

[0103] Also, the eyepiece lens according to this embodiment performs diopter adjustment by moving the first lens L1, the second lens L2, the third lens L3, and the fourth lens L4 integrally 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 the eye point EP.

[0104] The following Table 4 lists the specifications of the photographic lens according to this embodiment.

[0105] (Table 4) Example 4 [Overall specifications] Y0 5 TL 23.17110 [Surface 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] Visibility -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 of each lens] Initial surface f L1 1 12.84253 L2 3 -12.28670 L3 5 30.70855 L4 7 28.33712 [Condition formula corresponding values] 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] Figures 8(a), 8(b), and 8(c) are aberration diagrams at the diopter of -1 [1 / m], -5 [1 / m], and +5 [1 / m] of the eyepiece lens according to the fourth embodiment, respectively. From each aberration diagram, it can be seen that the eyepiece lens according to the fourth embodiment has good correction of various aberrations within the diopter adjustment range and has excellent optical performance.

[0107] (Fifth Embodiment) FIG. 9 is a cross-sectional view of the eyepiece lens according to the fifth embodiment at a diopter of -1 [1 / m]. As shown in FIG. 9, the eyepiece lens according to this embodiment includes, 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 a convex surface facing the eye point EP side, a third lens L3 which is a positive meniscus lens with a convex surface facing the eye point EP side, and a fourth lens L4 which is a positive meniscus lens with a convex surface facing the eye point EP side.

[0108] In the eyepiece lens according to this embodiment, the lens surfaces on the observation object Ob side and the eye point EP side of the first lens L1 are aspherical lenses, the lens surfaces on the observation object Ob side and the eye point EP side of the second lens L2 are aspherical lenses, the lens surfaces on the observation object Ob side and the eye point EP side of the third lens L3 are aspherical lenses, and the lens surfaces on the observation object Ob side and the eye point EP side of the fourth lens L4 are aspherical lenses.

[0109] Also, the eyepiece lens according to this embodiment performs diopter adjustment by moving the first lens L1, the second lens L2, the third lens L3, and the fourth lens L4 integrally 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 the eye point EP.

[0110] The following Table 5 lists the specifications of the photographic lens according to this embodiment.

[0111] (Table 5) Fifth Embodiment [Overall Specifications] Y0 5 TL 23.58660 [Surface 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] Visibility -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 of each lens] Initial surface f L1 1 13.60313 L2 3 -13.19877 L3 5 32.48781 L4 7 29.27539 [Condition formula 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] FIG. 10(a), FIG. 10(b), and FIG. 10(c) are aberration diagrams at a diopter of -1 [1 / m], -3 [1 / m], and +3 [1 / m] of the eyepiece according to the fifth embodiment, respectively. From each aberration diagram, it can be seen that the eyepiece according to the fifth embodiment has good correction of various aberrations within the diopter adjustment range and has excellent optical performance.

[0113] As described above, according to each of the above embodiments, an eyepiece with a high magnification, small size, and high optical performance can be realized. In particular, an eyepiece suitable for use in an electronic viewfinder for observing an image displayed on an image display element can be realized. Note that each of the above embodiments shows a specific example of the present embodiment, and the present embodiment is not limited thereto. The following contents can be appropriately adopted within a range that does not impair the optical performance of the eyepiece of the present embodiment.

[0114] As a numerical example of the eyepiece of the present embodiment, a four-element configuration is shown, but it is also applicable to other lens configurations such as a five-element configuration. Also, a configuration in which a lens is added on the side closest to the observed object or a configuration in which a lens is added on the side closest to the eye point may be used.

[0115] Further, the lens surface of the lens constituting the eyepiece of the present embodiment may be a spherical surface or a flat surface, or may be an aspherical surface. When the lens surface is a spherical surface or a flat surface, it is preferable because lens processing and assembly adjustment become easy, and deterioration of optical performance due to errors in lens processing and assembly adjustment can be prevented. Also, it is preferable because deterioration of the imaging performance is small even when the image plane is shifted. When the lens surface is an aspherical surface, it may be any of an aspherical surface by grinding, a glass mold aspherical surface formed by molding glass into an aspherical shape with a mold, or a composite aspherical surface formed by forming a resin provided on the glass surface into an aspherical shape. Further, the lens surface may be a diffractive surface, and the lens may be a gradient-index lens (GRIN lens) or a plastic lens.

[0116] Further, an antireflection film having a high transmittance in a wide wavelength range may be provided on the lens surface of the lens constituting the eyepiece lens of the present embodiment in order to reduce flare and ghost and achieve high-contrast optical performance.

[0117] In addition, the eyepiece lens of the present embodiment has been shown in a configuration in which the first lens L1, the second lens L2, the third lens L3, and the fourth lens L4 are integrated or the entire eyepiece lens moves integrally to perform diopter adjustment. However, the lens closest to the eye point is fixed, and the entire lens on the observation object side with respect to the lens moves integrally, or at least a part of the first lens L1, the second lens L2, the third lens L3, and the fourth lens L4 may move.

[0118] Next, an optical device including the eyepiece lens according to the present embodiment will be described. FIG. 11 shows a camera 1 as an optical device including the eyepiece lens according to the present embodiment. The camera 1 is a digital camera including an objective lens OL, an imaging element C such as a CCD or a CMOS, and an electronic viewfinder EVF. The electronic viewfinder EVF includes an image display element such as a liquid crystal display element that is an 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 embodiment as the eyepiece optical system EL.

[0119] In the camera 1 having such a configuration, light from an object (subject) (not shown) is condensed by the objective lens OL and forms an image of the subject on the imaging element C. The image of the subject formed on the imaging element C is imaged by the imaging element C, and the image of the subject imaged by the imaging element C is displayed on the image display element that is the observation object Ob. The photographer can magnify and observe the image of the object (subject) formed by the objective lens OL through the eyepiece optical system EL by positioning the eye at the eye point EP.

[0120] When a release button (not shown) is pressed by the photographer, an image captured by the imaging device C at this time, that is, an image corresponding to the image displayed on the image display device observed through the eyepiece optical system EL, is stored as an image of an object (subject) in a memory (not shown). In this way, the photographer can photograph an object (subject) with the camera 1.

[0121] According to the camera 1 as described above, by providing the eyepiece lens according to the first embodiment as the eyepiece optical system EL, a camera having an eyepiece optical system with high magnification, small size, and high optical performance can be realized. Even if a camera configured with the eyepiece lens according to the second to fifth embodiments is constructed, the same effects as those of the camera 1 can be achieved. Further, even when the zoom optical system according to each of the above embodiments is mounted on a camera of a type having a quick return mirror, the same effects as those of the camera 1 can be achieved. Also, the eyepiece lens according to the first to fifth embodiments may be mounted as the eyepiece optical system EL of a viewfinder device detachable from the camera body. A camera equipped with such a viewfinder device can also achieve the same effects as those of the camera 1.

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

[0123] The method for manufacturing the eyepiece lens according to the present embodiment is a method for manufacturing an eyepiece lens for observing an observation object, and as shown in FIG. 12, includes the following steps S1 and S2. Step S1: Configure the eyepiece lens to have, in order from the observation object side, a first lens having a positive refractive power, a second lens having a negative refractive power, a third lens having a positive refractive power, and a fourth lens having a positive refractive power. Step S2: Configure 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 on the observation object side of the second lens R1b: Radius of curvature of the lens surface on the eye point side of the first lens TL: Distance on the optical axis from the observation object surface to the lens surface on the most eye point side of the eyepiece lens when the diopter of the eyepiece lens is -1 [1 / m] fe: Focal length of the eyepiece lens when the diopter of the eyepiece lens is -1 [1 / m]

[0124] According to the manufacturing method of the eyepiece lens of this embodiment, an eyepiece lens with high magnification, small size, and high optical performance can be realized. In particular, an eyepiece lens suitable for use in an electronic viewfinder for observing an image displayed on an image display element can be realized.

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

[0126] Another manufacturing method of the eyepiece lens according to this embodiment is a manufacturing method of an eyepiece lens for observing an observation object, and as shown in FIG. 13, includes the following steps S1 and S2. Step S1: Configure the eyepiece lens to have, in order from the observation object side, a first lens having a positive refractive power, a second lens having a negative refractive power, a third lens having a positive refractive power, and a fourth lens having a positive refractive power. Step S2: Configure 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 on the observation object side of the first lens when the diopter of the eyepiece lens is -1 [1 / m] fe: The focal length of the eyepiece when the diopter of the eyepiece is -1 [1 / m]

[0127] According to another manufacturing method of the eyepiece of this embodiment, an eyepiece with high magnification, small size, and high optical performance can be realized. In particular, an eyepiece suitable for use in an electronic viewfinder for observing an image displayed on an image display element can be realized.

Explanation of reference numerals

[0128] L1 First lens L2 Second lens L3 Third lens L4 Fourth lens Op Observation object EP Exit pupil 1 Camera OL Objective lens C Imaging element EVF Electronic viewfinder EL Eyepiece optical system

Claims

[Claim 1] the optical system has, in order from the observation object side, a first lens having a positive refractive power, a second lens having a negative refractive power, a third lens having a positive refractive power, and a fourth lens having a positive refractive power; An eyepiece that satisfies the following conditions: 0.25<(-f2) / f3<0.53 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 lens is −1 [1 / m] fe: focal length of the eyepiece when the diopter of the eyepiece is −1 [1 / m]

Images