Eyepiece optical system

Abstract

To provide an eyepiece optical system EL having a large observation magnification and excellent optical performance, and an imaging apparatus having the eyepiece optical system EL.SOLUTION: The eyepiece optical system EL includes, in order from the observation object side, a first lens having a positive refractive power, a second lens having a negative refractive power and having a meniscus lens shape with a concave surface facing the observation object side, a third lens having a positive refractive power, and a fourth lens having a positive refractive power and having a meniscus lens shape with a concave surface facing the observation object side, and satisfies the following conditional expression: 1.38 <fe / f1 <1.651.600 <nd1 <1.800, where fe is a focal distance of the entire system of the ocular optical system EL, f1 is a focal distance of the first lens, and nd1 is an index of refraction of a medium of the first lens with respect to the d-line SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an eyepiece optical system. [Background technology]

[0002] Conventionally, eyepiece optical systems with high imaging performance have been proposed (see, for example, Patent Document 1). However, Patent Document 1 has a problem in that further improvement in optical performance is desired. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-075713 Summary of the Invention

[0004] The eyepiece optical system according to the first aspect of the present invention essentially comprises four lenses: a first lens having positive refractive power; a second lens having a meniscus shape with its concave surface facing the object; a third lens having positive refractive power; and a fourth lens having a meniscus shape with its concave surface facing the object; and satisfies the following condition: 1.38 < fe / f1 < 1.65 1.600 < nd1 < 1.800 however, fe: focal length of the entire eyepiece optical system f1: focal length of the first lens nd1: refractive index of the first lens medium for the d line [Brief explanation of the drawings]

[0005] [Figure 1] FIG. 2 is a cross-sectional view showing the lens configuration of the eyepiece optical system according to the first example. [Figure 2] 4A to 4C are diagrams showing various aberrations of the eyepiece optical system according to Example 1. [Figure 3]FIG. 10 is a cross-sectional view showing the lens configuration of an eyepiece optical system according to a second example. [Figure 4] 10A to 10C are diagrams showing various aberrations of the eyepiece optical system according to Example 2. [Figure 5] FIG. 10 is a cross-sectional view showing the lens configuration of an eyepiece optical system according to a third example. [Figure 6] 10A to 10C are diagrams showing various aberrations of the eyepiece optical system according to Example 3. [Figure 7] FIG. 10 is a cross-sectional view showing the lens configuration of an eyepiece optical system according to a fourth example. [Figure 8] 10A to 10C are diagrams showing various aberrations of the eyepiece optical system according to Example 4. [Figure 9] FIG. 10 is a cross-sectional view showing the lens configuration of an eyepiece optical system according to a fifth example. [Figure 10] 10A to 10C are diagrams showing various aberrations of the eyepiece optical system according to Example 5. [Figure 11] FIG. 13 is a cross-sectional view showing the lens configuration of an eyepiece optical system according to Example 6. [Figure 12] 13A to 13C are diagrams illustrating various aberrations in the eyepiece optical system according to Example 6. [Figure 13] FIG. 13 is a cross-sectional view showing the lens configuration of an eyepiece optical system according to Example 7. [Figure 14] 13A to 13C are diagrams illustrating various aberrations in the eyepiece optical system according to Example 7. [Figure 15] FIG. 13 is a cross-sectional view showing the lens configuration of an eyepiece optical system according to Example 8. [Figure 16] 13A to 13C are diagrams illustrating various aberrations of the eyepiece optical system according to Example 8. [Figure 17] FIG. 13 is a cross-sectional view showing the lens configuration of an eyepiece optical system according to Example 9. [Figure 18] 13A to 13C are diagrams illustrating various aberrations of the eyepiece optical system according to Example 9. [Figure 19] FIG. 23 is a cross-sectional view showing the lens configuration of an eyepiece optical system according to Example 10. [Figure 20] 13A to 13C are diagrams illustrating various aberrations of the eyepiece optical system according to the tenth example. [Figure 21] FIG. 19 is a cross-sectional view showing the lens configuration of an eyepiece optical system according to Example 11. [Figure 22]11A to 11C are diagrams illustrating various aberrations of the eyepiece optical system according to Example 11. [Figure 23] FIG. 2 is a cross-sectional view of a camera equipped with the above-mentioned eyepiece optical system. [Figure 24] 4 is a flowchart illustrating a method for manufacturing the eyepiece optical system. DETAILED DESCRIPTION OF THE INVENTION

[0006] Hereinafter, preferred embodiments will be described with reference to the drawings. As shown in Figure 1, the eyepiece optical system EL according to this embodiment has, in order from the observation object side (also simply referred to as "object"), a first lens component G1 having positive refractive power, a second lens component G2 having negative refractive power, a third lens component G3 having positive refractive power, and a fourth lens component G4 having positive refractive power.

[0007] Note that "lens component" refers to a single lens or a cemented lens. Furthermore, "lens element" refers to each lens that makes up a single lens or cemented lens. Furthermore, "reference diopter" refers to a diopter of -1 [1 / m]. Here, in terms of the unit [1 / m], diopter X [1 / m] indicates a state in which the image formed by the eyepiece optical system EL is positioned 1 / X [m (meters)] on the optical axis from the eyepoint (the sign is positive when the image is formed on the observer side (eyepoint side) of the eyepiece optical system EL).

[0008] Moreover, it is desirable that the eyepiece optical system EL according to this embodiment satisfy the following conditional expression (1).

[0009] 1.38 < fe / f1 < 3.00 (1) however, fe: focal length of the entire eyepiece optical system EL f1: focal length of the first lens component G1

[0010] Conditional formula (1) specifies the refractive power of the first lens component G1, which is closest to the object, in order to strengthen the overall refractive power of the eyepiece optical system EL while maintaining favorable spherical aberration and coma. In the eyepiece optical system EL described above, which has a refractive power arrangement of positive, negative, positive, and positive lenses from the object side, the first lens component G1, which is closest to the object, has the least effect on spherical aberration and coma. While the first lens component G1 significantly contributes to the deterioration of field curvature, the field curvature caused by the positive refractive power of the first lens component G1 can be corrected by the negative refractive power of the second lens component G2. Therefore, to increase the magnification of the eyepiece optical system EL while maintaining favorable spherical aberration and coma, it is necessary to impart strong positive refractive power to the first lens component G1, which is closest to the object. If the lower limit of conditional expression (1) is exceeded, the positive refractive power of the first lens component G1 closest to the object of observation will be weakened, weakening the refractive power of the entire eyepiece optical system EL and making it difficult to increase the observation magnification, which is undesirable. To ensure the effect of conditional expression (1), it is more desirable to set the lower limit of conditional expression (1) to 1.45, preferably 1.48, or even 1.50. If the upper limit of conditional expression (1) is exceeded, the positive refractive power of the first lens component G1 closest to the object of observation will be too strong, increasing the curvature of field generated by the first lens component G1 and making it impossible for the second lens component G2 to fully correct the curvature of field, which is undesirable. To ensure the effect of conditional expression (1), it is more desirable to set the upper limit of conditional expression (1) to 2.00, preferably 1.65.

[0011] Moreover, it is desirable that the eyepiece optical system EL according to this embodiment satisfy the following conditional expression (2).

[0012] 0.48 < fe / f12 < 3.00 (2) however, fe: focal length of the entire eyepiece optical system EL f12: composite focal length of the first lens component G1 and the second lens component G2

[0013] Conditional expression (2) defines the composite refractive power of the first lens component G1 and the second lens component G2 in order to increase the observation magnification and effectively correct curvature of field. The refractive powers of the first lens component G1 and the second lens component G2 have a significant impact on the correction and occurrence of curvature of field. To prevent curvature of field, it is desirable to weaken the composite refractive power of the first lens component G1 and the second lens component G2. However, weakening the composite refractive power of the first lens component G1 and the second lens component G2 weakens the refractive power of the entire eyepiece optical system EL, making it difficult to increase the observation magnification. Furthermore, if the composite refractive power of the first lens component G1 and the second lens component G2 is weak and an attempt is made to forcibly increase the observation magnification, the refractive power of the third lens component G3 and the fourth lens component G4 will become stronger, worsening spherical aberration and coma. If the lower limit of conditional expression (2) is not satisfied, the composite refractive power of the first lens component G1 and the second lens component G2 becomes too weak, making it impossible to increase the observation magnification, which is undesirable. Furthermore, if the observation magnification is increased when the lower limit of conditional expression (2) is not satisfied, spherical aberration and coma aberration worsen, which is undesirable. To ensure the effect of conditional expression (2), it is more desirable to set the lower limit of conditional expression (2) to 0.48, preferably 0.50, or even 0.55. Furthermore, if the upper limit of conditional expression (2) is exceeded, the composite refractive power of the first lens component G1 and the second lens component G2 becomes too strong, which is undesirable because curvature of field occurs. To ensure the effect of conditional expression (2), it is more desirable to set the upper limit of conditional expression (2) to 1.00, preferably 0.70.

[0014] Furthermore, in the eyepiece optical system EL according to this embodiment, if the lens surface closest to the eyepoint of the lens closest to the eyepoint is made convex toward the eyepoint, the exit angle of light rays near the center of the observed object from the lens surface closest to the eyepoint of the lens closest to the eyepoint becomes small, making it possible to suppress the amount of spherical aberration generated. On the other hand, the exit angle of light rays at the periphery of the image can be increased, making it possible to correct coma aberration.

[0015] In the eyepiece optical system EL according to this embodiment, it is desirable that at least one of the lens elements constituting the second lens component G2 satisfy the following conditional expression (3).

[0016] 15.0 < νd2 < 35.0 (3) however, νd2: Abbe number for the d-line of the medium of the lens element with the strongest negative refractive power among the lens elements constituting the second lens component G2

[0017] Conditional expression (3) defines the Abbe number of the lens element with the strongest negative refractive power among the lens elements constituting the second lens component G2 in order to effectively correct lateral chromatic aberration. In particular, if the combined refractive power of the first lens component G1 and the second lens component G2 is given a strong positive refractive power so as to satisfy the above-mentioned conditional expression (2), the negative refractive power of the second lens component G2 will be small. Therefore, by increasing the dispersion of the lens element with the strongest negative refractive power among the second lens component G2, it is possible to effectively correct lateral chromatic aberration even with the weak negative refractive power of the second lens component G2. Falling below the lower limit of conditional expression (3) is undesirable because lateral chromatic aberration is overcorrected, resulting in a worsening of lateral chromatic aberration. To ensure the effect of conditional expression (3), it is desirable to set the lower limit of conditional expression (3) to 20, or even 30. Furthermore, exceeding the upper limit of conditional expression (3) is undesirable because lateral chromatic aberration cannot be fully corrected. In order to ensure the effect of conditional expression (3), it is desirable to set the upper limit of conditional expression (3) to 22.

[0018] Moreover, it is desirable that the eyepiece optical system EL according to this embodiment satisfy the following conditional expression (4).

[0019] 0.01 < fe / f4 < 0.33 (4) however, fe: focal length of the entire eyepiece optical system EL f4: Focal length of the fourth lens element G4

[0020] Conditional expression (4) defines the refractive power of the lens closest to the eyepoint in order to effectively correct spherical aberration and coma. The fourth lens component G4, which is closest to the eyepoint, has the greatest effect on spherical aberration and coma. Therefore, exceeding the upper limit of conditional expression (4) is undesirable because the positive refractive power of the fourth lens component G4 becomes too strong, significantly worsening spherical aberration and coma. To ensure the effectiveness of conditional expression (4), it is more desirable to set the upper limit of conditional expression (4) to 0.30, preferably 0.25, or even 0.239. Furthermore, falling below the lower limit of conditional expression (4) is undesirable because it becomes difficult to increase the overall refractive power of the eyepiece optical system EL, making it impossible to achieve a high observation magnification. If the refractive power of the fourth lens component G4 were to fall below the lower limit of conditional expression (4) and the observation magnification were to be increased, the positive refractive power of the first lens component G1 and the third lens component G3 would become extremely strong, or the negative refractive power of the second lens component G2 would become weak, making it difficult to correct the curvature of field. In order to ensure the effect of conditional expression (4), it is more desirable to set the lower limit of conditional expression (4) to 0.10, or even 0.15.

[0021] It is also desirable that the eyepiece optical system EL according to this embodiment satisfy the following conditional expression (5).

[0022] -0.30<(G2R2-G3R1) / (G2R2+G3R1)<0.50 (5) however, G2R2: Radius of curvature of the lens surface closest to the eyepoint of the second lens component G2 G3R1: Radius of curvature of the lens surface of the third lens component G3 closest to the object

[0023] Conditional formula (5) defines the shape of the lens surface of the second lens component G2 closest to the eyepoint and the lens surface of the third lens component G3 closest to the object in order to effectively correct coma. The lens surface of the second lens component G2 closest to the eyepoint and the lens surface of the third lens component G3 closest to the object have a significant effect on the occurrence and correction of coma. To effectively correct coma, it is preferable that coma occurring on the lens surface of the second lens component G2 closest to the eyepoint be corrected on the lens surface of the third lens component G3 closest to the object. Furthermore, to effectively correct coma, it is desirable to make the shape of the lens surface of the second lens component G2 closest to the eyepoint similar to the shape of the lens surface of the third lens component G3 closest to the object, thereby making the coma occurring on the lens surface of the second lens component G2 closest to the eyepoint similar to the coma corrected on the lens surface of the third lens component G3 closest to the object, and thereby canceling out the coma. If the lower limit of conditional expression (5) is not satisfied, the similarity between the shape of the lens surface of the second lens component G2 closest to the eyepoint and the shape of the lens surface of the third lens component G3 closest to the observation object will be lost, which is undesirable, resulting in coma. To ensure the effect of conditional expression (5), it is desirable to set the lower limit of conditional expression (5) to -0.25. To ensure the effect of conditional expression (5), it is desirable to set the upper limit of conditional expression (5) to 0.25, or even -0.20, which is undesirable, resulting in coma. To ensure the effect of conditional expression (5), it is desirable to set the upper limit of conditional expression (5) to 0.25, or even more desirably -0.20.

[0024] It is also desirable that the eyepiece optical system EL according to this embodiment satisfy the following conditional expression (6).

[0025] -0.75<(G1R2+G1R1) / (G1R2-G1R1)<0.00 (6) however, G1R1: Radius of curvature of the lens surface of the first lens component G1 closest to the object G1R2: Radius of curvature of the lens surface closest to the eyepoint of the first lens component G1

[0026] Conditional expression (6) defines the shape of the first lens component G1 in order to increase the observation magnification while effectively correcting field curvature and distortion. The positive refractive power of the first lens component G1 generates field curvature, but the structure is such that the negative refractive power of the second lens component G2 corrects the field curvature. If the refractive power of the lens surface of the first lens component G1 closest to the eyepoint is increased, the field curvature generated by the first lens component G1 becomes large, and this cannot be fully corrected by the negative refractive power of the second lens component G2. On the other hand, in order to increase the observation magnification, it is necessary to increase the positive refractive power of the lens surface of the first lens component G1 closest to the observation object, and therefore the positive refractive power of the lens surface of the first lens component G1 closest to the observation object must be appropriately increased. However, if the positive refractive power of the lens surface of the first lens component G1 closest to the observation object is increased too much, distortion will worsen. Exceeding the upper limit of conditional expression (6) is undesirable because the refractive power of the first lens component G1 becomes too large, worsening distortion. To ensure the effect of conditional expression (6), it is more desirable to set the upper limit of conditional expression (6) to -0.20, and even more desirable to set it to -0.30. Falling below the lower limit of conditional expression (6) weakens the refractive power of the first lens component G1, making it impossible to increase the observation magnification. Increasing the observation magnification while falling below the lower limit of conditional expression (6) undesirably increases the refractive power of the lens surface of the first lens component G1 closest to the eyepoint, worsening field curvature. To ensure the effect of conditional expression (6), it is more desirable to set the lower limit of conditional expression (6) to -0.57, and even more desirable to set it to -0.56, and even more desirable to set it to -0.50.

[0027] Furthermore, the eyepiece optical system EL according to this embodiment can correct distortion by making the lens surface of the first lens component G1 closest to the observation object a rotationally symmetric aspheric surface, and it is possible to increase the refractive power of the lens surface of the first lens component G1 closest to the observation object, which is advantageous for increasing the observation magnification.

[0028] It is also desirable that the eyepiece optical system EL according to this embodiment satisfy the following conditional expression (7).

[0029] -1.00 < fe / EnP < -0.48 (7) however, fe: focal length of the entire eyepiece optical system EL EnP: Entrance pupil position of the eyepiece optical system EL at the reference diopter (the sign is positive with the eye point side as the reference, based on the observation object surface)

[0030] Conditional expression (7) defines the entrance pupil position to increase the observation magnification while maintaining a long eyepoint. Increasing the passage height of the chief ray for high image heights in a region close to the observation object plane facilitates increasing the observation magnification while maintaining a long eyepoint. To increase the passage height of the chief ray for high image heights in a region close to the observation object plane, it is effective to set the entrance pupil distance to a short distance from the observation object plane on the opposite side of the eyepoint. Exceeding the upper limit of conditional expression (7) is undesirable because the entrance pupil position is farther away from the observation object, making it impossible to increase the passage height of the chief ray for high image heights. This makes it impossible to achieve high magnification while maintaining a long eyepoint. To ensure the effect of conditional expression (7), it is desirable to set the upper limit of conditional expression (7) to -0.50. Furthermore, falling below the lower limit of conditional expression (7) is undesirable because the entrance pupil position is too close to the observation object, increasing the passage height of the chief ray for high image heights in the first lens component G1, resulting in significant curvature of field. In order to ensure the effect of conditional expression (7), it is more desirable to set the lower limit of conditional expression (7) to -0.70, and more preferably -0.65.

[0031] Moreover, it is desirable that the eyepiece optical system EL according to this embodiment satisfy the following conditional expression (8).

[0032] -0.40 < fe / f23 < -0.15 (8) however, fe: focal length of the entire eyepiece optical system EL f23: composite focal length of the second lens component G2 and the third lens component G3

[0033] Conditional expression (8) defines the ratio of the composite focal length of the second and third lens components G2 and G3 to the focal length of the entire eyepiece optical system EL to minimize deterioration in aberration performance when the optical axes of the second and third lens components G2 and G3 are misaligned during manufacturing. By making the composite focal length of the second and third lens components G2 and G3 smaller than the focal length of the entire eyepiece optical system EL, it is possible to minimize deterioration in aberration performance even when the optical axes of the second and third lens components G2 and G3 are misaligned due to manufacturing errors. It also minimizes deterioration in optical performance when the refractive index or curvature radius of the second and third lens components G2 and G3 change due to temperature changes. This is particularly effective when the second and third lens components G2 and G3 are made of optical resin. Below the lower limit of conditional expression (8), the negative composite refractive power of the second and third lens components G2 and G3 becomes too strong, significantly deteriorating aberration performance due to manufacturing errors, which is undesirable. In order to ensure the effect of conditional expression (8), it is desirable to set the lower limit of conditional expression (8) to -0.35. Furthermore, exceeding the upper limit of conditional expression (8) is undesirable because the negative refractive power of the second lens component G2 becomes small, resulting in insufficient correction of field curvature. In order to ensure the effect of conditional expression (8), it is more desirable to set the upper limit of conditional expression (8) to -0.20, and even more preferably -0.25.

[0034] Moreover, it is desirable that the eyepiece optical system EL according to this embodiment satisfy the following conditional expression (9).

[0035] 0.58 < D1 / f1 < 0.90 (9) however, D1: Air-equivalent distance from the object to the lens surface of the first lens component G1 closest to the object at the standard diopter f1: focal length of the first lens component G1

[0036] Conditional expression (9) defines the ratio of the air-equivalent distance from the object to the lens surface of the first lens component G1 closest to the object at the standard diopter to the focal length of the first lens component G1 in order to effectively correct coma. When the air-equivalent distance from the object to the lens surface of the first lens component G1 closest to the object at the standard diopter increases, the passing height of a light beam emitted from a point on the observation surface changes significantly on the first lens component G1. Therefore, when the air-equivalent distance D1 from the object to the lens surface of the first lens component G1 closest to the object increases, the positive refractive power of the first lens component G1 significantly increases coma, so the refractive power of the first lens component G1 must be reduced. On the other hand, in order to increase the refractive power of the first lens component G1, the air-equivalent distance D1 from the object to the lens surface of the first lens component G1 closest to the object must be reduced in order to reduce the coma generated by the first lens component G1. Exceeding the upper limit of conditional expression (9) is undesirable because the refractive power of the first lens component G1 becomes stronger relative to the air-equivalent distance D1 from the observation object to the lens surface of the first lens component G1 closest to the observation object, thereby worsening coma. To ensure the effect of conditional expression (9), it is preferable to set the upper limit of conditional expression (9) to 0.71, or even 0.68. Falling below the lower limit of conditional expression (9) is undesirable because the positive refractive power of the first lens component G1 becomes weak, making it impossible to increase the observation magnification. To ensure the effect of conditional expression (9), it is preferable to set the lower limit of conditional expression (9) to 0.60, or even 0.63.

[0037] It is also desirable that the eyepiece optical system EL according to this embodiment satisfy the following conditional expression (10): The total length of the eyepiece optical system EL is the distance on the optical axis from the observation object O to the lens surface of the eyepiece optical system EL closest to the eyepoint.

[0038] 1.50 < TL / fe < 1.80 (10) however, TL: Total length of the eyepiece optical system EL fe: focal length of the entire eyepiece optical system EL

[0039] Conditional expression (10) defines the ratio of the overall length of the eyepiece optical system EL to the focal length of the entire system in order to correct for field curvature. Below the lower limit of conditional expression (10), the overall refractive power of the eyepiece optical system EL becomes weak, making it difficult to increase the observation magnification, which is undesirable. To ensure the effect of conditional expression (10), it is preferable to set the lower limit of conditional expression (10) to 1.55, or even 1.60. Above the upper limit of conditional expression (10), it is undesirable because field curvature worsens. To ensure the effect of conditional expression (10), it is preferable to set the upper limit of conditional expression (10) to 1.70.

[0040] It is also desirable that the eyepiece optical system EL according to this embodiment satisfy the following conditional expression (11): When the first lens component G1 is composed of a cemented lens and has multiple lens elements, at least one of these lens elements satisfies conditional expression (11).

[0041] 1.550 < nd1 < 1.800 (11) however, nd1: refractive index of the medium of the lens element constituting the first lens component G1 for the d line

[0042] Conditional expression (11) defines the refractive index at the d-line of the medium of the lens elements constituting the first lens component G1 in order to effectively correct distortion and curvature of field. Below the lower limit of conditional expression (11), the first lens component G1 cannot be provided with refractive power, making it difficult to achieve high magnification while maintaining performance, which is undesirable. To ensure the effect of conditional expression (11), it is preferable to set the lower limit of conditional expression (11) to 1.600, and more preferably 1.700. Exceeding the upper limit of conditional expression (11) is undesirable because distortion worsens. To ensure the effect of conditional expression (11), it is preferable to set the upper limit of conditional expression (11) to 1.850.

[0043] It is also desirable that the eyepiece optical system EL according to this embodiment satisfy the following conditional expression (12): When the second lens component G2 is composed of a cemented lens and has multiple lens elements, at least one of these lens elements satisfies conditional expression (12).

[0044] 1.640 < nd2 < 1.800 (9) however, nd2: refractive index of the medium of the lens element constituting the second lens component G2 for the d line

[0045] Conditional expression (12) defines the refractive index at the d-line of the medium of the lens elements constituting the second lens component G2 in order to satisfactorily correct astigmatism. Falling below the lower limit of conditional expression (12) is undesirable because decentering of the second lens component G2 degrades optical performance. To ensure the effect of conditional expression (12), it is desirable to set the lower limit of conditional expression (12) to 1.650. Exceeding the upper limit of conditional expression (12) is undesirable because it makes it difficult to correct astigmatism. To ensure the effect of conditional expression (12), it is desirable to set the upper limit of conditional expression (12) to 1.750.

[0046] Furthermore, the eyepiece optical system EL according to this embodiment has a single lens configuration for the first lens component G1, the second lens component G2, the third lens component G3, and the fourth lens component G4, and can achieve sufficiently good aberration performance even when configured with four single lenses.

[0047] Furthermore, the eyepiece optical system EL according to this embodiment allows easy diopter adjustment by moving the entire eyepiece optical system in the direction of the optical axis.

[0048] It should be noted that the conditions and configurations described above each exert the effects described above, and are not limited to those that satisfy all of the conditions and configurations; the effects described above can be obtained by satisfying any one of the conditions or configurations, or a combination of any one of the conditions or configurations.

[0049] Next, a camera, which is an optical instrument (image capture device) equipped with an eyepiece optical system EL according to this embodiment, will be described with reference to FIG. 23. This camera 1 is a so-called mirrorless camera with an interchangeable lens system equipped with an objective lens (photographing lens) OL. In this camera 1, light from an object (subject) (not shown) is collected by the objective lens OL and passes through an OLPF (Optical Low Pass Filter) (not shown) to form a subject image on the imaging surface of the imaging unit C. The subject image is then photoelectrically converted by a photoelectric conversion element provided in the imaging unit C to generate an image of the subject. This image is displayed on an electronic viewfinder EVF (electronic viewfinder) provided in the camera 1. The electronic viewfinder EVF includes an image display element DP such as a liquid crystal display element and an eyepiece optical system EL for magnifying and observing the image displayed on the display surface of the image display element DP (the above-mentioned observation object O). This allows a photographer to position their eye at eyepoint EP and observe the image of the object (subject) formed by the objective lens OL through the eyepiece optical system EL.

[0050] Furthermore, when the photographer presses a release button (not shown), the image photoelectrically converted by the imaging unit C is stored in a memory (not shown). In this way, the photographer can photograph a subject using this camera 1. Note that although an example of a mirrorless camera has been described in this embodiment, the same effects as those of the camera 1 can be achieved even if the eyepiece optical system EL according to this embodiment is installed in a single-lens reflex camera that has a quick-return mirror in the camera body and observes a subject through a viewfinder optical system.

[0051] As described above, the eyepiece optical system EL according to this embodiment is an optical system (eyepiece) for magnifying and observing an image. Here, the image refers to 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 EL display, and preferably the display surface of an organic EL display. Therefore, the eyepiece optical system EL according to this embodiment is suitable for use as the eyepiece of, for example, electronic binoculars, head-mounted displays, or built-in or external electronic viewfinders for cameras, for observing images displayed on the display surface.

[0052] Although not shown in Fig. 1 etc., an optical member such as a cover glass or a prism may be arranged between the observation object O (the display surface of the image display element DP shown in Fig. 23) and the first lens component G1. Also, an optical member such as a cover glass may be arranged between the fourth lens component G4 and the eye point EP.

[0053] A manufacturing method for the eyepiece optical system EL according to this embodiment will be outlined below with reference to Fig. 24. First, the lenses are arranged to prepare a first lens component G1 having positive refractive power, a second lens component G2 having negative refractive power, a third lens component G3 having positive refractive power, and a fourth lens component G4 having positive refractive power (Step S100). Then, they are arranged so as to satisfy the conditions defined by predetermined conditional expressions (for example, the above-mentioned conditional expressions (1) and (2)) (Step S200).

[0054] 1, the eyepiece optical system EL is manufactured by arranging the lens components prepared in this manner in the order listed above: a first lens component G1, which includes an aspherical positive lens L11 having a biconvex positive shape and aspherical surfaces on both the object-side and eye-point-side; a second lens component G2, which includes an aspherical negative lens L12 having a negative meniscus shape and aspherical surfaces on both the object-side and eye-point-side, with its concave surface facing the object-side; a third lens component G3, which includes an aspherical positive lens L31 having a positive meniscus shape and aspherical surfaces on both the object-side and eye-point-side, with its concave surface facing the object-side; and a fourth lens component G4, which includes an aspherical positive lens L41 having a positive meniscus shape and aspherical surfaces on both the object-side and eye-point-side, with its concave surface facing the object-side.

[0055] With the above-described configuration, it is possible to provide an eyepiece optical system EL having a large observation magnification and good optical performance, an optical instrument (image pickup device) having this eyepiece optical system EL, and a method for manufacturing the eyepiece optical system EL. [Example]

[0056] Each embodiment of the present invention will be described below with reference to the drawings. Note that Figures 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, and 21 are cross-sectional views showing the configuration and refractive power distribution of the eyepiece optical system EL (EL1 to EL11) according to each embodiment.

[0057] In these examples, the aspherical surface is expressed by the following formula (a), where y is the height in the direction perpendicular to the optical axis, S(y) is the distance (amount of sag) along the optical axis from the tangent plane of the vertex of each aspherical surface at the height y to each aspherical surface, r is the radius of curvature (paraxial radius of curvature) of the reference spherical surface, K is the conic constant, and An is the n-th order aspherical coefficient. Note that in the following examples, "En" is expressed as "×10 -n " indicates.

[0058] S(y)=(y 2 / r) / {1+(1-K×y 2 / r 2 ) 1 / 2} +A4×y 4 +A6×y 6 +A8×y 8 +A10×y 10 +A12×y 12 (a)

[0059] In each example, the second-order aspherical coefficient A2 is 0. In the table for each example, aspherical surfaces are marked with an * to the right of the surface number.

[0060] [First Example] 1 is a diagram showing the configuration of an eyepiece optical system EL1 according to Example 1. This eyepiece optical system EL1 is composed of, in order from the observation object side, a first lens component G1 having positive refractive power, a second lens component G2 having negative refractive power, a third lens component G3 having positive refractive power, and a fourth lens component G4 having positive refractive power.

[0061] In this eyepiece optical system EL1, the first lens component G1 is composed of an aspherical positive lens L11 having a biconvex positive lens shape with aspherical surfaces facing the object and the eyepoint. The second lens component G2 is composed of an aspherical negative lens L12 having aspherical surfaces facing the object and the eyepoint and a negative meniscus lens shape with its concave surface facing the object. The third lens component G3 is composed of an aspherical positive lens L31 having aspherical surfaces facing the object and the eyepoint and a positive meniscus lens shape with its concave surface facing the object. The fourth lens component G4 is composed of an aspherical positive lens L41 having aspherical surfaces facing the object and the eyepoint and a positive meniscus lens shape with its concave surface facing the object.

[0062] The diopter adjustment in the eyepiece optical system EL1 is performed by moving the entire eyepiece optical system EL1 in the direction of the optical axis.

[0063] Table 1 below lists the specifications of the eyepiece optical system EL1. In Table 1, fe, listed under overall specifications, indicates the focal length of the entire system, H indicates the maximum object height, and TL indicates the overall length. In the lens data, column m indicates the order of the lens surfaces (surface number) from the object side along the direction of light propagation, column r indicates the radius of curvature of each lens surface, column d indicates the distance on the optical axis from each optical surface to the next optical surface (surface spacing), and columns nd and vd indicate the refractive index and Abbe number for the d-line (λ=587.6 nm). A radius of curvature of ∞ indicates a flat surface, and the refractive index of air, 1.00000, has been omitted. The object plane indicates the observed object O, and the image plane indicates the eyepoint EP.

[0064] Here, the focal length f (fOe, fEe, etc.), radius of curvature r, surface spacing d, and other length units listed in all of the following specifications are generally in "mm," but this is not limited to this because the optical system can achieve the same optical performance even when proportionally enlarged or reduced. The explanations of these symbols and specification tables also apply to the following examples.

[0065] As mentioned above, although not shown in the following embodiments including this embodiment, if an optical member such as a cover glass, a prism, or a display cover glass is disposed between the observation object O and the first lens component G1, or between the fourth lens component G4 and the eyepoint EP, the surface distance d is the air-equivalent length.

[0066] (Table 1) First Example [Overall specifications] fe = 17.641 H = 6.30 TL = 28.790 [Lens data] mrd nd νd Object surface ∞ D1 1* 29.01673 6.95 1.77377 47.25 2* -11.37822 3.03 3* -6.74812 1.50 1.63550 23.89 4* -58.92577 1.25 5* -48.01803 5.40 1.53110 55.91 6* -10.14569 0.50 7* -1037.93340 2.75 1.53110 55.91 8* -42.12958 D2 Image plane ∞

[0067] In this eyepiece optical system EL1, surfaces 1, 2, 3, 4, 5, 6, 7, and 8 are aspherical. Table 2 below shows the data for the aspherical surfaces, i.e., the conic constant K and the values ​​of each of the aspherical constants A4 to A12.

[0068] (Table 2) [Aspherical data] Front page K=-1.0414 A4 =-1.29144E-04 A6 =-4.67158E-07 A8 = 1.78024E-08 A10=-1.65828E-10 A12= 6.30320E-13 2nd side K=-2.2911 A4 =-1.46042E-04 A6 = 1.05047E-06 A8 =-8.71894E-09 A10= 3.48401E-11 A12= 0.00000E+00 3rd page K=-0.2684 A4 = 3.35859E-04 A6 = -4.37805E-06 A8 = 2.17895E-08 A10=-4.94107E-11 A12= 0.00000E+00 Side 4 K= 5.9869 A4 = 9.81668E-05 A6 = -1.20860E-06 A8 = 6.95819E-09 A10=-1.72138E-11 A12= 0.00000E+00 5th page K=5.9905 A4 = 2.82487E-05 A6 = 1.16190E-06 A8 =-1.23653E-08 A10= 4.18910E-11 A12= 0.00000E+00 Side 6 K= 0.3916 A4 = 1.91131E-04 A6 =-3.21702E-07 A8 =-3.26701E-09 A10= 2.35655E-11 A12= 0.00000E+00 Side 7 K= 1.0000 A4 =-1.52684E-04 A6 = 1.49017E-06 A8 =-1.20661E-08 A10= 5.44999E-11 A12= 0.00000E+00 Side 8 K= 3.6084 A4 =-2.40943E-04 A6 = 2.55221E-06 A8 =-1.68422E-08 A10= 5.77483E-11 A12= 0.00000E+00

[0069] In this eyepiece optical system EL1, the axial air distance D1 between the object being observed and the first lens component G1, and the axial air distance D2 between the fourth lens component G4 and the eyepoint EP, change during diopter adjustment. Furthermore, the entrance pupil position EnP also changes as these distances change. Table 3 below shows the variable distances and entrance pupil positions for each diopter. Note that diopters are represented as follows: -1 [1 / m] is represented as "-1 dpt," +2 [1 / m] as "+2 dpt," and -4 [1 / m] as "-4 dpt." This also applies to the following examples.

[0070] (Table 3) [Variable Interval Data] Diopter -1dpt +2dpt -4dpt D1 7.41 8.33 6.39 D2 20.60 19.68 21.62 EnP -29.03270 -30.46513 -27.64176

[0071] Table 4 below shows the values ​​corresponding to each conditional expression of this eyepiece optical system EL1.

[0072] (Table 4) f4 = 82.602 f12= ​​28.790 f23=-63.706 [Conditional expression corresponding value] (1) fe / f1=1.545 (2) fe / f12 = 0.613 (3)νd2=23.89 (4) fe / f4 = 0.214 (5)(G2R2-G3R1) / (G2R2+G3R1)= 0.102 (6)(G1R2+G1R1) / (G1R2-G1R1)=-0.437 (7)fe / EnP=-0.608 (8)fe / f23=-0.277 (9) D1 / f1=0.649 (10)TL / fe=1.632 (11)nd1=1.774 (12)nd2=1.636

[0073] In this way, the eyepiece optical system EL1 satisfies the above conditional expressions (1) to (11).

[0074] Figure 2 shows diagrams of spherical aberration, astigmatism, distortion, and coma for this eyepiece optical system EL1 at the reference diopter (-1 diopter). The horizontal axis of the spherical aberration and astigmatism diagrams is in units of 1 / m, indicated by "D" in the diagrams. The coma and lateral chromatic aberration diagrams are expressed in minutes of angle, with d and g representing the aberration curves at the d-line and g-line, respectively. The coma diagram also shows the aberration curve for each object height. The same explanations apply to the following examples. These aberration diagrams demonstrate that this eyepiece optical system EL1 achieves favorable aberration correction within the diopter adjustment range.

[0075] [Second Example] 3 is a diagram showing the configuration of the eyepiece optical system EL2 according to Example 2. This eyepiece optical system EL2 is configured to include, in order from the observation object side, a first lens component G1 having positive refractive power, a second lens component G2 having negative refractive power, a third lens component G3 having positive refractive power, and a fourth lens component G4 having positive refractive power.

[0076] In this eyepiece optical system EL2, the first lens component G1 is composed of an aspherical positive lens L11 having a biconvex positive lens shape with aspherical surfaces facing the object and the eyepoint. The second lens component G2 is composed of an aspherical negative lens L12 having aspherical surfaces facing the object and the eyepoint and a negative meniscus lens shape with its concave surface facing the object. The third lens component G3 is composed of an aspherical positive lens L31 having aspherical surfaces facing the object and the eyepoint and a positive meniscus lens shape with its concave surface facing the object. The fourth lens component G4 is composed of an aspherical positive lens L41 having aspherical surfaces facing the object and the eyepoint and a positive meniscus lens shape with its concave surface facing the object.

[0077] The diopter adjustment in the eyepiece optical system EL2 is performed by moving the entire eyepiece optical system EL2 in the direction of the optical axis.

[0078] Table 5 below lists the specifications of the eyepiece optical system EL2.

[0079] (Table 5) Second Example [Overall specifications] fe = 18.135 H = 6.30 TL = 28.100 [Lens data] mrd nd νd Object surface ∞ D1 1* 18.29768 7.45 1.53110 55.91 2* -8.02783 2.40 3* -5.08738 2.15 1.63550 23.89 4* -16.13188 0.50 5* -46.53675 5.00 1.53110 55.91 6* -9.74321 0.50 7* -62.07807 2.30 1.53110 55.91 8* -36.52997 D2 Image plane ∞

[0080] In this eyepiece optical system EL2, surfaces 1, 2, 3, 4, 5, 6, 7, and 8 are aspherical. Table 6 below shows the data for the aspherical surfaces, i.e., the conic constant K and the values ​​of each of the aspherical constants A4 to A12.

[0081] (Table 6) [Aspherical data] Front page K= 0.4135 A4 =-1.67471E-04 A6 =-2.55937E-06 A8 =4.54261E-08 A10=-3.19957E-10 A12= 1.06400E-12 2nd side K=-2.0545 A4 =-3.02431E-04 A6 = 3.45590E-06 A8 =-3.41508E-08 A10= 1.41269E-10 A12= 0.00000E+00 Page 3 K=-0.3061 A4 = 5.48726E-04 A6 =-5.11105E-06 A8 =-4.02571E-10 A10= 6.06422E-11 A12= 0.00000E+00 Page 4 K=-3.9720 A4 = 1.64809E-04 A6 =-6.23672E-07 A8 =-3.44304E-09 A10= 4.26001E-12 A12= 0.00000E+00 Page 5 K = 5.8883 A4 =-5.24409E-05 A6 = 5.07414E-07 A8 = 3.77890E-09 A10=-1.41672E-11 A12= 0.00000E+00 Page 6 K = 0.4195 A4 = 2.57996E-04 A6 =-1.85757E-06 A8 = 2.18453E-09 A10= 5.57891E-11 A12= 0.00000E+00 Page 7 K = 4.9451 A4 =-8.67424E-05 A6 = 9.74736E-07 A8 = 5.79036E-09 A10=-6.53413E-11 A12= 0.00000E+00 Page 8 K = 5.7525 A4 =-2.08333E-04 A6 = 2.55741E-06 A8 =-6.33475E-09 A10=-2.34517E-11 A12= 0.00000E+00

[0082] In this eyepiece optical system EL2, the axial air distance D1 between the object being observed and the first lens component G1, and the axial air distance D2 between the fourth lens component G4 and the eyepoint EP, change during diopter adjustment. Furthermore, the entrance pupil position EnP also changes as these distances change. Table 7 below shows the variable distances and entrance pupil positions for each diopter.

[0083] (Table 7) [Variable Interval Data] Diopter -1dpt +2dpt -4dpt D1 7.80 8.77 6.74 D2 20.60 19.63 21.66 EnP -34.92593 -37.22500 -32.79600

[0084] Table 8 below shows the values ​​corresponding to each conditional expression of this eyepiece optical system EL2.

[0085] (Table 8) f4 =162.068 f12= ​​33.567 f23=-93.824 [Conditional expression corresponding value] (1) fe / f1=1.557 (2) fe / f12 = 0.540 (3)νd2=23.89 (4) fe / f4=0.112 (5)(G2R2-G3R1) / (G2R2+G3R1)=-0.485 (6)(G1R2+G1R1) / (G1R2-G1R1)=-0.390 (7)fe / EnP=-0.519 (8)fe / f23=-0.193 (9) D1 / f1=0.670 (10)TL / fe=1.550 (11)nd1=1.531 (12)nd2=1.636

[0086] In this way, the eyepiece optical system EL2 satisfies the above conditional expressions (1) to (4) and (6) to (10).

[0087] Diagrams of spherical aberration, astigmatism, distortion, and coma for this eyepiece optical system EL2 at the reference diopter (-1 dpt) are shown in Figure 4. These aberration diagrams show that this eyepiece optical system EL2 achieves good aberration correction within the diopter adjustment range.

[0088] [Third Example] 5 is a diagram showing the configuration of an eyepiece optical system EL3 according to Example 3. This eyepiece optical system EL3 is configured to include, in order from the observation object side, a first lens component G1 having positive refractive power, a second lens component G2 having negative refractive power, a third lens component G3 having positive refractive power, and a fourth lens component G4 having positive refractive power.

[0089] In this eyepiece optical system EL3, the first lens component G1 is composed of an aspherical positive lens L11 having a biconvex positive lens shape with aspherical surfaces on the observation object side and the eyepoint side. The second lens component G2 is composed of an aspherical negative lens L12 having an aspherical biconcave negative lens shape with aspherical surfaces on the observation object side. The third lens component G3 is composed of an aspherical positive lens L31 having an aspherical biconvex positive lens shape with aspherical surfaces on the eyepoint side. The fourth lens component G4 is composed of an aspherical positive lens L41 having an aspherical positive meniscus lens shape with aspherical surfaces on the observation object side and the eyepoint side.

[0090] The diopter adjustment in the eyepiece optical system EL3 is performed by moving the entire eyepiece optical system EL3 in the direction of the optical axis.

[0091] Table 9 below lists the specifications of the eyepiece optical system EL3.

[0092] (Table 9) Third Example [Overall specifications] fe = 17.654 H = 6.30 TL = 29.118 [Lens data] mrd nd νd Object surface ∞ D1 1* 37.20780 7.34 1.82098 42.50 2* -10.78310 2.69 3* -6.86450 1.58 1.63550 23.89 4 403.03380 0.98 5 365.51190 5.94 1.53110 55.91 6* -10.45160 0.50 7* -40.06410 2.69 1.53110 55.91 8* -25.10660 D2 Image plane ∞

[0093] In this eyepiece optical system EL3, surfaces 1, 2, 3, 6, 7, and 8 are aspherical. Table 10 below shows the data for the aspherical surfaces, i.e., the conic constant K and the values ​​of each of the aspherical constants A4 to A12.

[0094] (Table 10) [Aspherical data] Front page K= 3.5010 A4 =-1.08770E-04 A6 =-7.76264E-07 A8 = 1.84546E-08 A10=-1.13779E-10 A12= 3.71750E-13 2nd side K=-2.3099 A4 =-1.29893E-04 A6 =9.59335E-07 A8 =-7.24273E-09 A10= 3.52620E-11 A12= 0.00000E+00 3rd page K=-0.1511 A4 = 4.02440E-04 A6 = -4.00609E-06 A8 = 2.11556E-08 A10=-1.51294E-10 A12= 0.00000E+00 Side 6 K= 0.5856 A4 = 2.62266E-04 A6 =-6.94589E-07 A8 =-3.75126E-09 A10= 2.70416E-11 A12= 0.00000E+00 Side 7 K= 1.0000 A4 =-1.21897E-04 A6 = 1.25808E-06 A8 =-5.29696E-09 A10= 4.01375E-11 A12= 0.00000E+00 Side 8 K= 0.9506 A4 =-2.35090E-04 A6 = 2.42051E-06 A8 =-1.44574E-08 A10= 7.36171E-11 A12= 0.00000E+00

[0095] In this eyepiece optical system EL3, the axial air distance D1 between the object being observed and the first lens component G1, and the axial air distance D2 between the fourth lens component G4 and the eyepoint EP, change during diopter adjustment. Furthermore, the entrance pupil position EnP also changes as these distances change. Table 11 below shows the variable distances and entrance pupil positions for each diopter.

[0096] (Table 11) [Variable Interval Data] Diopter -1dpt +2dpt -4dpt D1 7.41 8.34 6.40 D2 20.60 19.67 21.61 EnP -30.17343 -31.78442 -28.65171

[0097] Table 12 below shows the values ​​corresponding to each conditional expression of this eyepiece optical system EL3.

[0098] (Table 12) f4 =119.198 f12= ​​34.675 f23=-70.015 [Conditional expression corresponding value] (1) fe / f1=1.614 (2)fe / f12=0.509 (3)νd2=23.89 (4) fe / f4=0.148 (5)(G2R2-G3R1) / (G2R2+G3R1)= 0.049 (6)(G1R2+G1R1) / (G1R2-G1R1)=-0.551 (7)fe / EnP=-0.585 (8)fe / f23=-0.252 (9) D1 / f1=0.678 (10)TL / fe=1.649 (11)nd1=1.821 (12)nd2=1.636

[0099] In this way, the eyepiece optical system EL3 satisfies the above conditional expressions (1) to (11).

[0100] Diagrams of spherical aberration, astigmatism, distortion, and coma for this eyepiece optical system EL3 at the reference diopter (-1 dpt) are shown in Figure 6. These aberration diagrams show that this eyepiece optical system EL3 achieves good aberration correction within the diopter adjustment range.

[0101] [Fourth Example] 7 is a diagram showing the configuration of an eyepiece optical system EL4 according to Example 4. This eyepiece optical system EL4 is configured to include, in order from the observation object side, a first lens component G1 having positive refractive power, a second lens component G2 having negative refractive power, a third lens component G3 having positive refractive power, and a fourth lens component G4 having positive refractive power.

[0102] In this eyepiece optical system EL4, the first lens component G1 is composed of an aspherical positive lens L11 having a biconvex positive lens shape with aspherical surfaces facing the object and the eyepoint. The second lens component G2 is composed of an aspherical negative lens L12 having aspherical surfaces facing the object and the eyepoint and a negative meniscus lens shape with its concave surface facing the object. The third lens component G3 is composed of an aspherical positive lens L31 having aspherical surfaces facing the object and the eyepoint and a positive meniscus lens shape with its concave surface facing the object. The fourth lens component G4 is composed of an aspherical positive lens L41 having aspherical surfaces facing the object and the eyepoint and a positive meniscus lens shape with its concave surface facing the object.

[0103] The diopter adjustment in the eyepiece optical system EL4 is performed by moving the entire eyepiece optical system EL4 in the direction of the optical axis.

[0104] Table 13 below lists the specifications of the eyepiece optical system EL4.

[0105] (Table 13) Fourth Example [Overall specifications] fe = 17.636 H = 6.30 TL = 29.262 [Lens data] mrd nd νd Object surface ∞ D1 1* 24.08699 7.78 1.77377 47.25 2* -11.23946 2.66 3* -6.16897 1.50 1.63550 23.89 4* -35.90996 1.64 5* -30.97534 4.55 1.53110 55.91 6* -9.95862 0.50 7* -2317.28230 2.89 1.53110 55.91 8* -41.10583 D2 Image plane ∞

[0106] In this eyepiece optical system EL4, surfaces 1, 2, 3, 4, 5, 6, 7, and 8 are aspherical. Table 14 below shows the data for the aspherical surfaces, i.e., the conic constant K and the values ​​of each of the aspherical constants A4 to A12.

[0107] (Table 14) [Aspherical data] Front page K= 2.7110 A4 =-1.01182E-04 A6 =-1.33523E-06 A8 = 1.97743E-08 A10=-1.25195E-10 A12= 4.06080E-13 2nd side K=-2.9040 A4 =-1.58180E-04 A6 = 1.29335E-06 A8 =-1.01444E-08 A10= 4.38226E-11 A12= 0.00000E+00 3rd page K=-0.4456 A4 = 4.04109E-04 A6 = -4.62087E-06 A8 = 2.20818E-08 A10=-6.21510E-11 A12= 0.00000E+00 Side 4 K=-3.9080 A4 = 1.79698E-04 A6 =-1.03102E-06 A8 =-1.74072E-09 A10= 1.01196E-11 A12= 0.00000E+00 5th page K= 3.7707 A4 =-3.78236E-06 A6 = 1.16143E-06 A8 =-5.58959E-09 A10= 1.44702E-12 A12= 0.00000E+00 Side 6 K= 0.6581 A4 = 2.55240E-04 A6 =-5.27043E-07 A8 =-3.06199E-10 A10= 4.00895E-11 A12= 0.00000E+00 Side 7 K= 1.0000 A4 =-1.20441E-04 A6 = 1.18792E-06 A8 =-6.17544E-09 A10= 2.72498E-11 A12= 0.00000E+00 Side 8 K=-2.5146 A4 =-2.41805E-04 A6 = 2.45866E-06 A8 =-1.44853E-08 A10= 5.06379E-11 A12= 0.00000E+00

[0108] In this eyepiece optical system EL4, the axial air distance D1 between the object being observed and the first lens component G1, and the axial air distance D2 between the fourth lens component G4 and the eyepoint EP, change during diopter adjustment. Furthermore, the entrance pupil position EnP also changes as these distances change. Table 15 below shows the variable distances and entrance pupil positions for each diopter.

[0109] (Table 15) [Variable Interval Data] Diopter -1dpt +2dpt -4dpt D1 7.75 8.68 6.74 D2 20.60 19.67 21.61 EnP -28.77738 -30.14404 -27.47277

[0110] Table 16 below shows the values ​​corresponding to each conditional expression of this eyepiece optical system EL4.

[0111] (Table 16) f4 = 78.761 f12= ​​26.175 f23=-44.512 [Conditional expression corresponding value] (1) fe / f1=1.610 (2) fe / f12 = 0.674 (3)νd2=23.89 (4) fe / f4 = 0.224 (5)(G2R2-G3R1) / (G2R2+G3R1)= 0.074 (6)(G1R2+G1R1) / (G1R2-G1R1)=-0.364 (7)fe / EnP=-0.613 (8)fe / f23=-0.396 (9) D1 / f1=0.707 (10)TL / fe=1.659 (11)nd1=1.774 (12)nd2=1.636

[0112] In this way, the eyepiece optical system EL4 satisfies the above conditional expressions (1) to (11).

[0113] Diagrams of spherical aberration, astigmatism, distortion, and coma for this eyepiece optical system EL4 at the reference diopter (-1 dpt) are shown in Figure 8. These aberration diagrams show that this eyepiece optical system EL4 achieves good aberration correction within the diopter adjustment range.

[0114] [Fifth Example] 9 is a diagram showing the configuration of an eyepiece optical system EL5 according to Example 5. This eyepiece optical system EL5 is configured to include, in order from the observation object side, a first lens component G1 having positive refractive power, a second lens component G2 having negative refractive power, a third lens component G3 having positive refractive power, and a fourth lens component G4 having positive refractive power.

[0115] In this eyepiece optical system EL5, the first lens component G1 is composed of an aspherical positive lens L11 having a biconvex positive lens shape with aspherical surfaces facing the object and the eyepoint. The second lens component G2 is composed of an aspherical negative lens L12 having aspherical surfaces facing the object and the eyepoint and a negative meniscus lens shape with its concave surface facing the object. The third lens component G3 is composed of an aspherical positive lens L31 having aspherical surfaces facing the object and the eyepoint and a positive meniscus lens shape with its concave surface facing the object. The fourth lens component G4 is composed of an aspherical positive lens L41 having aspherical surfaces facing the object and the eyepoint and a positive meniscus lens shape with its concave surface facing the object.

[0116] The diopter adjustment in the eyepiece optical system EL5 is performed by moving the entire eyepiece optical system EL5 in the direction of the optical axis.

[0117] Table 17 below lists the specifications of the eyepiece optical system EL5.

[0118] (Table 17) Fifth Example [Overall specifications] fe = 18.132 H = 6.30 TL = 27.900 [Lens data] mrd nd νd Object surface ∞ D1 1* 18.12430 7.15 1.54392 55.90 2* -8.93740 2.70 3* -5.25010 2.10 1.63550 23.89 4* -15.01890 0.55 5* -24.00760 4.55 1.54392 55.90 6* -9.36770 0.55 7* -2317.28230 2.50 1.54392 55.90 8* -51.99250 D2 Image plane ∞

[0119] In this eyepiece optical system EL5, surfaces 1, 2, 3, 4, 5, 6, 7, and 8 are aspherical. Table 18 below shows the data for the aspherical surfaces, i.e., the conic constant K and the values ​​of each of the aspherical constants A4 to A12.

[0120] (Table 18) [Aspherical data] Front page K= 1.5721 A4 =-1.48925E-04 A6 =-2.27684E-06 A8 = 2.76091E-08 A10=-7.95927E-11 A12= 1.93700E-15 2nd side K=-2.1582 A4 =-2.07700E-04 A6 = 1.44079E-06 A8 =-1.32371E-08 A10= 7.80799E-11 A12= 0.00000E+00 3rd page K=-0.3642 A4 = 4.11218E-04 A6 = -4.53688E-06 A8 = 1.52134E-08 A10=-5.51553E-11 A12= 0.00000E+00 Side 4 K=-2.1105 A4 = 1.75549E-04 A6 =-6.55035E-07 A8 =-1.17880E-09 A10=-1.10549E-11 A12= 0.00000E+00 5th page K=-2.6173 A4 = 3.84318E-05 A6 = 5.26426E-07 A8 =-3.63630E-09 A10= 1.31408E-11 A12= 0.00000E+00 Side 6 K= 0.5270 A4 = 3.06334E-04 A6 =-1.20258E-06 A8 =-2.58312E-09 A10= 7.29168E-11 A12= 0.00000E+00 Side 7 K= 1.0000 A4 =-1.44498E-04 A6 = 6.56846E-07 A8 = 4.58887E-09 A10=-2.74632E-11 A12= 0.00000E+00 Side 8 K= 3.4680 A4 =-2.80056E-04 A6 = 2.69450E-06 A8 =-1.10674E-08 A10= 1.88829E-11 A12= 0.00000E+00

[0121] In this eyepiece optical system EL5, the axial air distance D1 between the object being observed and the first lens component G1, and the axial air distance D2 between the fourth lens component G4 and the eyepoint EP, change during diopter adjustment. Furthermore, the entrance pupil position EnP also changes as these distances change. Table 19 below shows the variable distances and entrance pupil positions for each diopter.

[0122] (Table 19) [Variable Interval Data] Diopter -1dpt +2dpt -4dpt D1 7.80 8.78 6.74 D2 20.70 19.72 21.76 EnP -34.42818 -36.66472 -32.37294

[0123] Table 20 below shows the values ​​corresponding to each conditional expression of this eyepiece optical system EL5.

[0124] (Table 20) f4 = 97.744 f12= ​​31.386 f23=-77.761 [Conditional expression corresponding value] (1) fe / f1=1.494 (2) fe / f12 = 0.578 (3)νd2=23.89 (4) fe / f4 = 0.186 (5)(G2R2-G3R1) / (G2R2+G3R1)=-0.230 (6)(G1R2+G1R1) / (G1R2-G1R1)=-0.339 (7)fe / EnP=-0.527 (8)fe / f23=-0.233 (9) D1 / f1=0.643 (10)TL / fe=1.539 (11)nd1=1.544 (12)nd2=1.636

[0125] In this way, the eyepiece optical system EL5 satisfies the above conditional expressions (1) to (10).

[0126] Diagrams of spherical aberration, astigmatism, distortion, and coma for this eyepiece optical system EL5 at the reference diopter (-1 dpt) are shown in Figure 10. These aberration diagrams show that this eyepiece optical system EL5 achieves good aberration correction within the diopter adjustment range.

[0127] [Sixth Example] 11 is a diagram showing the configuration of an eyepiece optical system EL6 according to Example 6. This eyepiece optical system EL6 is configured to include, in order from the observation object side, a first lens component G1 having positive refractive power, a second lens component G2 having negative refractive power, a third lens component G3 having positive refractive power, and a fourth lens component G4 having positive refractive power.

[0128] In this eyepiece optical system EL6, the first lens component G1 is composed of an aspherical positive lens L11 having a biconvex positive lens shape with aspherical surfaces on the observation object side and the eyepoint side. The second lens component G2 is composed of an aspherical negative lens L12 having a negative meniscus lens shape with aspherical surfaces on the observation object side and the eyepoint side, and a concave surface facing the observation object side. The third lens component G3 is composed of an aspherical positive lens L31 having a positive meniscus lens shape with aspherical surfaces on the observation object side and the eyepoint side, and a concave surface facing the observation object side. The fourth lens component G4 is composed of an aspherical positive lens L41 having a biconvex positive lens shape with aspherical surfaces on the observation object side and the eyepoint side.

[0129] The diopter adjustment in the eyepiece optical system EL6 is performed by moving the entire eyepiece optical system EL6 in the direction of the optical axis.

[0130] Table 21 below lists the specifications of the eyepiece optical system EL6.

[0131] (Table 21) Sixth Example [Overall specifications] fe = 18.123 H = 6.30 TL = 28.139 [Lens data] mrd nd νd Object surface ∞ D1 1* 16.56700 7.54 1.53110 55.91 2* -8.36450 2.40 3* -5.15230 2.11 1.63550 23.89 4* -15.20140 0.72 5* -23.94520 4.46 1.53110 55.91 6* -9.83340 0.50 7* 153.86920 2.57 1.53110 55.91 8* -57.12010 D2 Image plane ∞

[0132] In this eyepiece optical system EL6, surfaces 1, 2, 3, 4, 5, 6, 7, and 8 are aspherical. Table 22 below shows the data for the aspherical surfaces, i.e., the conic constant K and the values ​​of each of the aspherical constants A4 to A12.

[0133] (Table 22) [Aspherical data] Front page K= 0.7228 A4 =-1.63997E-04 A6 =-2.61921E-06 A8 = 3.31813E-08 A10=-1.23005E-10 A12= 1.44200E-13 2nd side K=-2.0402 A4 =-2.39241E-04 A6 = 1.88690E-06 A8 =-1.74329E-08 A10= 7.72117E-11 A12= 0.00000E+00 3rd page K=-0.4513 A4 = 4.08176E-04 A6 = -4.24658E-06 A8 = 1.05383E-08 A10=-4.81073E-11 A12= 0.00000E+00 Side 4 K=-2.0834 A4 = 1.95661E-04 A6 =-5.64298E-07 A8 =-2.58247E-09 A10=-1.66041E-11 A12= 0.00000E+00 5th page K=-3.9899 A4 = 7.61468E-06 A6 = 4.89100E-07 A8 = 5.08311E-10 A10=-5.69059E-12 A12= 0.00000E+00 Side 6 K= 0.4497 A4 = 2.70507E-04 A6 =-1.61737E-06 A8 =-1.10795E-09 A10= 7.33076E-11 A12= 0.00000E+00 Side 7 K=-4.0000 A4 =-1.50783E-04 A6 = 6.32142E-07 A8 = 8.23469E-09 A10=-5.41717E-11 A12= 0.00000E+00 Side 8 K= 4.7540 A4 =-2.61403E-04 A6 = 2.68176E-06 A8 =-9.54981E-09 A10= 4.35054E-12 A12= 0.00000E+00

[0134] In this eyepiece optical system EL6, the axial air distance D1 between the object being observed and the first lens component G1, and the axial air distance D2 between the fourth lens component G4 and the eyepoint EP, change during diopter adjustment. Furthermore, the entrance pupil position EnP also changes as these distances change. Table 23 below shows the variable distances and entrance pupil positions for each diopter.

[0135] (Table 23) [Variable Interval Data] Diopter -1dpt +2dpt -4dpt D1 7.84 8.82 6.78 D2 20.60 19.62 21.66 EnP -34.03960 -36.20254 -32.04697

[0136] Table 24 below shows the values ​​corresponding to each conditional expression of this eyepiece optical system EL6.

[0137] (Table 24) f4 = 78.767 f12= ​​30.113 f23=-49.345 [Conditional expression corresponding value] (1) fe / f1=1.550 (2) fe / f12 = 0.602 (3)νd2=23.89 (4) fe / f4 = 0.230 (5)(G2R2-G3R1) / (G2R2+G3R1)=-0.223 (6)(G1R2+G1R1) / (G1R2-G1R1)=-0.329 (7)fe / EnP=-0.532 (8)fe / f23=-0.367 (9) D1 / f1=0.671 (10)TL / fe=1.553 (11)nd1=1.531 (12)nd2=1.636

[0138] In this way, the eyepiece optical system EL6 satisfies the above conditional expressions (1) to (10).

[0139] Diagrams of spherical aberration, astigmatism, distortion, and coma for this eyepiece optical system EL6 at the reference diopter (-1 dpt) are shown in Figure 12. These aberration diagrams show that this eyepiece optical system EL6 achieves good aberration correction within the diopter adjustment range.

[0140] [Seventh Example] 13 is a diagram showing the configuration of an eyepiece optical system EL7 according to Example 7. This eyepiece optical system EL7 is configured to include, in order from the observation object side, a first lens component G1 having positive refractive power, a second lens component G2 having negative refractive power, a third lens component G3 having positive refractive power, and a fourth lens component G4 having positive refractive power.

[0141] In this eyepiece optical system EL7, the first lens component G1 is composed of an aspherical positive lens L11 having a biconvex positive lens shape with aspherical surfaces on the observation object side and the eyepoint side. The second lens component G2 is composed of an aspherical negative lens L12 having an aspherical surface on the observation object side and a negative meniscus lens shape with its concave surface facing the observation object side. The third lens component G3 is composed of an aspherical positive lens L31 having an aspherical surface on the eyepoint side and a positive meniscus lens shape with its concave surface facing the observation object side. The fourth lens component G4 is composed of an aspherical positive lens L41 having an aspherical surface on the observation object side and the eyepoint side with its aspherical surface facing the observation object side.

[0142] The diopter adjustment in the eyepiece optical system EL7 is performed by moving the entire eyepiece optical system EL7 in the direction of the optical axis.

[0143] Table 25 below lists the specifications of the eyepiece optical system EL7.

[0144] (Table 25) Seventh Example [Overall specifications] fe = 17.662 H = 6.30 TL = 28.320 [Lens data] mrd nd νd Object surface ∞ D1 1* 28.07266 7.30 1.74400 44.80 2* -10.67758 2.70 3* -6.63855 1.55 1.63550 23.89 4 -144.14719 1.00 5 -167.66045 5.95 1.53110 55.91 6* -11.29042 0.50 7* 1712.67070 2.70 1.53110 55.91 8* -31.84183 D2 Image plane ∞

[0145] In this eyepiece optical system EL7, surfaces 1, 2, 3, 6, 7, and 8 are aspherical. Table 26 below shows the data for the aspherical surfaces, i.e., the conic constant K and the values ​​of each of the aspherical constants A4 to A12.

[0146] (Table 26) [Aspherical data] Front page K=-2.0140 A4 =-1.26801E-04 A6 =-7.92018E-07 A8 = 1.72033E-08 A10=-1.32394E-10 A12= 5.48090E-13 2nd side K=-2.1884 A4 =-1.51405E-04 A6 = 8.63584E-07 A8 =-7.98722E-09 A10= 2.78537E-11 A12= 0.00000E+00 3rd page K=-0.1010 A4 = 3.80395E-04 A6 = -4.01258E-06 A8 = 2.22431E-08 A10=-1.81820E-10 A12= 0.00000E+00 Side 6 K= 0.6429 A4 = 2.44680E-04 A6 =-7.34170E-07 A8 =-4.17875E-09 A10= 2.11837E-11 A12= 0.00000E+00 Side 7 K= 1.0000 A4 =-1.23377E-04 A6 = 1.23089E-06 A8 =-5.34263E-09 A10= 3.90858E-11 A12= 0.00000E+00 Side 8 K=-0.0905 A4 =-2.34359E-04 A6 = 2.48218E-06 A8 =-1.41661E-08 A10= 7.75465E-11 A12= 0.00000E+00

[0147] In this eyepiece optical system EL7, the axial air distance D1 between the object being observed and the first lens component G1, and the axial air distance D2 between the fourth lens component G4 and the eyepoint EP, change during diopter adjustment. Furthermore, the entrance pupil position EnP also changes as these distances change. Table 27 below shows the variable distances and entrance pupil positions for each diopter.

[0148] (Table 27) [Variable Interval Data] Diopter -1dpt +2dpt -4dpt D1 6.62 7.55 5.61 D2 20.10 19.17 21.11 EnP -30.15672 -31.88364 -28.53315

[0149] Table 28 below shows the values ​​corresponding to each conditional expression of this eyepiece optical system EL7.

[0150] (Table 28) f4 = 58.892 f12= ​​34.529 f23=-45.926 [Conditional expression corresponding value] (1) fe / f1=1.562 (2) fe / f12 = 0.512 (3)νd2=23.89 (4) fe / f4 = 0.300 (5)(G2R2-G3R1) / (G2R2+G3R1)=-0.075 (6)(G1R2+G1R1) / (G1R2-G1R1)=-0.449 (7)fe / EnP=-0.586 (8)fe / f23=-0.385 (9) D1 / f1=0.586 (10)TL / fe=1.603 (11)nd1=1.744 (12)nd2=1.636

[0151] In this way, the eyepiece optical system EL7 satisfies the above conditional expressions (1) to (11).

[0152] Diagrams of spherical aberration, astigmatism, distortion, and coma for this eyepiece optical system EL7 at the reference diopter (-1 dpt) are shown in Figure 14. These aberration diagrams show that this eyepiece optical system EL7 achieves good aberration correction within the diopter adjustment range.

[0153] [Eighth Example] 15 is a diagram showing the configuration of an eyepiece optical system EL8 according to Example 8. This eyepiece optical system EL8 is configured to include, in order from the observation object side, a first lens component G1 having positive refractive power, a second lens component G2 having negative refractive power, a third lens component G3 having positive refractive power, and a fourth lens component G4 having positive refractive power.

[0154] In this eyepiece optical system EL8, the first lens component G1 is a cemented lens formed by cementing together an aspherical positive lens L11 having a biconvex positive lens shape with an aspherical lens surface facing the object of observation and an aspherical positive lens L12 having a positive meniscus lens shape with an aspherical lens surface facing the eyepoint and a concave surface facing the object of observation. The second lens component G2 is an aspherical negative lens L12 having a negative meniscus lens shape with an aspherical lens surface facing the object of observation and a concave surface facing the object of observation. The third lens component G3 is an aspherical positive lens L31 having a positive meniscus lens shape with an aspherical lens surface facing the eyepoint and a concave surface facing the object of observation. The fourth lens component G4 is an aspherical positive lens L41 having a positive meniscus lens shape with an aspherical lens surface facing the object of observation and an aspherical lens surface facing the object of observation and the eyepoint.

[0155] The diopter adjustment in the eyepiece optical system EL8 is performed by moving the entire eyepiece optical system EL8 in the direction of the optical axis.

[0156] Table 29 below lists the specifications of the eyepiece optical system EL8.

[0157] Table 29: Example 8 [Overall specifications] fe = 17.671 H = 6.30 TL = 28.340 [Lens data] mrd nd νd Object surface ∞ D1 1* 36.28535 1.50 1.75520 27.57 2 -256.85195 5.55 1.74400 44.80 3* -9.58387 2.70 4* -6.33627 1.60 1.63550 23.89 5 -309.22499 1.00 6 -340.41004 5.95 1.53110 55.91 7* -10.20313 0.50 8* -118.11140 2.70 1.53110 55.91 9* -33.13998 D2 Image plane ∞

[0158] In this eyepiece optical system EL8, surfaces 1, 3, 4, 7, 8, and 9 are aspherical. Table 30 below shows the data for the aspherical surfaces, i.e., the conic constant K and the values ​​of each of the aspherical constants A4 to A12.

[0159] (Table 30) [Aspherical data] Front page K=-2.0658 A4 =-1.42501E-04 A6 =-8.76658E-07 A8 = 1.88394E-08 A10=-1.09268E-10 A12= 3.68460E-13 3rd page K=-1.7532 A4 =-1.52859E-04 A6 = 8.23715E-07 A8 =-8.45101E-09 A10= 3.67563E-11 A12= 0.00000E+00 Side 4 K=-0.2498 A4 = 3.64026E-04 A6 = -4.01765E-06 A8 = 2.07275E-08 A10=-1.61058E-10 A12= 0.00000E+00 Side 7 K= 0.5740 A4 = 2.54149E-04 A6 =-6.32718E-07 A8 =-3.76424E-09 A10= 2.73994E-11 A12= 0.00000E+00 Side 8 K= 1.0000 A4 =-1.19587E-04 A6 = 1.18521E-06 A8 =-5.01478E-09 A10= 4.10280E-11 A12= 0.00000E+00 9th page K= 1.4393 A4 =-2.39375E-04 A6 = 2.51700E-06 A8 =-1.48286E-08 A10= 7.54336E-11 A12= 0.00000E+00

[0160] In this eyepiece optical system EL8, the axial air distance D1 between the object being observed and the first lens component G1, and the axial air distance D2 between the fourth lens component G4 and the eyepoint EP, change during diopter adjustment. Furthermore, the entrance pupil position EnP also changes as these distances change. Table 31 below shows the variable distances and entrance pupil positions for each diopter.

[0161] (Table 31) [Variable Interval Data] Diopter -1dpt +2dpt -4dpt D1 6.84 7.77 5.83 D2 20.10 19.17 21.11 EnP -31.23485 -33.09550 -29.49620

[0162] Table 32 below shows the values ​​corresponding to each conditional expression of this eyepiece optical system EL8.

[0163] (Table 32) f4 = 85.790 f12= ​​37.994 f23=-57.363 [Conditional expression corresponding value] (1) fe / f1=1.625 (2) fe / f12 = 0.465 (3)νd2=23.89 (4) fe / f4 = 0.206 (5)(G2R2-G3R1) / (G2R2+G3R1)=-0.048 (6)(G1R2+G1R1) / (G1R2-G1R1)=-0.582 (7)fe / EnP=-0.566 (8)fe / f23=-0.308 (9) D1 / f1=0.629 (10)TL / fe=1.604 (11)nd1=1.755 (12)nd2=1.636

[0164] In this way, the eyepiece optical system EL8 satisfies the above conditional expressions (1) to (11).

[0165] Diagrams of spherical aberration, astigmatism, distortion, and coma for this eyepiece optical system EL8 at the reference diopter (-1 dpt) are shown in Figure 16. These aberration diagrams show that this eyepiece optical system EL8 achieves good aberration correction within the diopter adjustment range.

[0166] [Ninth Example] 17 is a diagram showing the configuration of an eyepiece optical system EL9 according to Example 9. This eyepiece optical system EL9 is configured to include, in order from the observation object side, a first lens component G1 having positive refractive power, a second lens component G2 having negative refractive power, a third lens component G3 having positive refractive power, and a fourth lens component G4 having positive refractive power.

[0167] In this eyepiece optical system EL9, the first lens component G1 is composed of an aspherical positive lens L11 having a biconvex positive lens shape with aspherical surfaces on the observation object side and the eyepoint side. The second lens component G2 is composed of an aspherical negative lens L12 having an aspherical surface on the observation object side and a negative meniscus lens shape with its concave surface facing the observation object side. The third lens component G3 is composed of an aspherical positive lens L31 having an aspherical surface on the eyepoint side and a positive meniscus lens shape with its concave surface facing the observation object side. The fourth lens component G4 is composed of an aspherical positive lens L41 having an aspherical surface on the observation object side and the eyepoint side and a positive meniscus lens shape with its concave surface facing the observation object side.

[0168] The diopter adjustment in the eyepiece optical system EL9 is performed by moving the entire eyepiece optical system EL9 in the direction of the optical axis.

[0169] Table 33 below lists the specifications of the eyepiece optical system EL9.

[0170] Table 33: 9th Example [Overall specifications] fe = 17.664 H = 6.30 TL = 28.440 [Lens data] mrd nd νd Object surface ∞ D1 1* 30.06223 7.30 1.74300 49.25 2* -10.46380 2.70 3* -6.62848 1.55 1.65093 21.51 4 -43.12860 1.00 5 -44.49530 5.95 1.53110 55.91 6* -10.78420 0.50 7* -1133.34000 2.70 1.53110 55.91 8* -34.07780 D2 Image plane ∞

[0171] In this eyepiece optical system EL9, surfaces 1, 2, 3, 6, 7, and 8 are aspherical. Table 34 below shows the aspherical surface data, i.e., the conic constant K and the values ​​of each of the aspherical constants A4 to A12.

[0172] (Table 34) [Aspherical data] Front page K=-1.3191 A4 =-1.08297E-04 A6 =-5.23642E-07 A8 = 1.65142E-08 A10=-1.39777E-10 A12= 5.22770E-13 2nd side K=-2.1775 A4 =-1.37725E-04 A6 = 9.31664E-07 A8 =-7.77285E-09 A10= 2.31975E-11 A12= 0.00000E+00 3rd page K=-0.0873 A4 = 3.71838E-04 A6 = -4.12160E-06 A8 = 2.25930E-08 A10=-1.98410E-10 A12= 0.00000E+00 Side 6 K= 0.6318 A4 = 2.37664E-04 A6 =-7.12383E-07 A8 =-4.02440E-09 A10= 2.46401E-11 A12= 0.00000E+00 Side 7 K= 1.0000 A4 =-1.19476E-04 A6 = 1.21154E-06 A8 =-5.10047E-09 A10= 4.12044E-11 A12= 0.00000E+00 Side 8 K=-0.6189 A4 =-2.32309E-04 A6 = 2.50741E-06 A8 =-1.40702E-08 A10= 7.88020E-11 A12= 0.00000E+00

[0173] In this eyepiece optical system EL9, the axial air distance D1 between the object being observed and the first lens component G1, and the axial air distance D2 between the fourth lens component G4 and the eyepoint EP, change during diopter adjustment. Furthermore, the entrance pupil position EnP also changes as these distances change. Table 35 below shows the variable distances and entrance pupil positions for each diopter.

[0174] (Table 35) [Variable Interval Data] Diopter -1dpt +2dpt -4dpt D1 6.74 7.67 5.73 D2 20.00 19.07 20.01 EnP -31.17085 -32.51888 -29.03853

[0175] Table 36 below shows the values ​​corresponding to each conditional expression of this eyepiece optical system EL9.

[0176] (Table 36) f4 = 66.097 f12= ​​29.977 f23=-51.032 [Conditional expression corresponding value] (1) fe / f1=1.561 (2)fe / f12=0.589 (3)νd2=21.51 (4) fe / f4=0.267 (5)(G2R2-G3R1) / (G2R2+G3R1)=-0.016 (6)(G1R2+G1R1) / (G1R2-G1R1)=-0.484 (7)fe / EnP=-0.567 (8)fe / f23=-0.346 (9) D1 / f1=0.596 (10)TL / fe=1.610 (11)nd1=1.743 (12)nd2=1.651

[0177] In this way, the eyepiece optical system EL9 satisfies the above conditional expressions (1) to (12).

[0178] Diagrams of spherical aberration, astigmatism, distortion, and coma for this eyepiece optical system EL9 at the reference diopter (-1 dpt) are shown in Figure 18. These aberration diagrams show that this eyepiece optical system EL9 achieves good aberration correction within the diopter adjustment range.

[0179] [Tenth Example] 19 is a diagram showing the configuration of an eyepiece optical system EL10 according to Example 10. This eyepiece optical system EL10 is configured to include, in order from the observation object side, a first lens component G1 having positive refractive power, a second lens component G2 having negative refractive power, a third lens component G3 having positive refractive power, and a fourth lens component G4 having positive refractive power.

[0180] In this eyepiece optical system EL10, the first lens component G1 is composed of an aspherical positive lens L11 having a biconvex positive lens shape with aspherical surfaces facing the object and the eyepoint. The second lens component G2 is composed of an aspherical negative lens L21 having aspherical surfaces facing the object and the eyepoint and a negative meniscus lens shape with its concave surface facing the object. The third lens component G3 is composed of an aspherical positive lens L31 having aspherical surfaces facing the object and the eyepoint and a positive meniscus lens shape with its concave surface facing the object. The fourth lens component G4 is composed of an aspherical positive lens L41 having aspherical surfaces facing the object and the eyepoint and a positive meniscus lens shape with its concave surface facing the object.

[0181] The diopter adjustment in the eyepiece optical system EL10 is performed by moving the entire eyepiece optical system EL10 in the direction of the optical axis.

[0182] Table 37 below lists the specifications of the eyepiece optical system EL10.

[0183] Table 37: 10th Example [Overall specifications] fe = 17.655 H = 6.30 TL = 28.870 [Lens data] mrd nd νd Object surface ∞ D1 1* 27.64520 7.35 1.74300 49.25 2* -10.59980 2.70 3* -6.62160 1.50 1.66133 20.35 4* -30.41490 1.00 5* -33.42740 5.95 1.53110 55.91 6* -11.06910 0.50 7* -447.12000 2.70 1.53110 55.91 8* -33.61500 D2 Image plane ∞

[0184] In this eyepiece optical system EL10, surfaces 1, 2, 3, 4, 5, 6, 7, and 8 are aspherical. Table 38 below shows the data for the aspherical surfaces, i.e., the conic constant K and the values ​​of each of the aspherical constants A4 to A12.

[0185] (Table 38) [Aspherical data] Front page K= 1.8706 A4 =-1.58806E-04 A6 =-6.47977E-07 A8 = 2.00513E-08 A10=-1.19924E-10 A12= 3.39780E-13 2nd side K=-2.5122 A4 =-1.82235E-04 A6 = 1.26664E-06 A8 =-9.55146E-09 A10= 4.41287E-11 A12= 0.00000E+00 3rd page K=-0.1010 A4 = 3.59553E-04 A6 = -3.81376E-06 A8 = 2.31702E-08 A10=-1.65901E-10 A12= 0.00000E+00 Side 4 K= 1.2085 A4 = 9.08220E-06 A6 = 4.92684E-09 A8 = 2.99069E-11 A10= 0.00000E+00 A12= 0.00000E+00 5th page K=-0.6362 A4 = 2.08532E-05 A6 = 3.39041E-08 A8 =-4.09295E-10 A10= 0.00000E+00 A12= 0.00000E+00 Side 6 K= 0.5759 A4 = 2.44689E-04 A6 =-6.87340E-07 A8 =-4.20734E-09 A10= 2.20759E-11 A12= 0.00000E+00 Side 7 K= 1.0000 A4 =-1.28197E-04 A6 = 1.23524E-06 A8 =-5.32987E-09 A10= 3.98596E-11 A12= 0.00000E+00 Side 8 K= 0.3803 A4 =-2.29306E-04 A6 = 2.47452E-06 A8 =-1.42769E-08 A10= 7.86334E-11 A12= 0.00000E+00

[0186] In this eyepiece optical system EL10, the axial air distance D1 between the object being observed and the first lens component G1, and the axial air distance D2 between the fourth lens component G4 and the eyepoint EP, change during diopter adjustment. Furthermore, the entrance pupil position EnP also changes as these distances change. Table 39 below shows the variable distances and entrance pupil positions for each diopter.

[0187] (Table 39) [Variable Interval Data] Diopter -1dpt +2dpt -4dpt D1 7.17 8.10 6.16 D2 20.10 19.17 21.11 EnP -30.13523 -31.77608 -28.58721

[0188] Table 40 below shows the values ​​corresponding to each conditional expression of this eyepiece optical system EL10.

[0189] (Table 40) f4 = 68.284 f12= ​​26.280 f23=-47.435 [Conditional expression corresponding value] (1) fe / f1=1.572 (2) fe / f12 = 0.672 (3)νd2=20.35 (4) fe / f4=0.259 (5)(G2R2-G3R1) / (G2R2+G3R1)=-0.047 (6)(G1R2+G1R1) / (G1R2-G1R1)=-0.446 (7)fe / EnP=-0.586 (8)fe / f23=-0.372 (9) D1 / f1=0.638 (10)TL / fe=1.635 (11)nd1=1.743 (12)nd2=1.661

[0190] In this way, the eyepiece optical system EL10 satisfies the above conditional expressions (1) to (12).

[0191] Diagrams of spherical aberration, astigmatism, distortion, and coma for this eyepiece optical system EL10 at the reference diopter (-1 dpt) are shown in Figure 20. These aberration diagrams show that this eyepiece optical system EL10 achieves good aberration correction within the diopter adjustment range.

[0192] [Eleventh Example] 21 is a diagram showing the configuration of an eyepiece optical system EL11 according to Example 11. This eyepiece optical system EL11 is configured to include, in order from the observation object side, a first lens component G1 having positive refractive power, a second lens component G2 having negative refractive power, a third lens component G3 having positive refractive power, and a fourth lens component G4 having positive refractive power.

[0193] In this eyepiece optical system EL11, the first lens component G1 is composed of an aspherical positive lens L11 with a biconvex positive lens shape whose lens surface facing the object of observation is aspherical. The second lens component G2 is composed of a cemented lens formed by cementing together an aspherical negative lens L21 with a biconcave negative lens shape whose lens surface facing the object of observation is aspherical and an aspherical positive lens L22 with a biconvex positive lens shape whose lens surface facing the eyepoint is aspherical. The third lens component G3 is composed of an aspherical positive lens L31 with a positive meniscus lens shape whose lens surface facing the eyepoint is aspherical and whose concave surface faces the object of observation. The fourth lens component G4 is composed of an aspherical positive lens L41 with a positive meniscus lens shape whose lens surfaces facing the object of observation and the eyepoint are aspherical and whose concave surface faces the object of observation.

[0194] The diopter adjustment in the eyepiece optical system EL11 is performed by moving the entire eyepiece optical system EL11 in the direction of the optical axis.

[0195] Table 41 below lists the specifications of the eyepiece optical system EL11.

[0196] Table 41: 11th Example [Overall specifications] fe = 17.623 H = 6.30 TL = 30.240 [Lens data] mrd nd νd Object surface ∞ D1 1* 28.78836 7.35 1.82098 42.50 2 -11.25246 2.70 3* -7.11620 1.50 1.63550 23.89 4 564.01019 1.48 1.53110 55.91 5* -165.33547 1.00 6 -397.01843 5.95 1.53110 55.91 7* -11.70908 0.5 8* -87.51711 2.70 1.53110 55.91 9* -33.70935 D2 Image plane ∞

[0197] In this eyepiece optical system EL11, surfaces 1, 3, 5, 7, 8, and 9 are aspherical. Table 42 below shows the data for the aspherical surfaces, i.e., the conic constant K and the values ​​of each of the aspherical constants A4 to A12.

[0198] (Table 42) [Aspherical data] Front page K= 4.9064 A4 =-1.05219E-04 A6 =-6.21990E-07 A8 = 1.81446E-08 A10=-1.14918E-10 A12= 3.47790E-13 3rd page K=-2.7141 A4 =-1.22865E-04 A6 = 1.06684E-06 A8 =-6.77704E-09 A10= 4.48572E-11 A12= 0.00000E+00 5th page K=-0.1268 A4 = 3.96618E-04 A6 = -3.89261E-06 A8 = 2.32375E-08 A10=-1.45358E-10 A12= 0.00000E+00 Side 7 K= 0.5892 A4 = 2.52841E-04 A6 =-6.99186E-07 A8 =-4.09567E-09 A10= 2.38163E-11 A12= 0.00000E+00 Side 8 K= 1.0000 A4 =-1.15871E-04 A6 = 1.20055E-06 A8 =-5.20908E-09 A10= 4.32497E-11 A12= 0.00000E+00 9th page K= 2.7036 A4 =-2.43083E-04 A6 = 2.51325E-06 A8 =-1.39088E-08 A10= 7.50477E-11 A12= 0.00000E+00

[0199] In this eyepiece optical system EL11, the axial air distance D1 between the object being observed and the first lens component G1, and the axial air distance D2 between the fourth lens component G4 and the eyepoint EP, change during diopter adjustment. Furthermore, the entrance pupil position EnP also changes as these distances change. Table 43 below shows the variable distances and entrance pupil positions for each diopter.

[0200] (Table 43) [Variable Interval Data] Diopter -1dpt +2dpt -4dpt D1 7.06 7.98 6.04 D2 20.10 19.18 21.12 EnP -27.40929 -28.67303 -26.17269

[0201] Table 44 below shows the values ​​corresponding to each conditional expression of this eyepiece optical system EL11.

[0202] (Table 44) f4 =101.468 f12= ​​26.176 f23=-66.090 [Conditional expression corresponding value] (1) fe / f1=1.640 (2) fe / f12 = 0.673 (3)νd2=23.89 (4) fe / f4 = 0.174 (5)(G2R2-G3R1) / (G2R2+G3R1)=-0.412 (6)(G1R2+G1R1) / (G1R2-G1R1)=-0.438 (7)fe / EnP=-0.643 (8)fe / f23=-0.267 (9) D1 / f1=0.657 (10)TL / fe=1.716 (11)nd1=1.821 (12)nd2=1.636

[0203] In this way, the eyepiece optical system EL11 satisfies the above conditional expressions (1) to (4) and (6) to (11).

[0204] Diagrams of spherical aberration, astigmatism, distortion, and coma for this eyepiece optical system EL11 at the reference diopter (-1 dpt) are shown in Figure 22. These aberration diagrams show that this eyepiece optical system EL11 achieves good aberration correction within the diopter adjustment range.

[0205] The following contents can be appropriately adopted within the scope that does not impair the optical performance.

[0206] In this embodiment, a configuration with four lens components is shown as a numerical example of the eyepiece optical system EL, but other lens configurations, such as five lens components, are also applicable. Also, a configuration in which a lens component is added closest to the object side, or a configuration in which a lens component is added closest to the eyepoint side, may be used.

[0207] Alternatively, a single or multiple lens components may be moved so as to have a displacement component perpendicular to the optical axis, or rotated (oscillated) in a plane including the optical axis to form an image stabilization lens group that corrects image blur caused by camera shake. It is particularly preferable to use the third lens component G3 as an image stabilization lens group.

[0208] The lens surfaces of the lenses (lens components, lens elements) constituting the eyepiece optical system EL 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 the surface of glass is formed into an aspherical shape. The lens surface may also be a diffractive surface, and the lens may be a gradient index lens (GRIN lens) or a plastic lens.

[0209] In addition, the lens surfaces of the lenses (lens components, lens elements) that make up the eyepiece optical system EL 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.

[0210] In addition, the eyepiece optical system EL of this embodiment has been described as being configured such that the first lens component G1, the second lens component G2, the third lens component G3, and the fourth lens component G4 move integrally, or the entire eyepiece optical system EL moves integrally, but it may also be configured such that the lens component closest to the eyepoint is fixed and the entire lens component closer to the observation object than that lens component moves integrally, or at least some of the first lens component G1, the second lens component G2, the third lens component G3, and the fourth lens component G4 move. It is particularly preferable to move the first lens component G1 and keep the positions of the other lens components fixed relative to the image plane during diopter adjustment. It is preferable that the diopter-adjusting lens group be composed of a single lens. [Explanation of symbols]

[0211] EL (EL1~EL11) eyepiece optical system G1 First lens component G2 Second lens component G3 Third lens element G4 Fourth lens element 1. Camera (optical equipment)

Claims

[Claim 1] Starting from the observation object side, a first lens having a positive refractive power; a second lens having a negative refractive power and a meniscus lens shape with a concave surface facing the observation object side; a third lens having a positive refractive power; a fourth lens having a meniscus lens shape with a concave surface facing the observation object side and having a positive refractive power, and An eyepiece optical system that satisfies the following condition: 1.38 < fe / f1 < 1.65 1.600 < nd1 < 1.800 however, fe: focal length of the entire eyepiece optical system f1: focal length of the first lens nd1: refractive index of the medium of the first lens with respect to the d line

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