JP2022132633A - Eyepiece optical system and observation device having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an eyepiece optical system that is easily manufactured and facilitates an observation in a large view field, while well suppressing various aberrations and ensuring high optical performance.

SOLUTION: The eyepiece optical system is to be used for an observation of an image displayed on an image display screen, and the system is constituted by, successively arranged from the image display screen side to an observation side, a first lens having a positive refractive power, a second lens having a negative refractive power, a third lens, and a fourth lens having positive refractive power. An average value Nda of refractive indices of the lens materials for the first lens to the fourth lens with respect to d-line, a radius of curvature L1R2 of a lens surface on the observation side of the first lens, a radius of curvature L2R1 of a lens surface on the image display screen side of the second lens, a composite focal distance f34 of the third lens and the fourth lens, and a focal distance f of the eyepiece optical system are each appropriately set.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2022,JPO&INPIT

Description

The present invention relates to an eyepiece optical system and an observation device having the same, and is used for observing an image displayed on an image display surface of an image display element in an electronic viewfinder used in, for example, a video camera, a still camera, or a broadcasting camera. is preferred.

Conventionally, in an electronic viewfinder (observation device) used in an imaging device (camera) such as a video camera or a still camera, an ocular optical system is used for magnifying and observing an image displayed on a liquid crystal screen or the like. . In the electronic viewfinder, it is necessary to have a high observation magnification and a long eye relief in order to make the image display surface easy to see.

Furthermore, due to the demand for miniaturization of the observation device, the image display element used in the observation device is required to have a small dimension (for example, 20 mm or less in diagonal length).

Conventionally, various eyepiece optical systems with high observation magnification have been proposed (Patent Documents 1 to 3).

In Patent Document 1, from the image display element side to the observation side, a first lens with positive refractive power, a second lens with negative refractive power, a third lens with positive or negative refractive power, and a lens with positive refractive power. An eyepiece optical system comprising a fourth lens is disclosed.

In Patent Document 1, at least two lenses with positive refractive power, at least one lens with negative refractive power, and a diffractive optical element are used to satisfactorily correct various aberrations while miniaturizing the entire system. is used.

Further, Patent Document 2 discloses an endoscope eyepiece composed of a lens group with a negative refractive power and a lens group with a positive refractive surface.

Further, in Patent Document 3, in order from the image display element side to the observation side, a biconvex first lens with a positive refractive power, a second lens with a negative refractive power, a third lens with a positive refractive power, It discloses an eyepiece optical system consisting of a fourth lens of positive refractive power. Patent Document 3 discloses an eyepiece optical system in which various aberrations are satisfactorily corrected while having a high observation magnification.

JP 2001-066522 A JP-A-05-313073 JP 2015-075713 A

In an eyepiece optical system used in an observation device, it is important to appropriately set the lens configuration of the eyepiece optical system and the refractive power of each lens in order to ensure a high observation magnification and a long eye relief. . In addition, when using a small image display surface, it is important to appropriately set the ratio of the refractive power of the eyepiece optical system to the size of the image display surface.

An eyepiece for an image display device disclosed in Patent Document 1 uses a curved panel, a diffractive optical element, and a high refractive index material to correct various aberrations while ensuring a high observation magnification. Therefore, although it is easy to ensure optical performance and specifications, manufacturing tends to be difficult.

The endoscope eyepiece disclosed in Patent Document 2 uses a lens made of a high refractive index material and an aspherical lens to reduce the number of lenses and ensure a high observation magnification. However, since many materials with a high refractive index are used, it tends to be difficult to manufacture.

The eyepiece optical system disclosed in Patent Document 3 uses a material with a relatively low refractive index to ensure a high observation magnification. However, in order to increase the magnification, the curvature of the first lens surface and the second lens surface, which bounce the light rays, becomes sharper, and the light rays are shaped to change abruptly. For this reason, curvature of field tends to occur.

In addition, since many aspherical surfaces are used to facilitate correction of various aberrations, manufacturing tends to be complicated.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an eyepiece optical system that is easy to manufacture and that facilitates observation of a wide field of view while suppressing various aberrations satisfactorily and ensuring high optical performance.

An eyepiece optical system of the present invention is an eyepiece optical system for observing an image displayed on an image display surface, and is arranged in order from the image display surface side to the observation side, a first lens having a positive refractive power, It consists of a second lens, a third lens, and a fourth lens, each of which has a negative refractive power and a positive refractive power. , the radius of curvature of the observation side lens surface of the first lens is L1R2, the curvature radius of the lens surface of the second lens on the image display side side is L2R1, and the combined focal length of the third lens and the fourth lens is f34. , when the focal length of the eyepiece optical system is f,
1.600≦Nda≦1.730
-15.0 ≤ (L2R1 + L1R2) / (L2R1 - L1R2) ≤ 0.0
0.68≤f34/f≤1.30
It is characterized by satisfying the following conditional expression.

According to the present invention, it is possible to obtain an eyepiece optical system that is easy to manufacture and that facilitates wide-field observation while suppressing various aberrations satisfactorily and ensuring high optical performance.

1 is a cross-sectional view showing the lens configuration of an eyepiece optical system according to Example 1 of the present invention; Aberration diagrams of the eyepiece optical system according to Example 1 of the present invention FIG. 2 is a sectional view showing the lens configuration of an eyepiece optical system according to Reference Example 1 of the present invention; Aberration diagrams of the eyepiece optical system according to Reference Example 1 of the present invention Sectional view showing the lens configuration of the eyepiece optical system according to Reference Example 2 of the present invention. Aberration diagrams of the eyepiece optical system according to Reference Example 2 of the present invention Sectional view showing the lens configuration of an eyepiece optical system according to Reference Example 3 of the present invention. Aberration diagrams of the eyepiece optical system according to Reference Example 3 of the present invention A cross-sectional view showing the lens configuration of an eyepiece optical system according to Reference Example 4 of the present invention. Aberration diagrams of the eyepiece optical system according to Reference Example 4 of the present invention FIG. 2 is a cross-sectional view showing the lens configuration of an eyepiece optical system according to Example 2 of the present invention; Aberration diagrams of the eyepiece optical system according to Example 2 of the present invention

An eyepiece optical system of the present invention and an observation apparatus having the same will be described below. An eyepiece optical system of the present invention is an eyepiece optical system for observing an image displayed on an image display surface. The eyepiece optical system is composed of a first lens with positive refractive power, a second lens with negative refractive power, a third lens, and a fourth lens with positive refractive power, which are arranged in order from the image display side to the observation side. ing.

FIG. 1 is a lens sectional view of Example 1 of the eyepiece optical system of the present invention. FIG. 2 is an aberration diagram of Example 1 of the eyepiece optical system of the present invention when the diopter is -1.0 diopter (standard diopter).

FIG. 3 is a lens sectional view of Reference Example 1 of the eyepiece optical system of the present invention. FIG. 4 is an aberration chart of Reference Example 1 of the eyepiece optical system of the present invention when the diopter is -1.0 diopter.

FIG. 5 is a lens sectional view of Reference Example 2 of the eyepiece optical system of the present invention. FIG. 6 is an aberration diagram of Reference Example 2 of the eyepiece optical system of the present invention when the diopter is -1.0 diopter.

FIG. 7 is a lens sectional view of Reference Example 3 of the eyepiece optical system of the present invention. FIG. 8 is an aberration diagram of Reference Example 3 of the eyepiece optical system of the present invention when the diopter is -1.0 diopter.

FIG. 9 is a lens sectional view of Reference Example 4 of the eyepiece optical system of the present invention. FIG. 10 is an aberration diagram of Reference Example 4 of the eyepiece optical system of the present invention when the diopter is -1.0 diopter.

FIG. 11 is a lens sectional view of Example 2 of the eyepiece optical system of the present invention. FIG. 12 is an aberration diagram of Example 2 of the eyepiece optical system of the present invention when the diopter is -1.0 diopter.

The eyepiece optical system of each embodiment is used in an electronic viewfinder (observation device) of an imaging device such as a digital camera or a video camera. In the sectional view of the lens, the left side is the image display surface side, and the right side is the observation side (exit pupil side). In the lens sectional view, L0 is an eyepiece optical system. Li is the i-th lens. IP is an image display surface of an image display element made of liquid crystal, organic EL, or the like. EP is an observation plane (eyepoint) (exit pupil) for observation. CG1 is a cover glass.

In the spherical aberration diagrams among the aberration diagrams, the solid line d indicates the d-line (wavelength 587.6 nm), and the dotted line F indicates the F-line (wavelength 486.1 nm). In the astigmatism diagrams, ΔSd indicates a sagittal image plane for the d-line, and ΔMd indicates a meridional image plane for the d-line. ΔSF indicates the sagittal image plane of the F-line, and ΔMF indicates the meridional image plane of the F-line. Distortion is shown for the d-line. Lateral chromatic aberration is shown for the F-line. H is half the diagonal length (maximum image height) of the image display surface. Numerical values are values when numerical data to be described later are expressed in units of mm.

In order to observe a small image display surface (display panel) with a diagonal length of about 20 mm or less on the image display device with a large observation field (viewing angle of about 30 degrees or more), the entire eyepiece optical system must have a strong positive angle. must have a refractive power (power) of For this purpose, each lens constituting the eyepiece optical system needs to have strong positive and negative refractive powers. As a result, field curvature and lateral chromatic aberration often increase, making it difficult to correct these aberrations.

Therefore, in the eyepiece optical system according to each embodiment, as shown in each lens cross-sectional view, it is composed of four lens groups in order from the image display plane IP side (object side) to the observation plane (eyepoint) EP side. there is Specifically, it comprises a first lens L1 with positive refractive power, a second lens L2 with negative refractive power, a third lens L3 with positive or negative refractive power, and a fourth lens L4 with positive refractive power. there is

In each embodiment, the observation plane EP may move in the optical axis direction as long as the light rays from the outermost periphery of the image display plane IP pass through the observer's pupil. Also, the eye relief is the distance from the final lens surface (the observation side surface of the fourth lens L4) to the observation plane EP. The cover glass is a plate that protects the image display surface IP and the lenses.

In the eyepiece L0 of the present invention, Nda is the average value of the refractive indices for the d-line of the materials of the first lens L1 to the fourth lens L4. Let L1R2 be the radius of curvature of the observation side lens surface of the first lens L1, and L2R1 be the radius of curvature of the image display surface side lens surface of the second lens L2. Assume that the combined focal length of the third lens L3 and the fourth lens L4 is f34. Let f be the focal length of the eyepiece optical system.

At this time,
1.520≦Nda≦1.730 (1)
−15.0≦(L2R1+L1R2)/(L2R1−L1R2)≦0.0 (2)
0.68≦f34/f≦1.30 (3)
satisfies the following conditional expression.

Next, the technical meaning of each of the above conditional expressions will be explained.

Conditional expression (1) defines the average value of the refractive index of the material of each lens of the first lens L1 to the fourth lens L4 at the d-line. If the refractive index of each lens material exceeds the upper limit of conditional expression (1), the power of the entire system can be increased, making it easier to obtain a high observation magnification (increase viewing angle). However, as a material with a high refractive index, for example, glass or the like must be used frequently, which makes manufacturing difficult. Further, when the refractive index of the material of each lens becomes lower than the lower limit, the refractive power of the entire system becomes weak, making it difficult to increase the viewing angle.

Conditional expression (2) defines the shape of the air lens formed between the first lens L1 and the second lens L2. Conditional expression (2) is for satisfactorily correcting curvature of field while maintaining a high observation magnification. In each embodiment, the light rays emitted from the first lens L1 are bounced up by the second lens L2 in order to obtain a high observation magnification. If the lower limit of conditional expression (2) is not reached, the light rays bend too sharply between the first lens L1 and the second lens L2, making it difficult to correct various aberrations, particularly curvature of field. When the upper limit is exceeded, the bounce of light rays becomes insufficient, making it difficult to obtain a high observation magnification.

Conditional expression (3) defines the combined focal length of the combined system composed of the third lens L3 and the fourth lens L4 and the focal length of the entire system. If the upper limit of conditional expression (3) is exceeded, the positive refracting power of the synthetic system becomes weak, making it difficult to obtain a high observation magnification. If the lower limit of conditional expression (3) is not reached, the positive refractive power of the composite system becomes strong, making it difficult to secure a sufficiently long eye relief and making it difficult to observe the image display surface satisfactorily. .

Preferably, the numerical ranges of conditional expressions (1) to (3) are set as follows.
1.550≦Nda≦1.730 (1a)
−12.0≦(L2R1+L1R2)/(L2R1−L1R2)≦0.0 (2a)
0.68≦f34/f≦1.25 (3a)

More preferably, the numerical ranges of conditional expressions (1a) to (3a) are set as follows.
1.550≦Nda≦1.700 (1b)
−10.0≦(L2R1+L1R2)/(L2R1−L1R2)≦0.0 (2b)
0.70≦f34/f≦1.25 (3b)

As described above, according to the present invention, it is possible to obtain an optimal eyepiece optical system for an electronic viewfinder having high observation magnification and high optical performance.

More preferably, in each embodiment, one or more of the following conditional expressions should be satisfied. Let d3 be the distance on the optical axis between the first lens L1 and the second lens L2, and d5 be the distance on the optical axis between the second lens group L2 and the third lens L3. In an observation device having an image display element that displays an image and an eyepiece optical system that is used to observe the image displayed on the image display surface IP of the image display element, the diagonal length of the image display surface IP of the image display element is Let the half be PN. Let d1 be the distance on the optical axis from the image display surface IP to the lens surface of the first lens L1 on the image display surface side.

At this time, it is preferable to satisfy one or more of the following conditional expressions.
0.00≦d5/d3≦0.75 (4)
0.25<PN/f<0.55 (5)
0.0≦d1/f<0.8 (6)

Next, the technical meaning of each of the above conditional expressions will be explained. Conditional expression (4) defines the ratio of the distance between the first lens L1 and the second lens L2 to the distance between the second lens L2 and the third lens L3. Conditional expression (4) is for satisfactorily correcting lateral chromatic aberration while obtaining a large observation magnification.

If the distance between the second lens L2 and the third lens L3 increases beyond the upper limit of conditional expression (4), it becomes difficult to correct lateral chromatic aberration. Further, when the distance between the first lens L1 and the second lens L2 becomes narrower, the ray angle of the light beam incident on the second lens L2 becomes sharper, and the curvature of field increases particularly at high image heights. If the distance between the first lens L1 and the second lens L2 is increased below the lower limit, the height of the light rays incident on the second lens becomes low, so that the light rays are bounced up and it becomes difficult to obtain a high observation field magnification.

Conditional expression (5) defines the ratio of half the diagonal length of the image display surface of the image display device to the focal length of the entire system. Conditional expression (5) is for ensuring a high observation magnification while ensuring a long eye relief. If the focal length of the entire system is shortened beyond the upper limit of conditional expression (5), it is advantageous for high observation magnification, but it becomes difficult to ensure high optical performance. If the lower limit of conditional expression (5) is not reached, the refractive power of the entire system will be weak, making it difficult to ensure a high observation magnification.

Conditional expression (6) defines the length on the optical axis from the image display surface of the image display element to the lens surface of the first lens L1 on the image display surface side and the focal length of the entire system. If the upper limit is exceeded, the distance from the image display surface to the lens surface of the first lens on the image display surface side increases, making it difficult to reduce the size of the entire system.

Preferably, the numerical ranges of conditional expressions (4) to (6) are set as follows.
0.0≦d5/d3≦0.6 (4a)
0.25<PN/f<0.50 (5a)
0.00≦d1/f<0.60 (6a)

More preferably, the numerical ranges of conditional expressions (4a) to (6a) are set as follows.
0.0≦d5/d3≦0.5 (4b)
0.25<PN/f<0.45 (5b)
0.00≦d1/f<0.55 (6b)

Although preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of the gist.

Numerical data corresponding to each example of the present invention are shown below. In the numerical data, ω indicates the apparent field of view (half angle of view) when the diopter is -1 diopter (standard diopter). From the image display plane IP to the viewing side EP, "ri" indicates the paraxial radius of curvature of the i-th plane. "di" indicates the axial top surface distance between the i-th plane and the (i+1)-th plane in order from the image display plane IP. Furthermore, "Ndi" indicates the refractive index for the d-line (wavelength=578.6 nm) of the i-th material, and "νdi" indicates the Abbe number for the d-line of the i-th material. r0 is an image display surface IP, and r9 and r10 are cover glasses.

In numerical data, [mm] is used as the unit of length unless otherwise specified. However, since the optical system can obtain the same optical performance even if it is proportionally enlarged or proportionally reduced, the unit is not limited to [mm], and other appropriate units can be used. In the numerical data, the surface with the suffix "*" written in the paraxial radius of curvature column has an aspheric shape defined by the following formula (1).

In (Equation 1), x is the distance in the optical axis direction from the vertex of the lens surface, h is the height in the direction perpendicular to the optical axis, R is the paraxial radius of curvature at the vertex of the lens surface, and k is The conic constants, c2, c4, c6 are polynomial coefficients. In the aspherical coefficients, "Ei" represents a base 10 exponential expression, ie, "10-i".

Although preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of the gist.

[Numeric data 1]
Overall specifications Focal length Diagonal length of image display surface 2ω[°]
18.97 12.6 35.0

Lens Data Surface Paraxial Radius of Curvature Axial Top Distance Refractive Index (Nd) Abbe Number (νd)
r0 display panel d1 variable
r1 553.90 d2 3.30 1.821 42.7
*r2 -14.37 d3 2.84
*r4 -7.18 d4 1.65 1.636 23.9
r5 -50.31 d5 0.62
*r6 -31.65 d6 2.63 1.592 67.0
r7 -16.79 d7 0.22
r8 50.42 d8 6.50 1.535 55.7
*r9 -13.05 d9 variable
r10 0.00 d10 0.80 1.492 57.4
r11 0.00 d11 23.00
EP

Aspheric coefficient k C2 C4 C6 C8
r2 0.00E+00 0.00E+00 3.88E-05 3.65E-08 0.00E+00
r3 -8.22E-01 0.00E+00 -9.72E-05 -9.34E-07 0.00E+00
r5 0.00E+00 0.00E+00 1.10E-05 0.00E+00 0.00E+00
r8 -2.30E+00 0.00E+00 -4.87E-05 2.14E-07 -2.73E-10

Variable interval diopter [dpt] 0 -3 +1 -1
d1 7.76 6.66 8.15 7.42
d9 1.51 2.60 1.12 1.85

[Numeric data 2]
Overall specifications Focal length Diagonal length of image display surface 2ω[°]
13.37 9.9 40.6

Lens data surface Paraxial curvature radius Axial top surface distance Refractive index (Nd) Abbe number (νd)
r0 display panel d1 variable
*r1 13.421 d2 6.14 1.535 56.0
*r2 -8.334 d3 2.15
*r3 -5.637 d4 1.48 1.636 23.9
r4 -15.213 d5 0.17
r5 -34.833 d6 2.11 1.535 56.0
r6 -17.151 d7 0.15
r7 -152.436 d8 3.31 1.535 56.0
*r8 -11.013 d9 variable
r9 0.000 d10 0.70 1.492 57.4
r10 0.000 d11 18.00
EP

aspheric coefficient
k C2 C4 C6
r1 -6.34E+00 0.00E+00 0.00E+00 0.00E+00
r2 -1.68E+00 0.00E+00 -9.39E-05 0.00E+00
r3 -9.67E-01 0.00E+00 0.00E+00 0.00E+00
r8 -2.34E+00 0.00E+00 3.69E-06 3.31E-07

Variable interval diopter [dpt] 0 -3 +1 -1
d1 5.74 5.14 5.91 5.55
d9 0.67 1.26 0.50 0.86

[Numeric data 3]
Overall specifications Focal length Diagonal length of image display surface 2ω[°]
17.96 9.9 29.1

Lens data surface Paraxial curvature radius Axial top surface distance Refractive index (Nd) Abbe number (νd)
r0 display panel d1 variable
r1 24.08 d2 4.02 1.532 55.8
*r2 -9.64 d3 3.62
*r3 -5.70 d4 1.50 1.636 23.9
r4 -35.58 d5 1.30
r5 -16.99 d6 3.32 1.532 55.8
*r6 -9.80 d7 0.33
r7 39.45 d8 3.23 1.532 55.8
*r8 -16.38 d9 variable
r9 0.00 d10 1.00 1.516 64.1
r10 0.00 d11 21.00
EP

aspheric coefficient
k C2 C4 C6
r2 0.00E+00 0.00E+00 2.28E-04 0.00E+00
r3 -4.72E-01 0.00E+00 1.67E-04 0.00E+00
r6 0.00E+00 0.00E+00 1.67E-05 0.00E+00
r8 0.00E+00 0.00E+00 6.95E-05 5.15E-08

Variable interval diopter [dpt] 0 -3 +1 -1
d1 5.95 4.88 6.24 5.59
d9 0.79 1.86 0.50 1.15

[Numeric data 4]
Overall specifications Focal length Diagonal length of image display surface 2ω[°]
16.50 9.9 32.0

Lens Data Surface Paraxial Radius of Curvature Axial Top Distance Refractive Index (Nd) Abbe Number (νd)
r0 display panel d1 variable
r1 21.75 d2 4.95 1.535 55.7
*r2 -10.27 d3 2.39
*r3 -5.62 d4 1.75 1.636 23.9
r4 -18.39 d5 0.22
*r5 -22.78 d6 2.62 1.535 55.7
r6 -11.84 d7 0.22
r7 105.20 d8 3.87 1.535 55.7
*r8 -13.85 d9 variable
r9 0.00 d10 0.80 1.492 57.4
r10 0.00 d11 21.00
EP

Aspheric coefficient k C2 C4 C6 C8
r2 0.00E+00 0.00E+00 1.57E-04 8.64E-07 0.00E+00
r3 -7.62E-01 0.00E+00 8.52E-05 0.00E+00 0.00E+00
r5 0.00E+00 0.00E+00 -7.94E-05 0.00E+00 0.00E+00
r8 0.00E+00 0.00E+00 1.27E-04 -3.08E-07 3.21E-09

Variable interval diopter [dpt] 0 -3 +1 -1
d1 7.10 6.25 7.35 6.83
d9 1.05 1.90 0.80 1.32

[Numeric data 5]
Overall specifications Focal length Diagonal length of image display surface 2ω[°]
25.22 16.8 35.1

Lens Data Surface Paraxial Radius of Curvature Axial Top Distance Refractive Index (Nd) Abbe Number (νd)
r0 display panel d1 variable
r1 49.56 d2 6.43 1.535 55.7
*r2 -17.25 d3 4.39
*r3 -8.84 d4 1.95 1.636 23.9
r4 -30.05 d5 0.22
r5 266.69 d6 5.26 1.531 55.9
r6 -27.75 d7 0.22
r7 235.81 d8 5.82 1.535 55.7
*r8 -18.98 d9 variable
r9 0.00 d10 0.80 1.492 57.4
r10 0.00 d11 30.00
EP

Aspheric coefficient k C2 C4 C6
r1 0.00E+00 0.00E+00 2.91E-05 0.00.E+00
r2 -1.33E+00 0.00E+00 -1.12E-04 0.00.E+00
r8 -2.17E+00 0.00E+00 1.01E-05 1.04E-08

Variable interval diopter [dpt] 0 -3 +1 -1
d1 10.39 8.38 11.02 9.74
d9 2.04 4.05 1.41 2.69

[Numerical data 6]
Overall specifications Focal length Diagonal length of image display surface 2ω[°]
20.46 12.6 33.1

Lens Data Surface Paraxial Radius of Curvature Axial Top Distance Refractive Index (Nd) Abbe Number (νd)
r0 display panel d1 variable
r1 59.97 d2 5.95 1.694 53.2
*r2 -11.68 d3 2.38
*r3 -6.74 d4 1.67 1.636 23.9
r4 -28.97 d5 0.00
r5 -28.97 d6 3.09 1.535 56.0
r6 -35.80 d7 0.25
r7 61.73 d8 5.49 1.535 56.0
*r8 -12.03 d9 variable
r9 0.00 d10 0.80 1.492 57.4
r10 0.00 d11 24.00
EP

aspheric coefficient
k C2 C4 C6
r2 0.00E+00 0.00E+00 1.15E-04 2.75E-07
r3 -9.93E-01 0.00E+00 0.00E+00 0.00E+00
r8 -5.80E-01 0.00E+00 6.48E-05 8.67E-08

Variable interval diopter [dpt] 0 -3 +1 -1
d1 9.47 8.06 9.85 9.01
d9 0.87 2.28 0.50 1.34

L0 Eyepiece optical system L1 First lens L2 Second lens L3 Third lens L4 Fourth lens IP Image display surface EP Observation surface

Claims (5)

An eyepiece optical system for observing an image displayed on an image display surface, comprising a first lens with positive refractive power and a second lens with negative refractive power, which are arranged in order from the image display surface side to the observation side. , a third lens, and a fourth lens having a positive refractive power, wherein Nda is the average value of the refractive index of the material of each lens of the first lens to the fourth lens at the d-line, and the observation side of the first lens L1R2 is the curvature radius of the lens surface of the second lens, L2R1 is the curvature radius of the lens surface of the second lens on the image display surface side, f34 is the combined focal length of the third lens and the fourth lens, and the focal length of the eyepiece optical system is f,
1.600≦Nda≦1.730
-15.0 ≤ (L2R1 + L1R2) / (L2R1 - L1R2) ≤ 0.0
0.68≤f34/f≤1.30
An eyepiece optical system characterized by satisfying the following conditional expression: When the distance on the optical axis between the first lens and the second lens is d3, and the distance on the optical axis between the second lens and the third lens is d5,
0.00≤d5/d3≤0.75
2. An eyepiece optical system according to claim 1, wherein the following conditional expression is satisfied. 3. An observation apparatus comprising: an image display element for displaying an image; and the eyepiece optical system according to claim 1 or 2 used for observing the image displayed on the image display surface of the image display element. When half the diagonal length of the image display surface of the image display element is PN,
0.25<PN/f<0.55
4. The observation device according to claim 3, wherein the following conditional expression is satisfied. When the distance on the optical axis from the image display surface to the lens surface of the first lens on the image display surface side is d1,
0.0≦d1/f<0.8
5. The observation device according to claim 3, wherein the following conditional expression is satisfied.

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