Optical system

Abstract

Provided is an optical system that has good optical characteristics and that satisfies the requirements of wide angle of view and miniaturization.　The optical system includes, in order from a pupil plane EP side to a display plane IMG side: a first reflection-polarizing plate 11; a first 1 / 4 wavelength plate 21; an eyepiece fL having a positive refractive power; and a half mirror HMIMG. On the paraxial axis, the eyepiece fL has a convex surface on the display surface IMG side, and the eyepiece satisfies the following conditional expression when the focal length of the eyepiece fL is fL and the focal length of the entire optical system is f. (1) Conditional expression: 2 < fL / f < 10.

Description

optical system

[0001] The present invention relates to an optical system for magnifying an image (for example, an image displayed on an image display device).

[0002] 2. Description of the Related Art Known display devices using image display elements include electronic viewfinders, electronic binoculars, and head-mounted displays.

[0003] In such a display device, the distance between the image display element and the eye must be as short as possible, and the optical system for magnifying the image displayed on the image display element must be housed in a limited space. This often makes it difficult to eliminate various aberrations in the optical system, and the range of correction is also limited.

[0004] As is well known, visual acuity depends on the density of the cones in photoreceptor cells, and the eye has the characteristic of forming a clear image near the fovea of ​​the macula, i.e., the center of the pupil. Therefore, by utilizing this physiological optical characteristic of the eye to complement the aberration correction of the above-mentioned optical system, it is possible to obtain good optical performance. Specifically, narrowing the pupil increases the depth of focus and reduces the effects of spherical aberration and coma aberration, thereby reducing sensitivity to blur even if the aberration and refractive correction are excessive or insufficient. Furthermore, by utilizing the so-called Stiles-Crawford effect, a phenomenon in which the sensitivity of light rays incident from the periphery is lower than the sensitivity of light rays passing through the center of the pupil, the effects of spherical aberration, coma aberration, and chromatic aberration can be reduced. Furthermore, by maintaining this state, the eye gradually becomes accustomed to it, making it possible to reduce the effects of distortion aberrations and the like.

[0005] The optical systems installed in such display devices are required to be compact and have a wide angle of view in order to create an immersive feeling that draws the viewer into the images and videos.

[0006] Known examples of conventional optical systems include the optical system described in Patent Document 1. Patent Document 1 discloses an eyepiece optical system equipped with a Fresnel lens having a plurality of Fresnel zones formed on the lens surface facing the observation object.

[0007] Chinese Patent Application Publication No. 112424669

[0008] Even if an attempt is made to achieve a wide angle of view and compactness with the lens configuration described in Patent Document 1, it is extremely difficult to correct aberrations in the peripheral areas, and therefore good optical performance cannot be obtained.

[0009] The present invention has been made in view of the above-mentioned problems, and aims to provide an optical system that satisfies the demands for a wide angle of view and compactness in a balanced manner, while also having high resolving power with various aberrations well corrected.

[0010] The optical system according to the present invention comprises, in order from the pupil plane side to the display plane side, a first reflective polarizer, a first quarter-wave plate, an eyepiece lens having positive refractive power, and a half mirror. In this specification, the convex, concave, and flat surfaces of the lens refer to the paraxial shape, and the refractive power refers to the paraxial refractive power unless otherwise specified.

[0011] A reflective polarizer reflects linearly polarized light having one polarization direction and transmits linearly polarized light having an orthogonal polarization direction.

[0012] A quarter-wave plate delays the phase of polarized light by 1 / 4λ, thereby converting linearly polarized light into circularly polarized light and circularly polarized light into linearly polarized light.

[0013] The eyepiece has a positive refractive power, which suppresses spherical aberration, astigmatism, curvature of field, and distortion.

[0014] A half mirror transmits 50% of the light and reflects the remaining 50%.

[0015] In the optical system of the present invention, a pupil-side element group is formed by a first reflective polarizer, a first quarter-wave plate, and an eyepiece having positive refractive power, and a half mirror is disposed on the display surface side of the eyepiece, thereby realizing a compact optical system. Furthermore, the optical system of the present invention is not limited to the above configuration, and may be configured such that a pupil-side element group is formed by a first reflective polarizer, a first quarter-wave plate, and an eyepiece having positive refractive power, half mirrors are disposed on the pupil surface side and the display surface side of the eyepiece, and a display surface side element group is formed by a second quarter-wave plate and a second reflective polarizer. In such a configuration, by finally superimposing two beams of light, that is, light reflected by and light transmitted through the half mirrors on the pupil surface side and the display surface side, the optical system can be made compact while improving light efficiency.

[0016] It is desirable that the optical system having the above configuration satisfy the following conditional expression (1): (1) 2<fL / f<10 where fL is the focal length of the eyepiece, and f is the focal length of the entire optical system.

[0017] By satisfying the range of conditional expression (1), it becomes possible to make good corrections for spherical aberration, astigmatism, curvature of field, and distortion.

[0018] It is desirable that the optical system having the above configuration satisfy the following conditional expression (2): (2) -7.50<r2 / f<-1.75 where r2 is the paraxial radius of curvature of the surface of the eyepiece lens on the display surface side, and f is the focal length of the entire optical system.

[0019] By satisfying the range of conditional expression (2), it becomes possible to make good corrections for spherical aberration, astigmatism, curvature of field, and distortion.

[0020] It is desirable for the optical system with the above configuration to satisfy the following conditional expression (3): (3) -28.5<r2 / T1<-6.00 where r2 is the paraxial radius of curvature of the surface of the eyepiece on the display surface side, and T1 is the thickness of the eyepiece on the optical axis.

[0021] By satisfying the range of conditional expression (3), it becomes possible to achieve a low profile and to make good corrections for spherical aberration, astigmatism, curvature of field, and distortion.

[0022] It is desirable that the optical system configured as described above satisfy the following conditional expression (4): (4) -9.0<r2 / (DH1+T1)<-1.6, where r2 is the paraxial radius of curvature of the surface of the eyepiece on the display surface side, DH1 is the distance on the optical axis from the pupil plane to the surface of the eyepiece on the pupil surface side, and T1 is the thickness of the eyepiece on the optical axis.

[0023] By satisfying the range of conditional expression (4), it becomes possible to achieve a low profile and to make good corrections for spherical aberration, astigmatism, curvature of field, and distortion.

[0024] It is desirable that the optical system having the above configuration satisfy the following condition (5): (5) 0.19<f / νd1<0.51 where f is the focal length of the entire optical system, and νd1 is the Abbe number for the d-line of the eyepiece.

[0025] By satisfying the range of conditional expression (5), it becomes possible to make good corrections for spherical aberration, chromatic aberration, astigmatism, curvature of field, and distortion.

[0026] It is desirable that the optical system having the above configuration satisfy the following conditional expression (6): (6) 1.0<fL / νd1<3.8 where fL is the focal length of the eyepiece, and νd1 is the Abbe number of the eyepiece for the d-line.

[0027] By satisfying the range of conditional expression (6), it becomes possible to make good corrections for spherical aberration, chromatic aberration, astigmatism, curvature of field, and distortion.

[0028] It is desirable that the optical system having the above configuration satisfy the following condition (7): (7) 3.2<DH1 / Fno<9.3 where DH1 is the distance on the optical axis from the pupil plane to the surface of the eyepiece on the pupil plane side, and Fno is the F-number.

[0029] By satisfying the range of conditional expression (7), it becomes possible to make good corrections for astigmatism, curvature of field, and distortion.

[0030] It is desirable that the optical system having the above configuration satisfy the following conditional expression (8): (8) 39<νd1<73 where νd1 is the Abbe number for the d-line of the eyepiece.

[0031] By satisfying the range of conditional expression (8), chromatic aberration can be corrected satisfactorily.

[0032] It is desirable that the optical system having the above configuration satisfy the following condition (9): (9) -1.65<r2 / fL<-0.25 where r2 is the paraxial radius of curvature of the surface of the eyepiece on the display surface side, and fL is the focal length of the eyepiece.

[0033] By satisfying the range of conditional expression (9), it becomes possible to make good corrections for spherical aberration, astigmatism, curvature of field, and distortion.

[0034] It is desirable that the optical system having the above configuration satisfy the following condition (10): (10) -2.8<r2 / νd1<-0.5 where r2 is the paraxial radius of curvature of the surface of the eyepiece on the display surface side, and νd1 is the Abbe number of the eyepiece for the d-line.

[0035] By satisfying the range of conditional expression (10), it becomes possible to make good corrections for spherical aberration, chromatic aberration, astigmatism, curvature of field, and distortion.

[0036] It is desirable that the optical system having the above configuration satisfy the following conditional expression (11): (11) 0.45<f / (DH1+T1)<1.75 where f is the focal length of the entire optical system, DH1 is the distance on the optical axis from the pupil plane to the surface of the eyepiece on the pupil plane side, and T1 is the thickness of the eyepiece on the optical axis.

[0037] By satisfying the range of conditional expression (11), it becomes possible to achieve a low profile and to make good corrections for spheric aberration, astigmatism, curvature of field, and distortion.

[0038] It is desirable that the optical system having the above configuration satisfy the following condition (12): (12) 1.5<f / T1<6.6 where f is the focal length of the entire optical system, and T1 is the thickness of the eyepiece lens on the optical axis.

[0039] By satisfying the range of conditional expression (12), it becomes possible to achieve a low profile and to make good corrections for spheric aberration, astigmatism, curvature of field, and distortion.

[0040] It is desirable that the optical system having the above configuration satisfy the following conditional expression (13): (13) 2.5<fL / (DH1+T1)<9.1 where fL is the focal length of the eyepiece, DH1 is the distance on the optical axis from the pupil plane to the surface of the eyepiece on the pupil plane side, and T1 is the thickness of the eyepiece on the optical axis.

[0041] By satisfying the range of conditional expression (13), it becomes possible to achieve a low profile and to make good corrections for spherical aberration, astigmatism, curvature of field, and distortion.

[0042] The present invention makes it possible to obtain an optical system with high resolution and excellent correction of aberrations while satisfying the demands for a wide angle of view and compactness in a well-balanced manner. Furthermore, since the optical system according to the present invention effectively corrects aberrations, the number of lenses can be reduced, and by reducing the amount of lens material used, an environmentally friendly imaging lens can be provided.

[0043] FIG. 10A is a cross-sectional view showing a schematic configuration of an optical system according to Example 1 of the present invention. FIG. 10B is a partially enlarged view of the optical system shown in FIG. 1. FIG. 10C is an aberration diagram showing spherical aberration, astigmatism, and distortion of the optical system shown in FIG. 1. FIG. 10D is a cross-sectional view showing a schematic configuration of an optical system according to Example 2 of the present invention. FIG. 10E is a partially enlarged view of the optical system shown in FIG. 4. FIG. 10F is an aberration diagram showing spherical aberration, astigmatism, and distortion of the optical system shown in FIG. 4. FIG. 10G is a cross-sectional view showing a schematic configuration of an optical system according to Example 3 of the present invention. FIG. 10H is a partially enlarged view of the optical system shown in FIG. 7. FIG. 10H is an aberration diagram showing spherical aberration, astigmatism, and distortion of the optical system shown in FIG. 7.

[0044] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

[0045] 1, 4, and 7 are cross-sectional views showing the schematic configurations of the optical systems of Examples 1 to 3 according to this embodiment, respectively. Also, Fig. 2, 5, and 8 show enlarged partial views of the optical systems of Examples 1 to 3, respectively. The optical system according to this embodiment will be described in detail below with reference to the optical system of Example 1.

[0046] As shown in FIG. 1, the optical system according to this embodiment includes, in order from the pupil plane EP toward the display surface IMG of the image display element, a first reflective polarizer 11, a first quarter-wave plate 21, an eyepiece lens fL having positive refractive power, and a half mirror HMIMG on the display surface IMG side.

[0047] The optical system according to this embodiment may be mounted on any object, but may be mounted on a head-mounted display, for example, as an optical system for enlarging an image displayed on a display surface IMG. In this case, the pupil plane EP is where the observer's pupil is located. An aperture stop may be disposed on the pupil plane EP.

[0048] In the optical system according to this embodiment, anti-reflection films may be attached to both sides of the half mirror HMIMG. Since anti-reflection films have the function of preventing light reflection, this configuration can prevent a decrease in image contrast due to reflection of external light.

[0049] As shown in Figure 1, the eyepiece lens fL has a flat surface on the paraxial side facing the pupil plane EP and a convex surface on the paraxial side facing the display surface IMG. This shape of the eyepiece lens fL can suppress spherical aberration, astigmatism, field curvature, and distortion. The shape of the first lens L1 may be biconvex on the paraxial side, as in the optical systems described in Examples 2 and 3. In this case, the positive refractive power on both sides allows for the compactness of the optical system.

[0050] In the optical system according to the present embodiment, as shown in FIG. 2 , the first quarter-wave plate 21 is disposed between the first reflective polarizer 11 and the eyepiece fL. When the first quarter-wave plate 21 is disposed in this position, a composite film formed by bonding the first reflective polarizer 11 and the first quarter-wave plate 21 together can be attached to the eyepiece fL, which facilitates industrial manufacturing. This reduces costs and improves the axial accuracy of the first reflective polarizer 11 and the first quarter-wave plate 21. The optical system according to Example 2 is an example in which a composite film formed by bonding the first reflective polarizer 11 and the first quarter-wave plate 21 together is not attached to the eyepiece fL, as shown in FIG.

[0051] As shown in FIG. 8 , the optical system according to Example 3 includes, in order from the pupil plane EP toward the display surface IMG of the image display element, a first reflective polarizer 11, a first quarter-wave plate 21, an eyepiece lens fL with positive refractive power and half-mirror properties provided by vapor deposition on the pupil plane EP and display surface IMG sides, a second reflective polarizer 22, and a second quarter-wave plate 12. With this configuration, the light reflected by and transmitted through the half mirror HMIMG on the display surface IMG side and the half mirror HMEP on the pupil plane EP side are ultimately superimposed, thereby achieving a compact optical system while improving light efficiency. A filter IR, such as a glass block, is disposed between the optical system and the display surface IMG or between the optical system and the pupil plane EP. This filter IR can be omitted. A polarizer O1 is also disposed between the optical system and the pupil plane EP. The polarizing plate 01 allows only light polarized in a specific direction to pass through, and it is possible to omit the polarizing plate 01.

[0052] As a device having a display surface IMG, for example, a liquid crystal display or a micro OLED (Organic Light Emitting Diode) display can be adopted.

[0053] As shown in Fig. 10A of Fig. 10, light emitted from the display surface IMG is converted into linearly polarized light by the second reflective polarizer 12, converted into circularly polarized light by the second quarter-wave plate 22, and then incident on the half mirror HMIMG on the display surface IMG side. A portion of the light incident on the half mirror HMIMG on the display surface IMG side is transmitted through it and converted by the first quarter-wave plate 21 into linearly polarized light in the same polarization direction as when it passed through the second reflective polarizer 12, and then incident on the first reflective polarizer 11. This linearly polarized light is reflected by the polarization selectivity of the first reflective polarizer 11. The light reflected by the first reflective polarizer 11 is converted into circularly polarized light by the first quarter-wave plate 21 and incident on the half mirror HMIMG on the display surface IMG side, where it is reflected. The light reflected by the half mirror HMIMG on the display surface IMG side becomes circularly polarized light in the opposite direction to the light before reflection. Hereinafter, for convenience, the light traveling along this path will be referred to as "light along path 1." In the cross-sectional views of the optical system according to this embodiment shown in Figures 1, 4, and 7, only the light along path 1 is shown in order to clearly show the schematic configuration of the optical system.

[0054] On the other hand, as shown in Fig. 10B of Fig. 10, a portion of the light converted to circularly polarized light by the second quarter-wave plate 22 and incident on the half mirror HMEP on the pupil plane EP side is reflected, becomes reverse-circularly polarized light, and returns to the second quarter-wave plate 22. The circularly polarized light that returned to the second quarter-wave plate 22 is converted by the second quarter-wave plate 22 into linearly polarized light having a polarization direction perpendicular to the polarization direction when it first passed through the second reflective polarizer 12, and then incidents on the second reflective polarizer 12. This linearly polarized light is reflected due to the polarization selectivity of the second reflective polarizer 12. The light reflected by the second reflective polarizer 12 is converted to circularly polarized light by the second quarter-wave plate 22 and incidents on and transmits through the half mirror HMEP on the pupil plane EP side. Hereinafter, for convenience, the light traveling along this path will be referred to as "light on path 2."

[0055] The light on path 1 and the light on path 2 are converted by the first quarter-wave plate 21 into linearly polarized light having a polarization direction orthogonal to the polarization direction when the light first passed through the second reflective polarizer 12, and then enter the first reflective polarizer 11. This linearly polarized light passes through the first reflective polarizer 11 due to its polarization selectivity and is guided to the pupil plane EP.

[0056] The optical system of Example 3 achieves improved light efficiency while miniaturizing the optical system by ultimately superimposing two beams of light, one reflected by the half mirror HMIMG on the display surface IMG side and the other transmitted by the half mirror HMEP on the pupil surface EP side. However, depending on the required performance, only one semi-transparent surface may be used.

[0057] In the optical system according to the present embodiment, by using polarized light to fold the optical path, it is possible to make the optical system thin and shorten the focal length of the eyepiece optical system, thereby realizing image observation with a wide angle of view.

[0058] The optical system of this embodiment achieves desirable effects by satisfying the following conditional expressions (1) to (13). (1) 2<fL / f<10 (2) -7.50<r2 / f<-1.75 (3) -28.5<r2 / T1<-6.00 (4) -9.0<r2 / (DH1+T1)<-1.6 (5) 0.19<f / νd1<0.51 (6) 1.0<fL / νd1<3.8 (7) 3.2<DH1 / Fno<9.3 (8) 39<νd1<73 (9) -1.65<r2 / fL<-0.25 (10) -2.8<r2 / νd1<-0.5 (11) 0.45<f / (DH1+T1)<1.75 (12) 1.5<f / T1<6.6 (13) 2.5<fL / (DH1+T1)<9.1 where, Fno: F-number, νd1: Abbe number for the d-line of the eyepiece, DH1: distance on the optical axis X from the pupil plane to the pupil-side surface of the eyepiece fL, T1: thickness on the optical axis X of the eyepiece fL, f: focal length of the entire optical system, fL: focal length of the eyepiece, r2: paraxial radius of curvature of the display-side surface of the eyepiece

[0059] It is not necessary to satisfy all of the above conditional expressions, and by satisfying each conditional expression individually, it is possible to obtain the effects corresponding to each conditional expression.

[0060] Furthermore, the optical system of this embodiment will achieve more preferable effects if it satisfies the following conditional expressions (1a) to (13a). (1a) 3.25<fL / f<8.00 (2a) -6.0<r2 / f<-2.5 (3a) -23.5<r2 / T1<-9.5 (4a) -7.0<r2 / (DH1+T1)<-2.5 (5a) 0.29<f / νd1<0.47 (6a) 1.4<fL / νd1<3.2 (7a) 4.0<DH1 / Fno<7.7 (8a) 47<νd1<65 (9a) -1.35<r2 / fL<-0.40 (10a) -2.3<r2 / νd1<-1.0 (11a) 0.70<f / (DH1+T1)<1.45 (12a) 2.7<f / T1<5.5 (13a) 3.9<fL / (DH1+T1)<7.5 where the symbols in each conditional expression are the same as those explained in the previous paragraph. Note that for conditional expressions (1a) to (13a), the lower limit or upper limit may be the lower limit or upper limit of the corresponding conditional expressions (1) to (13).

[0061] In this embodiment, the aspherical shape adopted for the aspherical surface of the lens surface is expressed by Equation 1, where Z is the axis in the optical axis direction, H is the height in the direction perpendicular to the optical axis, R is the paraxial radius of curvature, k is the conic coefficient, and An is the n-th order aspherical coefficient.

[0062]

[0063] Next, examples of the optical system according to this embodiment will be shown. In each example, f represents the focal length of the entire optical system, Fno represents the F-number, ω represents the half angle of view, ih represents the maximum image height, and TTL represents the total optical length. Here, the total optical length is the distance on the optical axis from the pupil plane to the display surface. The values ​​of the total optical length and back focus are the distances obtained by converting the thickness of the filter IR placed between the optical system and the display surface IMG into air.

[0064] In addition, i denotes the surface number counted from the pupil surface side, r denotes the paraxial radius of curvature, d denotes the distance between lens surfaces on the optical axis (surface spacing), Nd denotes the refractive index of the d-line (reference wavelength), and νd denotes the Abbe number for the d-line. Aspherical surfaces are indicated by adding an asterisk (*) after the surface number i.

[0065] In the optical systems of each embodiment, the distance between the pupil plane EP, which is the eyepoint on the optical axis, and the lens surface closest to the pupil plane is called the pupil distance. In evaluating aberrations, there is a one-to-one correspondence between the aberration of a light ray that reaches the pupil plane EP when a light emitting point is provided on the display surface side and the aberration of a light ray that reaches the display surface IMG when a light emitting point is provided on the pupil plane EP side. For this reason, in each embodiment, the aberration of the light ray that reaches the display surface IMG is evaluated.

[0066] Example 1

[0067] The basic lens data is shown in Table 1 below.

[0068]

[0069] The optical system of Example 1 satisfies conditional expressions (1) to (13) as shown in Table 4.

[0070] FIG. 3 shows the spherical aberration (mm), astigmatism (mm), and distortion (%) for the optical system of Example 1. The spherical aberration diagram shows the amount of aberration for each wavelength of the F-line (486 nm), d-line (588 nm), and C-line (656 nm). The astigmatism diagram also shows the amount of aberration for the d-line at the sagittal image plane S (solid line) and the amount of aberration for the d-line at the tangential image plane T (dashed line) (the same applies to FIGS. 6 and 9). As shown in FIG. 3, each aberration is well corrected.

[0071] Example 2

[0072] The basic lens data is shown in Table 2 below.

[0073]

[0074] The optical system of Example 2 satisfies conditional expressions (1) to (13) as shown in Table 4.

[0075] 6 shows the spherical aberration (mm), astigmatism (mm), and distortion (%) for the optical system of Example 2. As shown in FIG. 6, each aberration is well corrected.

[0076] Example 3

[0077] The basic lens data is shown in Table 3 below.

[0078]

[0079] The optical system of Example 3 satisfies conditional expressions (1) to (13) as shown in Table 4.

[0080] 9 shows the spherical aberration (mm), astigmatism (mm), and distortion (%) for the optical system of Example 3. As shown in FIG. 9, each aberration is well corrected.

[0081] Table 4 shows the values ​​of the conditional expressions (1) to (13) in the optical systems of Examples 1 to 3.

[0082]

[0083] When the optical system according to the present invention is applied to an image display device, it contributes to a wide angle of view and miniaturization of the image display device, and also enables improvement in performance.

[0084] EP pupil plane fL eyepiece 01 polarizer 11 first reflective polarizer 21 first quarter-wave plate HMEP half mirror on the pupil plane EP side HMIMG half mirror on the display surface IMG side 22 second quarter-wave plate 12 second reflective polarizer IR filter IMG display surface

Claims

1. An optical system comprising, in order from the pupil plane side to the display surface side, a first reflective polarizing plate, a first quarter-wave plate, an eyepiece lens having positive refractive power, and a half mirror, the eyepiece lens having a convex surface on the display surface side in a paraxial direction, and satisfying the following conditional formula (1): (1) 2<fL / f<10, where fL is the focal length of the eyepiece lens, and f is the focal length of the entire optical system.

2. The optical system according to claim 1, characterized in that the following conditional expression (2) is satisfied: (2) -7.50<r2 / f<-1.75, where r2 is the paraxial radius of curvature of the surface of the eyepiece lens on the display surface side, and f is the focal length of the entire optical system.

3. The optical system according to claim 1, characterized in that the following conditional expression (3) is satisfied: (3) -28.5<r2 / T1<-6.00, where r2 is the paraxial radius of curvature of the surface of the eyepiece lens on the display surface side, and T1 is the thickness of the eyepiece lens on the optical axis.

4. The optical system according to claim 1, characterized in that it satisfies the following conditional expression (4): (4) -9.0<r2 / (DH1+T1)<-1.6, where r2 is the paraxial radius of curvature of the surface of the eyepiece on the display surface side, DH1 is the distance on the optical axis from the pupil surface to the surface of the eyepiece on the pupil surface side, and T1 is the thickness of the eyepiece on the optical axis.

5. The optical system according to claim 1, characterized in that the following conditional expression (5) is satisfied: (5) 0.19<f / νd1<0.51, where f is the focal length of the entire optical system, and νd1 is the Abbe number of the eyepiece lens for the d line.

6. The optical system according to claim 1, characterized in that the following conditional expression (6) is satisfied: (6) 1.0<fL / νd1<3.8, where fL is the focal length of the eyepiece, and νd1 is the Abbe number of the eyepiece for the d-line.

7. The optical system according to claim 1, characterized in that the following conditional expression (7) is satisfied: (7) 3.2<DH1 / Fno<9.3, where DH1 is the distance on the optical axis from the pupil plane to the surface of the eyepiece lens on the pupil plane side, and Fno is the F-number.

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