Sony Patent | Eyepiece and display apparatus

Patent: Eyepiece and display apparatus

Drawings: Click to check drawins

Publication Number: 20210302627

Publication Date: 20210930

Applicant: Sony

Abstract

An eyepiece according to the present disclosure includes a first lens and a second lens that are opposed to each other. The first lens includes a first Fresnel lens surface formed at least in a peripheral region of a lens surface that is opposed to the second lens. The second lens includes a second Fresnel lens surface formed at least in a peripheral region of a lens surface that is opposed to the first lens.

Claims

1. An eyepiece comprising a first lens and a second lens that are opposed to each other, the first lens including a first Fresnel lens surface formed at least in a peripheral region of a lens surface that is opposed to the second lens, the second lens including a second Fresnel lens surface formed at least in a peripheral region of a lens surface that is opposed to the first lens.

2. The eyepiece according to claim 1, wherein Mv.gtoreq.2.1 (1) is satisfied, where My is an image magnification.

3. The eyepiece according to claim 1, wherein the first lens is disposed closer to an eye point side than the second lens, and the first lens includes an eye-point-side lens surface that has a convex shape or a planar shape.

4. The eyepiece according to claim 1, wherein the first Fresnel lens is formed from a center to a periphery of the lens surface, of the first lens, that is opposed to the second lens, and the second Fresnel lens is formed from a center to a periphery of the lens surface, of the second lens, that is opposed to the first lens.

5. The eyepiece according to claim 1, wherein the first lens further includes a first non-Fresnel lens surface that is formed in a middle region of the lens surface that is opposed to the second lens, and the second lens further includes a second non-Fresnel lens surface that is formed in a middle region of the lens surface that is opposed to the first lens.

6. The eyepiece according to claim 1, wherein the eyepiece has a two-group two-lens configuration in which the first lens and the second lens are disposed in order from an eye point side toward an image side.

7. The eyepiece according to claim 6, wherein the first Fresnel lens surface and the second Fresnel lens surface each have two or more annular sections, the annular sections each have a border part on which a step surface is formed, and the step surface on each of the first Fresnel lens surface and the second Fresnel lens surface has an angle, with respect to an optical axis, that is 15 degrees or greater.

8. The eyepiece according to claim 1, further comprising a third lens that is disposed closer to an image side than the first lens and the second lens, wherein the eyepiece has a three-group three-lens configuration in which the first lens, the second lens, and the third lens are disposed in order from an eye point side toward the image side.

9. The eyepiece according to claim 8, wherein the first Fresnel lens surface and the second Fresnel lens surface each have two or more annular sections, the annular sections each have a border part on which a step surface is formed, and the step surface on each of the first Fresnel lens surface and the second Fresnel lens surface has an angle, with respect to an optical axis, that is 20 degrees or greater.

10. The eyepiece according to claim 1, wherein the first Fresnel lens surface and the second Fresnel lens surface each have positive refractive power.

11. The eyepiece according to claim 1, wherein the first Fresnel lens surface, the second Fresnel lens surface, or both include an aspherical surface having an inflection point.

12. The eyepiece according to claim 1, wherein nd.ltoreq.1.7 (2) is satisfied, where nd is a refractive index of each of the first lens and the second lens with respect to a d-line.

13. The eyepiece according to claim 1, wherein .psi.1.ltoreq..psi.2 (3) is satisfied, where .psi.1 is refractive power of the first Fresnel lens surface, and .psi.2 is refractive power of the second Fresnel lens surface.

14. The eyepiece according to claim 1, wherein 0.2

15. The eyepiece according to claim 1, wherein (.psi.+.psi.2)/.psi.all<0.30 (5) is satisfied, where .psi.1 is refractive power of the first Fresnel lens surface, .psi.2 is refractive power of the second Fresnel lens surface, and .psi.all is total refractive power of the eyepiece.

16. The eyepiece according to claim 1, wherein the first Fresnel lens surface and the second Fresnel lens surface each have two or more annular sections, and 0.1.ltoreq.L1.PHI.r1/.PHI.d1 (6) and 0.2.ltoreq.L2.PHI.r1/.PHI.d2 (7) are satisfied, where L1.PHI.r1 is a diameter of a first annular section from a center of the first Fresnel lens surface, .PHI.d1 is an effective diameter of the first Fresnel lens surface, L2.PHI.r1 is a diameter of a first annular section from a center of the second Fresnel lens surface, and .PHI.d2 is an effective diameter of the second Fresnel lens surface.

17. The eyepiece according to claim 1, wherein the first Fresnel lens surface and the second Fresnel lens surface each have two or more annular sections, and a pitch of the annular sections of the first Fresnel lens surface and a pitch of the annular sections of the second Fresnel lens surface are shifted from each other by a half period.

18. The eyepiece according to claim 1, wherein the first lens includes a third Fresnel lens surface that is formed on an eye-point-side lens surface.

19. A display apparatus comprising: an image display device; and an eyepiece that magnifies an image displayed on the image display device, the eyepiece including a first lens and a second lens that are opposed to each other, the first lens including a first Fresnel lens surface formed at least in a peripheral region of a lens surface that is opposed to the second lens, the first Fresnel lens surface having a Fresnel lens shape, the second lens including a second Fresnel lens surface formed at least in a peripheral region of a lens surface that is opposed to the first lens, the second Fresnel lens surface having a Fresnel lens shape.

20. The display apparatus according to claim 19, wherein the eyepiece has a lens diameter that is greater than a size of the image display device.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to: an eyepiece that magnifies an image (e.g., an image displayed on an image display device); and a display apparatus suitable for a head-mounted display, etc. using such an eyepiece.

BACKGROUND ART

[0002] As a display apparatus using an image display device, an electronic viewfinder, an electronic binocular, a head-mounted display (HMD), etc. are known. Particularly, the head-mounted display is used for a long time with a body of the display apparatus being worn in front of one’s eyes. It is therefore required that an eyepiece and the body of the display apparatus be small-sized and light-weighted. In addition, it is required that an image be viewable at a wide viewing angle. In order to reduce a weight and a total length of the eyepiece, there is a technique of using a Fresnel lens (see PTL 1).

CITATION LIST

Patent Literature

[0003] PTL 1: Japanese Unexamined Patent Application Publication No. H7-244246

[0004] PTL 2: Japanese Unexamined Patent Application Publication No. 2015-59959

SUMMARY OF THE INVENTION

[0005] Even if a Fresnel lens is used in an eyepiece, it is not always possible to obtain a sufficient optical effect depending on a surface on which the Fresnel lens is formed, a shape, etc.

[0006] It is desirable to provide: an eyepiece that allows for a wide viewing angle and favorable aberration correction while reducing a weight and a total length; and a display apparatus on which such an eyepiece is mounted.

[0007] An eyepiece according to an embodiment of the present disclosure includes a first lens and a second lens that are opposed to each other. The first lens includes a first Fresnel lens surface formed at least in a peripheral region of a lens surface that is opposed to the second lens. The second lens includes a second Fresnel lens surface formed at least in a peripheral region of a lens surface that is opposed to the first lens.

[0008] A display apparatus according to an embodiment of the present disclosure includes an image display device and an eyepiece that magnifies an image displayed on the image display device. The eyepiece includes the eyepiece according to the embodiment of the present disclosure described above.

[0009] The eyepiece or the display apparatus according to the embodiment of the present disclosure includes the first lens and the second lens that are opposed to each other, and a configuration of each of the lenses is optimized with use of a Fresnel lens.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 is an explanatory diagram illustrating a first configuration example of an eyepiece optical system to be used, for example, in a head-mounted display.

[0011] FIG. 2 is an explanatory diagram illustrating a second configuration example of an eyepiece optical system to be used, for example, in a head-mounted display.

[0012] FIG. 3 is an explanatory diagram regarding an image magnification.

[0013] FIG. 4 is an explanatory diagram regarding a configuration and workings of a typical Fresnel lens.

[0014] FIG. 5 is a lens cross-sectional view of a first configuration example of an eyepiece according to an embodiment of the present disclosure.

[0015] FIG. 6 is an explanatory diagram regarding a shape of a Fresnel lens.

[0016] FIG. 7 is an explanatory diagram illustrating comparison of a total length and a weight between an eyepiece according to a comparative example and the eyepiece according to the first configuration example of the present disclosure.

[0017] FIG. 8 is an explanatory diagram illustrating a first example of a method of forming a Fresnel lens surface.

[0018] FIG. 9 is an explanatory diagram illustrating a second example of the method of forming the Fresnel lens surface.

[0019] FIG. 10 is an explanatory diagram illustrating an example of a relationship between an annular-section height of the Fresnel lens surface and luminance unevenness in the eyepiece according to the first configuration example.

[0020] FIG. 11 is an explanatory diagram regarding a reason why the luminance unevenness varies in accordance with the annular-section height of the Fresnel lens surface in the eyepiece according to the first configuration example.

[0021] FIG. 12 is a partially-enlarged diagram illustrating, in an enlarged manner, opposed parts of two Fresnel lens surfaces illustrated in FIG. 11.

[0022] FIG. 13 is an explanatory diagram illustrating an example of an illuminance distribution of stray light in the eyepiece according to the first configuration example.

[0023] FIG. 14 is an explanatory diagram illustrating an example of a path of the stray light in the eyepiece according to the first configuration example.

[0024] FIG. 15 is a partially-enlarged diagram illustrating, in an enlarged manner, opposed parts of two Fresnel lens surfaces illustrated in FIG. 14.

[0025] FIG. 16 is an explanatory diagram illustrating an example of a relationship between step-surface angles of the two Fresnel lens surfaces and an illumination distribution of stray light in the eyepiece according to the first configuration example.

[0026] FIG. 17 is an explanatory diagram illustrating an example of a relationship between step-surface angles of two Fresnel lens surfaces and an illumination distribution of stray light in the eyepiece according to the second configuration example.

[0027] FIG. 18 is an explanatory diagram illustrating an example of a visibility state of annular lines in a virtual image plane of an optical system using the typical Fresnel lens.

[0028] FIG. 19 is an explanatory diagram illustrating an overview of a principle of generation of the annular lines.

[0029] FIG. 20 is an explanatory diagram illustrating an example of a typical method of improving the visibility state of the annular lines.

[0030] FIG. 21 is a lens cross-sectional view of a fifth configuration example of the eyepiece according to the embodiment.

[0031] FIG. 22 is an explanatory diagram illustrating an example of the visibility state of the annular lines in the eyepiece according to the fifth configuration example.

[0032] FIG. 23 is a lens cross-sectional view of a configuration example of an eyepiece according to a comparative example for the eyepiece according to the fifth configuration example.

[0033] FIG. 24 is an explanatory diagram illustrating a configuration example of the annular sections of the first Fresnel lens surface and the second Fresnel lens surface in the eyepiece according to the fifth configuration example, together with a comparative example.

[0034] FIG. 25 is an explanatory diagram illustrating an example of a sag amount of an aspherical shape to be a base for forming the first Fresnel lens surface in the eyepiece according to the fifth configuration example, together with a comparative example.

[0035] FIG. 26 is an explanatory diagram illustrating an example of a sag amount of an aspherical shape to be a base for forming the second Fresnel lens surface in the eyepiece according to the fifth configuration example, together with a comparative example.

[0036] FIG. 27 is an explanatory diagram illustrating a desirable configuration example of the annular sections of the first Fresnel lens surface and the second Fresnel lens surface in the eyepiece according to the fifth configuration example.

[0037] FIG. 28 is a lens cross-sectional view of an eyepiece according to Example 1-1.

[0038] FIG. 29 is an aberration diagram illustrating spherical aberration of the eyepiece according to Example 1-1.

[0039] FIG. 30 is an aberration diagram illustrating field curvature and distortion of the eyepiece according to Example 1-1.

[0040] FIG. 31 is a lens cross-sectional view of an eyepiece according to Example 1-2.

[0041] FIG. 32 is an aberration diagram illustrating spherical aberration of the eyepiece according to Example 1-2.

[0042] FIG. 33 is an aberration diagram illustrating field curvature and distortion of the eyepiece according to Example 1-2.

[0043] FIG. 34 is a lens cross-sectional view of an eyepiece according to Example 1-3.

[0044] FIG. 35 is an aberration diagram illustrating spherical aberration of the eyepiece according to Example 1-3.

[0045] FIG. 36 is an aberration diagram illustrating field curvature and distortion of the eyepiece according to Example 1-3.

[0046] FIG. 37 is a lens cross-sectional view of an eyepiece according to Example 1-4.

[0047] FIG. 38 is an aberration diagram illustrating spherical aberration of the eyepiece according to Example 1-4.

[0048] FIG. 39 is an aberration diagram illustrating field curvature and distortion of the eyepiece according to Example 1-4.

[0049] FIG. 40 is a lens cross-sectional view of an eyepiece according to Example 1-5.

[0050] FIG. 41 is an aberration diagram illustrating spherical aberration of the eyepiece according to Example 1-5.

[0051] FIG. 42 is an aberration diagram illustrating field curvature and distortion of the eyepiece according to Example 1-5.

[0052] FIG. 43 is a lens cross-sectional view of an eyepiece according to Example 1-6.

[0053] FIG. 44 is an aberration diagram illustrating spherical aberration of the eyepiece according to Example 1-6.

[0054] FIG. 45 is an aberration diagram illustrating field curvature and distortion of the eyepiece according to Example 1-6.

[0055] FIG. 46 is a lens cross-sectional view of an eyepiece according to Example 1-7.

[0056] FIG. 47 is an aberration diagram illustrating spherical aberration of the eyepiece according to Example 1-7.

[0057] FIG. 48 is an aberration diagram illustrating field curvature and distortion of the eyepiece according to Example 1-7.

[0058] FIG. 49 is a lens cross-sectional view of an eyepiece according to Example 1-8.

[0059] FIG. 50 is an aberration diagram illustrating spherical aberration of the eyepiece according to Example 1-8.

[0060] FIG. 51 is an aberration diagram illustrating field curvature and distortion of the eyepiece according to Example 1-8.

[0061] FIG. 52 is a lens cross-sectional view of an eyepiece according to Example 2.

[0062] FIG. 53 is an aberration diagram illustrating spherical aberration of the eyepiece according to Example 2.

[0063] FIG. 54 is an aberration diagram illustrating field curvature and distortion of the eyepiece according to Example 2.

[0064] FIG. 55 is a lens cross-sectional view of an eyepiece according to Example 3.

[0065] FIG. 56 is an aberration diagram illustrating spherical aberration of the eyepiece according to Example 3.

[0066] FIG. 57 is an aberration diagram illustrating field curvature and distortion of the eyepiece according to Example 3.

[0067] FIG. 58 is a lens cross-sectional view of an eyepiece according to Example 4.

[0068] FIG. 59 is an aberration diagram illustrating spherical aberration of the eyepiece according to Example 4.

[0069] FIG. 60 is an aberration diagram illustrating field curvature and distortion of the eyepiece according to Example 4.

[0070] FIG. 61 is a lens cross-sectional view of an eyepiece according to Example 5.

[0071] FIG. 62 is an aberration diagram illustrating spherical aberration of the eyepiece according to Example 5.

[0072] FIG. 63 is an aberration diagram illustrating field curvature and distortion of the eyepiece according to Example 5.

[0073] FIG. 64 is a lens cross-sectional view of an eyepiece according to Example 6.

[0074] FIG. 65 is an aberration diagram illustrating spherical aberration of the eyepiece according to Example 6.

[0075] FIG. 66 is an aberration diagram illustrating field curvature and distortion of the eyepiece according to Example 6.

[0076] FIG. 67 is a lens cross-sectional view of an eyepiece according to Example 7.

[0077] FIG. 68 is an aberration diagram illustrating spherical aberration of the eyepiece according to Example 7.

[0078] FIG. 69 is an aberration diagram illustrating field curvature and distortion of the eyepiece according to Example 7.

[0079] FIG. 70 is a lens cross-sectional view of an eyepiece according to Example 8.

[0080] FIG. 71 is an aberration diagram illustrating spherical aberration of the eyepiece according to Example 8.

[0081] FIG. 72 is an aberration diagram illustrating field curvature and distortion of the eyepiece according to Example 8.

[0082] FIG. 73 is an external perspective view of a head-mounted display as an example of a display apparatus, viewed obliquely from the front.

[0083] FIG. 74 is an external perspective view of the head-mounted display as the example of the display apparatus, viewed obliquely from the back.

MODES FOR CARRYING OUT THE INVENTION

[0084] In the following, embodiments of the present disclosure are described in detail with reference to the drawings. Note that the description is given in the following order.

[0085] 0. Comparative Example

[0086] 1. Overview of Eyepiece According to Embodiment (Basic Configuration of Eyepiece)

[0087] 2. Configuration Examples, Workings, and Effects of Eyepiece According to Embodiment

[0088] 3. Example of Application to Display Apparatus

[0089] 4. Numerical Examples of Lenses

[0090] 5. Other Embodiments

0. Comparative Example

[0091] FIG. 1 illustrates a first configuration example of an eyepiece optical system 102 to be used, for example, in a head-mounted display. FIG. 2 illustrates a second configuration example of the eyepiece optical system 102 to be used, for example, in a head-mounted display.

[0092] The eyepiece optical system 102 includes an eyepiece 101 and an image display device 100 in order from an eye point E.P. side along an optical axis Z1.

[0093] The image display device 100 is, for example, a display panel such as an LCD (Liquid Crystal Display) or an organic EL display. The eyepiece 101 is used to magnify and display an image displayed on the image display device 100. With use of the eyepiece 101, a viewer views a virtual image Im that is displayed in a magnified manner. A sealing glass, etc. adapted to protect the image display device 100 may be disposed on a front surface of the image display device 100. The eye point E.P. corresponds to a position of a pupil of the viewer and also serves as an aperture stop STO.

[0094] Here, FIG. 1 illustrates a configuration example in a case where a size of the image display device 100 is smaller than a lens diameter of the eyepiece 101. FIG. 2 illustrates a configuration example in a case where the size of the image display device 100 is larger than the lens diameter of the eyepiece 101.

[0095] In a head-mounted display that has a great viewing angle over 70.degree. and uses the coaxial eyepiece optical system 102, the image display device 100 is often larger than the lens diameter of the eyepiece 101. In such a head-mounted display, although an image magnification Mv can be suppressed to be small, a focal length f becomes relatively long. This leads to a concern that the eyepiece optical system 102 has a long total length. Further, the size of the eyepiece optical system 102 is sometimes limited not by the size of the eyepiece 101 but by the size of the image display device 100. This further leads to an issue of unsuitableness for reduction in size.

[0096] For example, as illustrated in FIG. 1, in a case where the size of the image display device 100 is small, the size of the eyepiece optical system 102 as a whole is limited by the size of the eyepiece 101. In contrast, as illustrated in FIG. 2, in a case where the size of the image display device 100 is large, the size of the eyepiece optical system 102 as a whole is limited by the size of the image display device 100.

[0097] Note that the image magnification Mv is expressed by Mv=.alpha.’/.alpha.. As illustrated in an upper part of FIG. 3, a represents the viewing angle in a case where the eyepiece 101 is not provided. Further, as illustrated in a lower part of FIG. 3, a’ represents the viewing angle (the viewing angle with respect to the virtual image Im) in a case where the eyepiece 101 is provided. In FIG. 3, his a maximum image height of the image to be viewed, and is, for example, a maximum image height of an image displayed on the image display device 100. For example, in a case where the image display device 100 has a rectangular shape, h is a half value of a diagonal size of the image display device 100. f represents a focal length of the eyepiece 101.

[0098] Further, the image magnification Mv is expressed by the following expression (A),

Mv=.omega.’/(tan.sup.-1(h/L)) (A) [0099] where .omega.’ is a half value (rad) of a maximum viewing angle, [0100] h is the maximum image height, and [0101] L is a total length (a distance from the eye point E.P. to an image).

[0102] Note that the image refers to an image displayed on the image display device 100, for example. For example, in the case where the image display device 100 has the rectangular shape, h is the half value of the diagonal size of the image display device 100, as described above. L corresponds to the total length of the eyepiece optical system 102 described above (a distance from the eye point E.P. to a display surface of the image display device 100), for example.

[0103] Setting the image magnification My to a high magnification of 2.1 or more and setting the size of the image display device 100 to be smaller with respect to the lens diameter of the eyepiece 101 as in the configuration example illustrated in FIG. 1 make it is possible to reduce a volume occupied by the eyepiece optical system 102. In such a case, however, because of the high magnification, various aberrations including field curvature and distortion are generated in great amounts. Therefore, in order to secure adequate image definition, for example, it can be necessary to provide at least three lenses in the eyepiece 101. Accordingly, there is an issue of an increase in weight or total length of the eyepiece 101.

[0104] To address this, a method of using a Fresnel lens is widely known as a means for reducing the weight or the total length of the eyepiece 101. PTL 1 (Japanese Unexamined Patent Application Publication No. H7-244246) discloses a technique related to an eyepiece optical system of a high-magnification head-mounted display using a Fresnel lens. The technique disclosed in PTL 1 achieves the reduction in weight and total length with use of the Fresnel lens, as compared with an eyepiece optical system using a standard lens. In the technique described in PTL 1, an image formation performance is enhanced by providing a most-eye-side lens surface with a concave shape and causing the most-eye-side lens surface to have a Fresnel lens surface. Therefore, there is an issue that the total length of the eyepiece optical system becomes longer or the lens diameter becomes larger in order to secure a sufficient distance between an eye and the most-eye-side lens.

[0105] Here, FIG. 4 illustrates a configuration and a working of a typical Fresnel lens 300.

[0106] The Fresnel lens 300 has two or more annular sections 301 formed concentrically about the optical axis Z1. The annular sections 301 each have a border part on which a step surface 302 is formed. The Fresnel lens 300 has a Fresnel lens surface Fr having a sawtooth-shaped cross-section.

[0107] As illustrated in FIG. 4, an eyepiece optical system using the Fresnel lens 300 involves generation of stray light in a direction that differs from a design path due to the step surface 302. This stray light is visually recognized as a ghost or a flare, leading to an issue of deterioration in image quality (in particular, contrast). As a means for reducing this stray light, there is a method of forming a light-blocking layer on the step surface 302 as in a technique described in PTL 2 (Japanese Unexamined Patent Application Publication No. 2015-59959). The light-blocking layer absorbs visible light. However, this method involves issues of difficulty in process, difficulty in highly-precise film formation, and an increase in manufacturing cost due to an increase in number of processes.

[0108] As described above, even if the Fresnel lens is used in the eyepiece, it is not always possible to obtain a sufficient optical effect depending on a surface on which the Fresnel lens is formed, a shape, etc.

[0109] Therefore, it is desired to develop an eyepiece that allows for a wide viewing angle and favorable aberration correction while reducing a weight and a total length with use of the Fresnel lens.

1. Overview of Eyepiece According to Embodiment (Basic Configuration of Eyepiece)

[0110] An eyepiece according to an embodiment of the present disclosure is applicable to, for example, the eyepiece optical system 102 of a head-mounted display, as with the comparative example described above.

[0111] The eyepiece according to the embodiment of the present disclosure includes a first lens and a second lens that are opposed to each other. The first lens includes a first Fresnel lens surface Fr1 formed at least in a peripheral region of a lens surface that is opposed to the second lens. The second lens includes a second Fresnel lens surface Fr1 formed at least in a peripheral region of a lens surface that is opposed to the first lens. Using two Fresnel lenses and so disposing the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 that the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 are opposed to each other make it possible to achieve an optical system having a short total length.

[0112] It is preferable that the eyepiece according to the embodiment of the present disclosure satisfy a conditional expression (1) to have the image magnification My of 2.1 or greater, and be applied to the eyepiece optical system 102 in which the size of the image display device 100 is smaller than the lens diameter of the eyepiece 101 as in the configuration example illustrated in FIG. 1.

Mv.gtoreq.2.1 (1)

[0113] Further, as in first to fourth configuration examples described later, it is preferable that a step-surface angle .theta.d of the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 with respect to the optical axis Z1 be a predetermined angle (e.g., 15.degree. or 20.degree.) or greater. This contributes to suppress generation of stray light, and to reduce generation of a ghost or a flare.

[0114] Alternatively, as in fifth to eighth configuration examples described later, it is preferable to provide a configuration that improves a visibility state of the annular section 301 in the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 with respect to the first to the fourth configuration examples.

[0115] The eyepiece according to the embodiment of the present disclosure can be used for a small and high-resolution image display device 100 such as an image display device 100 of 4k having a size of 1.5 inches or less, for example. This makes it possible to secure a wide viewing angle and high image definition while reducing a weight and a total length. Moreover, it is possible to suppress generation of a flare or a ghost, making it possible to provide a high-contrast visual image.

2. Configuration Examples, Workings, and Effects of Eyepiece According to Embodiment

[0116] A description is given below of the first to the fourth configuration examples that satisfy the above-described basic configuration of the eyepiece. In addition, the fifth to the eighth configuration examples in which the visibility state of the annular section 301 is improved compared with the first to the fourth configuration examples are described.

Definition of Terms

[0117] Note that, in the following configuration examples and the following Examples, an i-th lens from an eye side (the eye point E.P. side) is referred to as Li. For example, a lens closest to the eye side is referred to as a first lens L1. Further, regarding each lens, a surface on the eye point E.P. side is referred to as an R1 surface, and a surface on an image side (an image display device 100 side) that is magnified by the eyepiece is referred to as an R2 surface. For example, a surface, of the first lens L1, on the eye point E.P. side is referred to as an L1 (R1) surface, a surface, of the first lens L1, on the image side is referred to as an L1(R2) surface, and so on.

[0118] Further, in the following configuration examples and the following Examples, a usual lens surface which is not a Fresnel lens surface is referred to as a standard lens surface. The standard lens surface encompasses not only a spherical surface but also aspherical surfaces other than that having a Fresnel shape.

[0119] Further, in the following configuration examples and the following Examples, as with the Fresnel lens 300 illustrated in FIGS. 4 and 6, a surface that is not an effective lens surface in the Fresnel lens surface Fr is referred to as a step surface (the step surface 302). In the Fresnel lens surface Fr, a height of each of the annular sections 301 divided concentrically is referred to as an “annular-section height” (an annular-section height Rh), and a distance between vertices of two adjacent annular sections 301 is referred to as an “annular-section pitch” (an annular-section pitch Rp).

[0120] Further, an on-axial distance between the eye point E.P. and the lens surface (the L1(R1) surface), of the eyepiece, that is closest to the eye point E.P. side is referred to as an “eye relief” (eye relief E.R.).

(Conditions for Simulation of Stray Light Generation Amount)

[0121] Calculation for simulations (FIGS. 13, 16, and 17) of a generation amount of stray light (an illuminance distribution) was made under the following conditions unless otherwise specified. [0122] A light distribution characteristic of the image display device 100: Lambertian [0123] The size of the image display device 100: 17 mm.times.27 mm (vertical.times.horizontal) [0124] A pupil diameter: .phi. 4 mm [0125] A shape of the Fresnel lens surface: Annular-section height Rh=100 .mu.m (constant) (An annular-section pitch Rp is unequal) [0126] A reference wavelength: 587.6 nm (d-line)

First Configuration Example

[0127] FIG. 5 illustrates a first configuration example of the eyepiece according to the embodiment. This first configuration example corresponds to configurations (FIG. 28, etc.) of eyepieces according to Examples 1-1 to 1-8 described later.

[0128] The eyepiece according to the first configuration example of the present disclosure has a two-group two-lens configuration in which a first lens L1 and a second lens L2 are disposed in order from the eye point E.P. side toward the image side.

[0129] The first Fresnel lens surface Fr1 is formed in an entire region from a center to a periphery of a lens surface (a L1 (R2) surface), of the first lens L1, that is opposed to the second lens L2.

[0130] The second Fresnel lens surface Fr2 is formed in an entire region from a center to a periphery of a lens surface (a L2(R1) surface), of the second lens L2, that is opposed to the first lens L1.

[0131] Further, it is preferable that the first lens L1 include a lens surface (L1(R1) surface) on the eye point E.P. side that has a convex shape or a planar shape. This makes it possible to secure a long eye relief E.R., which achieves an easier-to-view structure. For example, in a concave lens having a great power, even if a certain degree of eye relief E.R. is secured, an edge part of the lens interferes with the eye, causing an adverse effect of difficulty in viewing.

[0132] Further, it is preferable that the step-surface angle .theta.d of the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 with respect to the optical axis Z1 be 15.degree. or greater.

[0133] Further, it is preferable that the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 each have positive refractive power. This makes it possible to efficiently correct various aberrations, making it possible to reduce the total length and the weight.

[0134] Further, it is preferable that the first lens L1, the second lens L2, or both include an aspherical surface having an inflection point. In the first lens L1 and the second lens L2, using one or more aspherical surfaces for a surface other than the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2, and providing the one or more aspherical surfaces with an inflection point make it possible to efficiently correct astigmatism, field curvature, and distortion with small number of lenses. Further, providing the aspherical shape with the inflection point makes it possible to efficiently correct distortion.

[0135] Further, it is preferable that the following conditional expression (2) be satisfied to have a refractive index nd of 1.7 or less, where nd is a refractive index of each of the first lens L1 and the second lens L2 with respect to the d-line. This makes it possible to reduce the weight of the eyepiece.

nd.ltoreq.1.7 (2)

[0136] Further, it is preferable that

.psi.1.ltoreq..psi.2 (3)

be satisfied where .psi.1 is refractive power of the first Fresnel lens surface Fr1, and .psi.2 is refractive power of the second Fresnel lens surface Fr2. This makes it possible to efficiently correct various aberrations, making it possible to reduce the total length and the weight.

[0137] Note that the refractive power .psi.1 is expressed by (nd1-1)/R1, where nd1 is a refractive index of the first Fresnel lens surface Fr1 with respect to the d-line, and R1 is a curvature radius of the first Fresnel lens surface Fr1. The refractive power .psi.2 is expressed by (nd2-1)/R2, where nd2 is a refractive index of the second Fresnel lens surface Fr2 with respect to the d-line, and R2 is a curvature radius of the second Fresnel lens surface Fr2.

[0138] In terms of easy processing of the Fresnel lens surface and the aspherical surface, it is desirable to use a resin material such as an acrylic-based material, a polyolefin-based material, or polycarbonate as the material of the first lens L1 and the second lens L2. Configuring the first lens L1 and the second lens L2 only with use of the resin material, it is possible to reduce the weight and the size, as compared with a case of a configuration including one or more glass lenses. A reason for this is that a glass material with a high refractive index used to gain refractive power is replaceable with a thin and light-weighted Fresnel lens.

(Effects of Fresnel Lens Surfaces Opposed to Each Other)

[0139] As described above, the eyepiece according to the first configuration example of the present disclosure is characterized in that the two Fresnel lens surfaces, i.e., the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 are opposed to each other. A reason for this is described below.

[0140] FIG. 7 illustrates the eyepieces according to Comparative examples 1 to 3 and the eyepiece according to the first configuration example of the present disclosure (Example 1), comparing the eyepieces in terms of total length and weight.

[0141] In FIG. 7, the eyepiece according to Comparative example 1 has a configuration in which the Fresnel lens surface (the first Fresnel lens surface Fr1) is formed only on the L1(R2) surface of the first lens L1. The eyepiece according to Comparative example 2 has a configuration in which the Fresnel lens surface (the second Fresnel lens surface Fr2) is formed only on the L2(R1) surface of the second lens L2. The eyepiece according to Comparative example 3 has a configuration in which two Fresnel lens surfaces are formed on the L1(R2) surface of the first lens L1 and the L2(R2) surface of the second lens L2 without being opposed to each other.

[0142] Specifications of the eyepieces according to Comparative examples 1 to 3 and Example 1 in FIG. 7 are as follows.

[0143] The maximum FOV (Field of view): 100.degree.

[0144] The eye relief E.R.: 13 mm

[0145] The size of the image display device 100: 17 mm.times.27 mm (vertical.times.horizontal)

[0146] Referring to FIG. 7, it is understood that the total length and the lens weight are allowed to be minimized by providing each of the L1(R2) surface of the first lens L1 and the L2(R1) surface of the second lens L2 with the Fresnel lens surface. A reason for this is that the use of the Fresnel lenses for the L1 (R2) surface and the L2(R1) surface that require refractive power makes it possible to refract light rays efficiently in terms of space.

[0147] The eyepiece according to the first configuration example of the present disclosure minimizes the total length and the lens weight. In addition thereto, the eyepiece according to the first configuration example of the present disclosure is an image-side telecentric optical system, making it possible to suppress sensitivity to eccentricity of the lens, the image display device 100, etc. to be low. Furthermore, it is also possible to reduce luminance unevenness, color unevenness, etc. caused by the viewing angle characteristic of the image display device 100, providing an advantage also in terms of image quality as compared with other configurations.

(Regarding Method of Dividing Fresnel Lens Surface into Annular Sections (Forming Method))

[0148] FIG. 8 illustrates a first example of a method of forming the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2. FIG. 9 illustrates a second example of the method of forming the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2.

[0149] In the first forming method illustrated in FIG. 8, a convex lens 400 is concentrically divided to so form two or more annular sections 301 that the annular-section height Rh is constant (the annular-section pitch Rp is unequal). In the second forming method illustrated in FIG. 9, the convex lens 400 is concentrically divided to so form two or more annular sections 301 that the annular-section pitch Rp is constant (the annular-section height Rh is unequal).

[0150] Regarding the eyepiece according to the present disclosure, it is preferable to so form the annular sections 301 that the annular-section height Rh is constant, as in the first forming method illustrated in FIG. 8. A reason for this is that, as compared with a structure having the constant annular-section pitch Rp as in the second forming method illustrated in FIG. 9, a central region of the lens is not divided, making it possible to secure image quality of the central region of the field of view which is important in the head-mounted display, etc.

[0151] Further, an optimal annular-section height Rh is described. FIG. 10 illustrates an example of a relationship between the annular-section height of the Fresnel lens surface and the luminance unevenness in the eyepiece according to the first configuration example. FIG. 11 is an explanatory diagram regarding a reason why the luminance unevenness varies depending on the annular-section height of the Fresnel lens surface in the eyepiece according to the first configuration example. FIG. 12 illustrates, in an enlarged manner, a region 600 of a part of the opposed parts of the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 illustrated in FIG. 11.

[0152] FIG. 10 illustrates a result of analyzing an illumination distribution in a virtual image plane when performing full-white display on the image display device 100, and illustrates annular-section height Rh dependence of the illuminance distribution. It can be appreciated that more luminance unevenness is generated in accordance with an increase in the annular-section height Rh. A reason for this is that, as illustrated in the region 600 in FIGS. 11 and 12, an area of a bundle of light rays passing through the step surfaces 302 of the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 differs depending on the image height, due to an influence of vignetting of light rays caused by the step surfaces 302, and the area of the bundle of light rays passing through the step surface 302 increases in accordance with an increase in the annular-section height Rh.

[0153] Referring to FIG. 10, remarkable luminance unevenness is observed in a case of over 400 .mu.m. It is therefore desirable that the annular-section height Rh be about 400 .mu.m or less. However, if the annular sections 301 are provided at excessively small pitches, there is an issue of low definition resulting from an influence of spreading of light caused by diffraction. In order not to impair the definition by the diffraction, it is desirable that annular-section height Rh be about 20 .mu.m or greater.

(Regarding Step Surface of Annular Section)

[0154] FIG. 13 illustrates an example of an illuminance distribution of stray light in the eyepiece according to the first configuration example. FIG. 14 illustrates an example of a path of the stray light in the eyepiece according to the first configuration example. FIG. 15 illustrates, in an enlarged manner, the region 600 of a part of the opposed parts of the two Fresnel lens surfaces illustrated in FIG. 14.

[0155] Varying a gradient angle (the step-surface angle .theta.d) of the step surface 302 of the annular section 301 on the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 makes it possible to reduce an amount of stray light entering an eye 500. FIG. 13 illustrates a result of extracting only a stray light component in the illuminance distribution of the virtual image plane in a case where the step-surface angle .theta.d of each of the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 is set to 0.degree. and white display is performed on the image display device 100 in the eyepiece according to the first configuration example of the present disclosure.

[0156] Note that, because the stray light is a factor of a flare or a ghost, it is ideally desirable that no stray light be generated, that is, it is desirable that the amount of the stray light be 0. FIGS. 14 and 15 illustrate results of analyzing a dominant path of this stray light. Referring to FIGS. 14 and 15, it can be appreciated that the stray light is a component that enters the eye 500 via the step surface 302. That is, appropriately setting the step surface 302 makes it possible to reduce an amount of the stray light entering the eye 500.

[0157] FIG. 16 illustrates an example of a relationship between step-surface angles .theta.d(L1) and .theta.d(L2) of the two Fresnel lens surfaces and an illuminance distribution of the stray light in the eyepiece according to the first configuration example (Example 1). Note that, in FIG. 16, .theta.d(L1) is the step-surface angle of the first Fresnel lens surface Fr1, and .theta.d(L2) is the step-surface angle of the second Fresnel lens surface Fr2.

[0158] FIG. 16 illustrates a result of calculating the illuminance distribution of the stray light on the virtual image plane in a case where the step-surface angle .theta.d(L1) of the first Fresnel lens surface Fr1 and the step-surface angle .theta.d(L2) of the second Fresnel lens surface Fr2 are varied. Referring to FIG. 16, regarding the eyepiece according to the first configuration example, setting each of the step-surface angles .theta.d(L1) and .theta.d(L2) to an angle of 15.degree. or greater makes it possible to reduce the dominant stray light, making it possible to provide a high-contrast visual image.

Second Configuration Example

[0159] An eyepiece according to a second configuration example of the present disclosure corresponds to a configuration (FIG. 52) of an eyepiece according to Example 2 described later.

[0160] Compared with the eyepiece according to the first configuration example described above, the eyepiece according to the second configuration example of the present disclosure has a configuration that further includes a third lens L3 disposed closer to the image side than the first lens L1 and the second lens L2. That is, the eyepiece according to the second configuration example of the present disclosure has a three-group three-lens configuration in which the first lens L1, the second lens L2, and the third lens L3 are disposed in order from the eye point E.P. side toward the image side.

[0161] The third lens L3 is a standard lens in which no Fresnel lens surface is used. It is preferable that the third lens L3 be an aspherical lens on which an aspherical surface having an inflection point is formed on at least one surface.

[0162] In a manner approximately similar to that of the eyepiece according to the first configuration example, the eyepiece according to the second configuration example of the present disclosure includes the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 that are opposed to each other in the first lens L1 and the second lens L2.

[0163] Compared with the eyepiece according to the first configuration example, the eyepiece according to the second configuration example of the present disclosure is increased in weight, total length of the optical system, etc. by the addition of the third lens L3; however, more adequate aberration correction is allowed, making it possible to provide a high-definition image, as described later in Example 2.

[0164] FIG. 17 illustrates an example of a relationship between the step-surface angles .theta.d(L1) and .theta.d(L2) of the two Fresnel lens surfaces and the illuminance distribution of the stray light in the eyepiece according to the second configuration example (Example 2). Note that, in FIG. 17, .theta.d(L1) is the step-surface angle of the first Fresnel lens surface Fr1, and .theta.d(L2) is the step-surface angle of the second Fresnel lens surface Fr2.

[0165] FIG. 17 illustrates a result of calculating the illuminance distribution of the stray light on the virtual image plane in the case where the step-surface angle .theta.d(L1) of the first Fresnel lens surface Fr1 and the step-surface angle .theta.d(L2) of the second Fresnel lens surface Fr2 are varied. Referring to FIG. 17, regarding the eyepiece according to the second configuration example (Example 2), setting each of the step-surface angles .theta.d(L1) and .theta.d(L2) to an angle of 20.degree. or greater makes it possible to reduce the dominant stray light, making it possible to provide a high-contrast visual image.

[0166] It is preferable that other configurations be approximately similar to those in the eyepiece according to the first configuration example described above.

Third Configuration Example

[0167] An eyepiece according to a third configuration example of the present disclosure corresponds to a configuration (FIG. 55) of an eyepiece according to Example 3 described later.

[0168] As with the eyepiece according to the first configuration example described above, the eyepiece according to the third configuration example of the present disclosure has a two-group two-lens configuration in which the first lens L1 and the second lens L2 are disposed in order from the eye point E.P. side toward the image side.

[0169] In a manner approximately similar to that of the eyepiece according to the first configuration example, the eyepiece according to the third configuration example of the present disclosure includes the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 that are opposed to each other in the first lens L1 and the second lens L2.

[0170] Note that, in the eyepiece according to the third configuration example of the present disclosure, the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 are formed only in a peripheral region.

[0171] In the eyepiece according to the third configuration example of the present disclosure, the first Fresnel lens surface Fr1 is formed only in the peripheral region on the lens surface (the L1(R2) surface), of the first lens L1, that is opposed to the second lens L2. A middle region of the L1 (R2) surface of the first lens L1 is provided as a first non-Fresnel lens surface (a spherical surface or an aspherical surface).

[0172] Similarly, in the eyepiece according to the third configuration example of the present disclosure, the second Fresnel lens surface Fr2 is formed only in the peripheral region on the lens surface (the L2(R1) surface), of the second lens L2, that is opposed to the first lens L1. A middle region of the L2(R1) surface of the second lens L2 is provided as a second non-Fresnel lens surface (a spherical surface or an aspherical surface).

[0173] Typically, the Fresnel lens has poor sharpness due to an influence of the step surface 302 or a manufacturing error, compared with the standard lens. In the eyepiece according to the third configuration example of the present disclosure, however, owing to the use of the standard lens in the middle region, it is possible to secure high definition in the central region of the image. Border parts of the optical system of the middle region and the peripheral region are smoothly coupled to each other, making it possible to prevent the borders from being visually recognized.

[0174] In the eyepiece (FIG. 55) according to Example 3 described later, an effective diameter .phi..sub.v1 of the middle region of the L1(R2) surface of the first lens L1 is 25.004, and an effective diameter .phi..sub.v2 of the middle region of the L2(R1) surface of the second lens L2 is 27.054. The effective diameters .phi..sub.v1 and .phi..sub.v2 of the middle regions are each an effective range that allows a bundle of light rays entering a pupil at an angle of 35.degree. to pass therethrough in a state where the pupil center is on the optical axis. Thus providing the border part between the Fresnel lens surface and the standard lens surface at about 35.degree. or greater in the field of view makes it more difficult for the border between the middle region and the peripheral region to be recognized, achieving a natural appearance. If it is much less than 35.degree., the border part becomes conspicuous, leading to a concern of deterioration of image quality.

[0175] It is preferable that other configurations be approximately similar to those in the eyepiece according to the first configuration example described above. [Fourth Configuration Example]

[0176] An eyepiece according to a fourth configuration example of the present disclosure corresponds to a configuration (FIG. 58) of an eyepiece according to Example 4 described later.

[0177] Compared with the eyepiece according to the third configuration example described above, the eyepiece according to the fourth configuration example of the present disclosure has a configuration that further includes a third lens L3 disposed closer to the image side than the first lens L1 and the second lens L2. That is, the eyepiece according to the fourth configuration example of the present disclosure has a three-group three-lens configuration in which the first lens L1, the second lens L2, and the third lens L3 are disposed in order from the eye point E.P. side toward the image side.

[0178] The third lens L3 is a standard lens in which no Fresnel lens surface is used. It is preferable that the third lens L3 be an aspherical lens on which an aspherical surface having an inflection point is formed on at least one surface.

[0179] Compared with the eyepiece according to the third configuration example, the eyepiece according to the fourth configuration example of the present disclosure is increased in weight, total length of the optical system, etc. by the addition of the third lens L3; however, more adequate aberration correction is allowed, making it possible to provide a high-definition image, as described later in Example 4.

[0180] In a manner approximately similar to that of the eyepiece according to the first configuration example, the eyepiece according to the fourth configuration example of the present disclosure includes the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 that are opposed to each other in the first lens L1 and the second lens L2.

[0181] Note that, in the eyepiece according to the fourth configuration example of the present disclosure, the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 are formed only in a peripheral region, as with the eyepiece according to the third configuration example.

[0182] In the eyepiece (FIG. 58) according to Example 4 described later, an effective diameter .phi..sub.v1 of the middle region of the L1(R2) surface of the first lens L1 is 24.116, and an effective diameter .phi..sub.v2 of the middle region of the L2(R1) surface of the second lens L2 is 27.038. The effective diameters .phi..sub.v1 and .phi..sub.v2 of the middle region are each an effective range that allows a bundle of light rays entering a pupil at an angle of 35.degree. to pass therethrough in a state where the pupil center is on the optical axis, as with the eyepiece according to Example 3.

[0183] It is preferable that other configurations be approximately similar to those in the eyepiece according to the third configuration example described above.

(Overview of Visibility State of Annular Section)

[0184] Next, a description is given of the fifth to the eighth configuration examples in which a visibility state of the annular section 301 is improved, compared with that in the first to the fourth configuration examples described above. First, an overview of the visibility state of the annular section 301 is described.

[0185] As described above, in the first to the fourth configuration examples, appropriately setting the step-surface angle .theta.d(L1) of the first Fresnel lens surface Fr1 and the step-surface angle .theta.d(L2) of the second Fresnel lens surface Fr2 allows for reduction in generation of stray light due to the step surface 302.

[0186] In contrast, as illustrated in (B) of FIG. 18, an optical system using a typical Fresnel lens has an issue that concentric lines (referred to as “annular lines”) derived from the annular sections 301 are visually recognized in the virtual image plane. Note that (A) of FIG. 18 illustrates an example of a state in which no annular line is visually recognized.

[0187] FIG. 19 illustrates an overview of a principle of generation of the annular lines. FIG. 20 illustrates an example of a method of improving the visibility state of typical annular lines. FIGS. 19 and 20 each illustrate an example of the two-group two-lens configuration in which the first lens L1 and the second lens L2 are disposed, and the lens surfaces opposed to each other are the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2, as in the eyepiece according to the first configuration example described above.

[0188] As illustrated in FIG. 19, the vignetting of the light resulting from the step surfaces 302 of the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 causes a generation amount of the vignetting to vary in accordance with the angle of view. As a result, the annular lines are visually recognized in the virtual image plane. As a means for solving this, as illustrated in FIG. 20, there is a method of causing an angle of a light ray entering the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 to coincide with the step-surface angle .theta.d. According to this method, the annular lines can be improved; however, because it is necessary to set the step-surface angle .theta.d to be smaller than the predetermined angle (e.g., 15.degree. or 20.degree.) described above in the first to the fourth configuration examples, stray light is generated, thereby lowering contrast. Therefore, it is difficult to achieve both reduction of the stray light and reduction of visibility of the annular lines in the first to the fourth configuration examples described above.

[0189] Therefore, a description is given of configuration examples of an eyepiece that makes it possible to further improve the visibility state of the annular lines and to provide a visual image with higher image quality, compared with the first to the fourth configuration examples. According to the fifth to the eighth configuration examples described below, image quality in a central region of the field of view is improved in particular.

(Overview of Fifth to Eighth Configuration Examples]

[0190] The fifth to the eighth configuration examples are different in the step-surface angle .theta.d from the first to the fourth configuration examples described above, but have basic configurations similar to those of the first to the fourth configuration examples described above. Each of the fifth to the eighth configuration examples includes at least the first lens L1 and the second lens L2, and the lens surfaces opposed to each other are provided as the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2. It is preferable that each of eyepieces according to the fifth to the eighth configuration examples satisfy the foregoing conditional expression (1) to have the image magnification My of 2.1 or greater, and be applied to the eyepiece optical system 102 in which the size of the image display device 100 is smaller than the lens diameter of the eyepiece 101 as in the configuration example illustrated in FIG. 1.

(Conditions for Simulation)

[0191] Calculation for simulations in the fifth to the eighth configuration examples was made under the following conditions unless otherwise specified. [0192] A light distribution characteristic of the image display device 100: Lambertian [0193] The size of the image display device 100: 17 mm.times.27 mm (vertical.times.horizontal) [0194] A pupil diameter: .phi. 4 mm [0195] A shape of the Fresnel lens surface: An annular-section height Rh=150 .mu.m (constant) (An annular-section pitch Rp is unequal) [0196] A reference wavelength: 587.6 nm (d-line)

Fifth Configuration Example

[0197] The eyepiece according to the fifth configuration example of the present disclosure corresponds to a configuration (FIG. 61) of an eyepiece according to Example 5 described later.

[0198] FIG. 21 illustrates the fifth configuration example of the eyepiece according to the embodiment. As illustrated in FIG. 21, compared with the configuration of the eyepiece according to the first configuration example described above, the eyepiece according to the fifth configuration example has a configuration that further includes a third lens L3 disposed closer to the image side than the first lens L1 and the second lens L2. That is, the eyepiece according to the fifth configuration example has a three-group three-lens configuration in which the first lens L1, the second lens L2, and the third lens L3 are disposed in order from the eye point E.P. side toward the image side.

[0199] The first Fresnel lens surface Fr1 is formed in an entire region from a center to a periphery of a lens surface (a L1(R2) surface), of the first lens L1, that is opposed to the second lens L2.

[0200] The second Fresnel lens surface Fr2 is formed in an entire region from a center to a periphery of a lens surface (a L2(R1) surface), of the second lens L2, that is opposed to the first lens L1.

[0201] The third lens L3 is a standard lens in which no Fresnel lens surface is used. It is preferable that the third lens L3 be an aspherical lens.

[0202] As illustrated in FIG. 21, it is desirable that the eyepiece according to the fifth configuration example satisfy

0.2

where L’ is a distance from a most-eye-point-side lens surface to the image plane, and d is a distance from the most-eye-point-side lens surface to a most-image-side lens surface.

[0203] A conditional expression (4) relates to an appropriate range of a ratio between the distance (L’) obtained by subtracting the eye relief E.R. from the total length of the eyepiece and the distance d from the most-eye-point-side lens surface to the most-image-side lens surface. Satisfying the conditional expression (4) makes it possible to perform balanced aberration correction with a short total length.

(Relationship Between Positions of Fresnel Lens Surfaces and Visibility State of Annular Lines)

[0204] FIG. 22 illustrates an example of the visibility state of the annular lines in the eyepiece according to the fifth configuration example. FIG. 23 illustrates a configuration example of the eyepiece according to a comparative example for the eyepiece according to the fifth configuration example.

[0205] Light from the image display device 100 involves vignetting occurring due to the step surfaces 302 of the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2. Accordingly, an in-plane luminance distribution in the vicinity of the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 has a great light-dark contrast as illustrated in (A) in FIG. 22. The eyepiece according to the fifth configuration example is characterized in that the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 are disposed on the side closer (for example, at about 15 mm) to the eye 500. A focal position of a human eye is at a position away from the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2, for example, at a position 100 mm or more away from the eye 500. Because the human eye cannot focus on the position of the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2, it is defocused as illustrated in (B) of FIG. 22 and visually recognized as the annular lines.

[0206] As described above, in the eyepiece according to the fifth configuration example, the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 are disposed on the side closer to the eye 500, allowing for an increase in a blurring amount of the annular lines and making it possible to lower the visibility of the annular lines. In contrast, in the eyepiece according to the comparative example in FIG. 23, the second Fresnel lens surface Fr2 is disposed on the image-side lens surface of the second lens L2. In the eyepiece according to the comparative example in FIG. 23, the second Fresnel lens surface Fr2 is disposed at a position further away from the eye 500, compared with the eyepiece according to the fifth configuration example, making it easier for the annular lines to be visually recognized than in the eyepiece according to the fifth configuration example.

(Relationship Between Positions of Annular Sections on Fresnel Lens Surfaces and Visibility State of Annular Lines)

[0207] FIG. 24 illustrates a configuration example of the annular sections 301 of the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 in the eyepiece according to the fifth configuration example, together with those according to the comparative example.

[0208] It is desirable that an eyepiece optical system such as a head-mounted display secure sufficient definition particularly in the central region of the field of view. As illustrated in the comparative example in (A) of FIG. 24, in a case where the annular sections 301 of the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 are in the central region, the definition is lowered due to the annular sections 301, making it easier for the annular lines to be visually recognized. Therefore, as illustrated in (B) of FIG. 24, it is desirable to provide the first annular section (the first annular section) counted from the center in a region as peripheral as possible in the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2.

[0209] As illustrated in FIGS. 8 and 9 described above, the two or more annular sections 301 in the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 are formed by, for example, concentrically dividing the convex lens 400. The convex lens 400 to be a base for forming the annular sections 301 has, for example, an aspherical shape. In order to provide the first annular section in the peripheral region, it is desirable that the aspherical shape of the base have refractive power, in a central region, which is suppressed to be small.

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