Optical Department

Abstract

To provide an optical system which satisfies demands on compactness and improvement in light intensity efficiency, and yet offers good optical characteristics.SOLUTION: An optical system is provided, comprising a first reflective polarizing plate 11, a first lens L1 having positive refractive power, a half mirror HM, a second lens L2 having positive refractive power, and a second reflective polarizing plate 12 arranged in order from the pupil plane (EP) side to the display surface (IMG) side, as well as a first 1 / 4 wavelength plate 21 located between the pupil plane (EP) and the half mirror HM, and a second 1 / 4 wavelength plate 22 located between the half mirror HM and the display surface (IMG). The second lens L2 has a pupil plane-side surface that is convex near an optical axis. A paraxial curvature radius r1 of a surface of the first lens L1 on the pupil plane (Ep) side and a paraxial curvature radius r2 of a surface of the first lens on the display surface side satisfy the following conditional expression: -3.2<r1 / r2<-0.9 ...(1).SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] As display devices using image display elements, electronic viewfinders, electronic binoculars, head-mounted displays and the like are known.

[0003] In such a display device, it is necessary to make the distance between the image display element and the eye as short as possible. Since the optical system mounted on the display device is accommodated in a limited space, it is difficult to eliminate various aberrations, and the correction range thereof is also limited. Therefore, it is important in the design of the optical system to make use of the physiological optical characteristics of the eye to achieve mutual complementation.

[0004] Visual acuity depends on the density of cones in photoreceptor cells, and the eye has the characteristic of forming a clear image at the fovea centralis of the macula, that is, near the center of the pupil. By narrowing the pupil, the depth of focus increases, and the effects of spherical aberration and coma are reduced, so that the sensitivity to blurring can be reduced even if there is excess or deficiency in these aberrations or refraction correction. In addition, the effects of spherical aberration, coma and chromatic aberration can be reduced by utilizing the phenomenon that the sensitivity of light rays incident from the periphery is lower than the sensitivity of light rays passing through the central part of the pupil, the so-called Stiles-Crawford effect. By maintaining this state, gradual adaptation occurs, so that the influence of distortion and the like can also be reduced.

[0005] Note that optical systems mounted on such display devices are often required to be compact and have high light quantity efficiency. Here, the light quantity efficiency refers to the ratio of the light quantity reaching the eye (pupil plane) when the light quantity on the display surface of the image display element is taken as 100%.

[0006] As a conventional optical system, for example, the optical system described in Patent Document 1 below is known. Patent Document 1 discloses an optical system comprising a partial optical system having two semi-transparent surfaces and a refractive optical element having power. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 3441188 [Overview of the project] [Problems that the invention aims to solve]

[0008] Even when attempting to miniaturize and improve light intensity efficiency using the optical system described in Patent Document 1, the two semi-transparent surfaces make it difficult to improve light intensity efficiency, and good optical performance cannot be obtained.

[0009] This invention has been made in view of the above-mentioned problems, and aims to provide an optical system that satisfies the requirements for miniaturization and improved light efficiency in a balanced manner, while also possessing high resolution with well-corrected aberrations. [Means for solving the problem]

[0010] The optical system according to the present invention comprises, in order from the pupil side to the display side, a first reflective polarizer, a first lens having positive refractive power, a half mirror, a second lens having positive refractive power, and a second reflective polarizer, as well as a first quarter-wave plate positioned between the pupil and the half mirror, and a second quarter-wave plate positioned between the half mirror and the display surface. The second lens is convex on the pupil side in the paraxial direction. In this specification, the convex, concave, and planar surfaces of a lens refer to the shape in the paraxial direction, and refractive power refers to the refractive power in the paraxial direction unless otherwise specified.

[0011] A reflective polarizer reflects linearly polarized light with a certain polarization direction and transmits linearly polarized light with a polarization direction perpendicular to it.

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

[0013] The first lens has positive refractive power, which suppresses spherical aberration, astigmatism, field curvature, and distortion.

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

[0015] The second lens, possessing positive refractive power, effectively corrects spherical aberration, coma aberration, astigmatism, field curvature, and distortion.

[0016] In the optical system of the present invention, a first reflective polarizer, a first lens having positive refractive power, and a first quarter-wave plate constitute the element group on the pupil side, and a second quarter-wave plate, a second lens having positive refractive power, and a second reflective polarizer constitute the element group on the display surface side. Since these element groups on the pupil side and the element group on the display surface side are arranged substantially symmetrically with respect to the semi-transparent surface of the half-mirror, the light reflected by the half-mirror and the light transmitted by the half-mirror are ultimately superimposed, thereby enabling miniaturization of the optical system while improving light efficiency.

[0017] In the optical system with the above configuration, it is desirable that the first lens has a convex surface on the pupil side in the paraxial direction.

[0018] By making the pupil-side surface of the first lens a convex surface in the paraxial direction, good correction of spherical aberration, astigmatism, field curvature, and distortion becomes possible.

[0019] Furthermore, in the optical system with the above configuration, it is desirable that the first lens has a convex surface on the display side in the paraxial direction.

[0020] By making the display-side surface of the first lens a convex surface in the paraxial direction, it becomes possible to effectively correct astigmatism, field curvature, and distortion.

[0021] In the optical system configured as described above, it is preferable that the second lens has a convex surface on the display surface side in the paraxial region.

[0022] By making the surface of the second lens on the display surface side a convex surface in the paraxial region, it is possible to favorably correct coma, astigmatism, field curvature, and distortion.

[0023] It is preferable that the optical system configured as described above satisfies the following conditional expression (1). (1)-3.2<r1 / r2<-0.9 Here, r1 is the paraxial radius of curvature of the surface of the first lens on the pupil plane side, and r2 is the paraxial radius of curvature of the surface of the first lens on the display surface side.

[0024] By satisfying the range of conditional expression (1), it is possible to favorably correct spherical aberration, astigmatism, field curvature, and distortion.

[0025] It is preferable that the optical system configured as described above satisfies the following conditional expression (2). (2)1.5<(T1 / f1)×100<7.0 Here, T1 is the distance on the optical axis from the surface of the first lens on the display surface side to the surface of the second lens on the pupil plane side, and f1 is the focal length of the first lens.

[0026] By satisfying the range of conditional expression (2), it is possible to reduce the height of the optical system and to favorably correct spherical aberration, astigmatism, field curvature, and distortion.

[0027] It is preferable that the optical system configured as described above satisfies the following conditional expression (3). (3)2.0<f1 / f<6.5 Here, f1 is the focal length of the first lens, and f is the focal length of the entire optical system.

[0028] By satisfying the range of conditional expression (3), it is possible to favorably correct spherical aberration, astigmatism, field curvature, and distortion.

[0029] It is preferable that the optical system configured as described above satisfies the following conditional expression (4). (4) 0.5 <f1 / f2<1.5 However, f1 is the focal length of the first lens, and f2 is the focal length of the second lens.

[0030] By satisfying the range of condition (4), good correction of spherical aberration, coma aberration, astigmatism, field curvature, and distortion becomes possible.

[0031] The optical system of the above configuration should preferably satisfy the following condition (5). (5)-1.5 <r1 / r4<-0.5 However, r1 is the paraxial radius of curvature of the pupil-side surface of the first lens, and r4 is the paraxial radius of curvature of the display-side surface of the second lens.

[0032] By satisfying the range of condition (5), good correction of spherical aberration, coma aberration, astigmatism, field curvature, and distortion becomes possible.

[0033] The optical system of the above configuration should preferably satisfy the following condition (6). (6)-79 <r2 / hm1<-20 However, r2 is the paraxial radius of curvature of the display-side surface of the first lens, and hm1 is the distance along the optical axis from the display-side surface of the first lens to the pupil-side surface of the half-mirror.

[0034] By satisfying the range of condition (6), it becomes possible to reduce the profile while also enabling good correction of astigmatism, field curvature, and distortion.

[0035] The optical system of the above configuration should preferably satisfy the following condition (7). (7) 55 <f2 / hm2<285 However, f2 is the focal length of the second lens, and hm2 is the distance along the optical axis from the display surface side of the half mirror to the pupil surface side of the second lens.

[0036] By satisfying the range of condition (7), the profile can be reduced, and good correction of spherical aberration, coma aberration, astigmatism, field curvature, and distortion can be achieved.

[0037] The optical system of the above configuration should preferably satisfy the following condition (8). (8) 27 < νd2 < 84 However, νd2 is the Abbe number for the d line of the second lens.

[0038] By satisfying the range of condition (8), good correction of chromatic aberration becomes possible.

[0039] The optical system of the above configuration should preferably satisfy the following condition (9). (9) 4.25 < (D1 / f1) × 100 < 16.50 However, D1 is the thickness of the first lens along its optical axis, and f1 is the focal length of the first lens.

[0040] By satisfying the range of condition (9), it becomes possible to reduce the profile while also achieving good correction of spherical aberration, astigmatism, field curvature, and distortion.

[0041] The optical system of the above configuration should preferably satisfy the following condition (10). (10) 4.25 < (D2 / f2) × 100 < 16.50 However, D2 is the thickness of the second lens along its optical axis, and f2 is the focal length of the second lens.

[0042] By satisfying the range of condition (10), the profile can be reduced, and good correction of spherical aberration, coma aberration, astigmatism, field curvature, and distortion can be achieved.

[0043] The optical system of the above configuration should preferably satisfy the following condition (11). (11) 2.0 <f2 / f<6.5 However, f2 is the focal length of the second lens, and f is the focal length of the entire optical system.

[0044] By satisfying the range of condition (11), good correction of spherical aberration, coma aberration, astigmatism, field curvature, and distortion becomes possible.

[0045] The optical system of the above configuration should preferably satisfy the following condition (12). (12)3 <r1 / f<10 However, r1 is the paraxial radius of curvature of the pupil-side surface of the first lens, and f is the focal length of the entire optical system.

[0046] By satisfying the range of condition (12), good correction of spherical aberration, astigmatism, field curvature, and distortion becomes possible.

[0047] The optical system of the above configuration should preferably satisfy the following condition (13). (13) 17.5 <r1 / T1<71.0 However, r1 is the paraxial radius of curvature of the pupil-side surface of the first lens, and T1 is the distance along the optical axis from the display-side surface of the first lens to the pupil-side surface of the second lens.

[0048] By satisfying the range of condition (13), it becomes possible to reduce the profile while also enabling good correction of spherical aberration, astigmatism, field curvature, and distortion.

[0049] The optical system of the above configuration should preferably satisfy the following condition (14). (14) 5.0 <r1 / (D1+T1)<18.5 However, r1 is the radius of paraxial curvature of the pupil-side surface of the first lens, D1 is the thickness of the first lens along the optical axis, and T1 is the distance along the optical axis from the display-side surface of the first lens to the pupil-side surface of the second lens.

[0050] By satisfying the range of condition (14), it becomes possible to reduce the profile while also enabling good correction of spherical aberration, astigmatism, field curvature, and distortion.

[0051] The optical system of the above configuration should preferably satisfy the following condition (15). (15)-1.5 <r2 / r3<-0.5 However, r2 is the paraxial radius of curvature of the display-side surface of the first lens, and r3 is the paraxial radius of curvature of the pupil-side surface of the second lens.

[0052] By satisfying the range of condition (15), good correction of coma aberration, astigmatism, field curvature, and distortion becomes possible.

[0053] The optical system of the above configuration should preferably satisfy the following condition (16). (16)-5.5 <r2 / f<-1.5 However, r2 is the paraxial radius of curvature of the display-side surface of the first lens, and f is the focal length of the entire optical system.

[0054] By satisfying the range of condition (16), good correction of astigmatism, field curvature, and distortion becomes possible.

[0055] The optical system of the above configuration should preferably satisfy the following condition (17). (17)-40.0 <r2 / T1<-8.5 However, r2 is the paraxial radius of curvature of the display-side surface of the first lens, and T1 is the distance along the optical axis from the display-side surface of the first lens to the pupil-side surface of the second lens.

[0056] By satisfying the range of condition (17), the profile can be reduced, and good correction of astigmatism, field curvature, and distortion can be achieved.

[0057] The optical system of the above configuration should preferably satisfy the following condition (18). (18) 1.5 <r3 / f<5.5 However, r3 is the paraxial radius of curvature of the pupil-side surface of the second lens, and f is the focal length of the entire optical system.

[0058] By satisfying the range of condition (18), good correction of coma aberration, astigmatism, field curvature, and distortion becomes possible.

[0059] The optical system of the above configuration should preferably satisfy the following condition (19). (19) 0.35 <r3 / f2<1.25 However, r3 is the paraxial radius of curvature of the pupil-side surface of the second lens, and f2 is the focal length of the second lens.

[0060] By satisfying the range of condition (19), good correction of spherical aberration, coma aberration, astigmatism, field curvature, and distortion becomes possible.

[0061] The optical system of the above configuration should preferably satisfy the following condition (20). (20)-0.85 <r3 / r4<-0.20 However, r3 is the paraxial radius of curvature of the pupil-side surface of the second lens, and r4 is the paraxial radius of curvature of the display-side surface of the second lens.

[0062] By satisfying the range of condition (20), good correction of coma aberration, astigmatism, field curvature, and distortion becomes possible.

[0063] The optical system of the above configuration should preferably satisfy the following condition (21). (21)-10 <r4 / f<-3 However, r4 is the paraxial radius of curvature of the display surface side of the second lens, and f is the focal length of the entire optical system.

[0064] By satisfying the range of condition (21), good correction of coma aberration, astigmatism, field curvature, and distortion becomes possible.

[0065] The optical system of the above configuration should preferably satisfy the following condition (22). (22)-2.5 <r4 / f2<-0.7 However, r4 is the paraxial radius of curvature of the display-side surface of the second lens, and f2 is the focal length of the second lens.

[0066] By satisfying the range of condition (22), good correction of spherical aberration, coma aberration, astigmatism, field curvature, and distortion becomes possible. [Effects of the Invention]

[0067] The present invention provides a high-resolution optical system with well-corrected aberrations while maintaining a good balance between miniaturization and improved light efficiency. Furthermore, because the optical system according to the present invention improves light efficiency, it is possible to provide an environmentally friendly optical system by reducing power consumption in the image display element. [Brief explanation of the drawing]

[0068] [Figure 1] This is a cross-sectional view showing the schematic configuration of the optical system according to Embodiment 1 of the present invention. [Figure 2] This is an aberration diagram showing the spherical aberration, astigmatism, and distortion of the optical system according to Embodiment 1 of the present invention. [Figure 3] This is a cross-sectional view showing a schematic configuration of the optical system according to Embodiment 2 of the present invention. [Figure 4] This is an aberration diagram showing the spherical aberration, astigmatism, and distortion of the optical system according to Embodiment 2 of the present invention. [Figure 5] This is a cross-sectional view showing the schematic configuration of the optical system according to Embodiment 3 of the present invention. [Figure 6] This is an aberration diagram showing the spherical aberration, astigmatism, and distortion of the optical system according to Embodiment 3 of the present invention. [Figure 7] Figure 1 is a magnified view of a portion of the optical system shown. [Figure 8] Fig. 8A is a cross-sectional view showing path 1 in the optical system shown in Figure 5. Fig. 8B is a cross-sectional view showing path 2 in the optical system shown in Figure 5. [Modes for carrying out the invention]

[0069] Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

[0070] Figures 1, 3, and 5 are cross-sectional views showing the schematic configuration of the optical systems of Examples 1 to 3 according to this embodiment, respectively. Figure 7 is a partially enlarged view of the optical system of Example 1. The optical systems according to this embodiment will be described in detail below with reference to the optical system of Example 1.

[0071] As shown in Figures 1 and 7, the optical system according to this embodiment includes, in order from the pupil plane EP side toward the display surface IMG side of the image display element, a first reflective polarizer 11, a first lens L1 having positive refractive power, a half mirror HM, a second lens L2 having positive refractive power, and a second reflective polarizer 12. The optical system also includes a first quarter-wave plate 21 positioned between the pupil plane EP and the half mirror HM, and a second quarter-wave plate 22 positioned between the half mirror HM and the display surface IMG. A filter IR, such as a glass block, is placed between the optical system and the display surface IMG. Note that this filter IR can be omitted.

[0072] In this optical system, the first reflective polarizer 11, the first lens L1, and the first quarter-wave plate 21 constitute the element group on the pupil side, while the second quarter-wave plate 22, the second lens L2, and the second reflective polarizer 12 constitute the element group on the display surface side. These element groups on the pupil side and the element group on the display surface are arranged in a substantially symmetrical configuration with respect to the semi-transparent surface of the half-mirror HM.

[0073] The optical system according to this embodiment is not limited to any particular application, but it can be used, for example, as the optical system for a head-mounted display. In this case, the observer's pupil will be located on the pupil plane EP. A light-intensity aperture may also be placed on the pupil plane EP.

[0074] The display surface IMG-side surface of the first reflective polarizing plate 11 and the pupil-side surface of the first lens L1 have the same shape, and the two are attached together with adhesive or the like. The first lens L1 has a biconvex shape in the paraxial direction. This suppresses spherical aberration, astigmatism, field curvature, and distortion.

[0075] The first quarter-wave plate 21, the half-mirror HM, and the second quarter-wave plate 22 each have a flat plate shape. In the optical system according to this embodiment, the first quarter-wave plate 21 is placed between the first lens L1 and the half-mirror HM, and the second quarter-wave plate 22 is placed between the half-mirror HM and the second lens L2, with the half-mirror HM sandwiched between the first quarter-wave plate 21 and the second quarter-wave plate 22. Furthermore, by attaching the first quarter-wave plate 21 and the second quarter-wave plate 22 to the half-mirror HM, the optical system is miniaturized while also improving ease of assembly.

[0076] Alternatively, the first quarter-wave plate 21 may be placed between the first reflective polarizer 11 and the first lens L1, and the second quarter-wave plate 22 may be placed between the second lens L2 and the second reflective polarizer 12.

[0077] The second lens L2 has a convex surface on the pupil side in the paraxial direction. In this embodiment, the second lens L2 has a biconvex shape in the paraxial direction. This shape of the second lens L2 allows for good correction of spherical aberration, coma aberration, astigmatism, field curvature, and distortion.

[0078] The display surface IMG side of the second lens L2 and the pupil surface EP side of the second reflective polarizing plate 12 have the same shape, and the two are attached together with an adhesive or the like.

[0079] As described above, in the optical system according to this embodiment, two biconvex lenses, namely the first lens L1 and the second lens L2, are arranged to sandwich the half mirror HM from both sides. In addition to this basic configuration, the light intensity efficiency of the optical system is improved by appropriately positioning the first reflective polarizer 11, the first quarter-wave plate 21, the second quarter-wave plate 22, and the second reflective polarizer 12. This point will be explained in detail below.

[0080] Devices equipped with a display surface IMG can, for example, employ a microOLED (Organic Light Emitting Diode) display. A microOLED display emits circularly polarized light from its display surface IMG.

[0081] As shown in Fig. 8A of Figure 8, light emitted from the display surface IMG is converted to linear polarization by the second reflective polarizer 12, converted to circular polarization by the second quarter-wave plate 22, and incident on the half-mirror HM. A portion of the light incident on the half-mirror HM passes through it and is converted to linear polarization with the same polarization direction as when it passed through the second reflective polarizer 12 by the first quarter-wave plate 21, and 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 to circular polarization by the first quarter-wave plate 21 and incident on the half-mirror HM, where it is reflected. The light reflected by the half-mirror HM is circularly polarized in the opposite direction to the light before reflection. Hereafter, 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, 3, and 5, only the light from path 1 is shown in order to clarify the schematic configuration of the optical system.

[0082] On the other hand, as shown in Fig. 8B of Figure 8, some of the light that is converted to circular polarization by the second quarter-wave plate 22 and incident on the half-mirror HM is reflected and becomes circularly polarized in the opposite direction, returning to the second quarter-wave plate 22. The circularly polarized light that returns 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 is incident 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 circular polarization by the second quarter-wave plate 22, incident on the half-mirror HM, and transmitted. Hereinafter, the light traveling along this path will be referred to as "light along path 2" for convenience.

[0083] The light from path 1 and the light from path 2 merge at the half-mirror HM. The circularly polarized light that merges at the half-mirror HM is converted by the first quarter-wave plate 21 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 incident on the first reflective polarizer 11. This linearly polarized light is transmitted through the first reflective polarizer 11 due to its polarization selectivity and guided to the pupil surface EP. As a result, the optical system according to this embodiment improves the light intensity efficiency of the optical system, and can be increased by up to 50%. At the same time, it is possible to reduce the power consumption of the image display element.

[0084] On the other hand, conventional optical systems of this type have a low light efficiency of 25% or less, and it was necessary to increase the brightness of the display surface in order to obtain a bright image at the pupil. Here, we will briefly explain this conventional optical system. Conventional optical systems generally consist of a reflective polarizer, a first quarter-wave plate, a lens with refractive power, a half mirror, and a second quarter-wave plate, arranged in order from the pupil side to the display surface side. In this optical system, light emitted from the display surface passes through the second quarter-wave plate, the half mirror, the lens, and the first quarter-wave plate, is reflected by the reflective polarizer, and then enters the half mirror again. Light that enters the half mirror is reflected by the half mirror, then passes through the first quarter-wave plate and the reflective polarizer to reach the pupil. In this light path, the light enters the half mirror twice, so the amount of light that reaches the pupil from the display surface is ultimately 25% or less. This means that in conventional optical systems, in order to obtain the same level of brightness at the pupil as in the optical system according to this embodiment, it is necessary to increase the brightness of the display surface, which increases the power consumption of the image display element.

[0085] In this regard, the optical system according to this embodiment actively utilizes the light emitted from the display surface IMG and reflected by the half-mirror HM as the light in the above-mentioned path 2, thereby achieving a higher light intensity efficiency than conventional systems.

[0086] The optical system in this embodiment achieves desirable effects by satisfying the following conditions (1) to (22). (1)-3.2 <r1 / r2<-0.9 (2) 1.5 < (T1 / f1) × 100 < 7.0 (3) 2.0 <f1 / f<6.5 (4) 0.5 <f1 / f2<1.5 (5)-1.5 <r1 / r4<-0.5 (6)-79 <r2 / hm1<-20 (7) 55 <f2 / hm2<285 (8) 27 < νd2 < 84 (9) 4.25 < (D1 / f1) × 100 < 16.50 (10) 4.25 < (D2 / f2) × 100 < 16.50 (11) 2.0 <f2 / f<6.5 (12)3 <r1 / f<10 (13) 17.5 <r1 / T1<71.0 (14) 5.0 <r1 / (D1+T1)<18.5 (15)-1.5 <r2 / r3<-0.5 (16)-5.5 <r2 / f<-1.5 (17)-40.0 <r2 / T1<-8.5 (18) 1.5 <r3 / f<5.5 (19) 0.35 <r3 / f2<1.25 (20)-0.85 <r3 / r4<-0.20 (21)-10 <r4 / f<-3 (22)-2.5 <r4 / f2<-0.7 however, νd2: Abbe number of the second lens L2 with respect to the d line D1: Thickness of the first lens L1 on the optical axis X. D2: Thickness of the second lens L2 on the X-axis. T1: Distance along the optical axis X from the display surface side of the first lens L1 to the pupil surface side of the second lens L2. hm1: Distance along the optical axis X from the display surface side of the first lens L1 to the pupil surface side of the half mirror HM. hm2: Distance along the optical axis X from the display surface side of the half mirror HM to the pupil surface side of the second lens L2. f: focal length of the entire optical system f1: Focal length of the first lens L1 f2: Focal length of the second lens L2 r1: Paraxial curvature radius of the pupil-side surface of the first lens L1 r2: Paraxial radius of curvature of the display surface side of the first lens L1 r3: Paraxial curvature radius of the pupil-side surface of the second lens L2 r4: Paraxial curvature radius of the display surface side of the second lens L2

[0087] It is not necessary to satisfy all of the above conditions; the effects corresponding to each condition can be obtained by satisfying each condition individually.

[0088] Furthermore, the optical system in this embodiment exhibits more favorable effects by satisfying the following conditions (1a) to (22a). (1a)-2.6 <r1 / r2<-1.0 (2a)2 < (T1 / f1) × 100 < 6 (3a) 2.5 <f1 / f<5.5 (4a) 0.75 <f1 / f2<1.25 (5a)-1.25 <r1 / r4<-0.75 (6a)-66 <r2 / hm1<-30 (7a)85 <f2 / hm2<235 (8a) 41 < νd2 < 70 (9a) 6.5 < (D1 / f1) × 100 < 14.0 (10a)6.5<(D2 / f2)×100<14.0 (11a)2.5 <f2 / f<5.5 (12a) 4.5 <r1 / f<8.5 (13a)25 <r1 / T1<60 (14a)7.5 <r1 / (D1+T1)<15.5 (15a)-1.25 <r2 / r3<-0.75 (16a)-4.5 <r2 / f<-2.0 (17a)-33.0 <r2 / T1<-12.5 (18a)2.0 <r3 / f<4.5 (19a) 0.55 <r3 / f2<1.05 (20a)-0.7 <r3 / r4<-0.3 (21a)-8.5 <r4 / f<-4.5 (22a)-2.1 <r4 / f2<-1.0 However, the signs of each conditional expression are the same as explained in the previous paragraph. Note that for conditions (1a) to (22a), the lower or upper limits of the corresponding conditions (1) to (22) may be applied.

[0089] In this embodiment, the aspherical shape adopted for the aspherical surface of the lens is expressed by Equation 1, where Z is the axis in the direction of the optical axis, H is the height in the direction perpendicular to the optical axis, R is the radius of paraxial curvature, k is the conicity coefficient, and A4, A6, A8, A10, A12, A14, A16, A18, A20 are the aspherical coefficients.

[0090]

number

[0091] Next, an embodiment of the optical system according to this embodiment is shown. In each embodiment, f is the focal length of the entire optical system, Fno is the F number, ω is the half-angle of view, ih is the maximum image height, and TTL is the total optical length. Here, the total optical length is the distance along the optical axis from the pupil plane to the display surface. The values ​​of the total optical length and back focus are obtained by converting the thickness of the filter IR placed between the optical system and the display surface IMG into air equivalent distances.

[0092] Furthermore, i represents the surface number counted from the pupil side, r is the radius of paraxial curvature, d is the distance between lens surfaces on the optical axis (interplanar spacing), Nd is the refractive index of the d-line (reference wavelength), and νd is the Abbe number for the d-line. For aspherical surfaces, an asterisk (*) is added after the surface number i.

[0093] In the optical system of each embodiment, the distance between the pupil plane EP, which serves as the eye point on the optical axis, and the lens surface closest to the pupil is called the pupil distance. In evaluating aberrations, there is a one-to-one correspondence between the aberration of light rays reaching the pupil plane EP when the light source is located on the display surface side and the aberration of light rays reaching the display surface IMG when the light source is located on the pupil plane EP side. For this reason, in each embodiment, the aberration of light rays reaching the display surface IMG will be evaluated. Figures 2, 4, and 6 show the aberration diagrams for the optical systems of Embodiments 1 to 3 when the pupil diameter of the observer (human) is Φ8.0 mm and the pupil distance is 12 mm.

[0094] (Example 1)

[0095] Basic lens data is shown in Table 1 below.

[0096] [Table 1]

[0097] The optical system of Example 1 satisfies conditions (1) to (22), as shown in Table 4.

[0098] Figure 2 shows the spherical aberration (mm), astigmatism (mm), and distortion (%) for the optical system of Example 1. The spherical aberration diagram shows the aberration amounts for each wavelength of the F line (486 nm), d line (588 nm), and C line (656 nm). The astigmatism diagram shows the aberration amount of the d line at the sagittal image plane S (solid line) and the aberration amount of the d line at the tangential image plane T (dashed line), respectively (the same applies to Figures 4 and 6). As shown in Figure 2, each aberration is well corrected.

[0099] (Example 2)

[0100] Basic lens data is shown in Table 2 below.

[0101] [Table 2]

[0102] The optical system of Example 2 satisfies conditions (1) to (22), as shown in Table 4.

[0103] Figure 4 shows the spherical aberration (mm), astigmatism (mm), and distortion (%) for the optical system of Example 2. As shown in Figure 4, each aberration is well corrected.

[0104] (Example 3)

[0105] Basic lens data is shown in Table 3 below.

[0106] [Table 3]

[0107] The optical system of Example 3 satisfies conditions (1) to (22) as shown in Table 4.

[0108] Figure 6 shows the spherical aberration (mm), astigmatism (mm), and distortion (%) for the optical system of Example 3. As shown in Figure 6, each aberration is well corrected.

[0109] Table 4 shows the values ​​of conditional equations (1) to (22) in the optical systems of Examples 1 to 3.

[0110] [Table 4] [Industrial applicability]

[0111] When the optical system according to the present invention is applied to an image display device, it contributes to miniaturization and improvement of light efficiency of the image display device, as well as improving its performance. [Explanation of Symbols]

[0112] EP pupil plane 11. First Reflective Polarizer L1 First Lens 21 First quarter-wave plate HM Half Mirror 22 Second quarter-wave plate L2 Second Lens 12. Second Reflective Polarizer IR filter IMG display surface

Claims

1. Starting from the pupil side and moving towards the display side, The first reflective polarizing plate, A first lens having positive refractive power, Half mirror and A second lens having positive refractive power, It has a second reflective polarizing plate, A first quarter-wave plate is positioned between the pupil surface and the half-mirror, It has a second quarter-wave plate positioned between the half-mirror and the display surface, The second lens has a convex surface on the pupil side in the paraxial direction. With respect to light emitted from the display surface, the light that passes through the second reflective polarizer is converted into circularly polarized light by the second quarter-wave plate and incident on the half mirror, the light that passes through the half mirror is converted into linearly polarized light by the first quarter-wave plate and reflected by the first reflective polarizer, then converted into circularly polarized light by the first quarter-wave plate and reflected by the half mirror, forming a first optical path, and the light reflected by the half mirror is converted into linearly polarized light by the second quarter-wave plate and reflected by the second reflective polarizer, then converted into circularly polarized light by the second quarter-wave plate and passes through the half mirror, forming a second optical path. The light from the first optical path and the second optical path merge at the half-mirror section, is converted into linearly polarized light by the first quarter-wave plate, passes through the first reflective polarizer plate, and is guided to the pupil surface. An optical system characterized by satisfying the following condition (1). (1) -3.2<r1 / r2<-0.9 however, r1: The radius of paraxial curvature of the pupil-side surface of the first lens. r2: Paraxial radius of curvature of the display surface side of the first lens, Let's assume that.

2. The optical system according to claim 1, characterized in that it satisfies the following condition (2). (2) 1.5<(T1 / f1)×100<7.0 however, T1: Distance along the optical axis from the display surface side of the first lens to the pupil surface side of the second lens. f1: Focal length of the first lens, Let's assume that.

3. The optical system according to claim 1, characterized in that it satisfies the following condition (3). (3) 2.0<f1 / f<6.5 however, f1: Focal length of the first lens, f: Focal length of the entire optical system, Let's assume that.

4. The optical system according to claim 1, characterized in that it satisfies the following condition (4). (4) 0.5<f1 / f2<1.5 however, f1: Focal length of the first lens, f2: Focal length of the second lens, Let's assume that.

5. The optical system according to claim 1, characterized in that it satisfies the following condition (5). (5) -1.5<r1 / r4<-0.5 however, r1: The radius of paraxial curvature of the pupil-side surface of the first lens. r4: Paraxial radius of curvature of the display surface side of the second lens, Let's assume that.

6. The optical system according to claim 1, characterized in that it satisfies the following condition (6). (6) -79<r2 / hm1<-20 however, r2: Paraxial radius of curvature of the display surface side of the first lens, hm1: Distance along the optical axis from the display surface side of the first lens to the pupil surface side of the half mirror. Let's assume that.

7. The optical system according to claim 1, characterized in that it satisfies the following condition (7). (7) 55<f2 / hm2<285 however, f2: Focal length of the second lens, hm2: Distance along the optical axis from the display surface side of the half mirror to the pupil surface side of the second lens. Let's assume that.

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