Optical system

Abstract

To provide an optical system having good optical characteristics while satisfying requirements for size reduction and improvement of light amount efficiency.SOLUTION: An optical system comprises, in order from a pupil plane EP to a display surface IMG of an image display element: a first lens L1 having positive refractive power and having biconvex shape in a paraxial direction; a half mirror HM; and a second lens L2 having positive refractive power and having a biconvex shape in the paraxial direction. The optical system has a first reflective polarizing plate 11 disposed between the pupil plane EP and the half mirror HM, a first quarter wavelength plate 21 disposed between the pupil plane EP and the half mirror HM, a second quarter wavelength plate 22 disposed between the half mirror HM and the display surface IMG, and a second reflective polarizing plate 12 disposed between the half mirror HM and the display surface IMG. The optical system satisfies a predetermined conditional expression.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

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

[0003] In such a display device, it is necessary to house an optical system for magnifying the image displayed on the image display element in a limited space while keeping the distance between the image display element and the eye as short as possible, which often makes it difficult to eliminate various aberrations in the optical system and limits the range of correction.

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

[0005] The optical systems installed in such display devices are required to be compact and have high light efficiency, where light efficiency refers to the ratio of the amount of light reaching the eye (pupil plane) when the amount of light 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 the following Patent Document 1 is known. Patent Document 1 discloses an optical system including a partial optical system having two semi-transmissive surfaces and a refractive optical element having power. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 3441188 Summary of the Invention [Problem to be solved by the invention]

[0008] Even if one attempts to reduce the size and improve the light efficiency by using the optical system described in Patent Document 1, it is difficult to improve the light efficiency due to the presence of two semi-transmitting surfaces, and good optical performance cannot be obtained.

[0009] The present invention has been made in consideration of the above-mentioned problems, and has an object to provide an optical system that has high resolving power with various aberrations well corrected while satisfying in a balanced manner the demands for compactness and improved light efficiency. [Means for solving the problem]

[0010] The optical system according to the present invention has, in order from the pupil surface side to the display surface side, a first lens having a paraxial biconvex shape with positive refractive power, a half mirror, and a second lens having a paraxial biconvex shape with positive refractive power, and the optical system has a first reflective polarizing plate arranged between the pupil surface and the half mirror, a first quarter-wave plate arranged between the pupil surface and the half mirror, a second quarter-wave plate arranged between the half mirror and the display surface, and a second first reflective polarizing plate arranged between the half mirror and the display surface. In this specification, the convex, concave, and flat surfaces of the lens refer to the shape in the paraxial direction, and the refractive power refers to the refractive power in the paraxial direction unless otherwise specified.

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

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

[0013] The first lens has positive refractive power and is biconvex on the paraxial direction, thereby suppressing spherical aberration, astigmatism, curvature of field, and distortion.

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

[0015] The second lens has positive refractive power and is biconvex on the paraxial direction, and therefore provides excellent correction for spherical aberration, coma, astigmatism, curvature of field, and distortion.

[0016] In the optical system of the present invention, the first reflective polarizer, the first lens having positive refractive power, and the first quarter-wave plate constitute a pupil-side element group, and the second quarter-wave plate, the second lens having positive refractive power, and the second reflective polarizer constitute a display-side element group. The pupil-side element group and the display-side element group are arranged substantially symmetrically with respect to the semi-transmissive surface of the half mirror, so that the two beams of light, that is, the light reflected by the half mirror and the light transmitted through it, are finally superimposed, thereby making it possible to miniaturize the optical system while improving the light efficiency.

[0017] It is desirable for the optical system having the above configuration to satisfy the following conditional expression (1): (1) 2.75<(D2 / f2)×100<5.95 Here, D2 is the thickness of the second lens on the optical axis, and f2 is the focal length of the second lens.

[0018] By satisfying the range of conditional expression (1), it is possible to achieve a low height and to satisfactorily correct spherical aberration, coma, astigmatism, curvature of field, and distortion.

[0019] It is desirable for the optical system having the above configuration to satisfy the following conditional expression (2). (2) -1.00 <r1 / r2<-0.13 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 plane side.

[0020] By satisfying the range of conditional expression (2), it becomes possible to satisfactorily correct spherical aberration, astigmatism, curvature of field, and distortion.

[0021] It is desirable for the optical system having the above configuration to satisfy the following conditional expression (3). (3) -1.50 <r2 / r3<-0.50 Here, r2 is the paraxial radius of curvature of the surface of the first lens on the display surface side, and r3 is the paraxial radius of curvature of the surface of the second lens on the pupil surface side.

[0022] By satisfying the range of conditional expression (3), coma, astigmatism, curvature of field, and distortion can be favorably corrected.

[0023] It is desirable for the optical system having the above configuration to satisfy the following conditional expression (4). (4)-4.00 <r2 / f1<-0.75 Here, r2 is the paraxial radius of curvature of the surface of the first lens facing the display surface, and f1 is the focal length of the first lens.

[0024] By satisfying the range of conditional expression (4), it becomes possible to satisfactorily correct spherical aberration, astigmatism, curvature of field, and distortion.

[0025] It is desirable for the optical system having the above configuration to satisfy the following conditional expression (5). (5)-5.50 <r3 / r4<-0.80 Here, r3 is the paraxial radius of curvature of the surface of the second lens on the pupil plane side, and r4 is the paraxial radius of curvature of the surface of the second lens on the display plane side.

[0026] By satisfying the range of conditional expression (5), coma, astigmatism, curvature of field, and distortion can be corrected satisfactorily.

[0027] It is desirable for the optical system having the above configuration to satisfy the following conditional expression (6). (6)-6.50 <r4 / f2×D2<-2.70 Here, r4 is the paraxial radius of curvature of the surface of the second lens on the display surface side, f2 is the focal length of the second lens, and D2 is the thickness of the second lens on the optical axis.

[0028] By satisfying the range of conditional expression (6), it is possible to achieve a low height and to satisfactorily correct spherical aberration, coma, astigmatism, curvature of field, and distortion.

[0029] It is desirable for the optical system having the above configuration to satisfy the following condition (7). (7)-26 <r4 / D2<-8 Here, r4 is the paraxial radius of curvature of the surface of the second lens on the display surface side, and D2 is the thickness of the second lens on the optical axis.

[0030] By satisfying the range of conditional expression (7), it is possible to achieve a low height and to satisfactorily correct coma, astigmatism, curvature of field, and distortion.

[0031] It is desirable for the optical system having the above configuration to satisfy the following conditional expression (8). (8) 2.75<(D1 / f1)×100<5.95 Here, D1 is the thickness of the first lens on the optical axis, and f1 is the focal length of the first lens.

[0032] By satisfying the range of conditional expression (8), it is possible to achieve a low height and to satisfactorily correct spherical aberration, astigmatism, curvature of field, and distortion.

[0033] It is desirable for the optical system having the above configuration to satisfy the following condition (9). (9) 0.6<(T1 / f1)×100<5.5 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 surface side, and f1 is the focal length of the first lens.

[0034] By satisfying the range of conditional expression (9), it is possible to achieve a low height and to satisfactorily correct spherical aberration, astigmatism, curvature of field, and distortion.

[0035] It is desirable for the optical system having the above configuration to satisfy the following condition (10): (10)9.5 <r1 / T1<100.0 Here, r1 is the paraxial radius of curvature of the pupil plane side surface of the first lens, and T1 is the distance on the optical axis from the display plane side surface of the first lens to the pupil plane side surface of the second lens.

[0036] By satisfying the range of conditional expression (10), it is possible to achieve a low height and to satisfactorily correct spherical aberration, astigmatism, curvature of field, and distortion.

[0037] It is desirable for the optical system having the above configuration to satisfy the following condition (11). (11)4.5 <r1 / (D1+T1)<28.0 where r1 is the paraxial radius of curvature of the pupil plane side surface of the first lens, D1 is the optical axial thickness of the first lens, and T1 is the optical axial distance from the display plane side surface of the first lens to the pupil plane side surface of the second lens.

[0038] By satisfying the range of conditional expression (11), it is possible to achieve a low height and to achieve favorable correction of spherical aberration, astigmatism, curvature of field, and distortion.

[0039] It is desirable for the optical system having the above configuration to satisfy the following condition (12): (12)0.3 <r1 / f1<1.3 Here, r1 is the paraxial radius of curvature of the surface of the first lens on the pupil plane side, and f1 is the focal length of the first lens.

[0040] By satisfying the range of conditional expression (12), it becomes possible to satisfactorily correct spherical aberration, astigmatism, curvature of field, and distortion.

[0041] It is desirable for the optical system having the above configuration to satisfy the following condition (13): (13)0.15 <r1 / (f1+f2)<0.65 Here, r1 is the paraxial radius of curvature of the surface of the first lens on the pupil plane side, f1 is the focal length of the first lens, and f2 is the focal length of the second lens.

[0042] By satisfying the range of conditional expression (13), it becomes possible to satisfactorily correct spherical aberration, coma, astigmatism, curvature of field, and distortion.

[0043] It is desirable for the optical system having the above configuration to satisfy the following condition (14): (14)-1.5<(r1 / r4) / (f1 / f2)<-0.5 Here, r1 is the paraxial radius of curvature of the pupil plane side surface of the first lens, r4 is the paraxial radius of curvature of the display plane side surface of the second lens, f1 is the focal length of the first lens, and f2 is the focal length of the second lens.

[0044] By satisfying the range of conditional expression (14), it becomes possible to satisfactorily correct spherical aberration, coma, astigmatism, curvature of field, and distortion.

[0045] It is desirable for the optical system having the above configuration to satisfy the following condition (15): (15)-15.2 <r2 / f<-4.0 Here, r2 is the paraxial radius of curvature of the surface of the first lens facing the display surface, and f is the focal length of the entire optical system.

[0046] By satisfying the range of conditional expression (15), it becomes possible to satisfactorily correct astigmatism, curvature of field, and distortion.

[0047] It is desirable for the optical system having the above configuration to satisfy the following condition (16): (16)-165 <r2 / T1<-30 Here, r2 is the paraxial radius of curvature of the surface of the first lens on the display surface side, and 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 surface side.

[0048] By satisfying the range of conditional expression (16), it is possible to achieve a low height and to satisfactorily correct astigmatism, curvature of field, and distortion.

[0049] It is desirable for the optical system having the above configuration to satisfy the following condition (17): (17)-330 <r2 / hm1<-65 Here, r2 is the paraxial radius of curvature of the surface of the first lens on the display surface side, and hm1 is the distance on the optical axis from the surface of the first lens on the display surface side to the surface of the half mirror on the pupil surface side.

[0050] By satisfying the range of conditional expression (17), it is possible to achieve a low height and to satisfactorily correct astigmatism, curvature of field, and distortion.

[0051] It is desirable for the optical system having the above configuration to satisfy the following condition (18): (18)4.0 <r3 / f<15.2 Here, r3 is the paraxial radius of curvature of the surface of the second lens on the pupil plane side, and f is the focal length of the entire optical system.

[0052] By satisfying the range of conditional expression (18), coma, astigmatism, curvature of field, and distortion can be corrected satisfactorily.

[0053] It is desirable for the optical system having the above configuration to satisfy the following condition (19): (19)0.75 <r3 / f2<4.00 Here, r3 is the paraxial radius of curvature of the surface of the second lens on the pupil plane side, and f2 is the focal length of the second lens.

[0054] By satisfying the range of conditional expression (19), it becomes possible to satisfactorily correct spherical aberration, coma, astigmatism, curvature of field, and distortion.

[0055] It is desirable for the optical system having the above configuration to satisfy the following condition (20): (20)-7.5 <r4 / f<-2.0 Here, r4 is the paraxial radius of curvature of the surface of the second lens on the display surface side, and f is the focal length of the entire optical system.

[0056] By satisfying the range of conditional expression (20), coma, astigmatism, curvature of field, and distortion can be corrected satisfactorily.

[0057] It is desirable for the optical system having the above configuration to satisfy the following condition (21). (21)-1.3 <r4 / f2<-0.3 Here, r4 is the paraxial radius of curvature of the surface of the second lens on the display surface side, and f2 is the focal length of the second lens.

[0058] By satisfying the range of conditional expression (21), it becomes possible to satisfactorily correct spherical aberration, coma, astigmatism, curvature of field, and distortion.

[0059] It is desirable for the optical system having the above configuration to satisfy the following condition (22): (22)-0.65 <r4 / (f1+f2)<-0.15 Here, r4 is the paraxial radius of curvature of the surface of the second lens on the display surface side, f1 is the focal length of the first lens, and f2 is the focal length of the second lens.

[0060] By satisfying the range of conditional expression (22), it becomes possible to satisfactorily correct spherical aberration, coma, astigmatism, curvature of field, and distortion.

[0061] It is desirable for the optical system having the above configuration to satisfy the following condition (23): (23)-13 <r4 / (D1+D2)<-4 Here, r4 is the paraxial radius of curvature of the surface of the second lens on the display surface side, D1 is the thickness of the first lens on the optical axis, and D2 is the thickness of the second lens on the optical axis.

[0062] By satisfying the range of conditional expression (23), it is possible to achieve a low height and to satisfactorily correct coma, astigmatism, curvature of field, and distortion.

[0063] It is desirable for the optical system having the above configuration to satisfy the following condition (24): (24) 5<(f1+f2) / f<20 Here, f1 is the focal length of the first lens, f2 is the focal length of the second lens, and f is the focal length of the entire optical system.

[0064] By satisfying the range of conditional expression (24), it becomes possible to satisfactorily correct spherical aberration, coma, astigmatism, curvature of field, and distortion.

[0065] It is desirable for the optical system having the above configuration to satisfy the following condition (25): (25)30 <f2 / hm2<845 Here, f2 is the focal length of the second lens, and hm2 is the distance on the optical axis from the surface of the half mirror on the display surface side to the surface of the second lens on the pupil surface side.

[0066] By satisfying the range of conditional expression (25), it is possible to achieve a low height and to satisfactorily correct spherical aberration, coma, astigmatism, curvature of field, and distortion. Effect of the Invention

[0067] According to the present invention, it is possible to obtain an optical system with high resolution in which various aberrations are well corrected while satisfying the requirements for miniaturization and improvement of light efficiency in a well-balanced manner. Furthermore, according to the optical system according to the present invention, since the light efficiency is improved, it is possible to provide an optical system that is environmentally friendly by reducing the power consumption of the image display element. [Brief description of the drawings]

[0068] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of an optical system according to Example 1 of the present invention. [Diagram 2] FIG. 2 is a partially enlarged view of the optical system shown in FIG. [Diagram 3] 2A to 2C are aberration diagrams showing spherical aberration, astigmatism, and distortion of the optical system shown in FIG. [Figure 4] FIG. 11 is a cross-sectional view showing a schematic configuration of an optical system according to Example 2 of the present invention. [Diagram 5] FIG. 5 is a partial enlarged view of the optical system shown in FIG. [Figure 6] 5A to 5C are aberration diagrams showing spherical aberration, astigmatism, and distortion of the optical system shown in FIG. [Figure 7] FIG. 11 is a cross-sectional view showing a schematic configuration of an optical system according to Example 3 of the present invention. [Figure 8] FIG. 8 is a partial enlarged view of the optical system shown in FIG. [Figure 9] 8A to 8C are aberration diagrams showing spherical aberration, astigmatism, and distortion of the optical system shown in FIG. 7. [Figure 10] Fig. 10A is a cross-sectional view showing a path 1 in the optical system shown in Fig. 7. Fig. 10B is a cross-sectional view showing a path 2 in the optical system shown in Fig. 7. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0069] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described in detail with reference to the drawings.

[0070] Fig. 1, Fig. 4 and Fig. 7 are cross-sectional views showing the schematic configuration of the optical systems of Examples 1 to 3 according to the present embodiment, respectively. Fig. 2, Fig. 5 and Fig. 8 show partial enlarged views of the optical systems of Examples 1 to 3, respectively. Hereinafter, the optical system according to the present embodiment will be described in detail with reference to the optical system of Example 1.

[0071] As shown in FIG. 1, the optical system of this embodiment has, in order from a pupil plane EP to a display surface IMG of an image display element, a first lens L1 having a paraxially biconvex shape with positive refractive power, a half mirror HM, and a second lens L2 having a paraxially biconvex shape with positive refractive power. The optical system has a first reflective polarizer 11 arranged between the pupil plane EP and the half mirror HM, a first quarter-wave plate 21 arranged between the pupil plane EP and the half mirror HM, a second quarter-wave plate 22 arranged between the half mirror HM and the display surface IMG, and a second reflective polarizer 12 arranged between the half mirror HM and the display surface IMG.

[0072] In this optical system, the first reflective polarizer 11, the first lens L1, and the first quarter-wave plate 21 form a group of elements on the pupil EP side, and the second quarter-wave plate 22, the second lens L2, and the second reflective polarizer 12 form a group of elements on the display surface IMG side. The group of elements on the pupil side and the group of elements on the display surface IMG side are arranged approximately symmetrically with respect to the semi-transmitting surface of the half mirror HM.

[0073] The optical system according to the present embodiment may be mounted on any object, but may be mounted on a head mounted display as an optical system for enlarging an image displayed on a display surface IMG. In this case, the pupil of the observer is located on the pupil plane EP. A light quantity diaphragm may be disposed on the pupil plane EP.

[0074] In the optical system according to the present embodiment, anti-reflective films may be attached to both sides of the half mirror HM. Since anti-reflective films have the function of preventing light reflection, this configuration can prevent a decrease in image contrast caused by the reflection of external light.

[0075] As shown in FIG. 2, the surface of the first reflective polarizer 11 on the display surface IMG side and the surface of the first lens L1 on the pupil surface side have the same shape, and both are attached with an adhesive or the like. The first lens L1 has a convex surface on the pupil surface side in the paraxial direction. The first lens L1 of this embodiment has a biconvex shape in the paraxial direction. This shape of the first lens L1 makes it possible to reduce the distance from the first reflective polarizer 11 to the half mirror HM, thereby reducing the effective diameter of the lens and thereby miniaturizing the optical system, while suppressing spherical aberration, astigmatism, curvature of field, and distortion.

[0076] In the optical system according to the present embodiment, the first quarter-wave plate 21 is attached to the surface of the half mirror HM on the pupil plane EP side, and the second quarter-wave plate 22 is attached to the surface of the half mirror HM on the display surface IMG side. This makes it possible to reduce the size of the optical system while improving ease of assembly. However, the positions of the first quarter-wave plate 21 and the second quarter-wave plate 22 are not limited to this. The position of the first quarter-wave plate 21 may be between the pupil plane EP and the half mirror HM, and the position of the second quarter-wave plate 22 may be between the half mirror HM and the display surface IMG.

[0077] As shown in Fig. 1, the second lens L2 has a convex surface on the display surface side in the paraxial direction. The second lens L2 of the present embodiment 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, curvature of field, and distortion.

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

[0079] As described above, in the optical system according to the present embodiment, the first lens L1 and the second lens L2 are arranged in such a manner that they sandwich the half mirror HM from both sides. In addition to this basic configuration, the first reflective polarizer 11, the first ¼ wavelength plate 21, the second ¼ wavelength plate 22, and the second reflective polarizer 12 are each arranged at an appropriate position to improve the light quantity efficiency of the optical system. This point will be described in detail below.

[0080] As a device having a display surface IMG, for example, a liquid crystal display or a micro OLED (Organic Light Emitting Diode) display can be adopted.

[0081] As shown in FIG. 10A of FIG. 10, the light emitted from the display surface IMG is converted into linearly polarized light by the second reflective polarizer 12, and then converted into circularly polarized light by the second quarter-wave plate 22 and enters the half mirror HM. A part of the light that enters the half mirror HM is transmitted through it and converted into linearly polarized light in the same polarization direction as when it passed through the second reflective polarizer 12 by the first quarter-wave plate 21, and enters the first reflective polarizer 11. This linearly polarized light is reflected by the polarization selectivity of the first reflective polarizer 11. The light reflected by the first reflective polarizer 11 is converted into circularly polarized light by the first quarter-wave plate 21 and enters the half mirror HM, where it is reflected. The light reflected by the half mirror HM becomes circularly polarized light in the opposite direction to the light before reflection. Hereinafter, the light that travels along this path will be referred to as "path 1 light" for convenience. In the cross-sectional views of the optical system according to the present embodiment shown in FIG. 1, FIG. 4 and FIG. 7, only the light of this path 1 is shown in order to clarify the schematic configuration of the optical system.

[0082] On the other hand, as shown in FIG. 10B of FIG. 10, a part of the light that is converted into circularly polarized light by the second quarter-wave plate 22 and enters the half mirror HM is reflected to become circularly polarized light in the reverse direction and returns 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 passes through the second reflective polarizer 12 and enters the second reflective polarizer 12. This linearly polarized light is reflected by the polarization selectivity of the second reflective polarizer 12. The light reflected by the second reflective polarizer 12 is converted into circularly polarized light by the second quarter-wave plate 22 and enters the half mirror HM and is transmitted therethrough. Hereinafter, the light that travels along this path will be referred to as "path 2 light" for convenience.

[0083] The light of the path 1 and the light of the path 2 are merged at the half mirror HM. The circularly polarized light merged 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 the light first passes through the second reflective polarizer 12, and enters the first reflective polarizer 11. This linearly polarized light passes through the first reflective polarizer 11 due to its polarization selectivity and is guided to the pupil plane EP. Therefore, according to the optical system of this embodiment, the light efficiency of the optical system is improved, and the light efficiency can be increased to a maximum of 50%. In addition, the power consumption of the image display element can be reduced.

[0084] On the other hand, this type of conventional general optical system has a low light efficiency of 25% or less, and in order to obtain a bright image on the pupil plane, it is necessary to increase the brightness of the display surface. Here, this conventional optical system will be briefly described. A conventional optical system is generally configured to include, in order from the pupil plane side to the display surface side, a reflective polarizing plate, a first 1 / 4 wavelength plate, a lens having refractive power, a half mirror, and a second 1 / 4 wavelength plate. In this optical system, light emitted from the display surface passes through the second 1 / 4 wavelength plate, the half mirror, the lens, and the first 1 / 4 wavelength plate, is reflected by the reflective polarizing plate, and then enters the half mirror again. The light that enters the half mirror is reflected by the half mirror, passes through the first 1 / 4 wavelength plate and the reflective polarizing plate, and reaches the pupil plane. In this light path, light enters the half mirror twice, so the amount of light that reaches the pupil plane from the display surface is ultimately 25% or less. This means that in the conventional optical system, in order to obtain the same level of brightness at the pupil plane as the optical system of the present embodiment, it is necessary to increase the luminance of the display surface, which results in increased power consumption of the image display element.

[0085] In this regard, in the optical system of this embodiment, the light emitted from the display surface IMG and reflected by the half mirror HM is actively utilized as light for path 2, thereby achieving a higher light efficiency than ever before.

[0086] The optical system in this embodiment exerts favorable effects by satisfying the following conditional expressions (1) to (25). (1) 2.75<(D2 / f2)×100<5.95 (2) -1.00 <r1 / r2<-0.13 (3) -1.50 <r2 / r3<-0.50 (4)-4.00 <r2 / f1<-0.75 (5)-5.50 <r3 / r4<-0.80 (6)-6.50 <r4 / f2×D2<-2.70 (7)-26 <r4 / D2<-8 (8) 2.75<(D1 / f1)×100<5.95 (9) 0.6<(T1 / f1)×100<5.5 (10)9.5 <r1 / T1<100.0 (11)4.5 <r1 / (D1+T1)<28.0 (12)0.3 <r1 / f1<1.3 (13)0.15 <r1 / (f1+f2)<0.65 (14)-1.5<(r1 / r4) / (f1 / f2)<-0.5 (15)-15.2 <r2 / f<-4.0 (16)-165 <r2 / T1<-30 (17)-330 <r2 / hm1<-65 (18)4.0 <r3 / f<15.2 (19)0.75 <r3 / f2<4.00 (20)-7.5 <r4 / f<-2.0 (21)-1.3 <r4 / f2<-0.3 (22)-0.65 <r4 / (f1+f2)<-0.15 (23)-13 <r4 / (D1+D2)<-4 (24) 5<(f1+f2) / f<20 (25)30 <f2 / hm2<845 however, D1: Thickness of the first lens L1 on the optical axis X D2: Thickness of the second lens L2 on the optical axis X T1: the distance on the optical axis X from the surface of the first lens L1 on the display surface side to the surface of the second lens L2 on the pupil surface side hm1: the distance on the optical axis X from the surface of the first lens L1 on the display surface side to the surface of the half mirror HM on the pupil surface side hm2: the distance on the optical axis X from the surface of the half mirror HM on the display surface side to the surface of the second lens L2 on the pupil surface side f: focal length of the entire optical system f1: focal length of the first lens L1 f2: focal length of second lens L2 r1: paraxial radius of curvature of the pupil surface side of the first lens L1 r2: paraxial radius of curvature of the surface of the first lens L1 on the display surface side r3: paraxial radius of curvature of the pupil surface side of the second lens L2 r4: paraxial radius of curvature of the surface of the second lens L2 on the display surface side

[0087] It is not necessary to satisfy all of the above conditional expressions. By satisfying each conditional expression individually, it is possible to obtain the effect corresponding to each conditional expression.

[0088] Moreover, the optical system in this embodiment exerts more preferable effects by satisfying the following conditional expressions (1a) to (25a). (1a) 3.00<(D2 / f2)×100<4.95 (2a)-0.8 <r1 / r2<-0.2 (3a)-1.25 <r2 / r3<-0.75 (4a)-3.15 <r2 / f1<-1.00 (5a)-4.50 <r3 / r4<-1.25 (6a)-5.25 <r4 / f2×D2<-2.90 (7a)-25.8 <r4 / D2<-13 (8a) 3.00<(D1 / f1)×100<4.95 (9a) 1.0<(T1 / f1)×100<4.5 (10a)14.5 <r1 / T1<82.0 (11a)7 <r1 / (D1+T1)<23 (12a)0.5 <r1 / f1<1.1 (13a) 0.25 <r1 / (f1+f2)<0.55 (14a)-1.25<(r1 / r4) / (f1 / f2)<-0.75 (15a)-15.2 <r2 / f<-6.0 (16a)-135 <r2 / T1<-50 (17a)-270 <r2 / hm1<-100 (18a)6.0 <r3 / f<15.2 (19a)1.05 <r3 / f2<3.30 (20a)-6.2 <r4 / f<-3.0 (21a)-1.1 <r4 / f2<-0.5 (22a)-0.55 <r4 / (f1+f2)<-0.25 (23a)-12.9 <r4 / (D1+D2)<-6.5 (24a) 8.5<(f1+f2) / f<16.0 (25a)50 <f2 / hm2<700 However, the symbols in each conditional expression are the same as those explained in the previous paragraph. Note that, for the conditional expressions (1a) to (25a), the lower limit value or upper limit value of the corresponding conditional expressions (1) to (25) may be applied.

[0089] In this embodiment, the aspheric shape adopted for the aspheric surface of the lens surface is expressed by Equation 1, where Z is the axis in the optical axis direction, H is the height in the direction perpendicular to the optical axis, R is the paraxial radius of curvature, k is the conic coefficient, and An is the n-th aspheric coefficient.

[0090]

number

[0091] Next, examples of the optical system according to the present embodiment will be shown. In each example, 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 on the optical axis from the pupil plane to the display surface.

[0092] In addition, i is the surface number counted from the pupil surface side, r is the paraxial radius of curvature, d is the distance between the lens surfaces on the optical axis (surface spacing), Nd is the refractive index of the d-line (reference wavelength), and νd is the Abbe number for the d-line. Aspheric surfaces are indicated by adding an asterisk (*) after the surface number i.

[0093] In the optical system of each embodiment, the distance between the pupil plane EP, which is the eyepoint on the optical axis, and the lens surface closest to the pupil plane is called the pupil distance. In evaluating aberration, there is a one-to-one correspondence between the aberration of a light ray that reaches the pupil plane EP when a light emitting point is provided on the display surface side and the aberration of a light ray that reaches the display surface IMG when a light emitting point is provided on the pupil plane EP side. For this reason, in each embodiment, the aberration of the light ray that reaches the display surface IMG is evaluated.

[0094] Example 1

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

[0096] [Table 1]

[0097] The optical system of the first embodiment satisfies the conditional expressions (1) to (25) as shown in Table 4.

[0098] Fig. 3 shows the spherical aberration (mm), astigmatism (mm), and distortion (%) for the optical system of Example 1. The spherical aberration diagram shows the amount of aberration for each wavelength of the F-line (486 nm), d-line (588 nm), and C-line (656 nm). The astigmatism diagram also shows the amount of aberration for the d-line at the sagittal image plane S (solid line) and the amount of aberration for the d-line at the tangential image plane T (dashed line) (the same applies to Figs. 6 and 9). As shown in Fig. 3, each aberration is well corrected.

[0099] Example 2

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

[0101] [Table 2]

[0102] The optical system of the second embodiment satisfies the conditional expressions (1) to (25) as shown in Table 4.

[0103] Fig. 6 shows the spherical aberration (mm), astigmatism (mm), and distortion (%) for the optical system of Example 2. As shown in Fig. 6, each aberration is well corrected.

[0104] Example 3

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

[0106] [Table 3]

[0107] The optical system of the third embodiment satisfies the conditional expressions (1) to (25) as shown in Table 4.

[0108] Fig. 9 shows the spherical aberration (mm), astigmatism (mm), and distortion (%) for the optical system of Example 3. As shown in Fig. 9, each aberration is well corrected.

[0109] Table 4 shows the values ​​of conditional expressions (1) to (25) 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 is possible to contribute to miniaturization of the image display device and improvement of the light efficiency, and also to improve the performance of the image display device. [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 IMG display surface

Claims

1. From the pupil plane to the display plane, a first lens having a paraxial biconvex shape and positive refractive power; A half mirror, An optical system having a second lens having a paraxial biconvex shape with positive refractive power, The optical system includes: a first reflective polarizing plate disposed between a pupil plane and the half mirror; a first quarter-wave plate disposed between a pupil plane and the half mirror; a second quarter-wave plate disposed between the half mirror and a display surface; a second reflective polarizer disposed between the half mirror and a display surface; An optical system characterized by satisfying the following conditional expression (1): (1) 2.75<(D2 / f2)×100<5.95 however, D2: thickness of the second lens on the optical axis, f2: focal length of the second lens, Let us assume that.

2. 2. The optical system according to claim 1, wherein the following condition (2) is satisfied: (2) -1.00<r1 / r2<-0.13 however, r1: paraxial radius of curvature of the pupil surface side of the first lens, r2: paraxial radius of curvature of the display surface side surface of the first lens, Let us assume that.

3. 2. The optical system according to claim 1, wherein the following condition (3) is satisfied: (3) -1.50<r2 / r3<-0.50 however, r2: paraxial radius of curvature of the display surface side surface of the first lens, r3: paraxial radius of curvature of the pupil surface side of the second lens, Let us assume that.

4. 2. The optical system according to claim 1, wherein the following condition (4) is satisfied: (4) -4.00<r2 / f1<-0.75 however, r2: paraxial radius of curvature of the display surface side surface of the first lens, f1: focal length of the first lens, Let us assume that.

5. 2. The optical system according to claim 1, wherein the following condition (5) is satisfied: (5) -5.50<r3 / r4<-0.80 however, r3: paraxial radius of curvature of the pupil surface side of the second lens, r4: paraxial radius of curvature of the surface of the second lens on the display surface side, Let us assume that.

6. 2. The optical system according to claim 1, wherein the following condition (6) is satisfied: (6) -6.50<r4 / f2×D2<-2.70 however, r4: paraxial radius of curvature of the surface of the second lens on the display surface side, f2: focal length of the second lens, D2: thickness of the second lens on the optical axis, Let us assume that.

7. 2. The optical system according to claim 1, wherein the following condition (7) is satisfied: (7) -26<r4 / D2<-8 however, r4: paraxial radius of curvature of the surface of the second lens on the display surface side, D2: thickness of the second lens on the optical axis, Let us assume that.

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