Observation optical system and observation device having the same

Abstract

To provide an observation optical system which is compact and has a wide angle while having the high optical performance and an observation device having the same.SOLUTION: An observation optical system for observing an image displayed on an image display surface comprises a first lens group and a second lens group arranged in the order from the observation side to the image display surface side. The first lens group comprises a semi-transmission reflecting element, a first lens in which a lens surface on the image display surface side is the convex surface, and a second lens which is the lens surface on the image display surface side and is joined to the first lens, arranged in the order from the observation side to the image display surface side. The lens surface on the image display surface side is the semi-transmission reflecting surface and the second lens group includes a third lens in which at least one lens surface is the aspherical surface.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an observation optical system. [Background technology]

[0002] In recent years, image display devices such as head-mounted displays have become known that provide a realistic experience by enlarging an original image displayed on an image display element such as a liquid crystal display (LCD) through an observation optical system to provide a large-screen image to the user. Image display devices are required to be small and lightweight so that they can be worn on the head, and to be thin so that the moment when worn on the head can be reduced. In addition, the observation optical systems used in image display devices are required to have high optical performance and a wide angle.

[0003] Conventionally, a concentric optical system using a reflecting surface has been known as a compact observation optical system (see Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-148627 [Patent Document 2] Patent No. 3212784 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the observation optical system of Patent Document 1 has most of its refractive power in the reflecting surface of the half mirror, and therefore does not adequately correct coma aberration and field curvature aberration in particular, making it difficult to achieve high optical performance.

[0006] Furthermore, the observation optical system of Patent Document 2 is composed of only lenses with positive refractive power, and therefore cannot sufficiently correct chromatic aberration.

[0007] An object of the present invention is to provide a compact, wide-angle observation optical system that has high optical performance, and an observation apparatus that includes the same. [Means for solving the problem]

[0008] An observation optical system according to one aspect of the present invention is an observation optical system for observing an image displayed on an image display surface, and is characterized in that it comprises a first lens group and a second lens group arranged in order from the observation side to the image display surface side, the first lens group including, arranged in order from the observation side to the image display surface side, a semi-transmissive reflective element, a first lens whose lens surface on the image display surface side is convex, and a second lens whose lens surface on the image display surface side is cemented to the first lens, the lens surface on the image display surface side being a semi-transmissive reflective surface, and the second lens group including a third lens whose lens surface is aspherical. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a compact, wide-angle observation optical system that has high optical performance, and an observation apparatus that includes the same. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 2 is a cross-sectional view of the lenses of the observation optical system of Example 1. [Figure 2] 3A to 3C are longitudinal aberration diagrams of the observation optical system of Example 1. [Figure 3] 10 is a cross section of a lens of an observation optical system according to a second embodiment. [Figure 4] 10A and 10B are longitudinal aberration diagrams of the observation optical system of Example 2. [Figure 5] 10 is a cross section of a lens of an observation optical system according to a third embodiment. [Figure 6] 10A and 10B are longitudinal aberration diagrams of the observation optical system of Example 3. [Figure 7] 10 is a cross section of a lens of an observation optical system according to a fourth embodiment. [Figure 8] 10A and 10B are longitudinal aberration diagrams of the observation optical system of Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same reference numerals are used to designate the same components, and redundant explanations will be omitted.

[0012] 1, 3, 5, and 7 are cross-sectional views of lenses in the observation optical systems of Examples 1 to 4 for observing an image displayed on an image display surface. In each cross-sectional view of the lens, the left side is the observation side and the right side is the image display surface side.

[0013] The observation optical system in each embodiment is used as a head-mounted display for enlarging and observing an original image displayed on an image display element such as a liquid crystal display (LCD).

[0014] The viewing optical system in each embodiment has a first lens group L1 and a second lens group L2 arranged in this order from the viewing side to the image display surface side.

[0015] SP is a pupil plane (observation plane) where the observer's pupil is located, and ID is an image display surface of the image display element.

[0016] The first lens group L1 includes, arranged in this order from the observation side to the image display surface side, a semi-transmissive reflector 11, a first lens G1 whose lens surface R on the image display surface side is convex (with its concave surface facing the pupil plane side), and a second lens G2 cemented to the first lens G1 at lens surface R. The semi-transmissive reflector 11 is, for example, a wire grid polarizer configured to reflect linearly polarized light polarized in the same direction as when it passed through the polarizing plate 14, and to transmit linearly polarized light polarized in a direction perpendicular to the direction when it passed through the polarizing plate 14.

[0017] The lens surface R of the first lens G1 on the image display surface side is a semi-transmissive reflective surface, and is, for example, a half mirror on which a dielectric multilayer film is formed.

[0018] It is preferable that the first lens group L1 is made up of a single element cemented together.

[0019] The second lens group L2 includes a third lens GP having at least one aspherical lens surface.

[0020] 2, 4, 6, and 8 are longitudinal aberration diagrams (eye relief 18 mm) of the viewing optical systems of Examples 1 to 4. The eye relief represents the distance between the eye point on the optical axis and the lens surface closest to the viewing side.

[0021] In the spherical aberration diagram, Fno is the F-number, and shows the amount of spherical aberration for the d-line (wavelength 587.6 nm) and g-line (wavelength 435.8 nm). In the astigmatism diagram, ΔS shows the amount of astigmatism on the sagittal image plane, and ΔM shows the amount of astigmatism on the meridional image plane. In the distortion diagram, the amount of distortion for the d-line is shown. In the chromatic aberration diagram, the amount of chromatic aberration for the g-line is shown. ω is the half angle of view (°).

[0022] In evaluating aberrations, the aberrations of a light ray reaching the observation side when a light emitting point is provided on the image display surface side correspond one-to-one to the aberrations of a light ray reaching the image display surface when a light emitting point is provided on the observation side, so for convenience, the aberrations at the image display surface are evaluated. Here, the diameter of the human pupil is, for example, approximately Φ3.5 mm, but the eyebox in each embodiment is set to be larger than Φ3.5 mm in consideration of fluctuations in the pupil plane position.

[0023] The optical path in the observation optical system of each embodiment will be described below. Light that emerges from the image display surface ID, is refracted by the second lens group L2, and then passes through lens surface R and enters the semi-transmissive reflecting element 11. The light that is reflected by the semi-transmissive reflecting element 11 is then incident on lens surface R. The light that is reflected by lens surface R is then incident on the semi-transmissive reflecting element 11 again. The light that passes through the semi-transmissive reflecting element 11 reaches pupil plane SP. While traveling along the above optical path, a divergent light beam emerging from a point on the image display surface ID is converted into approximately parallel light and guided to pupil plane SP. Therefore, an image displayed on the image display surface ID is observed as a virtual image formed at a distance by an observer whose pupil is positioned near pupil plane SP.

[0024] Next, the characteristic configuration of the observation optical system of each embodiment will be described.

[0025] The lens surface R of the first lens G1 on the image display surface side has positive refractive power when functioning as a reflecting surface, so the optical path can be folded, making it possible to realize a thin, wide-angle viewing optical system.

[0026] Furthermore, because lens surface R functions as the cemented surface between the first lens G1 and the second lens G2, it is possible to avoid the condition of total reflection when light passes through lens surface R, compared to when the semi-transmissive reflective surface is in contact with air. Furthermore, because the first lens G1 is a positive lens and the second lens G2 is a negative lens, chromatic aberration can be corrected, and high optical performance can be achieved.

[0027] The first lens unit L1 requires aberration correction because most of the refractive power is located on the reflecting surface of lens surface R. The second lens unit L2 includes a third lens element GP with at least one aspherical lens surface, which makes it possible to correct aberrations, particularly coma and field curvature, and achieves high optical performance.

[0028] With the above-described configuration, it is possible to realize a compact, wide-angle observation optical system that has high optical performance, and an observation apparatus that includes the same.

[0029] Next, the configuration and conditions that the observation optical system of each embodiment preferably satisfies will be described. The observation optical system of each embodiment preferably satisfies one or more of the following conditional expressions (1) to (3). Here, νd1 is the Abbe number of the first lens G1 at the d-line, and νd2 is the Abbe number of the second lens G2 at the d-line. n1 is the refractive index of the first lens G1 at the d-line, and n2 is the refractive index of the second lens G2 at the d-line. f2 is the focal length of the second lens group L2 at the d-line, and f is the focal length of the observation optical system at the d-line.

[0030] 0.20<νd2 / νd1<1.00 (1) 1.00 <n2 / n1<1.35 (2) 0.80 <f2 / f<10.00 (3) Conditional expression (1) defines the dispersion of the first lens G1 and the second lens G2. By satisfying conditional expression (1), a configuration is achieved that suppresses chromatic aberration, and high optical performance can be achieved. If the lower limit of conditional expression (1) is exceeded and the dispersion of the second lens G2 becomes large, chromatic aberration increases, degrading optical performance, which is undesirable. On the other hand, if the upper limit of conditional expression (1) is exceeded, it becomes difficult to correct chromatic aberration, which is undesirable.

[0031] Conditional formula (2) defines the refractive indices of the first lens G1 and the second lens G2. Below the lower limit of conditional formula (2), the refractive index of the first lens G1 becomes greater than the refractive index of the second lens G2. Focusing on the Betzval sum of the first lens group L1, the greater the refractive index of the first lens G1 becomes than the refractive index of the second lens G2, the closer it is to 0. However, since the second lens group L2 is provided in each embodiment, it is not necessary to make the Betzval sum of the first lens group L1 approach 0. The viewing optical system of each embodiment satisfies conditional formula (2), but also includes the second lens group L2, allowing the Betzval sum to approach 0 overall. Below the lower limit of conditional formula (2), considering the relationship between the refractive index and dispersion of existing glass materials, it becomes difficult to correct chromatic aberrations when selecting the glass material, making it impossible to achieve high optical performance, which is undesirable. If the upper limit of conditional expression (2) is exceeded, the refractive index of the second lens G2 becomes too large compared to the refractive index of the first lens G1, and the negative refractive power of the lens surface R when it functions as a transmitting surface becomes too strong. This causes the Betzval sum of the first lens group L1 to become too large in the negative direction, making it difficult to bring the Betzval sum of the entire projection optical system close to 0 using the second lens group L2. This is therefore undesirable because it is not possible to sufficiently correct the curvature of field and to achieve high optical performance.

[0032] Conditional expression (3) defines the refractive power of the second lens group L2. If the lower limit of conditional expression (3) is not met, the refractive power of the second lens group L2 relative to the observation optical system becomes too strong. If the upper limit of conditional expression (3) is exceeded, the refractive power of the first lens group L1 relative to the observation optical system becomes too strong. As a result, the positive refractive power of lens surface R when functioning as a reflecting surface becomes too strong, making it difficult to correct aberrations by providing third lens GP. This is therefore undesirable because it is not possible to achieve high optical performance.

[0033] It is preferable that the numerical ranges of the conditional expressions (1) to (3) be set to the numerical ranges of the following conditional expressions (1a) to (3a).

[0034] 0.25<νd2 / νd1<0.75 (1a) 1.05 <n2 / n1<1.30 (2a) 0.90 <f2 / f<8.00 (3a) It is more preferable that the numerical ranges of the conditional expressions (1) to (3) be the numerical ranges of the following conditional expressions (1b) to (3b).

[0035] 0.30<νd2 / νd1<0.50 (1b) 1.10 <n2 / n1<1.25 (2b) 1.00 <f2 / f<5.00 (3b) In the viewing optical system of each embodiment, it is preferable that the third lens GP has positive refractive power and that at least one lens surface of the third lens GP is an aspheric surface having an inflection point. Having the third lens GP with positive refractive power allows the focal length of the viewing optical system to be shortened. Furthermore, having at least one lens surface of the third lens GP with an inflection point allows astigmatism, field curvature, and distortion to be efficiently corrected even with a small number of lenses. Therefore, by having the third lens GP configured as described above, it is possible to realize a lightweight, wide-angle observation optical system that has high optical performance.

[0036] Furthermore, it is preferable that the viewing optical system of each embodiment satisfy one or more of the following conditional expressions (4) and (5): fp is the focal length of the third lens GP with respect to the d-line; Ypa is the distance from the optical axis to the inflection point of the third lens GP when at least one lens surface of the third lens GP is an aspheric surface having an inflection point; Ya is the maximum ray height with respect to the optical axis of the third lens GP when at least one lens surface of the third lens GP is an aspheric surface having an inflection point.

[0037] 1.00 <fp / f<10.00 (4) 0.20 <Ypa / Ya<0.75 (5) Conditional expression (4) defines the refractive power of the third lens GP. If the lower limit of conditional expression (4) is not met, the refractive power of the third lens GP becomes too strong, making it difficult to correct aberrations by providing the third lens GP. If the upper limit of conditional expression (4) is exceeded, the refractive power of the third lens GP becomes too weak relative to the observation optical system, making it impossible to sufficiently shorten the focal length of the observation optical system and thus making it impossible to achieve a wide-angle observation optical system.

[0038] Conditional expression (5) defines the position of the inflection point of the third lens element GP. In the viewing optical systems of the embodiments, the reflective surface of lens surface R has most of the refractive power, so it is necessary to correct coma and field curvature that occur at the reflective surface. Therefore, it is preferable to provide an inflection point on the aspherical surface to provide a power change. In this case, it is preferable that the aspherical surface of the third lens element GP having the inflection point satisfy conditional expression (5). If the lower limit of conditional expression (5) is not met, the position of the power change will be too close to the center of the optical axis, resulting in excessive correction of coma and field curvature, or excessive generation of high-order aberrations, which is undesirable. If the upper limit of conditional expression (5) is exceeded, the position of the power change will be located near the periphery of the image, making it impossible to sufficiently correct coma and field curvature at the center of the image.

[0039] If the third lens GP has a plurality of aspherical lens surfaces having inflection points, it is sufficient that at least one of the aspherical lens surfaces having the plurality of inflection points satisfies conditional expression (5). Also, if an aspherical lens surface having inflection points has a plurality of inflection points, it is sufficient that the inflection point located farthest from the optical axis satisfies conditional expression (5).

[0040] It is preferable that the numerical ranges of the conditional expressions (4) and (5) be set to the numerical ranges of the following conditional expressions (4a) and (5a).

[0041] 1.25 <fp / f<8.00 (4a) 0.23 <Ypa / Ya<0.70 (5a) It is more preferable that the numerical ranges of the conditional expressions (4) and (5) be set to the numerical ranges of the following conditional expressions (4b) and (5b).

[0042] 1.50 <fp / f<6.00 (4b) 0.25 <Ypa / Ya<0.65 (5b) The use of polarized light in the observation optical system of each embodiment will be described below with reference to the cross-sectional views of the lenses of each embodiment.

[0043] The first quarter-wave plate 12 is disposed between the semi-transmissive reflective element 11 and the first lens G1. The second quarter-wave plate 13 is disposed on the image display surface side of the second lens G2. The polarizing plate 14 is disposed on the image display surface side of the second quarter-wave plate 13.

[0044] The first quarter-wave plate 12 and the second quarter-wave plate 13 are arranged with their respective slow axes tilted at 90°. The first quarter-wave plate 12 is also arranged with its slow axis tilted at 45° with respect to the polarization transmission axis of the polarizing plate 14.

[0045] The light emitted from the image display surface ID is converted to linearly polarized light by the polarizing plate 14, converted to circularly polarized light by the second quarter-wave plate 13, and then incident on the lens surface R. A portion of the light that has entered the lens surface R is reflected by the lens surface R and converted to reverse circularly polarized light, and returns to the second quarter-wave plate 13. The reverse circularly polarized light that has returned to the second quarter-wave plate 13 is converted by the second quarter-wave plate 13 to linearly polarized light polarized in a direction perpendicular to the direction in which it initially passed through the polarizing plate 14, and returns to the polarizing plate 14, where it is absorbed.

[0046] On the other hand, another portion of the light incident on lens surface R passes through lens surface R and is converted by first quarter-wave plate 12 into linearly polarized light polarized in the same direction as when it passed through polarizing plate 14, and then enters semi-transmissive reflecting element 11. The light incident on semi-transmissive reflecting element 11 is reflected by semi-transmissive reflecting element 11, and is converted by first quarter-wave plate 12 into circularly polarized light in the opposite direction to when it was first circularly polarized by second quarter-wave plate 13, and then enters lens surface R. The light reflected by lens surface R becomes circularly polarized light in the opposite direction to the light before being reflected by lens surface R, and becomes linearly polarized light polarized in a direction perpendicular to the direction in which it entered first quarter-wave plate 12 and first passed through polarizing plate 14, and then enters semi-transmissive reflecting element 11. The light that entered semi-transmissive reflecting element 11 passes through semi-transmissive reflecting element 11 and is guided to pupil plane SP.

[0047] As described above, only the light that has been transmitted through lens surface R, reflected by semi-transmissive reflecting element 11, reflected by lens surface R, and transmitted through semi-transmissive reflecting element 11 is guided to pupil plane SP.

[0048] In the observation optical system of each embodiment, it is preferable that the observation-side surface of the first lens G1 is flat. This makes it possible to easily bond the semi-transmissive reflective element 11 and the first quarter-wave plate 12 to the observation-side surface of the first lens G1. This reduces the number of parts, allowing for a smaller and lighter observation optical system.

[0049] In addition, in the observation optical system of each embodiment, it is preferable that the lens surface on the image display side of the second lens G2 is flat. This makes it easy to attach the second quarter-wave plate 13 and the polarizing plate 14 to the surface on the screen display side of the second lens G2. This reduces the number of parts, allowing for a smaller and lighter observation optical system.

[0050] Because the observation-side surface of the first lens G1 is flat and the image display-side surface of the second lens G2 is flat, the first lens group L1 has most of its refractive power in the reflective surface of lens surface R and is configured with almost no flexibility for aberration correction. Therefore, by providing the third lens GP, aberration correction becomes possible, and high optical performance can be achieved.

[0051] In the observation optical system of each embodiment, it is preferable that both the first lens G1 and the second lens G2 of the first lens group L1 are glass lenses. Because the semi-transmissive reflecting element 11 reflects and transmits linearly polarized light depending on the polarization direction, if an optical element having birefringence is placed between the semi-transmissive reflecting element 11 and the polarizing plate 14, ghost light may be incident on the pupil plane SP. For this reason, it is preferable that each lens constituting the first lens group L1 be made of a glass lens with low birefringence.

[0052] In addition, in the observation optical system of each embodiment, it is preferable that the third lens GP be made of a resin lens. Because the third lens GP is not disposed between the semi-transmissive reflective element 11 and the polarizing plate 14, problems caused by ghost light do not occur even if the third lens GP is a resin lens having birefringence. By making the third lens GP of a resin lens, at least one lens surface can be easily made aspherical, and because a resin lens has a smaller specific gravity than a glass lens, the weight can be reduced.

[0053] Next, the observation optical system of each embodiment will be described in detail.

[0054] The observation optical system of Example 1 has a total angle of view of 70 degrees and a designed maximum pupil diameter of 10 mm. The second lens group L2 is composed of a third lens group GP and a positive lens, arranged in this order from the observation side to the image display surface side. By having the second lens group L2 composed of the third lens group GP and a positive lens, it is possible to further suppress field curvature and achieve high optical performance.

[0055] The observation optical system of Example 2 has a total angle of view of 80 degrees and a designed maximum pupil diameter of 10 mm. The second lens group L2 is composed of a third lens element GP and a positive lens, arranged in this order from the observation side to the image display surface side. In Example 2, the third lens element GP has a stronger positive refractive power than in Example 1, thereby realizing a wider-angle observation optical system.

[0056] The observation optical system of Example 3 has a total angle of view of 65 degrees and a designed maximum pupil diameter of 10 mm. The second lens group L2 is composed of a third lens element GP, which are arranged in this order from the observation side to the image display surface side. By having the second lens group L2 composed only of the third lens element GP, a lighter observation optical system can be realized.

[0057] The observation optical system of Example 4 has a total angle of view of 70 degrees and a designed maximum pupil diameter of 10 mm. The second lens group L2 is composed of a third lens GP arranged in this order from the observation side to the image display surface side. In Example 4, the refractive power of the second lens group L2 is made stronger than in Example 3, thereby realizing a wider-angle observation optical system.

[0058] Numerical Examples 1 to 4 corresponding to Examples 1 to 4, respectively, are shown below.

[0059] In the surface data of each numerical example, r represents the radius of curvature of each optical surface, and d (mm) represents the axial spacing (distance on the optical axis) between the mth surface and the (m+1)th surface. Here, m is the surface number counted from the pupil surface SP side. Also, nd represents the refractive index of each optical element at the d-line, and vd represents the Abbe number of the optical element. Note that the Abbe number vd of a certain material is given by Nd, NF, and NC, where Nd, NF, and NC are the refractive indices at the d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm) of the Fraunhofer lines, respectively. νd=(Nd-1) / (NF-NC) It is expressed as:

[0060] If the optical surface is aspherical, an asterisk (*) is added to the right of the surface number. The aspherical shape is expressed as follows: X is the displacement from the vertex of the surface in the optical axis direction, h is the height from the optical axis in the direction perpendicular to the optical axis, R is the paraxial radius of curvature, K is the conic constant, and A2, A4, A6, A8, A10, and A12 are the aspherical coefficients of each order. X=(h 2 / R) / [1+{1-(1+K)(h / R) 2} 1 / 2 +A2×h 2 +A4×h 4 +A6×h 6 +A8×h 8 +A10×h 10 In addition, "e±XX" in each aspherical coefficient is "×10± XX " means.

[0061] [Numerical Example 1] Unit: mm Surface Data Surface number rd nd νd 1(SP) ∞ 18.00 2 ∞ 0.20 1.51 50.0 3 ∞ 0.20 1.58 50.0 4 ∞ 6.63 1.48749 70.2 5 -57.143 -6.63 Reflective surface 6 ∞ -0.20 1.58 50.0 7 ∞ -0.20 1.51 50.0 8 ∞ 0.20 Reflective surface 9 ∞ 0.20 1.58 50.0 10 ∞ 6.63 1.48749 70.2 11 -57.143 1.34 1.80518 25.4 12 ∞ 0.20 1.58 50.0 13 ∞ 0.20 1.46 50.0 14 ∞ 2.27 15* -64.926 3.00 1.54390 56.0 16* -32.290 1.78 17 36.118 4.98 1.96300 24.1 18 ∞ 0.51 Image plane ∞ Aspheric data Page 15 K = 0.00000e+000 A 4= 5.22826e-005 A 6=-1.15849e-007 A 8=-1.72985e-010 A10=2.60573e-012 A12=-4.34549e-015 Page 16 K = 0.00000e+000 A 4= 1.25599e-004 A 6=-7.33671e-007 A 8= 2.74067e-009 A10=-3.57083e-012 Focal length 18.14 F-number 1.81 Half angle of view (degrees) 35.00 Image height 12.70 Lens length 53.36 BF 0.51 Lens group data Group starting plane focal length SP 1 ∞ L1 2 20.31 L2 15 28.23 [Numerical Example 2] Unit: mm Surface Data Surface number rd nd νd 1(SP) ∞ 18.00 2 ∞ 0.20 1.51 50.0 3 ∞ 0.20 1.58 50.0 4 ∞ 7.47 1.53996 59.5 5 -56.731 -7.47 Reflective surface 6 ∞ -0.20 1.58 50.0 7 ∞ -0.20 1.51 50.0 8 ∞ 0.20 Reflective surface 9 ∞ 0.20 1.58 50.0 10 ∞ 7.47 1.53996 59.5 11 -56.731 1.50 1.80810 22.8 12 ∞ 0.20 1.58 50.0 13 ∞ 0.20 1.46 50.0 14 ∞ 0.70 15* 49.176 4.19 1.54390 56.0 16* -19.000 0.50 17 39.365 4.10 2.00100 29.1 18∞0.50 Image plane ∞ Aspheric data Page 15 K = 0.00000e+000 A 4=-3.78860e-004 A 6= 3.55858e-006 A 8=-1.47846e-008 A10=2.95192e-011 A12=-2.23370e-014 Page 16 K = 0.00000e+000 A 4= 1.17084e-004 A 6= 1.55977e-007 A 8=-1.50577e-009 A10= 3.53048e-012 Focal length 15.14 F-number 1.51 Half angle of view (degrees) 40.00 Image height 12.70 Lens length 53.50 BF 0.50 Lens group data Group starting plane focal length SP 1 ∞ L1 2 19.16 L2 15 15.87 [Numerical Example 3] Surface Data Surface number rd nd νd 1(SP) ∞ 18.00 2 ∞ 0.20 1.51 50.0 3 ∞ 0.20 1.58 50.0 4 ∞ 5.25 1.48749 70.2 5 -60.425 -5.25 Reflective surface 6 ∞ -0.20 1.58 50.0 7 ∞ -0.20 1.51 50.0 8 ∞ 0.20 Reflective surface 9 ∞ 0.20 1.58 50.0 10 ∞ 5.25 1.48749 70.2 11 -60.425 1.50 1.70585 30.2 12 ∞ 0.20 1.58 50.0 13 ∞ 0.20 1.46 50.0 14∞6.50 15* -133.015 4.00 1.53110 55.9 16* -18.437 2.95 Image plane ∞ Aspheric data Page 15 K = 0.00000e+000 A 4=-6.58095e-005 A 6= 4.82916e-008 A 8= 3.03270e-009 A10=-9.81761e-012 A12= 1.08924e-014 Page 16 K = 0.00000e+000 A 4= 7.06395e-005 A 6=-3.34017e-007 A 8= 3.39605e-009 A10=-3.40888e-012 Focal length 19.94 F-number 1.99 Angle of view 32.50 Image height 12.70 Lens length 50.30 BF 2.95 Lens group data Group starting plane focal length SP 1 ∞ L1 2 21.29 L2 15 39.82 [Numerical Example 4] Unit: mm Surface Data Surface number rd nd νd 1(SP) ∞ 18.00 2 ∞ 0.20 1.51 50.0 3 ∞ 0.20 1.58 50.0 4 ∞ 6.27 1.69680 55.5 5 -60.762 -6.27 Reflective surface 6 ∞ -0.20 1.58 50.0 7 ∞ -0.20 1.51 50.0 8 ∞ 0.20 Reflective surface 9 ∞ 0.20 1.58 50.0 10 ∞ 6.27 1.69680 55.5 11 -60.762 1.34 1.96300 24.1 12 ∞ 0.20 1.58 50.0 13 ∞ 0.20 1.46 50.0 14∞4.69 15* -54.430 3.00 1.53110 55.9 16* -19.707 2.85 Image plane ∞ Aspheric data Page 15 K = 0.00000e+000 A 4= 7.15880e-007 A 6= 5.69825e-007 A 8=-2.61510e-009 A10=5.49014e-012 A12=-5.21942e-015 Page 16 K = 0.00000e+000 A 4= 1.51686e-004 A 6= 8.58463e-008 A 8=-1.19285e-009 A10= 1.43287e-012 Focal length 18.14 F-number 1.81 Half angle of view (degrees) 35.00 Image height 12.70 Lens length 50.31 BF 2.85 Lens group data Group starting plane focal length SP 1 ∞ L1 2 18.72 L2 15 56.47 The various values ​​in each numerical example are summarized in Table 1 below.

[0062] [Table 1]

[0063] Although the preferred embodiments and examples of the present invention have been described above, the present invention is not limited to these embodiments and examples, and various combinations, modifications, and changes are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0064] G1 First Lens G2 2nd lens GP third lens ID image display surface L1 First lens group L2 Second lens group R lens surface 11 Semi-transmissive reflective element

Claims

1. An observation optical system for observing an image displayed on an image display surface, The lens comprises a first lens group and a second lens group, which are arranged in this order from the observation side to the image display surface side, the first lens group includes, arranged in order from the observation side to the image display surface side, a semi-transmissive reflective element, a first quarter-wave plate, a first lens whose lens surface on the image display surface side is convex toward the image display surface side, a second lens whose lens surface on the image display surface side is cemented to the first lens, a second quarter-wave plate, and a polarizing plate; a lens surface of the first lens facing the image display surface is a semi-transmissive reflective surface, 10. An observation optical system, wherein the second lens group includes a third lens having at least one aspherical lens surface and a lens surface facing the image display surface that is convex toward the image display surface.

2. When the Abbe number of the first lens is νd1 and the Abbe number of the second lens is νd2, 0.20<νd2 / νd1<1.00 2. The viewing optical system according to claim 1, wherein the following condition is satisfied:

3. When the refractive index of the first lens is n1 and the refractive index of the second lens is n2, 1.00<n2 / n1<1.35 3. The viewing optical system according to claim 1, wherein the following condition is satisfied:

4. When the focal length of the second lens group with respect to the d-line is f2 and the focal length of the observation optical system with respect to the d-line is f, 0.80<f2 / f<10.00 4. The viewing optical system according to claim 1, wherein the following condition is satisfied:

5. the third lens has a positive refractive power, 5. The viewing optical system according to claim 1, wherein at least one lens surface of the third lens is an aspheric surface having an inflection point.

6. When the focal length of the third lens with respect to the d-line is fp and the focal length of the observation optical system with respect to the d-line is f, 1.00<fp / f<10.00 6. The viewing optical system according to claim 1, wherein the following condition is satisfied: 1.0<1.0<1.

0.

7. at least one lens surface of the third lens is an aspheric surface having an inflection point; When the distance from the optical axis of the third lens to the inflection point is Ypa and the maximum ray height of the aspherical surface with respect to the optical axis of the third lens is Ya, 0.20<Ypa / Ya<0.75 7. The viewing optical system according to claim 1, wherein the following condition is satisfied: 1.0<f<1.0<f<1.

0.

8. 8. The observation optical system according to claim 1, wherein the first quarter-wave plate and the second quarter-wave plate are arranged with their slow axes tilted by 90 degrees.

9. 9. The observation optical system according to claim 1, wherein the first quarter-wave plate is disposed with its slow axis tilted at 45 degrees with respect to the polarization transmission axis of the polarizer.

10. 10. The viewing optical system according to claim 1, wherein the lens surface of the first lens on the viewing side is flat.

11. 11. The viewing optical system according to claim 1, wherein a lens surface of the second lens on the image display side is flat.

12. 12. The observation optical system according to claim 1, wherein the first lens and the second lens are both glass lenses.

13. 13. The observation optical system according to claim 1, wherein the third lens is made of a resin lens.

14. 14. The viewing optical system according to claim 1, wherein the second lens group comprises the third lens and a positive lens, arranged in this order from the viewing side to the image display surface side.

15. 14. The viewing optical system according to claim 1, wherein the second lens group is made up of the third lenses arranged in order from the viewing side to the image display surface side.

16. 16. The observation optical system according to claim 1, wherein light emitted from the image display surface is refracted by the second lens group, passes through a lens surface on the image display surface side, is reflected by the semi-transmissive reflecting element, is reflected by the lens surface on the image display surface side, passes through the semi-transmissive reflecting element, and reaches a pupil plane.

17. An observation device comprising the observation optical system according to any one of claims 1 to 16.

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