Observation optical system and observation apparatus 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 Art

[0002] In recent years, an image display device such as a head-mounted display that provides an immersive experience by magnifying and displaying an original image displayed on an image display element such as a liquid crystal display (LCD) through an observation optical system and providing a large-screen image to the user is known. The image display device is desired to be small and lightweight for head mounting and thin to reduce the moment when head-mounted. In addition, the observation optical system used in the image display device is required to have a wide angle while having high optical performance.

[0003] Conventionally, a concentric optical system using a reflecting surface is known as an observation optical system with a small configuration (see Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the observation optical system of Patent Document 1, since most of the refractive power is on the reflecting surface of the half mirror, particularly the correction of coma aberration and field curvature aberration is not sufficient, and it is difficult to have high optical performance.

[0006] In addition, since the observation optical system of Patent Document 2 is composed only of lenses with positive refractive power, chromatic aberration cannot be sufficiently corrected.

[0007] An object of the present invention is to provide an observation optical system that is small and has a wide angle while having high optical performance, and an observation apparatus having the same.

Means for Solving the Problems

[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 includes 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 includes a semi-transmissive reflection element, The first quarter-wave plate, a first lens having a convex lens surface on the image display surface side, and a second lens joined to the first lens at the lens surface on the image display surface side , consists of a second quarter-wave plate and a polarizing plate. The lens surface on the image display surface side of the second lens is bonded with the second quarter-wave plate and the polarizing plate. wherein the lens surface on the image display surface side is a semi-transmissive reflection surface, See, the third lens is made of a resin lens. and the second lens group includes a third lens having at least one aspherical lens surface.

Figure 1

Effects of the Invention

[0009] According to the present invention, it is possible to provide an observation optical system that is small and has a wide angle while having high optical performance, and an observation apparatus having the same.

Brief Description of the Drawings

[0010]

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In each figure, the same members are denoted by the same reference numerals, and redundant descriptions are omitted.

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

[0013] The observation optical system of each embodiment is used, for example, as a head-up display that enlarges and displays an original image displayed on an image display element such as a liquid crystal display (LCD) and observes it.

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

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

[0016] The first lens group L1 includes a semi-transmissive reflective element 11, a first lens G1 whose lens surface R on the image display surface side is convex (facing the concave surface toward the pupil plane side), and a second lens G2 joined to the first lens G1 at the lens surface R. The semi-transmissive reflective element 11 is a wire grid polarizer configured to reflect linearly polarized light polarized in the same direction as the direction when passing through the polarizing plate 14 and transmit linearly polarized light polarized in a direction orthogonal to the direction when passing through the polarizing plate 14.

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

[0018] Note that the first lens group L1 is preferably composed of one element bonded to each other.

[0019] The second lens group L2 includes a third lens GP in which at least one lens surface is an aspherical surface.

[0020] Figs. 2, 4, 6, and 8 are respectively the longitudinal aberration diagrams (eye relief: 18 mm) of the observation 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 observation side.

[0021] In the spherical aberration diagram, Fno is the F-number, indicating the amount of spherical aberration with respect to the d-line (wavelength: 587.6 nm) and the g-line (wavelength: 435.8 nm). In the astigmatism diagram, ΔS indicates the amount of astigmatism on the sagittal image plane, and ΔM indicates the amount of astigmatism on the meridional image plane. The distortion aberration diagram shows the amount of distortion aberration with respect to the d-line. The chromatic aberration diagram shows the amount of chromatic aberration at the g-line. ω is the imaging semi-field angle (°).

[0022] Note that in the evaluation of aberrations, since the aberrations of the light rays reaching the observation side with a light-emitting point provided on the image display surface side and the aberrations of the light rays reaching the image display surface side with a light-emitting point provided on the observation side correspond one-to-one, for convenience, the aberrations on the image display surface are evaluated. Here, the pupil diameter of a human is about Φ3.5 mm as an example, but the eyebox of each example is set to be larger than Φ3.5 mm in consideration of the fluctuation of the pupil plane position.

[0023] The optical path in the observation optical system of each embodiment will be described below. The light emitted from the image display surface ID, refracted by the second lens group L2, and then transmitted through the lens surface R is incident on the semi-transmissive reflective element 11. The light reflected by the semi-transmissive reflective element 11 is incident on the lens surface R. The light reflected by the lens surface R is incident on the semi-transmissive reflective element 11 again. The light transmitted through the semi-transmissive reflective element 11 reaches the pupil plane SP. When tracing the above optical path, the divergent light beam emitted from a point on the image display surface ID is converted into substantially parallel light and guided to the pupil plane SP. Therefore, the image displayed on the image display surface ID is observed by an observer with a pupil placed near the pupil plane SP as a virtual image formed in the distance.

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

[0025] Since the lens surface R on the image display surface side of the first lens G1 has a positive refractive power when functioning as a reflecting surface, the optical path can be folded, and a thin and wide-angle observation optical system can be realized.

[0026] In addition, since the lens surface R functions as the joint surface between the first lens G1 and the second lens G2, the total reflection condition when passing through the lens surface R can be avoided compared with the case where the semi-transmissive reflecting surface is in contact with air. Also, since the first lens G1 is a positive lens and the second lens G2 is a negative lens, chromatic aberration correction is possible, and high optical performance can be realized.

[0027] Since the first lens group L1 has most of the refractive power on the reflecting surface of the lens surface R, aberration correction is required. Since the second lens group L2 includes the third lens GP in which at least one lens surface is an aspherical surface, correction of coma aberration and field curvature aberration is particularly possible, and high optical performance can be realized.

[0028] By having the above-described configuration, it is possible to realize a small and wide-angle observation optical system having high optical performance and an observation device having the same.

[0029] Next, the preferable configurations 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 with respect to the d-line, and νd2 is the Abbe number of the second lens G2 with respect to the d-line. n1 is the refractive index of the first lens G1 with respect to the d-line, and n2 is the refractive index of the second lens G2 with respect to the d-line. f2 is the focal length of the second lens group L2 with respect to the d-line, and f is the focal length of the observation optical system with respect to 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 for suppressing chromatic aberration can be achieved, and high optical performance can be realized. If the dispersion of the second lens G2 increases below the lower limit value of conditional expression (1), chromatic aberration increases and optical performance deteriorates, which is not preferable. On the other hand, if it exceeds the upper limit value of conditional expression (1), correction of chromatic aberration becomes difficult, which is not preferable.

[0031] Conditional expression (2) defines the refractive indices of the first lens G1 and the second lens G2. If it is below the lower limit value of conditional expression (2), the refractive index of the first lens G1 becomes larger than the refractive index of the second lens G2. Here, paying attention to the Abbe number sum of the first lens group L1, the closer the refractive index of the first lens G1 is larger than that of the second lens G2, the closer it gets to 0. However, since the second lens group L2 is provided in each embodiment, it is not necessary to make the Abbe number sum of the first lens group L1 approach 0. Although the observation optical system of each embodiment does not satisfy conditional expression (2), since it has the second lens group L2, overall, the Abbe number sum can be made to approach 0. If it is below the lower limit value of conditional expression (2), considering the relationship between the refractive index and dispersion of existing optical materials, it becomes difficult to correct chromatic aberration in the selection of optical materials, and high optical performance cannot be achieved, so this is not preferable. If it exceeds the upper limit value of conditional expression (2), the refractive index of the second lens G2 becomes too large compared to the refractive index of the first lens G1, so the negative refractive power when the lens surface R functions as a transmission surface becomes too strong. For this reason, the Abbe number sum of the first lens group L1 becomes too large in the negative direction, and it becomes difficult to make the Abbe number sum of the entire projection optical system approach 0 with the second lens group L2. Therefore, field curvature cannot be sufficiently corrected, and high optical performance cannot be achieved, so this is not preferable.

[0032] Conditional expression (3) defines the refractive power of the second lens group L2. If it is below the lower limit value of conditional expression (3), the refractive power of the second lens group L2 with respect to the observation optical system becomes too strong. If it exceeds the upper limit value of conditional expression (3), the refractive power of the first lens group L1 with respect to the observation optical system becomes too strong. For this reason, the positive refractive power when the lens surface R functions as a reflection surface becomes too strong, and it becomes difficult to correct aberrations by arranging the third lens GP. Therefore, high optical performance cannot be achieved, so this is not preferable.

[0033] Note that it is preferable that the numerical ranges of conditional expressions (1) to (3) be 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) Furthermore, it is more preferable that the numerical ranges of the conditional expressions (1) to (3) are 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 addition, in the observation optical system of each embodiment, it is preferable that the third lens GP has a positive refractive power and at least one lens surface of the third lens GP is an aspherical surface having an inflection point. By having the third lens GP have a positive refractive power, the focal length of the observation optical system can be shortened. Also, by having at least one lens surface of the third lens GP have an inflection point, it is possible to efficiently correct spherical aberration, field curvature, and distortion aberration while using a small number of lenses. Therefore, by having the third lens GP have the above configuration, it is possible to realize a lightweight and wide-angle observation optical system with high optical performance.

[0036] In addition, it is preferable that the observation optical system of each embodiment satisfies 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 of the third lens GP to the inflection point when at least one lens surface of the third lens GP is an aspherical 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 aspherical 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 it is below the lower limit value of conditional expression (4), the refractive power of the third lens GP becomes too strong, making it difficult to correct aberrations by arranging the third lens GP. If it exceeds the upper limit value of conditional expression (4), the refractive power of the third lens GP with respect to the observation optical system becomes too weak, so that the focal length of the observation optical system cannot be made sufficiently short and a wide-angle observation optical system cannot be realized.

[0038] Conditional expression (5) defines the inflection point position of the third lens GP. In the observation optical systems of the respective embodiments, since the reflecting surface of the lens surface R has most of the refractive power, it is necessary to correct coma aberration and field curvature aberration generated at the reflecting surface. Therefore, it is preferable to provide an inflection point on the aspherical surface to give a power change. At this time, the aspherical surface having the inflection point of the third lens GP preferably satisfies conditional expression (5). If it is below the lower limit value of conditional expression (5), the position of the power change becomes too close to the center of the optical axis, overcorrecting coma aberration and field curvature, or the generation of higher-order aberrations becomes too large, which is not preferable. If it exceeds the upper limit value of conditional expression (5), the position of the power change is at the peripheral part of the screen, and coma aberration and field curvature at the center of the image cannot be sufficiently corrected.

[0039] In addition, when the third lens GP includes a plurality of lens surfaces that are aspherical surfaces having inflection points, at least one of the lens surfaces that are aspherical surfaces having a plurality of inflection points only needs to satisfy conditional expression (5). Further, when a plurality of inflection points are provided on the lens surface that is an aspherical surface having an inflection point, the inflection point located at the farthest distance from the optical axis only needs to satisfy conditional expression (5).

[0040] Note that it is preferable that the numerical ranges of conditional expressions (4) and (5) are the numerical ranges of conditional expressions (4a) and (5a) below.

[0041] 1.25 < fp / f < 8.00 (4a) 0.23 < Ypa / Ya < 0.70 (5a) Further, it is more preferable that the numerical ranges of conditional expressions (4) and (5) are the numerical ranges of conditional expressions (4b) and (5b) below.

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

[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 disposed such that their respective slow axes are inclined by 90°. Further, the first quarter-wave plate 12 is disposed such that its slow axis is inclined by 45° with respect to the polarization transmission axis of the polarizing plate 14.

[0045] The light emitted from the image display surface ID becomes linearly polarized by the polarizing plate 14, becomes circularly polarized by the second quarter-wave plate 13, and enters the lens surface R. A part of the light incident on the lens surface R is reflected by the lens surface R and becomes counterclockwise circularly polarized light, and returns to the second quarter-wave plate 13. The counterclockwise circularly polarized light that returns to the second quarter-wave plate 13 returns to the polarizing plate 14 as linearly polarized light polarized in a direction orthogonal to the direction when it first passed through the polarizing plate 14 by the second quarter-wave plate 13, and is absorbed by the polarizing plate 14.

[0046] On the other hand, another part of the light incident on the lens surface R passes through the lens surface R and becomes linearly polarized light polarized in the same direction as the direction when it passed through the polarizing plate 14 by the first quarter-wave plate 12, and enters the semi-transmissive reflective element 11. The light incident on the semi-transmissive reflective element 11 is reflected by the semi-transmissive reflective element 11, becomes counterclockwise circularly polarized light opposite to the case when it first became circularly polarized by the second quarter-wave plate 13 by the first quarter-wave plate 12, and enters the lens surface R. The light reflected by the lens surface R becomes circularly polarized light in the opposite direction to the light before being reflected by the lens surface R, and becomes linearly polarized light polarized in a direction orthogonal to the direction when it first passes through the polarizing plate 14 after entering the first quarter-wave plate 12, and enters the semi-transmissive reflection element 11. The light that has entered the semi-transmissive reflection element 11 passes through the semi-transmissive reflection element 11 and is guided to the pupil plane SP.

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

[0048] Also, in the observation optical system of each embodiment, it is preferable that the observation-side surface of the first lens G1 is a flat surface. Thereby, the semi-transmissive reflection element 11 and the first quarter-wave plate 12 can be easily bonded to the observation-side surface of the first lens G1. Therefore, the number of components can be reduced, and miniaturization and weight reduction of the observation optical system can be realized.

[0049] Also, 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 a flat surface. Thereby, the second quarter-wave plate 13 and the polarizing plate 14 can be easily bonded to the screen display-side surface of the second lens G2. Therefore, the number of components can be reduced, and miniaturization and weight reduction of the observation optical system can be realized.

[0050] Since the observation-side surface of the first lens G1 is a flat surface and the image display-side surface of the second lens G2 is a flat surface, the first lens group L1 has almost all the refractive power on the reflecting surface of the lens surface R, and there is almost no degree of freedom for aberration correction. Therefore, by providing the third lens GP, aberration correction becomes possible, and high optical performance can be realized.

[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. Since the semi-transmissive reflection element 11 reflects and transmits light according to the polarization direction of linearly polarized light, if an optical element having birefringence is disposed between the semi-transmissive reflection element 11 and the polarizing plate 14, there is a risk that ghost light enters the pupil plane SP. For this reason, each lens constituting the first lens group L1 is preferably made of a glass lens having low birefringence.

[0052] In the observation optical system of each embodiment, it is preferable that the third lens GP is made of a resin lens. Since the third lens GP is not disposed between the semi-transmissive reflection element 11 and the polarizing plate 14, even if the third lens GP is a resin lens having birefringence, problems due to ghost light do not occur. Since the third lens GP is made of a resin lens, at least one lens surface can be easily formed into an aspherical surface, and since the resin lens has a smaller specific gravity than the 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 the first embodiment has an overall angle of view of 70 degrees and a maximum pupil diameter in design of Φ10 mm. The second lens group L2 is composed of a third lens GP and a positive lens, which are arranged in order from the observation side to the image display surface side. By configuring the second lens group L2 from the third lens GP and a positive lens, it is possible to further suppress field curvature and realize high optical performance.

[0055] The observation optical system of the second embodiment has an overall angle of view of 80 degrees and a maximum pupil diameter in design of Φ10 mm. The second lens group L2 is composed of a third lens GP and a positive lens, which are arranged in order from the observation side to the image display surface side. In the second embodiment, by giving the third lens GP a stronger positive refractive power as compared with the first embodiment, a wider-angle observation optical system can be realized.

[0056] The observation optical system of Example 3 has a total field angle of 65 degrees and a maximum pupil diameter of Φ10 mm in design. The second lens group L2 is composed of a third lens GP arranged in order from the observation side to the image display surface side. By configuring the second lens group L2 only with the third lens GP, a lighter observation optical system can be realized.

[0057] The observation optical system of Example 4 has a total field angle of 70 degrees and a maximum pupil diameter of Φ10 mm in design. The second lens group L2 is composed of a third lens GP arranged in order from the observation side to the image display surface side. In Example 4, compared with Example 3, by making the refractive power of the second lens group L2 stronger, a wider-angle observation optical system can be realized.

[0058] The numerical Examples 1 to 4 corresponding to Examples 1 to 4 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 interval (distance on the optical axis) between the m-th surface and the (m + 1)-th surface. However, m is the surface number counted from the pupil surface SP side. Also, nd represents the refractive index with respect to the d-line of each optical member, and νd represents the Abbe number of the optical member. The Abbe number νd of a certain material, when 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 are Nd, NF, and NC, νd=(Nd - 1) / (NF - NC) is represented by.

[0060] Also, when the optical surface is an aspherical surface, an asterisk symbol is attached to the right side of the surface number. The aspherical shape, when X is the displacement amount 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, 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×h6 +A8×h 8 +A10×h 10 It is represented by. Note that "e±XX" in each aspherical coefficient means "×10± XX ".

[0061] [Numerical Example 1] Unit: mm Surface data Surface number r d 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 ∞ Aspherical data The 15th surface 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 The 16th surface K = 0.00000e+000 A4 = 1.25599e-004 A6 = -7.33671e-007 A8 = 2.74067e-009 A10 = -3.57083e-012 Focal length 18.14 F number 1.81 Half field angle (degrees) 35.00 Image height 12.70 Overall lens length 53.36 BF 0.51 Lens group data Group Starting surface Focal length SP 1 ∞ L1 2 20.31 L2 15 28.23 [Numerical Example 2] Unit: mm Surface data Surface number r d 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 ∞ Aspherical data Surface 15 K = 0.00000e+000 A4=-3.78860e-004 A6= 3.55858e-006 A8=-1.47846e-008 A10= 2.95192e-011 A12=-2.23370e-014 Surface 16 K = 0.00000e+000 A4= 1.17084e-004 A6= 1.55977e-007 A8=-1.50577e-009 A10= 3.53048e-012 Focal length 15.14 F-number 1.51 Half field angle (degrees) 40.00 Image height 12.70 Overall lens length 53.50 BF 0.50 Lens group data Group Starting surface Focal length SP 1 ∞ L1 2 19.16 L2 15 15.87 [Numerical Example 3] Surface data Surface number r d 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 Reflecting 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 ∞ Aspherical data The 15th surface 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 The 16th surface 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 Field angle 32.50 Image height 12.70 Overall length of lens 50.30 BF 2.95 Lens group data Group Starting surface Focal length SP 1 ∞ L1 2 21.29 L2 15 39.82 [Numerical Example 4] Unit: mm Surface data Surface number r d 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 Reflecting surface 6 ∞ -0.20 1.58 50.0 7 ∞ -0.20 1.51 50.0 8 ∞ 0.20 Reflecting 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 ∞ Aspherical data The 15th surface 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 The 16th surface 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 field angle (degrees) 35.00 Image height 12.70 Overall lens length 50.31 BF 2.85 Lens group data Group starting surface 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] As described above, the preferred embodiments and examples of the present invention have been described. However, 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 thereof.

Explanation of reference numerals

[0064] G1 First lens G2 Second 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, comprising: 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 includes, in order from the observation side to the image display surface side, a semi-transmissive reflection element, a first quarter-wave plate, a first lens having a convex lens surface on the image display surface side, a second lens joined to the first lens at the lens surface on the image display surface side, a second quarter-wave plate, and a polarizing plate; the lens surface of the first lens on the image display surface side is a semi-transmissive reflection surface; the lens surface of the second lens on the image display surface side has the second quarter-wave plate and the polarizing plate bonded thereto, and the second lens group includes a third lens having at least one aspherical lens surface; the third lens is made of a resin lens, characterized in that the observation optical system.

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 The observation optical system according to claim 1, characterized by satisfying the conditional expression.

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 The observation optical system according to claim 1 or 2, characterized by satisfying the conditional expression.

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 The observation optical system according to any one of claims 1 to 3, characterized by satisfying the conditional expression.

5. The third lens has a positive refractive power, The observation optical system according to any one of claims 1 to 4, characterized in that at least one lens surface of the third lens is an aspherical 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 The observation optical system according to any one of claims 1 to 5, characterized by satisfying the conditional expression.

7. At least one lens surface of the third lens is an aspherical 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 The observation optical system according to any one of claims 1 to 6, characterized by satisfying the following conditional expression.

8. The observation optical system according to any one of claims 1 to 7, further comprising a first quarter-wave plate disposed between the semi-transmissive reflection element and the first lens.

9. The observation optical system according to any one of claims 1 to 8, further comprising a second quarter-wave plate disposed on the image display surface side of the second lens.

10. A first quarter-wave plate disposed between the semi-transmissive reflection element and the first lens, and a second quarter-wave plate disposed on the image display surface side of the second lens, The observation optical system according to any one of claims 1 to 9, wherein the first quarter-wave plate and the second quarter-wave plate are disposed such that their slow axes are inclined by 90°.

11. A first quarter-wave plate disposed between the semi-transmissive reflection element and the first lens, a second quarter-wave plate disposed on the image display surface side of the second lens, and a polarizing plate disposed on the image display surface side of the second quarter-wave plate, The observation optical system according to any one of claims 1 to 10, wherein the first quarter-wave plate is disposed such that its slow axis is inclined by 45° with respect to the polarization transmission axis of the polarizing plate.

12. The observation optical system according to any one of claims 1 to 11, wherein the lens surface on the observation side of the first lens is a flat surface.

13. The observation optical system according to any one of claims 1 to 12, wherein the lens surface on the image display side of the second lens is a flat surface.

14. The observation optical system according to any one of claims 1 to 13, wherein both the first lens and the second lens are glass lenses.

15. The observation optical system according to any one of claims 1 to 14, wherein the second lens group is composed of the third lens and a positive lens, which are arranged in order from the observation side to the image display surface side.

16. The observation optical system according to any one of claims 1 to 14, wherein the second lens group is composed of the third lens, which is arranged in order from the observation side to the image display surface side.

17. The light emitted from the image display surface is refracted by the second lens group, transmitted through the lens surface on the image display surface side, reflected by the semi-transmissive reflective element, reflected by the lens surface on the image display surface side, transmitted through the semi-transmissive reflective element, and reaches the pupil surface. The observation optical system according to any one of claims 1 to 16, characterized in that.

18. An observation device, characterized by having the observation optical system according to any one of claims 1 to 17.

Images