Optical system and image display unit

Abstract

To provide a small optical system having a wide field of view and high optical performance.SOLUTION: The optical system at least includes: a first lens G1 guiding light from a display element ID to an observation side and having a first translucent reflection surface HM1; and a second lens G2 having a second translucent reflection surface HM2. The light from the display element is guided to the observation side via transmission through the second translucent reflection surface, reflection on the first translucent reflection surface, reflection on the second translucent reflection surface and transmission through the first translucent reflection surface. A negative lens is included as any one of the first lens, the second lens and other lenses. The optical system is configured such that when a focal distance of the negative lens is denoted by fn, a focal distance of the optical system is denoted by f, 1.0≤|fn / f|≤20.0 is satisfied or light from the display element passes through the negative lens only once and is guided to the observation side.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an optical system suitable for image display devices such as head mounted displays and smart glasses. [Background technology]

[0002] An observation optical system that allows a user to view an enlarged original image displayed on a display element such as an LCD is required to have a wide field of view, high optical performance, and be small. Patent Document 1 discloses an observation optical system having a first lens with positive refractive power on the observation side and a second lens with positive refractive power on the display element side, a flat semi-transmissive reflective surface on the display element side of the first lens, and a semi-transmissive reflective surface with a concave shape toward the observation side on the display element side of the second lens. In this observation optical system, light from the display element passes through the semi-transmissive reflective surface of the second lens, is refracted by receiving positive optical power at the second lens, and is reflected by the semi-transmissive reflective surface of the first lens. Next, the light is refracted by receiving positive optical power at the second lens, and is reflected by receiving positive optical power at the semi-transmissive reflective surface of the second lens. Furthermore, the light passes through the semi-transmissive reflective surface of the first lens, is refracted by receiving positive optical power at the first lens, and is emitted to the observation side. In this way, in the observation optical system of Patent Document 1, when the light receives optical power in refraction and reflection, the light receives all positive optical power. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2022 / 038777 Summary of the Invention [Problem to be solved by the invention]

[0004] The observation optical system of Patent Document 1 is configured so as not to optically correct chromatic aberration occurring due to refraction. When an electronic display element such as an LCD is used as a display element, it is possible to electronically correct the magnification chromatic aberration of the observation optical system by adjusting the magnification of the image to be displayed for each RGB color channel. However, chromatic aberration occurring within each RGB color channel cannot be electronically corrected. For this reason, when a high-definition display element with a narrow pixel pitch is used, there is a risk that the quality of the displayed image will be degraded due to the chromatic aberration of the observation optical system.

[0005] The present invention provides an optical system that has a wide field of view, is compact, and yet has high optical performance for effectively correcting chromatic aberration, and an image display device using the same. [Means for solving the problem]

[0006] An optical system according to one aspect of the present invention is an optical system that guides light from a display element to the observation side. The optical system has at least a first lens having a first semi-transmissive reflective surface, and a second lens having a second semi-transmissive reflective surface. The light from the display element is guided to the observation side via transmission through the second semi-transmissive reflective surface, reflection at the first semi-transmissive reflective surface, reflection at the second semi-transmissive reflective surface, and transmission through the first semi-transmissive reflective surface. Any of the first lens, the second lens, and the other lenses includes a negative lens. When the focal length of the negative lens is fn and the focal length of the optical system is f, 1.0≦|fn / f|≦20.0 The present invention is characterized in that it satisfies the following conditions.

[0007] Another aspect of the present invention is an optical system that guides light from a display element to the observation side. The optical system has at least a first lens having a first semi-transmissive reflective surface and a second lens having a second semi-transmissive reflective surface. The light from the display element is guided to the observation side via transmission through the second semi-transmissive reflective surface, reflection at the first semi-transmissive reflective surface, reflection at the second semi-transmissive reflective surface, and transmission through the first semi-transmissive reflective surface. The optical system includes a negative lens as any one of the first lens, the second lens, and the other lens, and is characterized in that the light from the display element is guided to the observation side by passing through the negative lens only once. An image display device having the above optical system also constitutes another aspect of the present invention. Effect of the Invention

[0008] According to the present invention, in a wide-field, compact optical system, high optical performance that satisfactorily corrects chromatic aberration can be obtained. [Brief description of the drawings]

[0009] [Figure 1] FIG. 2 is a cross-sectional view of the observation optical system of the first embodiment. [Diagram 2] 4A to 4C are longitudinal aberration diagrams of the observation optical system of Example 1. [Diagram 3] FIG. 11 is a cross-sectional view of the observation optical system according to the second embodiment. [Figure 4] 6A to 6C are longitudinal aberration diagrams of the observation optical system of Example 2. [Diagram 5] FIG. 11 is a cross-sectional view of the observation optical system according to the third embodiment. [Figure 6] 11A to 11C are longitudinal aberration diagrams of the observation optical system of Example 3. [Figure 7] FIG. 11 is a cross-sectional view of the observation optical system according to the fourth embodiment. [Figure 8] 13A to 13C are longitudinal aberration diagrams of the observation optical system of Example 4. [Figure 9] 1A and 1B are diagrams illustrating a configuration in which polarized light is used. [Figure 10] FIG. 13 is a diagram illustrating another configuration that utilizes polarized light. [Figure 11] FIG. 1 is a diagram showing an HMD using the observation optical systems according to Examples 1 to 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. Figures 1, 3, 5 and 7 show the configurations of observation optical systems according to embodiments 1, 2, 3 and 4 of the present invention, respectively.

[0011] Prior to the detailed description of Examples 1 to 4, a description will be given of matters common to each of the Examples. The observation optical system of each of the Examples is used in an image display device such as a head mounted display or smart glasses, and allows an observer to observe an image displayed on a display element by enlarging the image.

[0012] The observation optical system has at least a first lens G1 having a first semi-transmissive reflective surface HM1 and a second lens G2 having a second semi-transmissive reflective surface HM2, which are arranged in order from the observation side (the pupil plane side of the observation optical system where the observer's eye is positioned) to the display element side. The first semi-transmissive reflective surface HM1 is provided on the display element side surface of the first lens G1, and the second semi-transmissive reflective surface HM2 is provided on the observation side or display element side surface of the second lens G2.

[0013] The observation optical system in each embodiment employs a triple-path configuration in which light from the display element is transmitted through HM2, reflected by HM1, reflected by HM2, transmitted through HM1, and guided to the observation side. By employing such a triple-path configuration, it is possible to make the observation optical system thinner while ensuring the optical path length.

[0014] Moreover, the observation optical system of each embodiment utilizes polarized light in a triple-pass configuration, as described below. This prevents changes in the polarization characteristics of the first lens G1 due to birefringence or the like from affecting unwanted light such as ghosts, providing freedom in the selection of materials and processing methods for the first lens G1. In addition, the observation optical system has a wide viewing angle by allocating strong positive optical power to the reflecting action of the second semi-transmissive reflective surface HM2 disposed on the second lens G2.

[0015] Furthermore, the observation optical system of each embodiment includes an appropriate negative lens Gn, which effectively corrects chromatic aberration while suppressing an increase in the size of the observation optical system and an increase in the curvature of field. Specifically, the observation optical system is configured so that the negative lens Gn has at least one of the following configurations 1 and 2. The negative lens Gn may be any of the first lens G1, the second lens G2, and other lenses.

[0016] [Configuration 1] When the focal length in air of the negative lens Gn is fn and the focal length in air of the entire observation optical system is f, the condition of the following formula (1) is satisfied.

[0017] 1.0≦|fn / f|≦20.0 (1) By optimizing the focal length of the negative lens Gn, it is possible to achieve a wide viewing angle and a compact observation optical system, and to achieve good correction of chromatic aberration. If |fn / f| falls below the lower limit of formula (1), the optical power of the negative lens Gn becomes too strong compared to the optical power of the entire observation optical system, which results in overcorrection of chromatic aberration and difficulty in achieving a wide viewing angle, which is undesirable. In addition, when the negative lens Gn is arranged on the observation side where axial chromatic aberration and lateral chromatic aberration are easily corrected, the negative lens Gn is arranged to largely diverge light rays, which increases the optical effective diameter of the second lens G2 (the diameter of the portion through which light rays that contribute to image formation in the lens pass), which is undesirable. On the other hand, if |fn / f| exceeds the upper limit of formula (1), the optical power of the negative lens Gn becomes too weak compared to the optical power of the entire observation optical system, which results in insufficient correction of chromatic aberration, which is undesirable.

[0018] It is more preferable that the numerical range of the formula (1) is as follows:

[0019] 1.3≦|fn / f|≦17.0 (1a) Moreover, it is more preferable that the numerical range of formula (1) is set to the following range.

[0020] 1.6≦|fn / f|≦14.0 (1b) [Configuration 2] The negative lens Gn is disposed in a single-path optical path in which light from the display element passes through the negative lens Gn only once. By disposing the negative lens Gn in a single path, it is possible to achieve a good balance between the correction of the field curvature and chromatic aberration of the observation optical system. In an observation optical system using two semi-transmissive reflective surfaces as in each embodiment, a wide viewing angle of the observation optical system can be realized by allocating a strong positive power to the reflective action of at least one of the semi-transmissive reflective surfaces.

[0021] Here, the Petzval term occurring at the reflecting surface has a different sign from the Petzval term occurring at the refracting surface. In other words, in order to correct the Petzval image plane occurring at the reflecting surface with positive optical power, a refracting surface with positive optical power (a lens with positive refractive power) is required. Therefore, when arranging a negative lens in an observation optical system using two semi-transmissive reflecting surfaces, it is important to optimize the lens arrangement in the observation optical system. When using a negative lens to correct chromatic aberration, if the negative lens is arranged in the triple path of the observation optical system, the light beam will be subjected to three negative refraction actions, making it difficult to correct the curvature of field. For this reason, by adopting a configuration in which the negative lens is arranged in the single path of the observation optical system and the light beam is subjected to only one negative refraction action, it is possible to achieve both the correction of the curvature of field and the correction of the chromatic aberration. In addition, when adopting a configuration using polarized light, which will be described later, unnecessary light such as ghosts will be generated due to the birefringence of the optical material. In a single pass, the optical path length through the optical medium is 1 / 3 of that in a triple pass, so the effect of birefringence in the optical material can also be reduced to 1 / 3. From this perspective, it is also advisable to place the negative lens Gn for correcting chromatic aberration within the single pass.

[0022] By optimizing the basic configuration of the observation optical system having the two semi-transmissive reflective surfaces described above and the configuration related to the negative lens Gn, it is possible to provide an observation optical system that has a wide field of view, is thin, and has high optical performance with well-corrected chromatic aberration.

[0023] In each embodiment, the negative lens Gn is made of a resin material, which is advantageous in terms of weight reduction compared to when a glass material is used.

[0024] In each embodiment, the Abbe number of the negative lens Gn based on the d-line is νdn. The focal length in air of the positive lens with the largest refractive power among at least one positive lens included in the observation optical system is fp. The radius of curvature (reference radius of curvature) of the spherical surface passing through the surface vertex on the optical axis of the second semi-transmissive reflecting surface HM2 arranged on the second lens G2 and the end position of the optical effective diameter of the second semi-transmissive reflecting surface HM2 is HM2_refR. The radius of curvature (reference radius of curvature) of the spherical surface passing through the surface vertex on the optical axis of the first semi-transmissive reflecting surface HM1 arranged on the first lens G1 and the end position of the optical effective diameter of the first semi-transmissive reflecting surface HM1 is HM1_refR. When the reference radius of curvature is negative, it means that the semi-transmissive reflecting surface has a concave shape toward the observation side, and when it is positive, it means that the semi-transmissive reflecting surface has a convex shape toward the observation side.

[0025] The distance on the optical axis from the apex of the surface on the optical axis of the observation optical system closest to the observation side to the display surface of the display element is defined as OAL. Note that if a glass block such as a cover glass that has no refractive power is provided near the display element, the distance OAL should include the distance of the glass block converted into air.

[0026] Under the above definitions, it is preferable to satisfy at least one of the conditions of the following expressions (2) to (7).

[0027] 10.0≦νdn≦40.0 (2) -1.1≦fp / fn≦-0.1 (3) 1.0≦fp / f≦8.0 (4) -5.0≦HM2_refR / f≦-1.0 (5) -0.2≦HM2_refR / HM1_refR≦1.0 (6) 0.5≦OAL / f≦1.5 (7) The condition of formula (2) indicates an appropriate range of the Abbe number of the negative lens Gn arranged in the observation optical system based on the d-line. By optimizing the Abbe number of the negative lens Gn, it is possible to achieve both correction of chromatic aberration and correction of monochromatic aberration such as curvature of field. If νdn is too small below the lower limit of formula (2), the chromatic aberration in the entire observation optical system will be overcorrected, and the transmittance of the entire observation optical system will decrease due to the large internal absorption of the lens material, which is not preferable. If νdn is too large above the upper limit of formula (2), the correction of chromatic aberration in the entire observation optical system will be insufficient, or it will be necessary to give the negative lens Gn a stronger negative refractive power to correct the chromatic aberration, making it difficult to achieve both correction of chromatic aberration and correction of monochromatic aberration, which is not preferable.

[0028] The condition of formula (3) indicates an appropriate range of the ratio of the focal length in air between the negative lens Gn arranged in the observation optical system and the positive lens with the largest refractive power arranged in the observation optical system. By optimizing the focal length of the negative lens Gn and the positive lens, it is possible to correct both chromatic aberration and curvature of field. If fp / fn is below the lower limit of formula (3), the power of the positive lens is too small compared to the negative lens Gn, and the positive refractive power of the entire observation optical system is too weak, making it difficult to correct the curvature of field, which is not preferable. If fp / fn is above the upper limit of formula (3), the power of the positive lens is too large compared to the negative lens Gn, and the correction of chromatic aberration in the entire observation optical system is insufficient, which is not preferable.

[0029] The condition of formula (4) indicates an appropriate range of the ratio between the focal length in air of the positive lens with the greatest refractive power arranged in the observation optical system and the focal length of the entire observation optical system. By optimizing the focal length of the positive lens, it is possible to effectively correct the field curvature while controlling the occurrence of chromatic aberration. If the power of the positive lens is too large so that fp / f is below the lower limit of formula (4), this is advantageous for correcting the field curvature, but is undesirable because the chromatic aberration generated by the refractive action of the positive lens becomes too large. If the power of the positive lens is too small so that fp / f is above the upper limit of formula (4), it is undesirable because it becomes difficult to correct the field curvature in the entire observation optical system.

[0030] The condition of formula (5) indicates an appropriate range of the reference radius of curvature of the second semi-transmissive reflecting surface HM2 arranged on the second lens G2. By arranging the second semi-transmissive reflecting surface HM2 as a reflecting surface (concave mirror) with positive power during reflection, the observation optical system can have a wider viewing angle (higher magnification). If HM2_refR / f becomes too large (negative side) below the lower limit of formula (5), the positive power obtained during reflection becomes too weak, making it difficult to achieve a wider viewing angle of the observation optical system, which is not preferable. If HM2_refR / f becomes too small, exceeding the upper limit of formula (5), the positive power obtained during reflection becomes too strong, making it difficult to correct the curvature of field, which is not preferable.

[0031] The condition of formula (6) indicates an appropriate range of the ratio between the reference radius of curvature of the first semi-transmissive reflecting surface HM1 arranged on the first lens G1 and the reference radius of curvature of the second semi-transmissive reflecting surface HM2 arranged on the second lens G2. By optimizing the reference radii of curvature of these two semi-transmissive reflecting surfaces, it is possible to reduce the size of the observation optical system, widen the viewing angle, and satisfactorily correct the curvature of field. If the above ratio falls below the lower limit of formula (6), the reference radii of curvature of HM1 and HM2 will have opposite signs (concave and convex, or convex and concave), and the reference radius of curvature of HM2 will be too small compared to the reference radius of curvature of HM1. In this case, if HM2 has a convex shape toward the observation side, HM2 will become a convex mirror with a strong negative power during reflection, and HM1 will become a convex mirror with a negative power during reflection. As a result, the positive power cannot be shared by the reflection of the two semi-transmissive reflecting surfaces, making it difficult to widen the viewing angle of the observation optical system, which is not preferable. Furthermore, if HM2 has a concave shape toward the observation side, HM2 becomes a concave mirror having a strong positive power during reflection, and HM1 becomes a concave mirror having a positive power during reflection. As a result, it is difficult to correct the curvature of field that occurs on the reflecting surface with positive power, which is not preferable. On the other hand, if the above ratio exceeds the upper limit of formula (6), the reference radii of curvature of HM1 and HM2 have the same sign, and the reference radius of curvature of HM2 becomes too large compared to the reference radius of curvature of HM1. In this case, if both of the two semi-transmissive reflecting surfaces have a convex shape toward the observation side, HM1 becomes a concave mirror having a strong positive power during reflection, and HM2 becomes a convex mirror having a negative power during reflection. As a result, the two semi-transmissive reflecting surfaces are not arranged concentrically with respect to the exit pupil of the observation optical system so as to have symmetry, which is not preferable because it is difficult to correct the aberration that occurs off-axis. Furthermore, if both semi-transmissive reflective surfaces have a concave shape toward the observation side, HM1 becomes a convex mirror with a strong negative power when reflecting, and HM2 becomes a concave mirror with a positive power when reflecting, which is undesirable because it becomes difficult to achieve a wide viewing angle for the observation optical system and the outer diameter of the second lens G2 becomes large due to the strong light divergence effect of HM1 as a convex mirror.

[0032] The condition of formula (7) indicates an appropriate range of the ratio between the total optical length of the observation optical system (hereinafter referred to as the total lens length) and the focal length of the entire observation optical system. The observation optical system of each embodiment has a configuration that is advantageous for reducing the total lens length by forming a triple path using two semi-transmissive reflective surfaces. If OAL / f is below the lower limit of formula (7), the total lens length becomes too small compared to the focal length of the entire observation optical system. At this time, in order to ensure the edge thickness of the second lens G2 while satisfying this condition, it is difficult to give a large curvature to the second semi-transmissive reflective surface HM2. In other words, since the second semi-transmissive reflective surface HM2 cannot share the strong positive power during the reflection action, it is difficult to make the observation optical system have a wide viewing angle, which is not preferable. If OAL / f exceeds the upper limit of formula (7), the total lens length becomes too large compared to the focal length of the entire observation optical system, making it impossible to utilize the triple path using two semi-transmissive reflective surfaces, and the observation optical system becomes large, which is not preferable.

[0033] It is more preferable that the numerical ranges of the formulas (2) to (7) are as follows:

[0034] 13.0≦νdn≦35.0 (2a) -1.0≦fp / fn≦-0.2 (3a) 2.0≦fp / f≦7.0 (4a) -4.0≦HM2_refR / f≦-1.4 (5a) -0.1≦HM2_refR / HM1_refR≦0.8 (6a) 0.6≦OAL / f≦1.3 (7a) Moreover, it is more preferable that the numerical ranges of the formulas (2) to (7) are as follows:

[0035] 16.0≦νdn≦30.0 (2b) -0.9≦fp / fn≦-0.3 (3b) 3.0≦fp / f≦6.0 (4b) -3.5≦HM2_refR / f≦-1.8 (5b) 0.0≦HM2_refR / HM1_refR≦0.6 (6b) 0.7≦OAL / f≦1.1 (7b) The negative lens Gn may also be disposed on the most observation side of the observation optical system (see Examples 1 and 4). By disposing the negative lens Gn on the most observation side where the heights of both the object paraxial ray and the pupil paraxial ray are large, the axial chromatic aberration and the chromatic aberration of magnification can be corrected well. In this case, the negative lens Gn may be disposed as the first lens G1. By providing the negative lens Gn and the first lens G1 having the first semi-transmissive reflecting surface HM1 as the same lens, the number of lenses constituting the observation optical system can be reduced, and the weight of the observation optical system can be reduced. In addition, the first semi-transmissive reflecting surface HM1 disposed on the first lens G1 may be formed as a curved surface. By forming the first semi-transmissive reflecting surface HM1 as a curved surface, it is possible to share the power during transmission and reflection, and to ensure the degree of freedom in aberration correction.

[0036] Furthermore, the negative lens Gn may be disposed closer to the display element than the first lens G1 (see Examples 2 and 3). By disposing the negative lens Gn on the display element side where the height of the pupil paraxial ray is greater, it is possible to effectively correct lateral chromatic aberration in particular. In this case, the negative lens Gn may be cemented with the second lens G2 to form a cemented lens. By cementing the negative lens Gn with the second lens G2, the air gap between the lenses can be reduced, and the overall lens length can be made smaller.

[0037] In addition, the second semi-transmissive reflective surface HM2 disposed on the second lens G2 may be disposed on the cemented surface between the second lens G2 and the negative lens Gn. This makes it possible to avoid total reflection, which is a problem when the second semi-transmissive reflective surface HM2 is given a reflective action with a strong positive power in order to widen the viewing angle of the observation optical system. In addition, since the cemented surface is less exposed to the external environment, it is advantageous in terms of environmental resistance when a half mirror made of a metal film or a dielectric multilayer film is used as the semi-transmissive reflective surface.

[0038] Also, the first semi-transmissive reflective surface HM1 arranged on the first lens G1 may be a flat surface (see Example 2). When adopting a configuration using polarized light described later, the observation optical system can be made thinner by bonding and arranging a polarizing element (a polarization-selective semi-transmissive reflective element and a quarter-wave plate in FIG. 9, and a linear polarizing plate and a quarter-wave plate in FIG. 10) on the flat surface. Furthermore, by making the bonding surface with the polarizing element a flat surface, bonding processing of the polarizing element becomes easier.

[0039] At least one of the two semi-transmissive reflective surfaces may be made of a polarization-selective semi-transmissive reflective element. This can block unwanted light such as ghosts that are generated by using polarized light when adopting a configuration using polarized light, which will be described later. Examples of polarization-selective semi-transmissive reflective elements include a wire grid element such as Asahi Kasei's WGF, a reflective linear polarizing element such as 3M's IQP-E, and a circularly polarized reflective element using cholesteric liquid crystal. When a reflective linear polarizing element is used, a quarter-wave plate is placed between the two semi-transmissive reflective surfaces.

[0040] The polarizing element is omitted in the figures of each embodiment. There are various methods for arranging the polarizing element, such as bonding a film-like polarizing element to the optical surface of the lens, or molding a wire grid structure integrally with the lens base material when molding the resin lens.

[0041] The following describes the configuration using polarized light. By adopting this configuration, it is possible to suppress the decrease in the amount of light in the normal optical path in the observation optical system, while reducing unnecessary light (leakage light) such as ghosts that passes through the semi-transmissive reflective surface without being reflected even once and proceeds toward the observation side.

[0042] [Polarized Configuration 1] Fig. 9 shows a first configuration that uses polarized light. The first configuration has a polarization-selective semi-transmissive reflector (PBS) A arranged on the observation side (pupil surface SP side) and a half mirror (HM) C arranged on the display element side (display surface ID side). A first quarter-wave plate (QWP1) B is arranged between the PBS and HM. In addition, a second quarter-wave plate (QWP2) D and a linear polarizer (POL) E are arranged between the HM and ID from the HM side.

[0043] Here, the PBS is configured to reflect linearly polarized light having the same polarization direction as the linearly polarized light transmitted through the POL, and transmit linearly polarized light having a polarization direction perpendicular to that. The PBS is, for example, a wire grid polarizer or a reflective polarizer having a laminated retardation film structure. In this case, the wire grid-formed surface or retardation film surface of the PBS functions as the second semi-transmissive reflective surface.

[0044] Furthermore, QWP1 and QWP2 are arranged with their slow axes tilted at 45° with respect to the polarization transmission axis of the POL. It is also preferable that QWP1 and QWP2 are arranged with their slow axes tilted at 90° with respect to each other. With this arrangement, the wavelength dispersion characteristics of QWP1 and QWP2 are cancelled out when light passes through them.

[0045] Furthermore, HM is, for example, a half mirror formed by a dielectric multilayer film or metal deposition, and functions as a first semi-transmissive reflective surface, and POL is, for example, an absorptive linear polarizer.

[0046] The unpolarized light emitted from the ID becomes a first linearly polarized light by the POL, and the first linearly polarized light is converted to a first circularly polarized light by the QWP2 and enters the HM. A part of the first circularly polarized light that enters the HM is reflected by the HM and becomes a second circularly polarized light with a polarization direction opposite to that of the first circularly polarized light, and the second circularly polarized light returns to the QWP2. The second circularly polarized light that has returned to the QWP2 is converted to a second linearly polarized light with a polarization direction perpendicular to the polarization direction of the first linearly polarized light. The second linearly polarized light returns to the POL and is absorbed by the POL.

[0047] On the other hand, the other part of the first circularly polarized light that entered the HM is transmitted through it and converted by the QWP1 into a third linearly polarized light having the same polarization direction as the first linearly polarized light, and the third linearly polarized light enters the PBS, where it is reflected by the polarization selectivity of the PBS.

[0048] The third linearly polarized light reflected by the PBS is converted by QWP1 into third circularly polarized light with the same rotation as the first circularly polarized light. The third circularly polarized light enters the HM and is reflected, becoming fourth circularly polarized light with the opposite rotation to the third circularly polarized light. The fourth circularly polarized light enters QWP1 and is converted into fourth linearly polarized light with a polarization direction perpendicular to the polarization direction of the third linearly polarized light. The fourth linearly polarized light enters the PBS, passes through it due to the polarization selectivity of the PBS, and is guided to the SP.

[0049] Due to the above optical action, only the light that passes through the HM, is reflected by the PBS, is reflected by the HM, and passes through the PBS is guided to the SP and enters the eye (pupil) of the observer placed at the SP.

[0050] [Polarization Configuration 2] FIG. 10 shows a second configuration that uses polarized light. The second configuration has a polarization-selective semi-transmissive reflector (PBS) A arranged on the display element side (display surface ID side) and a half mirror (HM) C arranged on the observation side (pupil surface SP side). A first quarter-wave plate (QWP1) B is arranged between the PBS and HM. In addition, a second quarter-wave plate (QWP2) D and a linear polarizer (POL) E are arranged from the HM side between the HM and SP. The configuration of each element and the preferred orientation of the optical axis are the same as in the first configuration.

[0051] The unpolarized light emitted from the ID enters the PBS. Due to the wavelength selectivity of the PBS, only the first linearly polarized light with a polarization direction perpendicular to the transmission axis of the POL is transmitted through the PBS. The first linearly polarized light that passes through the PBS is converted to first circularly polarized light by QWP1, and this first circularly polarized light enters the HM. A portion of the first circularly polarized light that enters the HM is transmitted through and enters QWP2, where it is converted to second linearly polarized light with the same polarization direction as the first linearly polarized light. The second linearly polarized light enters the POL and is absorbed by the POL.

[0052] Meanwhile, the other part of the first circularly polarized light that entered the HM is reflected by the HM and becomes the second circularly polarized light with a polarization direction opposite to that of the first circularly polarized light, and the second circularly polarized light returns to QWP1. The second circularly polarized light that returned to QWP1 is converted by QWP1 into the third linearly polarized light with a polarization direction perpendicular to the polarization direction of the first linearly polarized light. The third linearly polarized light returns to the PBS. The third linearly polarized light that returned to the PBS is reflected by the polarization selectivity of the PBS and returns to QWP1 again, where it is converted into the third circularly polarized light with the same rotation as the first circularly polarized light. The third circularly polarized light enters the HM again, passes through it, and enters QWP2, where it is converted by QWP2 into the fourth linearly polarized light with a polarization direction parallel to the transmission axis of the POL. The fourth linearly polarized light passes through the POL and is guided to the SP.

[0053] Due to the above optical action, only the light that passes through the PBS, is reflected by the HM, is reflected by the PBS, and passes through the HM is guided to the SP and enters the eye of an observer placed at the SP.

[0054] In addition, in the observation optical system of each embodiment, the diopter adjustment can be performed by various methods. For example, the diopter adjustment can be performed by moving the whole or part of the observation optical system or the display element in the optical axis direction. In this case, the inner focus method in which the first lens G1 arranged on the most observation side is fixed and the second lens G2 is moved is preferable in terms of dust-proof structure. In addition to the method of moving the lens in the optical axis direction, the diopter adjustment can be performed by providing an optical element whose refractive power can be changed by mechanical or electrical action, such as a shape-changing lens or a liquid crystal lens using pressure or electrowetting.

[0055] The following is a specific description of the observation optical systems of Examples 1 to 4. The observation optical system of each Example can use either the first or second configuration using polarized light described above.

[0056] After the description of Example 4, Numerical Examples 1 to 4 corresponding to Examples 1 to 4 are shown. In each Numerical Example, the surface number i indicates the order of the surface when counted from the observation side (pupil surface side). r is the radius of curvature (mm) of the i-th surface from the observation side, d is the lens thickness or air gap (mm) between the i-th and (i+1)-th surfaces, and nd is the refractive index at the d-line of the optical material between the i-th and (i+1)-th surfaces. νd is the Abbe number based on the d-line of the optical material between the i-th and (i+1)-th surfaces. The Abbe number νd based on the d-line is expressed as νd=(Nd-1) / (NF-NC), where Nd, NF, and NC are the refractive indices at the d-line (wavelength 587.6 nm), F-line (wavelength 486.1 nm), and C-line (wavelength 656.3 nm) of the Fraunhofer lines.

[0057] The effective diameter is the diameter of the area of ​​the i-th surface through which light rays that contribute to image formation pass, and is also called the optical effective diameter. The total lens length is the distance on the optical axis from the surface closest to the observation side in the observation optical system to the display surface of the display element, as mentioned above.

[0058] An "*" next to a surface number means that the surface has an aspheric shape. An aspheric shape is expressed by the following formula, where x is the displacement from the apex of the surface in the optical axis direction, h is the height from the optical axis in a direction perpendicular to the optical axis, the direction of light travel is positive, R is the paraxial radius of curvature, K is the conic constant, and A4 to A10 are aspheric coefficients. The conic constant and the aspheric coefficients "e±Z" are x 10 ±Z means...

[0059] x=(h 2 / R) / [1+{1-(1+k)(h / R) 2} 1 / 2 ] +A4·h 4 +A6·h 6 +A8·h 8 +A10·h 10 EXAMPLES

[0060] The observation optical system of Example 1 (Numerical Example 1) shown in Fig. 1 is an optical system with a total viewing angle of about 90 degrees. The observation optical system of Example 1 has a first lens G1 with negative refractive power and a concave meniscus shape and a second lens G2 with positive refractive power and a plano-convex shape, as lenses arranged in this order from the pupil surface SP side to the display surface ID side. A first semi-transmissive reflective surface HM1 is arranged on the concave curved surface of the first lens G1 facing the observation side on the display element side. A second semi-transmissive reflective surface HM2 is arranged on the concave curved surface of the second lens G2 facing the observation side.

[0061] Light from the display surface ID passes through HM2, is reflected by HM1, is reflected by HM2, passes through HM1 and is directed to the pupil surface SP. The first lens G1 is a negative lens Gn made of a high dispersion optical material.

[0062] In addition, when the first configuration using polarization is used in this embodiment, a QWP1 is placed on the curved surface of the first lens G1 facing the display element together with a PBS as HM1, a QWP2 is placed on the flat surface of the observation side of the second lens G2, and a POL is placed on the observation side surface of the glass block CG.

[0063] The values ​​of the above formulas (1) to (7) in Numerical Example 1 are summarized in Table 1. The observation optical system of Numerical Example 1 satisfies all of the conditions of formulas (1) to (7).

[0064] FIG. 2 shows the longitudinal aberration (spherical aberration, astigmatism, distortion, and lateral chromatic aberration) of the observation optical system (visor: -0.5 diopter) of Numerical Example 1. In the spherical aberration diagram, Fno indicates the F-number, the solid line indicates the spherical aberration for the d-line, the two-dot chain line indicates the spherical aberration for the C-line, and the one-dot chain line indicates the spherical aberration for the F-line. In the astigmatism diagram, the solid line ΔS indicates the astigmatism on the sagittal image plane, and the dashed line ΔM indicates the astigmatism on the meridional image plane. The distortion aberration diagram shows the distortion aberration at the d-line. The lateral chromatic aberration diagram shows the lateral chromatic aberration for the C-line (two-dot chain line) and the F-line (one-dot chain line). ω is the half field angle (°). The explanations regarding these longitudinal aberration diagrams are the same for the other numerical examples. EXAMPLES

[0065] The observation optical system of Example 2 (Numerical Example 2) shown in Fig. 3 is an optical system with a total viewing angle of about 90 degrees. The observation optical system of Example 2 has, as lenses arranged in order from the pupil surface SP side to the display surface ID side, a cemented lens in which a first lens G1 with a concave-flat shape and negative refractive power, a second lens G2 with a biconvex shape and positive refractive power, and a third lens G3 with a concave meniscus shape and negative refractive power are cemented together.

[0066] A first semi-transmissive reflective surface HM1 is disposed on the flat surface of the first lens G1 facing the display element side, and a second semi-transmissive reflective surface HM2 is disposed on the concave curved surface (the joint surface with the third lens G3) of the second lens G2 facing the observation side on the display element side.

[0067] Light from the display surface ID passes through HM2, is reflected by HM1, is reflected by HM2, passes through HM1 and is directed to the pupil surface SP. The first lens G1 and the third lens G3 are negative lenses Gn formed of a high dispersion optical material.

[0068] In this embodiment, the surface of the first lens G1 on which the first semi-transmissive reflective surface HM1 is located is made flat, which facilitates the bonding process of the polarization-selective semi-transmissive reflective element when the first semi-transmissive reflective surface HM1 is composed of a polarization-selective semi-transmissive reflective element.

[0069] Furthermore, by making the first lens G1 and the third lens G3 negative lenses Gn, chromatic aberration in the entire observation optical system is effectively corrected.

[0070] The values ​​of the above formulas (1) to (7) in Numerical Example 2 are summarized in Table 1. The observation optical system of Numerical Example 2 satisfies all of the conditions of formulas (1) to (7).

[0071] FIG. 4 shows the longitudinal aberration of the observation optical system of Numerical Example 2 (visibility: −0.5 diopter). EXAMPLES

[0072] 5 is an optical system with a total viewing angle of about 80 degrees. The observation optical system of Example 3 includes, as lenses arranged in order from the pupil surface SP side to the display surface ID side, a cemented lens in which a first lens G1 with negative refractive power and a concave meniscus shape, a lens G3 with positive refractive power and a biconcave second lens G2 with negative refractive power are cemented together.

[0073] A first semi-transmissive reflective surface HM1 is disposed on the concave curved surface of the first lens G1 facing the observation side on the display element side, and a second semi-transmissive reflective surface HM2 is disposed on the concave curved surface of the second lens G2 facing the observation side (the joint surface with the third lens G3).

[0074] Light from the display surface ID passes through HM2, is reflected by HM1, is reflected by HM2, passes through HM1, and is guided to the pupil surface SP. The first lens G1 and the second lens G2 are negative lenses Gn.

[0075] In this embodiment, the surface of the first lens G1 on which the first semi-transmissive reflective surface HM1 is located is made flat, which facilitates the bonding process of the polarization-selective semi-transmissive reflective element when the first semi-transmissive reflective surface HM1 is composed of a polarization-selective semi-transmissive reflective element.

[0076] In addition, the first lens G1 and the second lens G2 are arranged as negative lenses Gn, thereby effectively correcting chromatic aberration in the entire observation optical system. In particular, the second lens G2 is made of a high-dispersion optical material, which effectively corrects lateral chromatic aberration.

[0077] The values ​​of the above formulas (1) to (7) in Numerical Example 3 are summarized in Table 1. The observation optical system of Numerical Example 3 satisfies all of the conditions of formulas (1) to (7).

[0078] FIG. 6 shows the longitudinal aberration of the observation optical system of Numerical Example 3 (visual aberration: −0.5 diopter). EXAMPLES

[0079] 7 is an optical system with a total viewing angle of about 100 degrees. The observation optical system of Example 4 has, as lenses arranged in order from the pupil surface SP side to the display surface ID side, a first lens G1 with negative refractive power having a flat-based concave Fresnel surface on the observation side, and a second lens G2 with positive refractive power and a convex meniscus shape.

[0080] A first semi-transmissive reflective surface HM1 is disposed on the concave curved surface of the first lens G1 facing the observation side, which is the display element side, and a second semi-transmissive reflective surface HM2 is disposed on the concave curved surface of the second lens G2 facing the observation side.

[0081] Light from the display surface ID passes through HM2, is reflected by HM1, is reflected by HM2, passes through HM1, and is guided to the pupil surface SP. The first lens G1 is a negative lens Gn.

[0082] In order to correct chromatic aberration and monochromatic aberration, it is preferable that the observation-side surface of the first lens G1 is a curved surface that is concave toward the observation side. However, when the effective optical diameter of each lens is increased to accommodate a wide viewing angle and the curvature of the concave curved surface toward the observation side is increased, the peripheral sag amount of the first lens G1 increases toward the observation side, thereby reducing the eye relief. For this reason, by making the observation-side surface of the first lens G1 a concave Fresnel surface based on a flat surface as in this embodiment, it is possible to ensure the eye relief while providing an appropriate negative refractive power to the refractive surface on the observation side.

[0083] The values ​​of the above formulas (1) to (7) in Numerical Example 4 are summarized in Table 1. The observation optical system of Numerical Example 4 satisfies all of the conditions of formulas (1) to (7).

[0084] FIG. 8 shows the longitudinal aberration of the observation optical system of Numerical Example 4 (visibility: −0.5 diopter). (Numerical example 1) Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 (pupil plane) ∞ (variable) 4.00 2* -39.352 2.00 1.66100 20.4 24.20 3* -66.497 1.89 35.00 4 ∞ 7.83 1.49200 57.4 42.00 5* -39.361 -7.83 42.00 6∞ -1.89 42.00 7* -66.497 1.89 35.00 8 ∞ 7.83 1.49200 57.4 42.00 9* -39.361 1.45 42.00 10 ∞ 0.70 1.51633 64.1 30.00 11 ∞ 0.00 30.00 Display surface ∞ Aspheric Data 2nd side K = 0.00000e+00 A 4=-7.48059e-07 A 6=-3.09602e-08 A 8=-1.86005e-10 3rd page K = 0.00000e+00 A 4= 1.10420e-05 A 6=-1.23159e-08 5th page K =-1.13788e+00 A 4=-1.09601e-06 A 6=-1.75150e-10 A 8=-2.63639e-12 A10= 4.72911e-15 Side 7 K = 0.00000e+00 A 4= 1.10420e-05 A 6=-1.23159e-08 9th page K =-1.13788e+00 A 4=-1.09601e-06 A 6=-1.75150e-10 A 8=-2.63639e-12 A10= 4.72911e-15 Various data Focal length 16.76 Pupil diameter 4.00 Half viewing angle (°) 45.00 Lens length 13.63 (in AIR) d 1 14.00 Entrance pupil position 0.00 Exit pupil position 48.88 Front principal point position 22.53 Back principal point position -16.62 Lens Group Data Group Starting plane Focal length Lens length Front principal point position Rear principal point position 1 2 16.76 11.72 8.53 -14.71 Single lens data Lens starting surface focal length G1 1 -150.24 G2 4 80.00 CG 10∞ (Numerical example 2) Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 (pupil plane) ∞ (variable) 4.00 2* -126.777 2.00 1.63500 23.9 24.20 3∞2.58 38.00 4* 142.148 7.13 1.54400 56.0 42.50 5* -58.915 -7.13 42.50 6* 142.148 -2.58 42.50 7∞2.58 38.00 8* 142.148 7.13 1.54400 56.0 36.00 9* -58.915 2.50 1.60700 27.0 36.00 10* 933.545 1.84 32.30 11 ∞ 0.70 1.51680 64.2 30.00 12∞0.0030.00 Display surface ∞ Aspheric Data 2nd side K = 0.00000e+00 A 4=-1.94169e-05 A 6= 4.86428e-08 A 8=-2.17267e-10 Side 4 K = 0.00000e+00 A 4= 2.05745e-05 A 6=-6.92001e-08 5th page K =-1.63982e+01 A 4=-6.66421e-06 A 6= 2.06294e-08 A 8=-7.47409e-11 A10= 4.55146e-14 Page 6 K = 0.00000e+00 A 4= 2.05745e-05 A 6=-6.92001e-08 Side 8 K = 0.00000e+00 A 4= 2.05745e-05 A 6=-6.92001e-08 9th page K =-1.63982e+01 A 4=-6.66421e-06 A 6= 2.06294e-08 A 8=-7.47409e-11 A10= 4.55146e-14 Side 10 K = 0.00000e+00 A 4=-5.94358e-05 A 6= 1.30329e-07 A 8=-1.52999e-10 Various data Focal length 17.51 Pupil diameter 4.00 Half viewing angle (°) 45.00 Lens length 16.51 (in AIR) d 1 13.00 Entrance pupil position 0.00 Exit pupil position 67.19 Front principal point position 22.08 Back principal point position -17.35 Lens Group Data Group Starting plane Focal length Lens length Front principal point position Rear principal point position 1 2 17.51 ​​14.21 9.08 -15.06 Single lens data Lens starting surface focal length G1 1 -199.65 G2 4 77.53 G3 9 -91.21 CG 11∞ (Numerical example 3) Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 (pupil plane) ∞ (variable) 4.00 2* -29.873 2.00 1.49200 57.4 20.40 3* -48.736 1.59 27.40 4 ∞ 6.04 1.54400 56.0 33.30 5* -34.597 -6.04 33.30 6 ∞ -1.59 33.30 7* -48.736 1.59 27.40 8 ∞ 6.04 1.54400 56.0 33.30 9* -34.597 2.50 1.64200 22.0 33.30 10* 45.784 1.31 22.00 11 ∞ 0.70 1.51680 64.2 30.00 12∞0.0030.00 Display surface ∞ Aspheric Data 2nd side K = 0.00000e+00 A 4= 1.46505e-07 A 6=-7.96364e-08 A 8=-6.59310e-10 3rd page K = 0.00000e+00 A 4= 2.29647e-05 A 6=-3.00982e-08 5th page K =-5.66760e+00 A 4=-1.39953e-05 A 6= 2.42032e-08 A 8=-4.77856e-11 A10= 4.84425e-14 Side 7 K = 0.00000e+00 A 4= 2.29647e-05 A 6=-3.00982e-08 9th page K =-5.66760e+00 A 4=-1.39953e-05 A 6= 2.42032e-08 A 8=-4.77856e-11 A10= 4.84425e-14 Side 10 K = 0.00000e+00 A 4=-3.14198e-04 A 6= 2.11563e-06 A 8=-5.53991e-09 Various data Focal length 16.03 Pupil diameter 4.00 Half viewing angle (°) 40.00 Lens length 13.90 (in AIR) d 1 14.00 Entrance pupil position 0.00 Exit pupil position -147.43 Front principal point position 14.29 Back principal point position -15.90 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position 1 2 16.03 12.13 0.29 -14.14 Single lens data Lens starting surface focal length G1 1 -162.56 G3 4 63.60 G2 9 -30.33 CG 11∞ (Numerical example 4) Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 (pupil plane) ∞ (variable) 4.00 2*∞ 4.00 1.68000 19.4 36.80 3* -60.519 2.21 42.00 4* -111.765 8.50 1.54400 56.0 50.00 5* -42.395 -8.50 50.00 6* -111.765 -2.21 50.00 7* -60.519 2.21 42.00 8* -111.765 8.50 1.54400 56.0 50.00 9* -42.395 4.59 50.00 10 ∞ 0.70 1.51680 64.2 50.00 11 ∞ 0.00 50.00 Display surface ∞ Aspheric Data Second surface (Fresnel surface based on a plane) R =-3.61989e+01 K =-5.55719e+00 A 4=-3.75810e-06 A 6=-1.18256e-08 A 8=-1.19864e-11 3rd page K = 0.00000e+00 A 4= 6.66609e-06 A 6=-2.61379e-09 Side 4 K = 0.00000e+00 A 4= 6.50527e-07 5th page K =-5.55719e+00 A 4=-8.32895e-06 A 6= 7.90557e-09 A 8=-7.95730e-12 A10 = 4.08906e-15 Page 6 K = 0.00000e+00 A 4= 6.50527e-07 Side 7 K = 0.00000e+00 A 4= 6.66609e-06 A 6=-2.61379e-09 Side 8 K = 0.00000e+00 A 4= 6.50527e-07 9th page K =-5.55719e+00 A 4=-8.32895e-06 A 6= 7.90557e-09 A 8=-7.95730e-12 A10 = 4.08906e-15 Various data Focal length 21.09 Pupil diameter 4.00 Half viewing angle (°) 50.00 Lens length 19.76 (in AIR) d 1 12.00 Entrance pupil position 0.00 Exit pupil position 2445.33 Front principal point position 21.32 Back principal point position -20.84 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position 1 2 21.09 14.71 9.32 -15.79 Single lens data Lens starting surface focal length G1 1 -141.92 G2 4 120.36 CGI 10 0.00

[0085] [Table 1]

[0086] [Image display device] 11 shows a head mounted display (HMD) as an image display device using the observation optical system of Examples 1 to 4. The HMD is worn on the head (in front of the eyes) of a viewer by means of a mounting gear (not shown).

[0087] The HMD has image display elements RID and LID for the right and left eyes, a right-eye observation optical system ROS that guides display light from the right-eye image display element RID to the observer's right eye, and a left-eye observation optical system LOS that guides display light from the left-eye image display element LID to the observer's left eye.

[0088] By using the observation optical systems shown in Examples 1 to 4 as the right-eye and left-eye observation optical systems ROS and LOS, it is possible to realize a small-sized HMD that enables observation of high-quality images with a wide viewing angle.

[0089] The above embodiment includes the following configurations.

[0090] (Configuration 1) An optical system that guides light from a display element to an observation side, a first lens having a first semi-transmissive reflective surface; a second lens having a second semi-transmissive reflective surface; the light from the display element is guided to an observation side via transmission through the second semi-transmissive reflective surface, reflection on the first semi-transmissive reflective surface, reflection on the second semi-transmissive reflective surface, and transmission through the first semi-transmissive reflective surface; Any one of the first lens, the second lens, and the other lens includes a negative lens; When the focal length of the negative lens is fn and the focal length of the optical system is f, 1.0≦|fn / f|≦20.0 An optical system characterized by satisfying the following conditions. (Configuration 2) 2. The optical system according to configuration 1, wherein the light from the display element is transmitted through the negative lens only once and guided to the observation side. (Configuration 3) An optical system that guides light from a display element to an observation side, a first lens having a first semi-transmissive reflective surface; a second lens having a second semi-transmissive reflective surface; the light from the display element is guided to an observation side via transmission through the second semi-transmissive reflective surface, reflection on the first semi-transmissive reflective surface, reflection on the second semi-transmissive reflective surface, and transmission through the first semi-transmissive reflective surface; Any one of the first lens, the second lens, and the other lens includes a negative lens; An optical system, characterized in that the light from the display element is transmitted through the negative lens only once and is guided to an observation side. (Configuration 4) the first semi-transmissive reflective surface is provided on a surface of the first lens on a display element side, 4. The optical system according to any one of configurations 1 to 3, wherein the second semi-transmissive reflective surface is provided on a surface of the second lens on the observation side or on the display element side. (Configuration 5) 5. The optical system according to any one of configurations 1 to 4, wherein the negative lens is made of a resin material. (Configuration 6) When the Abbe number of the negative lens based on the d line is νdn, 10.0≦νdn≦40.0 6. The optical system according to any one of configurations 1 to 5, wherein the following condition is satisfied: (Configuration 7) When the focal length of the positive lens having the greatest refractive power among at least one positive lens included in the optical system is fp, -1.1≦fp / fn≦-0.1 7. The optical system according to any one of configurations 1 to 6, wherein the following condition is satisfied: (Configuration 8) When the focal length of the positive lens having the greatest refractive power among at least one positive lens included in the optical system is fp, 1.0≦fp / f≦8.0 8. The optical system according to any one of configurations 1 to 7, wherein the following condition is satisfied: (Configuration 9) When the radius of curvature of a spherical surface passing through the surface vertex of the second semi-transmissive reflective surface on the optical axis of the optical system and the end position of the optical effective diameter of the second semi-transmissive reflective surface is HM2_refR, -5.0≦HM2_refR / f≦-1.0 9. The optical system according to any one of configurations 1 to 8, which satisfies the following condition: (Configuration 10) Let HM1_refR be the radius of curvature of a spherical surface passing through the surface vertex of the first semi-transmissive reflective surface on the optical axis of the optical system and an end position of the optical effective diameter of the first semi-transmissive reflective surface, and let HM2_refR be the radius of curvature of a spherical surface passing through the surface vertex of the second semi-transmissive reflective surface on the optical axis of the optical system and an end position of the optical effective diameter of the second semi-transmissive reflective surface, -0.2≦HM2_refR / HM1_refR≦1.0 10. The optical system according to any one of configurations 1 to 9, which satisfies the following condition: (Configuration 11) When the distance on the optical axis from the surface of the optical system closest to the observation side to the display surface of the display element is OAL, 0.5≦OAL / f≦1.5 11. The optical system according to any one of configurations 1 to 10, which satisfies the following condition: (Configuration 12) 12. The optical system according to any one of configurations 1 to 11, wherein the negative lens is disposed on the most observation side in the optical system. (Configuration 13) 13. The optical system according to configuration 12, wherein the negative lens is the first lens. (Configuration 14) 14. The optical system according to any one of configurations 1 to 13, wherein the first semi-transmissive reflective surface is provided on a curved surface of the first lens. (Configuration 15) 14. The optical system according to any one of configurations 1 to 13, wherein the negative lens is disposed closer to the display element than the first lens. (Configuration 16) 16. The optical system according to configuration 15, wherein the other lens as the negative lens is cemented with the second lens. (Configuration 17) 17. The optical system according to configuration 16, wherein the second semi-transmissive reflective surface is provided on a cemented surface between the second lens and the negative lens. (Configuration 18) 18. The optical system according to any one of configurations 1 to 17, wherein the first semi-transmissive reflective surface is provided on a flat surface of the first lens. (Configuration 19) 19. The optical system according to any one of configurations 1 to 18, wherein at least one of the first and second semi-transmissive reflective surfaces is configured by a polarization-selective semi-transmissive reflective element. (Configuration 20) An optical system according to any one of configurations 1 to 19; An image display device comprising the display element.

[0091] The embodiments described above are merely representative examples, and various modifications and alterations are possible for each embodiment when implementing the present invention. [Explanation of symbols]

[0092] SP pupil plane ID display surface G1 1st lens G2 2nd lens HM1 1st semi-transparent reflective surface HM2 2nd semi-transparent reflective surface

Claims

1. An optical system that guides light from a display element to the observation side, A first lens having a first semi-transparent reflective surface on the side facing the display element, It comprises at least a second lens having a second semi-transparent reflective surface, The light from the display element is guided to the observation side via transmission through the second semi-transparent reflective surface, reflection through the first semi-transparent reflective surface, reflection through the second semi-transparent reflective surface, and transmission through the first semi-transparent reflective surface. Any of the first lens, the second lens, and the other lens is a negative lens A. The first lens has its concave surface facing the observation side. When the focal length of the negative lens A is fn and the focal length of the optical system is f, 1.0≦|fn / f|≦20.0 An optical system characterized by satisfying the following conditions.

2. The optical system according to claim 1, characterized in that the light from the display element is transmitted through the negative lens A only once and guided to the observation side.

3. The optical system according to claim 1, characterized in that the negative lens A is formed of a resin material.

4. When the Abbe number with respect to the d line of the negative lens A is denoted as νdn, 10.0 ≤ νdn ≤ 40.0 The optical system according to claim 1, characterized in that it satisfies the following conditions.

5. When fp is the focal length of the positive lens with the greatest refractive power among the at least one positive lens included in the optical system, -1.1 ≤ fp / fn ≤ -0.1 The optical system according to claim 1, characterized in that it satisfies the following conditions.

6. When fp is the focal length of the positive lens with the greatest refractive power among the at least one positive lens included in the optical system, 1.0 ≤ fp / f ≤ 8.0 The optical system according to claim 1, characterized in that it satisfies the following conditions.

7. When HM2_refR is the radius of curvature of a spherical surface passing through the vertex of the second semi-transparent reflecting surface on the optical axis of the optical system and the end position of the optically effective diameter of the second semi-transparent reflecting surface, -5.0≦HM2_refR / f≦-1.0 The optical system according to claim 1, characterized in that it satisfies the following conditions.

8. When HM1_refR is the radius of curvature of a sphere passing through the vertex of the first semi-transparent reflecting surface on the optical axis of the optical system and the end position of the optically effective diameter of the first semi-transparent reflecting surface, and HM2_refR is the radius of curvature of a sphere passing through the vertex of the second semi-transparent reflecting surface on the optical axis of the optical system and the end position of the optically effective diameter of the second semi-transparent reflecting surface, -0.2≦HM2_refR / HM1_refR≦1.0 The optical system according to claim 1, characterized in that it satisfies the following conditions.

9. When OAL is defined as the distance along the optical axis from the observation-side surface of the optical system to the display surface of the display element, 0.5 ≤ OAL / f ≤ 1.5 The optical system according to claim 1, characterized in that it satisfies the following conditions.

10. The optical system according to claim 1, characterized in that the negative lens A is positioned on the observation side in the optical system.

11. The optical system according to claim 10, characterized in that the negative lens A is the first lens.

12. The optical system according to claim 1, characterized in that the first semi-transparent reflective surface is provided on the curved surface of the first lens.

13. The optical system according to claim 1, characterized in that the negative lens A is positioned closer to the display element than the first lens.

14. The optical system according to claim 13, characterized in that the other lens, which is the negative lens A, is joined to the second lens.

15. The optical system according to claim 14, characterized in that the second semi-transparent reflective surface is provided at the bonding surface between the second lens and the negative lens A.

16. The optical system according to claim 1, characterized in that the first semi-transparent reflective surface is provided on the plane of the first lens.

17. The optical system according to claim 1, characterized in that at least one of the first and second semi-transparent reflective surfaces is composed of a polarization-selective semi-transparent reflective element.

18. An optical system that guides light from a display element to the observation side, A first lens having a first semi-transparent reflective surface, It comprises at least a second lens having a second semi-transparent reflective surface, The light from the display element is guided to the observation side via transmission through the second semi-transparent reflective surface, reflection through the first semi-transparent reflective surface, reflection through the second semi-transparent reflective surface, and transmission through the first semi-transparent reflective surface. Any of the first lens, the second lens, and the other lens is a negative lens A. An optical system characterized in that the light from the display element passes through the negative lens A only once and is guided to the observation side.

19. The first semi-transparent reflective surface is provided on the display element side of the first lens, The optical system according to claim 18, characterized in that the second semi-transparent reflective surface is provided on the observation side or display element side of the second lens.

20. The optical system according to claim 18, characterized in that the negative lens A is formed of a resin material.

21. When the Abbe number with respect to the d line of the negative lens A is denoted as νdn, 10.0 ≤ νdn ≤ 40.0 The optical system according to claim 18, characterized in that it satisfies the following conditions.

22. When fp is the focal length of the positive lens with the greatest refractive power among the at least one positive lens included in the optical system, -1.1 ≤ fp / fn ≤ -0.1 The optical system according to claim 18, characterized in that it satisfies the following conditions.

23. When fp is the focal length of the positive lens with the greatest refractive power among the at least one positive lens included in the optical system, 1.0 ≤ fp / f ≤ 8.0 The optical system according to claim 18, characterized in that it satisfies the following conditions.

24. When HM2_refR is the radius of curvature of a spherical surface passing through the vertex of the second semi-transparent reflecting surface on the optical axis of the optical system and the end position of the optically effective diameter of the second semi-transparent reflecting surface, -5.0≦HM2_refR / f≦-1.0 The optical system according to claim 18, characterized in that it satisfies the following conditions.

25. When HM1_refR is the radius of curvature of a sphere passing through the vertex of the first semi-transparent reflecting surface on the optical axis of the optical system and the end position of the optically effective diameter of the first semi-transparent reflecting surface, and HM2_refR is the radius of curvature of a sphere passing through the vertex of the second semi-transparent reflecting surface on the optical axis of the optical system and the end position of the optically effective diameter of the second semi-transparent reflecting surface, -0.2≦HM2_refR / HM1_refR≦1.0 The optical system according to claim 18, characterized in that it satisfies the following conditions.

26. When OAL is defined as the distance along the optical axis from the observation-side surface of the optical system to the display surface of the display element, 0.5 ≤ OAL / f ≤ 1.5 The optical system according to claim 18, characterized in that it satisfies the following conditions.

27. The optical system according to claim 18, characterized in that the negative lens A is positioned on the observation side in the optical system.

28. The optical system according to claim 27, characterized in that the negative lens A is the first lens.

29. The optical system according to claim 18, characterized in that the first semi-transparent reflective surface is provided on the curved surface of the first lens.

30. The optical system according to claim 18, characterized in that the negative lens A is positioned closer to the display element than the first lens.

31. The optical system according to claim 30, characterized in that the other lens, which is the negative lens A, is joined to the second lens.

32. The optical system according to claim 31, characterized in that the second semi-transparent reflective surface is provided at the bonding surface between the second lens and the negative lens A.

33. The optical system according to claim 18, characterized in that the first semi-transparent reflective surface is provided on the plane of the first lens.

34. An optical system according to any one of claims 1 to 33, A display device characterized by having the aforementioned display element.

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