Optical system, display apparatus, and imaging apparatus

Abstract

As a folding optical system, an optical system having higher optical performance than before is required.SOLUTION: The optical system includes, in order from the first side to the second side, a first transmissive-reflective surface HM1, a second transmissive-reflective surface HM2, and a third transmissive-reflective surface HM3, and a diffractive surface DOE as a transmissive surface different from the first, second, and third transmissive-reflective surfaces.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical system suitable for display devices such as headset displays and imaging devices such as digital cameras. [Background technology]

[0002] As such an optical system, a so-called folded optical system using a plurality of transmissive and reflective surfaces has been proposed. Summary of the Invention [Problem to be solved by the invention]

[0003] There is a demand for a folding optical system that has higher optical performance than conventional optical systems. [Means for solving the problem]

[0004] An optical system according to one aspect of the present invention comprises a first transmission-reflection surface, a second transmission-reflection surface, and a third transmission-reflection surface arranged in this order from a first side to a second side, and a diffractive surface as a transmission surface different from the first, second, and third transmission-reflection surfaces. A display device and an imaging device using the optical system also constitute another aspect of the present invention. [Brief explanation of the drawings]

[0005] [Figure 1] FIG. 2 is a cross-sectional view of the optical system of the first embodiment (a diagram showing a first optical path). [Figure 2] FIG. 3 is a cross-sectional view of the optical system of the first embodiment (a diagram showing a second optical path). [Figure 3] 4A and 4B are diagrams showing longitudinal aberration in the first optical path of the optical system of Example 1. [Figure 4] 5A and 5B are diagrams showing longitudinal aberration in the second optical path of the optical system of Example 1. [Figure 5] FIG. 10 is a cross-sectional view of the optical system of Example 2 (a diagram showing a first optical path). [Figure 6] FIG. 10 is a cross-sectional view of the optical system of Example 2 (a diagram showing a second optical path). [Figure 7] 10A and 10B are longitudinal aberration diagrams in the first optical path of the optical system of Example 2. [Figure 8] 10A and 10B are diagrams showing longitudinal aberration in the second optical path of the optical system of Example 2. [Figure 9] FIG. 10 is a cross-sectional view of the optical system of Example 3 (a diagram showing a first optical path). [Figure 10] FIG. 10 is a cross-sectional view of the optical system of Example 3 (a diagram showing a second optical path). [Figure 11] 10A and 10B are longitudinal aberration diagrams in the first optical path of the optical system of Example 3. [Figure 12] 10A and 10B are longitudinal aberration diagrams in the second optical path of the optical system of Example 3. [Figure 13] FIG. 10 is a cross-sectional view of the optical system of Example 4 (a diagram showing a first optical path). [Figure 14] FIG. 10 is a cross-sectional view of the optical system of Example 4 (a diagram showing the second optical path). [Figure 15] 10A and 10B are longitudinal aberration diagrams in the first optical path of the optical system of Example 4. [Figure 16] 10A and 10B are longitudinal aberration diagrams in the second optical path of the optical system of Example 4. [Figure 17] Diagram of the optical path using polarized light. [Figure 18] FIG. 1 is a diagram showing a display device using the optical systems of Examples 1 to 3. [Figure 19] FIG. 10 is a diagram showing an imaging device using the optical system of Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0006] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0007] 1 and 2, 5 and 6, 9 and 10 respectively show cross sections of the optical systems of Examples 1, 2 and 3. Figures 1, 5 and 9 show the first optical path, and Figures 2, 6 and 10 show the second optical path. The optical systems of Examples 1 to 3 are display optical systems used in display devices such as head-mounted displays (HMDs), and guide light from the display surface side to the observation side.

[0008] 13 and 14 show cross sections of the optical system of Example 4. Fig. 13 shows the first optical path, and Fig. 14 shows the second optical path. The optical system of Example 2 is an imaging optical system used in an imaging device such as a digital camera, which guides light from the object side to the image side.

[0009] First, we will explain matters common to all Examples 1 to 4 before specifically explaining Examples 1 to 4. The ratio of transmittance to reflectance of the "transmissive-reflective surface" in each Example may be 50:50, or may be a different ratio.

[0010] The optical system of each embodiment includes three transmissive-reflective surfaces. Specifically, it includes a first transmissive-reflective surface HM1, a second transmissive-reflective surface HM2, and a third transmissive-reflective surface HM3, which are arranged in this order from a first side, or enlargement side (pupil plane side in a display optical system, object side in an imaging optical system), to a second side, or reduction side (display surface side in a display optical system, image side in an imaging optical system). By arranging these three transmissive-reflective surfaces coaxially and folding the optical path, it is possible to achieve a compact and thin optical system while forming two effective optical paths within a single optical system.

[0011] The optical system of each embodiment has multiple lenses Gi (G=1, 2, 3, ...). Gi indicates the order of the lenses counted from the magnification side. The three transmissive-reflective surfaces are provided on the magnification or reduction side of one of the lenses.

[0012] Furthermore, the optical system of each example has a diffractive surface DOE, which is provided as a transmitting surface different from the above-mentioned transmitting-reflecting surface. Diffractive surfaces have high dispersion and tend to generate chromatic aberration in the opposite direction to that of refractive surfaces, so by placing such a surface in the optical system, chromatic aberration can be reduced.

[0013] In this way, the optical system of each embodiment has high transmittance and high optical performance with well-reduced (corrected) field curvature and chromatic aberration due to the appropriate arrangement of the three transmissive-reflective surfaces and diffractive surface.

[0014] The first and second optical paths as the two effective optical paths mentioned above will be described below.

[0015] [1st optical path] 1, light emitted from the display surface ID of the display element passes through the third transmission-reflection surface HM3, passes through the second transmission-reflection surface HM2, is reflected by the first transmission-reflection surface HM1, and is reflected by the second transmission-reflection surface HM2. The light that passes through the first transmission-reflection surface HM1 is diffracted by the diffraction surface DOE and reaches the pupil plane SP on the observation side. The user's (observer's) eye is positioned at the pupil plane SP.

[0016] 5, light incident from an object is diffracted by the diffractive surface DOE, passes through the first transmissive-reflecting surface HM1, is reflected by the second transmissive-reflecting surface HM2, is reflected by the first transmissive-reflecting surface HM1, passes through the second transmissive-reflecting surface HM2, and passes through the third transmissive-reflecting surface HM3 before reaching the image plane IM, where the imaging surface of an imaging element such as a CCD sensor or CMOS sensor is located.

[0017] [Second optical path] 2, light emitted from display surface ID passes through third transmission-reflection surface HM3, is reflected by second transmission-reflection surface HM2, is reflected by third transmission-reflection surface HM3, and passes through second transmission-reflection surface HM2. The light that passes through first transmission-reflection surface HM1 is diffracted by diffraction surface DOE and reaches pupil plane SP.

[0018] In FIG. 6, light incident from an object is diffracted by the diffraction surface DOE, passes through the first transmission-reflection surface HM1, passes through the second transmission-reflection surface HM2, is reflected by the third transmission-reflection surface HM3, is reflected by the second transmission-reflection surface HM2, passes through the third transmission-reflection surface HM3, and reaches the image plane IM.

[0019] The first and second optical paths described above are preferably formed so that their focal lengths and back focal lengths are identical. The back focal length is the air-equivalent distance on the optical axis from the final surface (the surface closest to the reduction side) of the optical system to the surface where light reaches (display surface ID or image surface IM). The term "identical" here refers to the design, and is considered identical even if there are differences within the manufacturing tolerance range in the actual optical system. This allows the first and second optical paths to overlap within the optical system, achieving an effect equivalent to doubling the transmittance of the entire optical system.

[0020] In each embodiment, two of the three transmissive-reflective surfaces preferably have a curvature and are curved surfaces (concave mirrors) with positive optical power (the reciprocal of the focal length) for the reflected display light. By disposing two concave mirrors, the positive optical power of the entire optical system is shared between them, realizing a compact optical system with high specifications (such as a wider viewing angle in the display optical system and a larger aperture in the imaging optical system).

[0021] In each embodiment, the diffractive surface DOE is preferably disposed closer to the magnification side than the three transmissive-reflective surfaces (i.e., the first transmissive-reflective surface HM1). A surface relief type diffractive surface is preferably used as the diffractive surface DOE. By disposing this diffractive surface DOE as close to the magnification side as possible, the relief shape can be formed outside the user's diopter adjustment range, preventing the so-called ring from being seen.

[0022] In each embodiment, it is preferable that one of the three transmission-reflection surfaces is formed as a flat surface. A flat transmission-reflection surface is disadvantageous in terms of aberration correction and optical power distribution, but is advantageous in terms of reducing parallel decentration sensitivity. In particular, when a film-like polarizing element is used as the transmission-reflection surface, the element can be used without stretching, which is advantageous in terms of manufacturing.

[0023] In each embodiment, two of the three transmissive-reflective surfaces are preferably configured with reflective polarizing elements. By using reflective polarizing elements as the transmissive-reflective surfaces and adopting a polarized light configuration (described later), it is possible to block unwanted light such as ghost light while directing the display light to follow one of the two effective optical paths.

[0024] In each embodiment, it is preferable that at least one of the two reflective polarizing elements has a positive optical power with respect to the refracted display light. By arranging a refractive surface with a positive optical power in the optical system, the Petzval term generated in the concave mirror can be corrected by the refractive surface, and the field curvature of the entire optical system can be corrected.

[0025] In each embodiment, it is preferable that the two reflective polarizing elements have the same surface shape. Here, "same" refers to the same in terms of design, and is considered to be the same even if there are differences within the manufacturing tolerance range in the actual optical system. This ensures the symmetry of the optical system and allows the two reflective polarizing elements to be manufactured using a common manufacturing process.

[0026] Furthermore, in each embodiment, when the sum of the optical powers Φn (n=1, 2, 3) possessed by the light refracted at the three transmissive-reflective surfaces is ΣΦn and the optical power of the diffractive surface DOE is Φdoe, it is preferable to satisfy the condition of the following equation (1):

[0027] 0.0<(ΣΦn) / Φdoe≦3.0 (1) Note that ΣΦn is the sum of the optical power Φn of all the transmissive and reflective surfaces in the optical system as refractive surfaces, calculated for each of the first and second optical paths. The optical power Φn of each refractive surface is given by the following equation, where Nd is the refractive index at the d-line of the medium on the incident side of the light ray, Nd' is the refractive index at the d-line of the medium on the outgoing side of the light ray, and R is the radius of curvature of the refractive surface: Φn=(Nd′-Nd) / R In addition, when there are multiple diffractive surfaces, Φdoe is the optical power of the diffractive surface having the largest absolute value of optical power among the multiple diffractive surfaces. When the quadratic phase function coefficient of the diffractive surface is U2, the optical power Φdoe of the diffractive surface is expressed as follows: Φdoe=-2×U2 It is expressed as:

[0028] The condition in equation (1) indicates the appropriate ratio of the optical power of the diffractive surface DOE to that of the transflective surface HM as a refractive surface. By satisfying the condition in equation (1), it is possible to achieve both achromatism and correction of field curvature throughout the optical system. Specifically, by correcting the Petzval term generated by the reflective surface with the refractive surface and correcting the chromatic aberration generated by the refractive surface with the diffractive surface, high optical performance is achieved throughout the optical system. If (ΣΦn) / Φdoe falls below the lower limit of equation (1), the resulting power arrangement results in inverse correction of field curvature and chromatic aberration, which is undesirable. If (ΣΦn) / Φdoe exceeds the upper limit of equation (1), the optical power of the diffractive surface becomes too large compared to the refractive surface, resulting in overcorrection of chromatic aberration throughout the optical system, which is undesirable.

[0029] The upper limit of formula (1) may be set to 2.5, 2.0, 1.5, or 1.0. The lower limit of formula (1) may be set to 0.01, 0.014, or 0.018. If Φdoe / (ΣΦn) is less than 0.01, the optical power of the diffractive surface becomes too small compared to the refractive surface, resulting in insufficient correction of chromatic aberration in the entire optical system, which is undesirable.

[0030] In addition, by adopting the following polarization configuration in each embodiment, it is possible to suppress a decrease in the amount of light in each effective optical path while reducing unnecessary light that is transmitted without being reflected even once by the transmissive-reflective surface.

[0031] [Polarized configuration] A configuration using polarized light will be described using Figure 17. The transmission-reflection surface located on the enlargement side of the optical system is designated as a polarization-selective transmission-reflection element (PBS1) A, the transmission-reflection surface located on the reduction side is designated as a polarization-selective transmission-reflection element (PBS2) E, and the transmission-reflection surface located between these two transmission-reflection surfaces is designated as a half mirror (HM) C. Furthermore, a first quarter-wave plate (QWP1) B is located between the polarization-selective transmission-reflection element A and the half mirror C, and a second quarter-wave plate (QWP2) D is located between the half mirror C and the polarization-selective transmission-reflection element E.

[0032] The polarization-selective transmission-reflection element A is an element configured to transmit a first linearly polarized light and reflect a second linearly polarized light that is orthogonal to the first linearly polarized light. The polarization-selective transmission-reflection element E is an element configured to transmit the second linearly polarized light and reflect the first linearly polarized light. That is, the polarization-selective transmission-reflection elements A and E are arranged so that their polarization transmission axes are orthogonal to each other.

[0033] The polarization-selective transmission / reflection element is, for example, a wire grid polarizer or a reflective polarizer with a laminated retardation film structure. In this case, the wire grid-formed surface or retardation film surface of the polarization-selective transmission / reflection elements A and E functions as the transmission / reflection surface. Note that the wire grid polarizer does not necessarily have to be one in which metal wires are aligned, but may be any element that has thin metal or dielectric layers at predetermined intervals and functions as a polarization-selective transmission / reflection element. For example, an element in which metal or dielectric layers are aligned by vapor deposition can be used.

[0034] Furthermore, the first quarter-wave plate B and the second quarter-wave plate D are arranged with their slow axes tilted at 45° with respect to the polarization transmission axes of the polarization-selective transmission-reflection elements A and E. In the arrangement shown in Fig. 17, the first quarter-wave plate B and the second quarter-wave plate D are arranged with their slow axes tilted at 90° with respect to each other. With this arrangement, when light passes through the first quarter-wave plate B and the second quarter-wave plate D, the wavelength dispersion characteristics of the wave plates B and D cancel each other out.

[0035] The half mirror C is a half mirror formed by, for example, a dielectric multilayer film or metal deposition, and functions as a transmissive and reflective surface.

[0036] Unpolarized light emitted from display surface ID passes through polarization-selective transflector E and becomes linearly polarized light. This linearly polarized light is converted into circularly polarized light by second quarter-wave plate D and then enters half mirror C. The light that passes through half mirror C travels along the first optical path, and the reflected light travels along the second optical path.

[0037] [Polarized light in the first optical path] The light that has passed through half mirror C is converted by first quarter-wave plate B into linearly polarized light in the same polarization direction as when it passed through polarization-selective transmission-reflector E, and then enters polarization-selective transmission-reflector A. Due to the polarization selectivity of polarization-selective transmission-reflector A, linearly polarized light in the same polarization direction as when it passed through polarization-selective transmission-reflector E is reflected by polarization-selective transmission-reflector A.

[0038] The light reflected by the polarization-selective transmission-reflection element A is converted by the first quarter-wave plate B into the same circularly polarized light as when it was first converted into circularly polarized light by the second quarter-wave plate D, and then enters the half mirror C. The light reflected by the half mirror C becomes circularly polarized in the opposite direction to the circularly polarized light before reflection, enters the first quarter-wave plate B, and is converted into linearly polarized light with a polarization direction orthogonal to that when it first passed through the polarization-selective transmission-reflection element E, and then enters the polarization-selective transmission-reflection element A. Due to the polarization selectivity of the polarization-selective transmission-reflection element A, the linearly polarized light with a polarization direction orthogonal to that when it passed through the polarization-selective transmission-reflection element E passes through the polarization-selective transmission-reflection element A and is guided to the pupil plane SP.

[0039] [Polarized light in the second optical path] The light reflected by half mirror C becomes circularly polarized light in the opposite direction to before it entered half mirror C, and returns to second quarter-wave plate D. The reverse circularly polarized light that has returned to second quarter-wave plate D is converted by second quarter-wave plate D into linearly polarized light in a polarization direction perpendicular to that when it first passed through polarization-selective transmission-reflection element E, and then enters polarization-selective transmission-reflection element E. Due to the polarization selectivity of polarization-selective transmission-reflection element E, linearly polarized light in a polarization direction perpendicular to that when it passed through polarization-selective transmission-reflection element E is reflected by polarization-selective transmission-reflection element E.

[0040] The light reflected by the polarization-selective transmission-reflection element E is converted by the second quarter-wave plate D into circularly polarized light in the opposite direction to when it was first circularly polarized by the second quarter-wave plate D, and then enters the half mirror C. The light that has passed through the half mirror C enters the first quarter-wave plate B and is converted into linearly polarized light with a polarization direction orthogonal to when it first passed through the polarization-selective transmission-reflection element E, and then enters the polarization-selective transmission-reflection element A. Here, due to the polarization selectivity of the polarization-selective transmission-reflection element A, the linearly polarized light with a polarization direction orthogonal to when it passed through the polarization-selective transmission-reflection element E is transmitted through the polarization-selective transmission-reflection element A and directed to the pupil plane SP.

[0041] Due to the above actions, the light of the first optical path, which transmits through PBS2, transmits through HM, is reflected by PBS1, is reflected by HM and transmits through PBS1, and the light of the second optical path, which transmits through PBS2, is reflected by HM, is reflected by PBS2, transmits through HM and transmits through PBS1, are guided to the pupil plane SP. Furthermore, due to the polarization selectivity of the light-selective transmission-reflection element and the action of the quarter-wave plate, the light of the optical path that does not reflect even once by the transmission-reflection surface does not reach the pupil plane SP by transmitting through PBS2, transmits through HM and transmits through PBS1.

[0042] Furthermore, in order to block unwanted light paths where light reflected by the half mirror HM toward the reduction side is reflected again on the display panel surface or the image sensor surface, it is preferable to place a circular polarizer on the reduction side of the polarization-selective transmission / reflection element PBS2. The circular polarizer can be composed of a linear polarizer having a transmission axis in the same direction as the polarization transmission axis of PBS2 and a quarter-wave plate having a slow axis tilted 45° with respect to the polarization transmission axis of PBS2. Furthermore, in order to block reflection from the polarization-selective transmission / reflection element PBS1 of unpolarized external light incident from the pupil plane SP side, it is preferable to place a linear polarizer having a transmission axis in the same direction as the polarization transmission axis of PBS1 on the magnification side of PBS1.

[0043] In addition, in the optical systems of each embodiment, diopter adjustment and focus adjustment can be performed by moving the entire or part of the optical system along the optical axis. In this case, an inner focus system in which the first lens G1 on the magnification side is fixed and the second lens G2 on the reduction side is moved along the optical axis is preferable from the perspective of dustproof construction, etc. Furthermore, for diopter adjustment and focus adjustment other than the system of moving a lens along the optical axis, the optical system may include optical elements that change their refractive power through mechanical or electrical action, such as shape-changeable lenses or liquid crystal lenses that utilize pressure or electrowetting. Furthermore, diopter adjustment and focus adjustment may be performed by moving a display element or an image sensor along the optical axis.

[0044] Below, Examples 1 to 4 will be specifically described. After Example 4, Numerical Examples 1 to 4 corresponding to Examples 1 to 4, respectively, are shown. [Example]

[0045] The optical system of Example 1 (Numerical Example 1) shown in Figures 1 and 2 is a display optical system with a total field of view angle of approximately 100°. The optical system of Example 1 is composed of three lenses arranged in order from the observation (pupil plane SP) side to the display surface (ID) side: a parallel-shaped first lens G1; a second lens G2 with convex surfaces on the observation side and the display surface side; a substrate made of a parallel plate; and a third lens G3 with convex surfaces on both sides. CG in the figures indicates a cover glass with no refractive power that is arranged to cover the display surface ID.

[0046] In this embodiment, a diffractive DOE surface is disposed on the observation-side surface of the first lens G1, thereby effectively correcting chromatic aberration throughout the entire optical system. A semi-transmissive reflective surface HM1 is disposed on the observation-side surface of the second lens G2, a planar semi-transmissive reflective surface HM2 is disposed on the observation-side surface of a parallel plate substrate, and a semi-transmissive reflective surface HM3 is disposed on the display-side surface of the third lens G3. Light from the display surface ID travels through HM3, HM2, is reflected by HM1, HM2, and HM1 along a first optical path before being directed to the pupil plane SP. Light from the display surface ID travels through HM3, is reflected by HM2, is reflected by HM3, is transmitted through HM2, and HM1 along a second optical path before being directed to the pupil plane SP.

[0047] The focal length and back focus of the first and second optical paths are the same. This results in an optical system with high transmittance and excellent optical performance with corrected field curvature and chromatic aberration. In addition, by providing a diffractive DOE surface on the first lens G1, which is closest to the observation side, the visibility of the rings on the diffractive surface of the surface relief pattern is reduced.

[0048] By appropriately arranging a polarizing element in the optical system, the aforementioned "polarized light utilization configuration" can be adopted. It is preferable to arrange polarization-selective transmission / reflection elements as HM1 and HM3, and arrange a stack of a quarter-wave plate, a half mirror, and another quarter-wave plate as HM2. This configuration is preferable because it allows the QWP to be arranged on a plane.

[0049] Furthermore, in order to reduce ghost light and improve the contrast of the display light, it is preferable to place a linear polarizer between HM3 and display surface ID. Furthermore, in order to block light reflected by display surface ID, it is preferable to place a quarter-wave plate between HM3 and display surface ID. Furthermore, in order to block external light from being reflected by HM1, it is preferable to place a linear polarizer that blocks external light reflection on the flat surface of first lens G1 facing the display surface. [Example]

[0050] The optical system of Example 2 (Numerical Example 2) shown in Figures 5 and 6 is a display optical system with a total viewing angle of approximately 90°. The basic configuration of the optical system of Example 2 is the same as that of Example 1. In Example 2, the lens configuration of the optical system is changed from that of Example 1.

[0051] The optical system of Example 2 is configured using three lenses, arranged in order from the observation side toward the display surface ID side: a first lens G1 as a plano-convex lens with a convex surface on the observation side, a second lens G2 as a plano-convex lens with a convex surface on the observation side, a substrate made of a parallel plate, and a third lens G3 as a plano-convex lens with a convex surface on the display surface side. In this example, a diffractive surface DOE is also arranged on the observation side surface of the first lens G1.

[0052] In this embodiment, the second lens G2, the parallel plate substrate, and the third lens G3 are cemented together to reduce the number of interfaces with air, thereby reducing ghosts caused by light reflected at the interfaces. [Example]

[0053] 9 and 10 is a display optical system with a total viewing angle of approximately 90°. The basic configuration of the optical system of Example 3 is the same as that of Example 1. In Example 3, the lens configuration of the optical system and the arrangement of the diffractive surface are changed from those of Example 1.

[0054] The optical system of Example 3 is composed of four lenses arranged in order from the observation side to the display surface ID side: a first lens G1 as a plano-convex lens with a convex surface on the observation side; a second lens G2 as a plano-convex lens with a convex surface on the observation side; a substrate made of a parallel plate; a third lens G3 as a plano-convex lens with a convex surface on the display surface side; and a fourth lens G4 as a plano-convex lens with a convex surface on the display surface side.

[0055] In this embodiment, a diffractive surface DOE is located on the display surface side of the fourth lens G4. By increasing the number of lenses constituting the optical system, field curvature and field curvature are effectively corrected. Furthermore, by locating the diffractive surface DOE on the fourth lens G4, which has a small pupil paraxial ray height, lateral chromatic aberration is selectively corrected without significantly affecting axial chromatic aberration. [Example]

[0056] The optical system of Example 4 (Numerical Example 4) shown in FIGS. 13 and 14 is a large-aperture imaging optical system with a focal length of about 30 mm and an F-number of about 1.

[0057] The optical system of Example 4 is composed of six lenses, arranged in order from the object side to the imaging plane IM side: a first lens G1 with a positive meniscus shape, a second lens G2 with a positive meniscus shape, an aperture stop SS, a third lens G3 with a negative biconcave shape, a fourth lens G4 as a plano-convex lens with a convex surface on the object side, a fifth lens G5 as a plano-convex lens with a convex surface on the image side, and a sixth lens G6 with a positive meniscus shape and a convex surface on the object side. The fourth lens G4 and the fifth lens G5 form a cemented lens.

[0058] In this embodiment, a diffractive surface DOE is disposed on the object-side surface of the third lens G3. By disposing the diffractive surface DOE near the aperture stop SS, axial chromatic aberration is effectively corrected in a large-diameter lens. A first transmissive-reflective surface HM1 is disposed on the object-side surface of the fourth lens G4. A second transmissive-reflective surface HM2 is disposed on the planar cemented surface between the fourth lens G4 and the fifth lens G5. A third transmissive-reflective surface HM3 is disposed on the image-side surface of the fifth lens G5.

[0059] Numerical Examples 1 to 4 are shown below. In each numerical example, surface number i indicates the order of the surface when counted from the object side. r is the radius of curvature (mm) of the ith surface from the object side, and d is the lens thickness or air gap (mm) on the optical axis between the ith and (i+1)th surfaces. nd is the refractive index at the d-line of the optical material between the ith and (i+1)th surfaces. νd is the Abbe number based on the d-line of the optical material between the ith and (i+1)th surfaces.

[0060] 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 Fraunhofer d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm). The effective diameter (mm) indicates the radius (mm) of the area on the i-th surface through which light rays that contribute to imaging pass.

[0061] BF represents the back focus (mm) mentioned above. The total length of a lens is the distance on the optical axis from the front surface (the surface furthest from the magnification side) to the final surface of the optical system, plus the back focus.

[0062] An "*" next to a surface number indicates that the surface has an aspherical shape. The aspherical shape is expressed by the following formula, where x is the displacement from the vertex 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 aspherical coefficients. Note that the conic constant and the aspherical coefficients "e±M" are expressed as x 10 ±M means.

[0063] 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 The (diffraction) attached to the surface number means that the surface is a diffractive surface. The phase function of a diffractive surface at the design wavelength is expressed by the following equation, where U2 to U10 are the phase function coefficients of the surface.

[0064] ψ0=U2·h 2 +U4·h 4 +U6·h 6 +U8·h 8 +U10·h 10 Numerical values ​​relating to the conditions of formula (1) in Numerical Examples 1 to 4 are summarized in Table 1. "E±M" is ×10±M The optical systems of Numerical Examples 1 to 4 satisfy the condition of Expression (1).

[0065] 3 and 4, 7 and 8, and 11 and 12 respectively show longitudinal aberrations (spherical aberration, astigmatism, distortion, and chromatic aberration) in the first and second optical paths of the optical systems of Numerical Examples 1 to 3 when focused on an object at infinity. In Numerical Examples 1 to 3, which are display optical systems, the vertical axis of the spherical aberration diagram represents pupil diameter, and the vertical axis ω of the astigmatism, distortion, and chromatic aberration represents half field angle (°). The horizontal axis represents the amount of each aberration. In the spherical aberration diagrams, the solid line represents spherical aberration for the d-line (wavelength 587.6 nm), and the two-dot chain line represents spherical aberration for the F-line (wavelength 486.1 nm). In the astigmatism diagrams, the solid line S represents astigmatism on the sagittal image plane, and the dashed line M represents astigmatism on the meridional image plane. The distortion diagrams show distortion at the d-line. The chromatic aberration diagram shows lateral chromatic aberration at the F-line.

[0066] 15 and 16 respectively show longitudinal aberrations in the first and second optical paths of the optical system of Numerical Example 4 when focused on an object at infinity. In Numerical Example 2, which is an imaging optical system, the vertical axis of the spherical aberration diagram represents Fno, and the vertical axis ω of the astigmatism, distortion, and chromatic aberration represents the half angle of view (°). The horizontal axis represents the amount of each aberration. In the spherical aberration diagram, the solid line represents spherical aberration for the d-line (wavelength 587.6 nm), and the two-dot chain line represents spherical aberration for the g-line (wavelength 435.8 nm). In the astigmatism diagram, the solid line S represents astigmatism on the sagittal image plane, and the dashed line M represents astigmatism on the meridional image plane. The distortion diagram shows distortion at the d-line. The chromatic aberration diagram shows chromatic aberration of magnification at the g-line. (Numerical Example 1) [First optical path] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 (Aperture) ∞ (Variable) 6.00 2(diffraction) ∞ 2.00 1.58800 28.0 40.80 3 ∞ 1.00 40.80 4 158.039 4.65 1.48749 70.2 57.80 5 -1927.355 1.04 57.80 6 ∞ 0.10 1.50000 30.0 57.80 7 ∞ -0.10 Reflective surface 57.80 8 ∞ -1.04 57.80 9 -1927.355 -4.65 1.48749 70.2 57.80 10 158.039 4.65 Reflective surface 57.80 11 -1927.355 1.04 57.80 12 ∞ 0.10 1.50000 30.0 57.80 13 ∞ 0.50 1.51633 64.1 57.80 14 ∞ 0.10 1.50000 30.0 57.80 15 ∞ 0.71 57.80 16 1927.355 4.65 1.48749 70.2 57.80 17 -158.039 29.25 57.80 18 ∞ 1.00 1.51633 64.1 65.00 19 ∞ 0.00 65.00 Image plane ∞ Aspheric data Surface 2 (diffractive surface) A 2=-5.71058e-04 A 4= 4.15836e-07 Various data Focal length 39.10 Pupil diameter 6.00 Half viewing angle (°) 51.21 Lens length 45.00 (in G) BF 29.91 (in AIR) d 1 15.00 Single lens data Lens starting surface focal length G1 1 875.57 G2 4 299.84 G3 16 299.84 CG 18 0.00 [Second optical path] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 (Aperture) ∞ (Variable) 6.00 2(diffraction) ∞ 2.00 1.58800 28.0 40.80 3 ∞ 1.00 40.80 4 158.039 4.65 1.48749 70.2 57.80 5 -1927.355 1.04 57.80 6 ∞ 0.10 1.50000 30.0 57.80 7 ∞ 0.50 1.51633 64.1 57.80 8 ∞ 0.10 1.50000 30.0 57.80 9 ∞ 0.71 57.80 10 1927.355 4.65 1.48749 70.2 57.80 11 -158.039 -4.65 57.80 12 1927.355 -0.71 57.80 13 ∞ -0.10 1.50000 30.0 57.80 14 ∞ -0.50 1.51633 64.1 57.80 15 ∞ 0.50 57.80 16 ∞ 0.10 1.50000 30.0 57.80 17 ∞ 0.71 57.80 18 1927.355 4.65 1.48749 70.2 57.80 19 -158.039 29.25 57.80 20 ∞ 1.00 1.51633 64.1 65.00 21 ∞ 0.00 65.00 Image plane ∞ Aspheric data Surface 2 (diffractive surface) A 2=-5.71058e-04 A 4= 4.15836e-07 Various data Focal length 39.10 Pupil diameter 6.00 Half viewing angle (°) 51.21 Lens length 45.00 (in G) BF 29.91 (in AIR) d 1 15.00 Single lens data Lens starting surface focal length G1 1 875.57 G2 4 299.84 G3 10 299.84 7 11 299.84 CG 20 0.00 (Numerical Example 2) [First optical path] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 (Aperture) ∞ (Variable) 6.00 2 (diffraction) 106.093 2.59 1.58800 28.0 28.00 3∞ 1.00 28.00 4* 65.969 5.39 1.49171 57.4 37.90 5 ∞ 0.10 1.50000 50.0 37.90 6 ∞ -0.10 Reflective surface 37.90 7 ∞ -5.39 1.49171 57.4 37.90 8* 65.969 5.39 Reflective surface 37.90 9 ∞ 0.10 1.50000 50.0 37.90 10 ∞ 0.50 1.51633 64.1 37.90 11 ∞ 0.10 1.50000 50.0 37.90 12 ∞ 4.90 1.49171 57.4 37.90 13* -65.969 7.48 37.90 14 ∞ 0.80 1.51633 64.1 30.00 15 ∞ 0.00 30.00 Image plane ∞ Aspheric data 2nd side K = 0.00000e+00 A 4=-8.88987e-08 A 6=-4.33773e-08 A 8=-3.37397e-12 Surface 2 (diffractive surface) U2=-1.26533e-03 Side 4 K = 0.00000e+00 A 4=-1.46400e-06 A 6= 3.49719e-09 A 8=-3.60054e-12 Side 8 K = 0.00000e+00 A 4=-1.46400e-06 A 6= 3.49719e-09 A 8=-3.60054e-12 Page 13 K = 0.00000e+00 A 4= 1.46400e-06 A 6=-3.49719e-09 A 8= 3.60054e-12 Various data Focal length 17.25 Pupil diameter 6.00 Half viewing angle (°) 45.00 Lens length 22.86 (in G) BF 8.01 (in AIR) d 1 12.00 Single lens data Lens starting surface focal length G1 1 123.87 G2 4 134.16 G3 12 134.16 CG 14 0.00 [Second optical path] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 (Aperture) ∞ (Variable) 6.00 2 (diffraction) 106.093 2.59 1.58800 28.0 28.00 3∞ 1.00 28.00 4* 65.969 5.39 1.49171 57.4 37.90 5 ∞ 0.10 1.50000 50.0 37.90 6 ∞ 0.50 1.51633 64.1 37.90 7 ∞ 0.10 1.50000 50.0 37.90 8 ∞ 4.90 1.49171 57.4 37.90 9* -65.969 -4.90 Reflective surface 37.90 10 ∞ -0.10 1.50000 50.0 37.90 11 ∞ -0.50 1.51633 64.1 37.90 12 ∞ 0.50 Reflective surface 37.90 13 ∞ 0.10 1.50000 50.0 37.90 14 ∞ 4.90 1.49171 57.4 37.90 15* -65.969 7.48 37.90 16 ∞ 0.80 1.51633 64.1 30.00 17 ∞ 0.00 30.00 Image plane ∞ Aspheric data 2nd side K = 0.00000e+00 A 4=-8.88987e-08 A 6=-4.33773e-08 A 8=-3.37397e-12 Surface 2 (diffractive surface) U2=-1.26533e-03 Side 4 K = 0.00000e+00 A 4=-1.46400e-06 A 6= 3.49719e-09 A 8=-3.60054e-12 9th page K = 0.00000e+00 A 4= 1.46400e-06 A 6=-3.49719e-09 A 8= 3.60054e-12 Page 15 K = 0.00000e+00 A 4= 1.46400e-06 A 6=-3.49719e-09 A 8= 3.60054e-12 Various data Focal length 17.25 Pupil diameter 6.00 Half viewing angle (°) 45.00 Lens length 22.86 (in G) BF 8.01 (in AIR) d 1 12.00 Single lens data Lens starting surface focal length G1 1 123.87 G2 4 134.16 G3 8 134.16 CG 16 0.00 (Numerical Example 3) [First optical path] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 (Aperture) ∞ (Variable) 6.00 2* 126.106 2.40 1.49171 57.4 28.00 3∞ 1.00 28.00 4* 63.706 5.60 1.49171 57.4 40.00 5 ∞ 0.10 1.50000 30.0 40.00 6 ∞ -0.10 Reflective surface 40.00 7 ∞ -5.60 1.49171 57.4 40.00 8* 63.706 5.60 Reflective surface 40.00 9 ∞ 0.10 1.50000 30.0 40.00 10 ∞ 0.50 1.51633 64.1 40.00 11 ∞ 0.10 1.50000 30.0 40.00 12 ∞ 5.11 1.49171 57.4 40.00 13* -63.706 5.03 40.00 14 ∞ 3.80 1.60700 27.0 28.50 15 (diffraction) -27.829 0.56 26.50 16 ∞ 0.80 1.51633 64.1 30.00 17 ∞ 0.00 30.00 Image plane ∞ Aspheric data 2nd side K = 0.00000e+00 A 4= 7.81405e-06 A 6=-1.23662e-07 A 8= 1.14374e-10 Side 4 K = 0.00000e+00 A 4=-3.18495e-06 A 6= 1.00219e-08 A 8=-1.13669e-11 Side 8 K = 0.00000e+00 A 4=-3.18495e-06 A 6= 1.00219e-08 A 8=-1.13669e-11 Page 13 K = 0.00000e+00 A 4= 3.18495e-06 A 6=-1.00219e-08 A 8= 1.13669e-11 Page 15 K = 0.00000e+00 A 4= 1.06790e-04 A 6= 1.65503e-07 A 8=-1.32987e-09 Surface 15 (diffractive surface) A2=-6.96621e-03 Various data Focal length 16.70 Pupil diameter 6.00 Half viewing angle (°) 45.00 Lens length 25.00 (in G) BF 1.09 (in AIR) d 1 12.00 Single lens data Lens starting surface focal length G1 1 256.46 G2 4 129.56 G3 12 129.56 G4 14 27.98 CG 16 0.00 [Second optical path] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 (Aperture) ∞ (Variable) 6.00 2* 126.106 2.40 1.49171 57.4 28.00 3∞ 1.00 28.00 4* 63.706 5.60 1.49171 57.4 40.00 5 ∞ 0.10 1.50000 50.0 40.00 6 ∞ 0.50 1.51633 64.1 40.00 7 ∞ 0.10 1.50000 30.0 40.00 8 ∞ 5.11 1.49171 57.4 40.00 9* -63.706 -5.11 40.00 10 ∞ -0.10 1.50000 30.0 40.00 11 ∞ -0.50 1.51633 64.1 40.00 12 ∞ 0.50 40.00 13 ∞ 0.10 1.50000 30.0 40.00 14 ∞ 5.11 1.49171 57.4 40.00 15* -63.706 5.03 40.00 16 ∞ 3.80 1.60700 27.0 28.50 17 (diffraction) -27.829 0.56 26.50 18 ∞ 0.80 1.51633 64.1 30.00 19 ∞ 0.00 30.00 Image plane ∞ Aspheric data 2nd side K = 0.00000e+00 A 4= 7.81405e-06 A 6=-1.23662e-07 A 8= 1.14374e-10 Side 4 K = 0.00000e+00 A 4=-3.18495e-06 A 6= 1.00219e-08 A 8=-1.13669e-11 9th page K = 0.00000e+00 A 4= 3.18495e-06 A 6=-1.00219e-08 A 8= 1.13669e-11 Page 15 K = 0.00000e+00 A 4= 3.18495e-06 A 6=-1.00219e-08 A 8= 1.13669e-11 Page 17 K = 0.00000e+00 A 4= 1.06790e-04 A 6= 1.65503e-07 A 8=-1.32987e-09 Surface 17 (diffractive surface) A2=-6.96621e-03 Various data Focal length 16.70 Pupil diameter 6.00 Half viewing angle (°) 45.00 Lens length 25.00 (in G) BF 1.09 (in AIR) d 1 12.00 Single lens data Lens starting surface focal length G1 1 256.46 G2 4 129.56 G3 8 129.56 G4 16 27.98 CG 18 0.00 (Numerical Example 4) [First optical path] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 29.944 5.32 1.48749 70.2 29.70 2 214.523 9.78 29.00 3* -106.281 3.00 1.58313 59.4 25.00 4 -50.342 2.00 24.60 5 (Aperture) ∞ 3.04 22.40 6 (diffraction) -40.402 3.43 1.73800 32.3 21.50 7 105.830 1.00 21.20 8 98.088 4.25 1.51742 52.4 32.00 9 ∞ 4.25 1.51742 52.4 32.00 10 -98.088 -4.25 Reflective surface 32.00 11 ∞ 4.25 Reflective surface 32.00 12 -98.088 (variable) 32.00 13 36.890 6.00 1.48749 70.2 30.70 14 3422.068 8.70 30.20 15 ∞ 1.00 1.51633 64.1 35.00 16 ∞ 0.00 35.00 Image plane ∞ Aspheric data 3rd page K = 0.00000e+00 A 4=-7.25778e-06 A 6= 1.65539e-08 A 8=-4.12646e-11 A10= 9.14634e-14 Side 6 K = 0.00000e+00 A 4=-4.42752e-06 A 6=-1.60868e-08 Surface 6 (diffractive surface) A2= -1.00000e-04 Various data Focal length 29.66 F-number 1.00 Half angle of view (°) 24.73 Lens length 53.78 (in G) BF 9.36 (in AIR) d12 2.00 Single lens data Lens starting surface focal length G1 1 70.72 G2 3 160.84 G3 6 -39.23 G4 8 189.57 G5 9 189.57 G6 13 76.45 CG 15 0.00 [Second optical path] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 29.944 5.32 1.48749 70.2 29.70 2 214.523 9.78 29.00 3* -106.281 3.00 1.58313 59.4 25.00 4 -50.342 2.00 24.60 5 (Aperture) ∞ 3.04 22.40 6 (diffraction) -40.402 3.43 1.73800 32.3 21.50 7 105.830 1.00 21.20 8 98.088 4.25 1.51742 52.4 32.00 9 ∞ -4.25 Reflective surface 32.00 10 98.088 4.25 Reflective surface 32.00 11 ∞ 4.25 1.51742 52.4 32.00 12 -98.088 (variable) 32.00 13 36.890 6.00 1.48749 70.2 30.70 14 3422.068 8.70 30.20 15 ∞ 1.00 1.51633 64.1 35.00 16 ∞ 0.00 35.00 Image plane ∞ Aspheric data 3rd page K = 0.00000e+00 A 4=-7.25778e-06 A 6= 1.65539e-08 A 8=-4.12646e-11 A10= 9.14634e-14 Side 6 K = 0.00000e+00 A 4=-4.42752e-06 A 6=-1.60868e-08 Surface 6 (diffractive surface) A2= -1.00000e-04 Various data Focal length 29.66 F-number 1.00 Half viewing angle (°)24.73 Lens length 53.78 (in G) BF 9.36 (in AIR) d12 2.00 Single lens data Lens starting surface focal length G1 1 70.72 G2 3 160.84 G3 6 -39.23 G4 8 189.57 G5 11 189.57 G6 13 76.45 CG 15 0.00

[0067] [Table 1]

[0068] [Display device] 18 shows a head-mounted display (HMD) as a display device using the display optical systems of Examples 1 to 3. The HMD is worn on the head (in front of the eyes) of the viewer by means of a wearing gear (not shown).

[0069] The HMD has display elements RID and LID for the right and left eyes, a right-eye display optical system ROS that guides display light from the right-eye display element RID to the observer's right eye, and a left-eye display optical system LOS that guides display light from the left-eye display element LID to the observer's left eye.

[0070] [Imaging device] 19 shows a digital still camera as an imaging device using the imaging optical system of Example 4. Reference numeral 20 denotes the camera body, and 21 denotes the imaging optical system of Example 4. Reference numeral 22 denotes a solid-state imaging element such as a CCD sensor or CMOS sensor that is built into the camera body 20 and captures an optical image (subject image) formed by the imaging optical system 21. Reference numeral 23 denotes a recording unit that records image data generated by processing an imaging signal from the imaging element 22, and 24 denotes a rear display that displays the image data. The camera may be a single-lens reflex camera having a quick-turn mirror, or a mirrorless camera without a quick-turn mirror.

[0071] The above embodiment includes the following configurations.

[0072] (Configuration 1) a first transmissive-reflective surface, a second transmissive-reflective surface, and a third transmissive-reflective surface, which are arranged in this order from the first side to the second side; an optical system having a diffractive surface as a transmission surface different from the first, second and third transmission-reflection surfaces; (Configuration 2) The light from the second side the light reaches the first side along a first optical path of transmitting through the third transmission-reflection surface, transmitting through the second transmission-reflection surface, being reflected at the first transmission-reflection surface, being reflected at the second transmission-reflection surface, and transmitting through the first transmission-reflection surface; the optical system described in Configuration 1, characterized in that the light reaches the first side via a second optical path in which the light passes through the third transmission-reflection surface, is reflected at the second transmission-reflection surface, is reflected at the third transmission-reflection surface, passes through the second transmission-reflection surface, and passes through the first transmission-reflection surface. (Configuration 3) The light from the side of said 1, the first light beam passes through the first transmission-reflection surface, is reflected by the second transmission-reflection surface, is reflected by the first transmission-reflection surface, is transmitted through the second transmission-reflection surface, and is transmitted through the third transmission-reflection surface, and reaches the second side along a first optical path; The optical system described in Configuration 1, characterized in that light passes through the first transmission-reflection surface, passes through the second transmission-reflection surface, is reflected at the third transmission-reflection surface, is reflected at the second transmission-reflection surface, and reaches the second side via a second optical path that passes through the third transmission-reflection surface. (Configuration 4) 4. The optical system according to any one of configurations 1 to 3, wherein the diffractive surface is disposed closer to the first side than the first transmission-reflection surface. (Configuration 5) 5. The optical system according to any one of configurations 1 to 4, wherein the focal length in the first optical path and the focal length in the second optical path are the same, and the air-equivalent distance from the surface closest to the second side in the first optical path to a display surface or an image surface is the same as the air-equivalent distance in the second optical path. (Configuration 6) The optical system described in any one of configurations 1 to 5, wherein the first to third transmission-reflection surfaces include two transmission-reflection surfaces having curvatures so as to have positive optical power for the light to be reflected. (Configuration 7) When the sum of the optical powers Φn of the surfaces on which the first to third transmission-reflection surfaces are provided, respectively, is ΣΦn, and the optical power of the diffractive surface is Φdoe, then: 0.0<Φdoe / (ΣΦn)≦3.0 7. The optical system according to any one of configurations 1 to 6, wherein the following condition is satisfied: (Configuration 8) 8. The optical system according to any one of configurations 1 to 7, wherein at least one of the first to third transmission-reflection surfaces is a flat surface. (Configuration 9) 9. The optical system according to any one of configurations 1 to 8, wherein the first to third transmission-reflection surfaces include two transmission-reflection surfaces formed of reflective polarizing elements. (Configuration 10) The optical system described in configuration 9, wherein at least one of the two transmission-reflection surfaces formed by the reflective polarizing element has a positive optical power with respect to refracted light. (Configuration 11) The optical system according to configuration 9 or 10, wherein the two transmission-reflection surfaces formed by the reflective polarizing element have the same surface shape. (Configuration 12) a display element disposed on the second side; and the optical system according to any one of configurations 1, 2, and 4 to 11; A display device characterized in that light from the display element is guided to a pupil plane on the first side. (Configuration 13) a display element disposed on the second side; and the optical system according to any one of configurations 1 and 3 to 11; An imaging device that guides light from an object on the first side to the imaging element.

[0073] The embodiments described above are merely representative examples, and various modifications and alterations are possible to each embodiment when implementing the present invention. [Explanation of symbols]

[0074] ID display surface IM image plane HM1 1st transmissive reflective surface HM2 2nd transmissive reflective surface HM3 3rd transmissive reflective surface POL linear polarizer PBS Polarization Selective Transmittance and Reflection Element QWP quarter wave plate

Claims

1. a first transmission-reflection surface, a second transmission-reflection surface, and a third transmission-reflection surface, which are arranged in this order from the first side to the second side; an optical system comprising a diffractive surface as a transmission surface different from said first, second and third transmission-reflection surfaces;

2. The light from the second side is the light reaches the first side along a first optical path of transmitting through the third transmission-reflection surface, transmitting through the second transmission-reflection surface, being reflected at the first transmission-reflection surface, being reflected at the second transmission-reflection surface, and transmitting through the first transmission-reflection surface; 2. The optical system according to claim 1, wherein the light reaches the first side via a second optical path in which the light passes through the third transmission-reflection surface, is reflected by the second transmission-reflection surface, is reflected by the third transmission-reflection surface, passes through the second transmission-reflection surface, and passes through the first transmission-reflection surface.

3. The light from the first side is the first light beam passes through the first transmission-reflection surface, is reflected by the second transmission-reflection surface, is reflected by the first transmission-reflection surface, is transmitted through the second transmission-reflection surface, and is transmitted through the third transmission-reflection surface, and reaches the second side along a first optical path; 2. The optical system according to claim 1, wherein the light reaches the second side via a second optical path in which the light passes through the first transmission-reflection surface, passes through the second transmission-reflection surface, is reflected by the third transmission-reflection surface, is reflected by the second transmission-reflection surface, and passes through the third transmission-reflection surface.

4. 2. The optical system according to claim 1, wherein the diffractive surface is disposed on the first side of the first transmission-reflection surface.

5. 2. The optical system according to claim 1, wherein the focal length in the first optical path and the focal length in the second optical path are the same, and the air-equivalent distance from the surface closest to the second side in the first optical path to the display surface or image plane is the same as the air-equivalent distance in the second optical path.

6. 2. The optical system according to claim 1, wherein the first to third transmissive-reflective surfaces include two transmissive-reflective surfaces having curvatures so as to have positive optical power for the light to be reflected.

7. When the sum of the optical powers Φn of the surfaces on which the first to third transmission-reflection surfaces are provided, respectively, is ΣΦn, and the optical power of the diffractive surface is Φd oe, then: 0.0<Φdoe / (ΣΦn)≦3.0 2. The optical system according to claim 1, wherein the following condition is satisfied:

8. 2. The optical system according to claim 1, wherein at least one of the first to third transmissive-reflective surfaces is a flat surface.

9. 2. The optical system according to claim 1, wherein the first to third transmission-reflection surfaces include two transmission-reflection surfaces formed of reflective polarizing elements.

10. 10. The optical system according to claim 9, wherein at least one of the two transmissive-reflective surfaces formed by the reflective polarizing element has a positive optical power with respect to refracted light.

11. 10. The optical system according to claim 9, wherein the two transmissive / reflective surfaces formed by the reflective polarizing element have the same surface shape.

12. a display element disposed on the second side; and an optical system according to any one of claims 1, 2, and 4 to 11, A display device characterized in that light from the display element is guided to a pupil plane on the first side.

13. a display element disposed on the second side; and an optical system according to any one of claims 1 and 3 to 11, An imaging device that guides light from an object on the first side to the imaging element.

Images