Optical system and viewing device having the same

Abstract

The present disclosure relates to an optical system and an observation device having the same. The optical system is configured to form a magnified image of a display surface of an image display element and sequentially includes a first semi-transmissive reflective surface and a second semi-transmissive reflective surface from an exit pupil side to the display surface side. The optical system has a first optical path on which light from the display surface is transmitted through the second semi-transmissive reflective surface, reflected by the first semi-transmissive reflective surface, reflected by the second semi-transmissive reflective surface, transmitted through the first semi-transmissive reflective surface, and directed to an exit pupil, and a second optical path on which light from the exit pupil side is transmitted through the first semi-transmissive reflective surface, transmitted through the second semi-transmissive reflective surface, and directed to an image sensor.

Description

Technical Field

[0001] One aspect of this disclosure relates to an optical system and an observation device having the optical system. Background Technology

[0002] Conventionally, an observation device is known to have the function of magnifying and displaying the original image on an image display element via an eyepiece optical system, and the function of using an iris image for personal authentication and using an imaging optical system that captures the observer's pupil for gaze detection. PCT application, domestic publication No. (“JP”) 2015-508182 discloses a configuration that uses the same optical system with a free-form surface prism for both: an observation optical path for image observation and an imaging optical path for gaze tracking.

[0003] The configuration disclosed in JP 2015-508182 allows for a larger freeform prism and a thicker optical system in an attempt to increase the field of view of the eyepiece optical system.

[0004] A common configuration that can increase the viewing angle and become thinner is one that uses a double-sided semi-reflective mirror to fold the observation optical path along the optical axis (a triple-pass optical system). When placing the imaging optics within a triple-pass optical system, it is conceivable to position the imaging optics outside the eyepiece optics system, such as... Figure 7 As shown in the diagram. However, in this configuration, the large lens outer diameter of the eyepiece optics system with a wide field of view results in an excessively large imaging angle of the observer's pupil, and the pupil image and iris image are obstructed due to eyelid and eyeball rotation. Summary of the Invention

[0005] One aspect of this disclosure provides a small and thin optical system with a wide viewing angle and high optical performance, as well as an observation device having the optical system.

[0006] An optical system according to one aspect of this disclosure is configured to form a magnified image of a display surface of an image display element, and sequentially includes a first semi-transparent reflective surface and a second semi-transparent reflective surface from the exit pupil side to the display surface side. The optical system has a first optical path and a second optical path, in which light from the display surface is transmitted through the second semi-transparent reflective surface, reflected by the first semi-transparent reflective surface, reflected again by the second semi-transparent reflective surface, transmitted through the first semi-transparent reflective surface, and guided to the exit pupil; and in the second optical path, light from the exit pupil side is transmitted through the first semi-transparent reflective surface, transmitted through the second semi-transparent reflective surface, and guided to an image sensor. An observation device including the above-described optical system also constitutes another aspect of this disclosure.

[0007] Other features of this disclosure will become clear from the following description of exemplary embodiments with reference to the accompanying drawings. Attached Figure Description

[0008] Figure 1 It is a cross-sectional view of the optical system based on Example 1.

[0009] Figure 2 It is a cross-sectional view of the optical system based on Example 2.

[0010] Figure 3 It is a cross-sectional view of the optical system based on Example 3.

[0011] Figure 4 It is a cross-sectional view of the optical system based on Example 4.

[0012] Figure 5 It is a cross-sectional view of the optical system based on Example 5.

[0013] Figure 6 This explains the polarization configuration used in the eyepiece optical system.

[0014] Figure 7 This is a cross-sectional view of the optical system based on the comparative example. Detailed Implementation

[0015] A detailed description of embodiments according to the present disclosure will now be given with reference to the accompanying drawings. Corresponding elements in the various figures will be denoted by the same reference numerals, and repeated descriptions thereof will be omitted.

[0016] Figures 1 to 5 These are cross-sectional views of the optical systems according to Examples 1 to 5. The optical systems according to each example are optical systems used in observation devices such as head-mounted displays (HMDs) and form magnified images of the image display surface ID of image display elements such as LCDs.

[0017] In each cross-sectional view, the left side is the exit pupil side (exit pupil side or observation side), and the right side is the image display surface ID side. EYE represents the observer's eye. SP represents the exit pupil (pupil plane). CAM represents a camera with an image sensor.

[0018] The optical systems according to various examples have an observation optical path (first optical path) that guides light from the image display surface ID to the exit pupil SP, and an imaging optical path (second optical path) that guides light from the exit pupil SP side to the image sensor. The optical systems according to various examples include, sequentially from the exit pupil SP side to the image display surface ID side, a first semi-transparent reflective surface HM1 and a second semi-transparent reflective surface HM2. The optical systems according to various examples include an eyepiece optical system for magnifying, displaying, and observing an image displayed on the image display surface ID, and an imaging optical system for imaging light from the exit pupil SP side onto the image sensor. The eyepiece optical system is a coaxial optical system using the observation optical path. In the observation optical path, light from the image display surface ID is transmitted through the second semi-transparent reflective surface HM2, reflected by the first semi-transparent reflective surface HM1, reflected by the second semi-transparent reflective surface HM2, and transmitted through the first semi-transparent reflective surface HM1, and guided to the exit pupil SP. The imaging optical system is an optical system using an imaging optical path that incorporates a portion of the eyepiece optical system. In the imaging optical path, light from the exit pupil SP side is transmitted through the first semi-transparent reflective surface HM1 and the second semi-transparent reflective surface HM2, and is guided to the image sensor. In the imaging optical path, light from the exit pupil SP side is not reflected by the first semi-transparent reflective surface HM1 or the second semi-transparent reflective surface HM2.

[0019] Due to the above configuration, the observation optical path has a triple-pass configuration, and the imaging optical path has a single-pass configuration where at least a portion of the eyepiece optics is transmitted through. By deploying the eyepiece optics in a triple-pass configuration that enables a thin configuration with a wide field of view, and by deploying the imaging optics on the image display surface ID side, the offset of the image sensor in a direction orthogonal to the optical axis of the imaging optical path can be reduced. That is, the imaging angle on the exit pupil SP side of the imaging optics can be reduced.

[0020] The above configuration enables a small and thin optical system with a wide viewing angle and high optical performance.

[0021] The configurations that can be satisfied by the optical systems according to the various examples will now be described.

[0022] The refractive region RR can be positioned outside the optically effective region of the observation optical path and within the optically effective region of the imaging optical path. Here, "outside the optically effective region" refers to the optically ineffective region, and "within the optically effective region" refers to the region within the optically effective region. In the imaging optical path, light from the exit pupil SP side is transmitted through the first semi-transparent reflective surface HM1, the second semi-transparent reflective surface HM2, and the refractive region RR, and is guided to the image sensor. This allows the image sensor to be closer to the optical axis of the eyepiece optics system and reduces the imaging angle on the exit pupil SP side of the imaging optics system. In the optical systems according to various examples, the refractive region RR is a refractive surface.

[0023] The refractive surface can be rotationally symmetric relative to the optical axis of the observation path. This simplifies the fabrication of the refractive surface in eyepiece optical systems that function as coaxial optical systems. In the case of lenses using resin materials to construct eyepiece optical systems with polarization configurations, as described below, controlling molded birefringence becomes crucial. Rotationally symmetric lenses are advantageous for reducing molded birefringence.

[0024] The refractive surface can be a plane (flat surface). Therefore, in imaging optical systems, aberrations that would otherwise occur on the refractive surface can be reduced.

[0025] In the imaging optical path, the rotationally asymmetric optical element (OE) can be deployed closer to the image sensor than the refractive surface. This allows for the correction of aberrations that would otherwise occur in the observation optical system, which shares a portion with the eyepiece optical system, within the imaging optical system, and enables imaging of the exit pupil SP side with greater precision. The effective optical surface of the OE on the image sensor side can be planar. This configuration reduces aberrations that would otherwise occur on the effective optical surface of the OE on the image sensor side. The OE can be bonded (or joined) to the refractive surface. This stabilizes the configuration of the OE and other optical elements.

[0026] In the optical systems according to the various examples, the first semi-transmissive reflective surface HM1 can be planar. Using this structure and appropriately deploying the refractive region RR, the imaging optical system can reduce aberrations that would otherwise occur in the observation optical path shared with the eyepiece optical system. For example, in Figure 5 In the configuration shown, the common portion of the imaging optics and the eyepiece optics acts as a parallel plate.

[0027] The first semi-transmissive reflective surface HM1 can be a surface provided for a polarization-selective reflective polarization element. A circular polarization conversion element can be deployed on the image display surface ID side of the second semi-transmissive reflective surface HM2. The circular polarization conversion element can include a linear polarizer (or polarizer) and a quarter-wave plate. This configuration, when utilizing polarization, as described below, can shield the single-pass optical path in the eyepiece optics system and achieve high-quality virtual image observation. The linear polarizer can be deployed in the observation optical path. Since no linear polarizer is deployed in the imaging optical path, light reduction caused by absorption by the polarization element can be prevented.

[0028] The optical systems described in the various examples may include a single cemented lens. This configuration allows for a reduction in thickness, including the lens barrel, while achieving the necessary and adequate aberration correction.

[0029] The optical systems of each example can satisfy the following inequality (1).

[0030] 0.5 < Cx / Ltp < 1.5 (1)

[0031] Where Ltp is the distance on the optical axis of the observation optical path from the surface closest to the exit pupil SP to the second semi-transmissive reflective surface HM2, and Cx is the distance on the optical axis of the observation optical path from the surface closest to the exit pupil SP to the center of the image sensor.

[0032] Inequality (1) defines the arrangement of the imaging optical system. If the value is below the lower limit of inequality (1), it becomes difficult to reduce the imaging angle on the exit pupil SP side of the imaging optical system and the eyepiece optical system becomes thicker. If the value is above the upper limit of inequality (1), the imaging angle on the exit pupil SP side of the imaging optical system can be reduced, but the image pickup device CAM becomes thicker.

[0033] The numerical range of inequality (1) can be replaced by the numerical range of the following inequality (1a).

[0034] 0.7 <Cx / Ltp<1.3(1a)

[0035] The numerical range of inequality (1) can be replaced by the numerical range of the following inequality (1b).

[0036] 0.8 <Cx / Ltp<1.1(1b)

[0037] Now for reference Figures 1 to 6 The description will utilize the configuration of polarization. Figure 6 This explains the use of polarization configuration in the eyepiece optical system.

[0038] The first semi-transmissive reflective surface HM1, starting from the exit pupil SP side, includes a polarization-selective semi-transmissive reflective element (PBS) and a first quarter-wave plate (QWP1). The second semi-transmissive reflective surface HM2 includes a semi-reflective mirror, for example, made of a dielectric multilayer film or metal vapor deposition. The second quarter-wave plate (QWP2) and a linear polarizer (POL) are deployed between the semi-reflective mirror (second semi-transmissive reflective surface HM2) and the image display surface ID.

[0039] A polarization-selective semi-transmissive reflective element (PBS) is an element configured to reflect linearly polarized light polarized in the same direction as the light passing through a linear polarizer (POL) and transmit linearly polarized light orthogonal to that direction. The polarization-selective semi-transmissive reflective element (PBS) is, for example, a wire-grid polarizer, and the wire-grid forming surface serves as the semi-transmissive and semi-reflective surface. A first quarter-wave plate (QWP1) and a second quarter-wave plate (QWP2) are arranged such that their slow axes are tilted by 90°. The first quarter-wave plate (QWP1) is deployed such that its slow axis is tilted by 45° relative to the polarization transmission axis of the linear polarizer (POL).

[0040] Light emitted from the image display surface ID is converted into linearly polarized light by a linear polarizer (POL), then into circularly polarized light by a second quarter-wave plate (QWP2), and enters a semi-reflective mirror (second semi-transmissive reflective surface HM2). A portion of the light that has reached the semi-reflective mirror (second semi-transmissive reflective surface HM2) is reflected to become circularly polarized light in the opposite rotation direction and returns to the second quarter-wave plate (QWP2). The circularly polarized light that has returned to the second quarter-wave plate (QWP2) is converted into linearly polarized light by the second quarter-wave plate (QWP2) in a direction orthogonal to the direction of the light after passing through the linear polarizer (POL), and returns to the linear polarizer (POL) where it is absorbed.

[0041] A portion of the light that has reached the semi-reflective mirror (second semi-transparent reflective surface HM2) is transmitted through the semi-reflective mirror (second semi-transparent reflective surface HM2). Thereafter, the first quarter-wave plate (QWP1) converts the light into linearly polarized light in the same direction as the light after passing through the linear polarizer (POL), and this light enters the polarization-selective semi-transparent reflective element (PBS). The linearly polarized light, in the same direction as the light after passing through the linear polarizer (POL), is polarized selectively by the polarization-selective semi-transparent reflective element (PBS). The light reflected by the polarization-selective semi-transparent reflective element (PBS) is converted by the first quarter-wave plate (QWP1) into circularly polarized light in the opposite direction of rotation to the light after it has been converted into circular polarization by the second quarter-wave plate (QWP2), and this light enters the semi-reflective mirror (second semi-transparent reflective surface HM2).

[0042] The light reflected by the semi-reflective mirror (second semi-transmissive reflective surface HM2) becomes circularly polarized light, polarized in the opposite direction to the direction of the light before reflection. The light then enters the first quarter-wave plate (QWP1) and becomes linearly polarized light, polarized in a direction orthogonal to the direction of the light previously passing through the linear polarizer (POL), and enters the polarization-selective semi-transmissive reflective element (PBS).

[0043] Linearly polarized light, polarized in a direction orthogonal to the direction of light previously passing through the linear polarizer (POL), is transmitted through the polarization-selective semi-transmissive reflector (PBS) due to the polarization selectivity of the PBS and is guided to the exit pupil SP.

[0044] As described above, the light transmitted through the semi-reflective mirror (second semi-transparent reflective surface HM2) is reflected by the polarization-selective semi-transparent reflective element (PBS), reflected by the semi-reflective mirror (second semi-transparent reflective surface HM2), and guided to the exit pupil SP.

[0045] Example 1

[0046] Now for reference Figure 1 A description of the observation apparatus based on this example will be given.

[0047] The observation device according to this example includes, sequentially from the exit pupil SP side to the image display surface ID side, a first lens G1, a second lens G2, and a third lens G3. A first semi-transmissive reflective surface HM1 is disposed on the exit pupil SP side of the first lens G1. A second semi-transmissive reflective surface HM2 is disposed on the exit pupil SP side of the second lens G2. The observation device according to this example includes an image display element and a camera CAM including an image sensor. The observation device according to this example includes an eyepiece optical system and an imaging optical system as a coaxial optical system having a diagonal viewing angle of approximately 58 degrees. The aspect ratio of the image display surface ID is 4:3. Dashed lines represent the effective light beam (luminous flux) in the observation optical path, and solid lines represent the effective light beam in the imaging optical path.

[0048] In the observation optical path, light from the image display surface ID is transmitted through the second semi-transparent reflective surface HM2, reflected by the first semi-transparent reflective surface HM1, reflected again by the second semi-transparent reflective surface HM2, transmitted through the first semi-transparent reflective surface HM1, and guided to the exit pupil SP. The eyepiece optical system uses a three-way configuration to achieve a wide viewing angle and a low profile for the observation device.

[0049] In the imaging optical path, light is transmitted through the first semi-transparent reflective surface HM1, then through the second semi-transparent reflective surface HM2, and is guided to the image sensor. This configuration can reduce the imaging angle on the exit pupil SP side of the imaging optical system.

[0050] The refractive region RR is positioned outside the optically effective region of the observation optical path and within the optically effective region of the imaging optical path. This allows the camera CAM (image sensor) to be positioned closer to the optical axis of the eyepiece optics and further reduces the imaging angle on the exit pupil SP side of the imaging optics. In this example, the refractive region RR is a spherical surface that is rotationally symmetric with respect to the optical axis of the observation optical path.

[0051] Example 2

[0052] Now for reference Figure 2 A description of the observation apparatus based on this example will be given.

[0053] The basic configuration of the observation apparatus in this example is similar to that of the observation apparatus in Example 1. The difference between this example and Example 1 lies in the configuration of the eyepiece optical system and the arrangement of the imaging optical system. This example will discuss configurations different from those in Example 1, and descriptions of configurations similar to those in Example 1 will be omitted.

[0054] The observation device according to this example includes a first lens G1 and a second lens G2 sequentially from the exit pupil SP side to the image display surface ID side. A first semi-transmissive reflective surface HM1 is disposed on the exit pupil SP side of the first lens G1. A second semi-transmissive reflective surface HM2 is disposed on the exit pupil SP side of the second lens G2.

[0055] The eyepiece optics system according to this example has a diagonal field of view of approximately 80 degrees and includes a single cemented lens.

[0056] The refractive region RR is positioned outside the optically effective region of the observation optical path and within the optically effective region of the imaging optical path. In this example, the refractive region RR is a conical surface that is rotationally symmetric with respect to the optical axis of the observation optical path.

[0057] Example 3

[0058] Now for reference Figure 3 A description of the observation apparatus based on this example will be given.

[0059] The basic configuration of the observation apparatus in this example is similar to that of the observation apparatus in Example 2. The difference between this example and Example 2 lies in the configuration of the refraction region RR. In this example, the configuration different from that in the second example will be described, and descriptions of configurations similar to those in Example 2 will be omitted.

[0060] In this example, the refractive region RR is a plane that is rotationally symmetric with respect to the optical axis of the observation path. Making the refractive region RR a plane can reduce asymmetric aberrations caused by refraction in the refractive region RR, especially astigmatic components.

[0061] Example 4

[0062] Now for reference Figure 4 A description of the observation apparatus based on this example will be given.

[0063] The basic configuration of the observation device in this example is similar to that of the observation device in Example 2. The difference between this example and Example 2 is that a rotationally asymmetric optical element (OE) is deployed on the image sensor side of the refractive region (RR). This example will discuss configurations different from those in Example 2, and descriptions of configurations similar to those in Example 2 will be omitted.

[0064] Optical elements (OEs) play a role in correcting asymmetric aberrations that would otherwise appear in the refractive region (RR), which is a conical surface. Gluing the OE to the RR and making the surface of the OE on the image sensor side of the imaging optics flat can satisfactorily correct asymmetric aberrations remaining in the imaging optics system, particularly astigmatism.

[0065] Example 5

[0066] Now for reference Figure 5 A description of the observation apparatus based on this example will be given.

[0067] The basic configuration of the observation apparatus in this example is similar to that of the observation apparatus in Example 1. The difference between this example and Example 1 lies in the configuration of the eyepiece optical system and the arrangement of the imaging optical system. This example will discuss configurations different from those in Example 1, and descriptions of configurations similar to those in the first example will be omitted.

[0068] The observation device according to this example includes, sequentially from the exit pupil SP side to the image display surface ID side, a first lens G1 to a seventh lens G7. A first semi-transmissive reflective surface HM1 is disposed on the exit pupil SP side of the first lens G1. A second semi-transmissive reflective surface HM2 is disposed on the exit pupil SP side of the second lens G2.

[0069] The eyepiece optics system according to this example has a diagonal viewing angle of approximately 69 degrees and is configured to form an intermediate image.

[0070] The first semi-transmissive reflective surface HM1 is planar, and the first lens G1 and the second lens G2 are formed as cemented lenses made of the same material. Due to this configuration, the common portion of the eyepiece optics and the imaging optics can be considered as a parallel plate, minimizing the impact on aberrations. In this case, there is no need to design a dedicated imaging camera CAM for the exit pupil SP, and a general camera module can be used.

[0071] The eyepiece optics system according to this example includes a first lens G1 and a second lens G2 made of the same materials as described above, and are considered as parallel plates. A first semi-transmissive reflective surface HM1 on the exit pupil SP side of the first lens G1 is deployed as a polarization-selective semi-transmissive reflective element and a quarter-wave plate. The quarter-wave plate is deployed on the surface of the image display surface IP side of the second lens G2, and the reflective surface (the ninth surface in numerical example 3) is deployed as a planar combiner including the polarization-selective semi-transmissive reflective element. This configuration can realize a so-called optical perspective eyepiece optics system, in which external light passes through the cemented lens once and is observed with approximately equal magnification, and the image light from the image display element passes through the cemented lens three times and is observed in a magnified manner.

[0072] The following descriptions will now be given: numerical example 1 corresponding to example 1, numerical example 2 corresponding to examples 2 through 4, and numerical example 3 corresponding to example 3.

[0073] In the surface data of each numerical example, r represents the radius of curvature of each optical surface, d (mm) represents the axial distance (distance along the optical axis) between the m-th surface and the (m+1)-th surface, where m is the surface number counted from the exit pupil SP side. nd represents the refractive index of each optical component with respect to the d-line, and νd represents the Abbe number of the optical element. The Abbe number νd of a certain material is expressed as follows:

[0074] νd=(Nd-1) / (NF-NC)

[0075] Nd, NF, and NC are the refractive indices of the d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm) in the Fraunhofer lines, respectively.

[0076] The viewing angle is the viewing angle along the short side of the image display surface ID.

[0077] When the optical surface is aspherical, an asterisk (*) is appended to the right of the surface number. The shape of an aspherical surface is represented as follows:

[0078] 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

[0079] Where X is the displacement from the surface vertex along the optical axis, h is the height from the optical axis in the direction orthogonal to the optical axis, R is the paraxial radius of curvature, K is the conic constant, and A4, A6, A8, and A10 are aspheric coefficients of various orders. "e±XX" in each aspheric coefficient represents "×10" ±XX ".

[0080] [Numerical Example 1]

[0081] Unit: millimeters

[0082] Surface data

[0083]

[0084] Aspherical data

[0085] Fourth surface

[0086] K=0.00000e+00A 4=1.14783e-05A 6=8.12048e-08A 8=-3.42503e-10

[0087] A10 = 1.00372e-12

[0088] Sixth Surface

[0089] K=0.00000e+00A 4=1.14783e-05A 6=8.12048e-08A 8=-3.42503e-10

[0090] A10 = 1.00372e-12

[0091] Eighth surface

[0092] K=0.00000e+00A 4=1.14783e-05A 6=8.12048e-08A 8=-3.42503e-10

[0093] A10 = 1.00372e-12

[0094] Tenth Surface

[0095] K=0.00000e+00A 4=-2.17485e-04A 6=1.14074e-06A 8=-3.03928e-09

[0096] A10 = 2.89322e-12

[0097] Various data

[0098]

[0099] Single lens data

[0100]

[0101]

[0102] [Numerical Example 2]

[0103] Unit: millimeters

[0104] Surface data

[0105]

[0106] Aspherical data

[0107] Fourth surface

[0108] K=0.00000e+00A 4=-2.58220e-06A 6=1.47199e-08A 8=-5.32418e-11

[0109] A10 = 7.50680e-14

[0110] Sixth Surface

[0111] K=0.00000e+00A 4=-2.58220e-06A 6=1.47199e-08A 8=-5.32418e-11

[0112] A10 = 7.50680e-14

[0113] Seventh Surface

[0114] K=0.00000e+00A 4=1.82030e-04A 6=-1.33313e-06A 8=2.80530e-09

[0115] Various data

[0116]

[0117] Single lens data

[0118]

[0119] [Numerical Example 3]

[0120] Unit: millimeters

[0121] Surface data

[0122]

[0123]

[0124] Aspherical data

[0125] Fourth surface

[0126] K=0.00000e+00A 4=7.33649e-07A 6=-1.66877e-09A 8=5.28772e-12

[0127] A10 = -5.05759e-15

[0128] Sixth Surface

[0129] K=0.00000e+00A 4=7.33649e-07A 6=-1.66877e-09A 8=5.28772e-12

[0130] A10 = -5.05759e-15

[0131] The Eighteenth Surface

[0132] K=0.00000e+00A 4=-5.74635e-04

[0133] The Nineteenth Surface

[0134] K=0.00000e+00A 4=5.49158e-05A 6=6.48873e-06

[0135] Various data

[0136]

[0137] Single lens data

[0138]

[0139] Table 1 below summarizes the various values ​​in the numerical examples.

[0140] Table 1

[0141] 1 14.81 14.0 0.945 2 14.20 13.1 0.923 3 14.20 14.2 1.000 4 14.20 15.3 1.077 5 13.34 11.0 0.825

[0142] Each of the examples above can provide a small and thin optical system with a wide viewing angle and high optical performance, as well as an observation device with such an optical system.

[0143] While this disclosure has been described with reference to exemplary embodiments, it should be understood that this disclosure is not limited to the disclosed exemplary embodiments. The scope of the appended claims should be given the broadest interpretation to cover all such modifications and equivalent structures and functions.

Claims

1. An optical system configured to form a magnified image of a display surface of an image display element, said optical system comprising, from the exit pupil side to the display surface side, a first semi-transmissive reflective surface and a second semi-transmissive reflective surface, in, The optical system has: In the first optical path, light from the display surface is transmitted through the second semi-transmissive reflective surface, reflected by the first semi-transmissive reflective surface, reflected again by the second semi-transmissive reflective surface, transmitted through the first semi-transmissive reflective surface, and guided to the exit pupil. In the second optical path, light from the exit pupil side is transmitted through the first semi-transparent reflective surface, then through the second semi-transparent reflective surface, and guided to the image sensor. The refractive region is positioned outside the optically effective region of the first optical path and within the optically effective region of the second optical path. In the second optical path, light from the exit pupil side is transmitted through the first semi-transparent reflective surface, through the second semi-transparent reflective surface, through the refractive region, and is guided to the image sensor. Wherein, the refractive region is a refractive surface, and The refracting surface is rotationally symmetrical with respect to the optical axis of the first optical path.

2. The optical system according to claim 1, wherein, The refractive surface is a plane.

3. The optical system of claim 1 further includes an optical element that is rotationally asymmetric and is deployed in the second optical path closer to the image sensor than the refractive surface.

4. The optical system according to claim 3, wherein, The effective optical surface of the optical element on the image sensor side is planar.

5. The optical system according to claim 3, wherein, The optical element is bonded to the refractive surface.

6. The optical system according to claim 1, wherein, The first semi-transmissive reflective surface is a plane.

7. The optical system according to claim 1, wherein, The first semi-transmissive reflective surface is a surface disposed on a polarization selective reflective polarization element.

8. The optical system of claim 1 further includes a circular polarization conversion element, the circular polarization conversion element being deployed closer to the display surface than the second semi-transmissive reflective surface.

9. The optical system according to claim 8, wherein, The circular polarization conversion element includes a linear polarizer and a quarter-wave plate.

10. The optical system according to claim 9, wherein, The linear polarizer is deployed within the first optical path.

11. The optical system according to claim 1, wherein, The optical system includes a single cemented lens.

12. The optical system according to claim 1, wherein, The following inequalities must be satisfied: 0.5 < Cx / Ltp < 1.5 Wherein, Ltp is the distance on the optical axis of the first optical path from the surface closest to the exit pupil to the second semi-transmissive reflective surface, and Cx is the distance on the optical axis of the first optical path from the surface closest to the exit pupil to the center of the image sensor.

13. The optical system according to any one of claims 1 to 12, further comprising: As an eyepiece optical system using the first optical path; as well as Imaging optical system using the second optical path.

14. An observation device, comprising: Image display elements; Image sensor; as well as The optical system according to any one of claims 1 to 13.

Images