Optical system and image display device

Abstract

To provide a small optical system which makes an observer feel less strange when the observer is observing a picture of an outside world.SOLUTION: The optical system includes: an imaging optical system (105) for guiding light from an object to an imaging element; and an eye optical system (102) for guiding the light from the display element to an observer. The imaging optical system is a coaxial optical system and the eye optical system is an eccentric optical system. The optical axis of the imaging optical system and the optical axis of the eye optical system are partially located on the same straight line. When the entrance pupil of the imaging optical system and the exit pupil of the eye optical system are distant by a distance D (mm) on the straight line, the conditional expression of 20≤D≤60 is established.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical system and to an image display device that allows a viewer to view a captured image and a displayed image superimposed on each other. [Background technology]

[0002] Head-mounted displays (HMDs) have been known as image display devices that provide mixed reality (MR) and augmented reality (AR). In an HMD, if the exit pupil position and optical axis of the eyepiece optical system are misaligned with the entrance pupil position and optical axis of the imaging optical system, the viewer will experience discomfort when viewing the displayed image.

[0003] Patent Document 1 discloses an HMD in which the optical axes of the imaging optical system and the eyepiece optical system are aligned and the entrance pupil position and exit pupil position are adjusted to reduce the viewer's sense of discomfort. Patent Document 2 discloses an HMD in which the imaging device is located on the opposite side of the image display element. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 3604979 [Patent Document 2] Special Publication No. 2017-524281 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the HMD disclosed in Patent Document 1 has components outside the imaging and display angles of view, making it difficult to reduce its size. Patent Document 2 does not provide any explanation about the configuration of the eyepiece optical system or the imaging and display angles of view that would enable the device to be reduced in size.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an optical system and an image display device that are compact yet capable of reducing the sense of discomfort felt by the viewer. [Means for solving the problem]

[0007] An optical system according to one aspect of the present invention is an optical system having an imaging optical system that guides light from an object to an imaging element and an eyepiece optical system that guides light from a display element to an observer, wherein the imaging optical system is a coaxial optical system and the eyepiece optical system is a decentered optical system. ,before The optical axis of the imaging optical system and a part of the optical axis of the eyepiece optical system are positioned on the same straight line. ,before The distance between the entrance pupil of the imaging optical system and the exit pupil of the eyepiece optical system on the straight line is D (mm). , the focal length of the eyepiece optical system is F (mm) When 20≦D≦60 10≦F≦18.6 The following condition is satisfied.

[0008] Other objects and features of the present invention will be described in the following embodiments. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an optical system and an image display device that are small in size and yet can reduce the sense of discomfort felt by the viewer. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is an explanatory diagram of an image display device according to a first embodiment. [Figure 2] FIG. 2 is a detailed explanatory diagram of the eyepiece optical system according to the first embodiment. [Figure 3] 1 is an external view of an image display device according to a first embodiment. [Figure 4] FIG. 10 is a detailed explanatory diagram of an eyepiece optical system according to a second embodiment. [Figure 5] FIG. 10 is a detailed explanatory diagram of an eyepiece optical system according to a third embodiment. [Figure 6]FIG. 10 is a detailed explanatory diagram of an eyepiece optical system according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0012] Video see-through head-mounted displays (HMDs) are image display devices (image observation devices) that seamlessly combine real and virtual spaces in real time to provide mixed reality (MR) and augmented reality (AR). HMDs use imaging optics and imaging elements to capture the external world (optical image) observed by the observer from their pupil position (exit pupil position of the eyepiece optical system), and then display a display image on the image display element by superimposing a computer graphics (CG) image on the captured image. This allows the observer to view the display image through the eyepiece optical system.

[0013] In such HMDs, if the exit pupil position and optical axis of the eyepiece optical system are misaligned with the entrance pupil position and optical axis of the imaging optical system, the viewer will experience a sense of discomfort when viewing the displayed image. It is also known that making the HMD smaller and lighter not only reduces the weight burden on the viewer, but also has a favorable effect on reducing motion sickness. Therefore, to improve the comfort of HMDs, it is necessary to make the HMD smaller and lighter, in addition to reducing the sense of discomfort mentioned above.

[0014] (First embodiment) First, an image display device (image display device) 100 according to a first embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 is an explanatory diagram of the image display device 100.

[0015] Reference numeral 101 denotes the eye of the observer (user). Reference numeral 102 denotes an eyepiece optical system (a decentered eyepiece optical system) comprising a prism (a free-form prism) and a mirror. Reference numeral 103 denotes an image display element (display element), which is a flat-panel image display element such as an organic EL display or a liquid crystal display. Reference numeral 104 denotes an imaging element. The image display element 103 displays an image generated using a signal from the imaging element 104. Reference numeral 105 denotes an imaging optical system (a coaxial imaging optical system). Note that the imaging element 104 and the imaging optical system 105 may each be separate structures or may be an integrated camera module.

[0016] The image display device 100 includes an optical system having an imaging optical system 105 that guides light from an object to an imaging element 104 and an eyepiece optical system 102 that guides light from the image display element 103 to a viewer, an image display element 103, and an imaging element 104. The imaging optical system 105 is a coaxial optical system, and the eyepiece optical system 102 is a decentered optical system. Parts of the optical axes of the imaging optical system 105 and the eyepiece optical system 102 are positioned on approximately the same straight line (a line including the optical axis of the imaging optical system 105 and a line including the optical axis of the eyepiece optical system 102 are approximately the same). The imaging element 104 and the imaging optical system 105 form an imaging system. The imaging element 104 and the eyepiece optical system 102 are arranged on a straight line including the optical axis of the imaging optical system 105.

[0017] The HMD of this embodiment is a video see-through type. Therefore, a display image is generated from an external image (captured image) formed on an image sensor 104 via an image sensor optical system 105, and the display image is displayed on an image display device 103, which can be observed via an eyepiece optical system 102. The eyepiece optical system 102 enlarges and projects the original image displayed on the image display device 103 as a virtual image, and guides it to the observer's eye 101.

[0018] E is the eye relief, which corresponds to the distance from the viewer's eye 101 to the eyepiece optical system 102. D is the distance from the exit pupil position of the viewer's eye 101 to the entrance pupil position of the light beam entering the imaging optical system 105 (i.e., the amount of shift (pupil shift) between the exit pupil position and the entrance pupil position). L is the thickness of the eyepiece optical system 102. The eye relief E, thickness L, and distance D are closely related to one another.

[0019] FIG. 2 is a detailed explanatory diagram of the eyepiece optical system 102 of this embodiment, showing the optical path including the cross section of the eyepiece optical system 102. The eyepiece optical system 102 has a focal length F1 of 18.6 mm and a display angle of view of 30.4° horizontally, 23° vertically, and 37.5° diagonally. The eyepiece optical system 102 of this embodiment is a prism in which the space between three optical surfaces 1021, 1022, and 1023 is filled with a medium having a refractive index nd = 1.53. 102S is the exit pupil of the eyepiece optical system 102. 1020 is the optical axis of the eyepiece optical system 102. The imaging optical system 105 is a rotationally symmetric coaxial optical system without bending, and its optical axis is defined in the same way as in a general optical system. In contrast, the eyepiece optical system 102 is a decentered optical system, and therefore requires a different definition of its optical axis than in a general optical system. Therefore, the ray of light traveling from the center of the exit pupil 102S toward the center of the observation range is defined as the central angle of view chief ray, and the axis including the line segment in space connecting the central angle of view chief ray between the eyepiece optical system 102 and the exit pupil 102S is defined as the optical axis 1020 of the eyepiece optical system 102.

[0020] The cross section in Figure 2 is a y-z cross section in a coordinate system in which the z-axis is parallel to the optical axis 1020, the y-axis is perpendicular to the z-axis on the cross section, and the x-axis is in the depth direction of the page. In this embodiment, the three optical surfaces 1021, 1022, and 1023 of the decentered prism that makes up the eyepiece optical system 102 are asymmetrical surfaces with plane-symmetric shapes, with the y-z cross section as the only plane of symmetry. As a result, even if the central angle of view chief ray is refracted or reflected, it remains on the y-z cross section, making it easier to define and measure the optical system.

[0021] Next, the optical path in the eyepiece optical system 102 will be described. Light from an image displayed on the display surface 1031 of the image display element 103 enters the eyepiece optical system 102 from optical surface 1023, is totally internally reflected by optical surface 1021, is reflected by optical reflecting surface 1022, which is coated with a reflective film, and is then transmitted through optical surface 1021 to be guided to exit pupil 102S. 1024 denotes a plane perpendicular to the optical axis 1020 that includes the intersection of a ray passing through the surface at the position closest to exit pupil 102S after total internal reflection or transmission at optical surface 1021, i.e., the minimum z position, among the effective ray beams reaching exit pupil 102S. 1025 denotes a plane perpendicular to the optical axis 1020 that includes a point at which the effective ray beams reaching exit pupil 102S from display surface 1031 pass through the maximum z position on any surface.

[0022] In this embodiment, exit pupil 102S is located 28 mm away from plane 1024, and has a pupil diameter of 5 mm. In this embodiment, it is assumed that the viewer's pupil is preferably positioned 10 mm away from the center of exit pupil 102S in the z-axis direction, i.e., eye relief E is 18 mm. However, the viewer's pupil does not have to be positioned at a position where eye relief E = 18 mm. For example, it may be positioned within a range of approximately 5 mm to 50 mm from plane 1024, preferably 5 mm to 30 mm (i.e., eye relief E (mm) should satisfy the condition 5≦E≦30).

[0023] Under these conditions, the distance D from the viewer's pupil to the entrance pupil of the imaging system is set to 20 mm to 60 mm. That is, the distance D (mm) between the entrance pupil of the imaging optical system 105 and the exit pupil of the eyepiece optical system 102 on the same straight line satisfies the condition: 20≦D≦60. If the distance from the viewer's pupil to the entrance pupil of the imaging system is greater than 60 mm, the difference between the observed image of the outside world when the viewer is wearing the HMD and when not is significant, creating a sense of discomfort. On the other hand, if the distance from the viewer's pupil to the entrance pupil of the imaging system is less than 20 mm, the eye relief becomes too short, causing a sense of oppression for the viewer, or the imaging system and eyepiece system become too thin, resulting in a narrow angle of view, a lack of realism, and reduced image quality. In this embodiment, the thickness of the eyepiece optical system 102 is determined as the distance between the two planes 1024 and 1025, and is set to within 14 mm, allowing the distance D from the viewer's pupil to be set to 20 mm to 60 mm.

[0024] Preferably, the distance D (mm) from the entrance pupil position of the imaging optical system 105 to the exit pupil position of the eyepiece optical system 102 on a line including the optical axis of the imaging optical system 105 is set to satisfy the condition 20≦D≦55. More preferably, the distance D (mm) is set to satisfy the condition 30≦D≦45.

[0025] Furthermore, when the eye relief E is set to 30 mm, the display angle of view of the observed image is 30.4° horizontally, 23° vertically, and 37.5° diagonally, so that the entire image is not visible, but rather some areas are obscured and cannot be seen, thereby reducing the thickness of the eyepiece optical system 102. This allows the eyepiece optical system 102 to be 14 mm thick. With the above configuration, the size of the eyepiece optical system 102 can be reduced.

[0026] Next, the appearance of the image display device 100 will be described with reference to FIG. 3. FIG. 3 is an external view of the image display device 100. The image display device 100 includes an HMD 111 having an eyepiece optical system 102, and an image processing unit 121. The image processing unit 121 generates a display image from an external image formed by the imaging optical system 105. Because the HMD 111 is a head-mounted image display device, it is preferably lightweight. Furthermore, if the eyepiece optical system 102 is small, the amount of discontinuity at the connection between video see-through observation and surrounding observation not via the HMD 111 is reduced, enabling seamless observation between video see-through observation and surrounding observation.

[0027] In the case of a video see-through HMD 111, an external image captured (acquired) by the imaging optical system 105 and the imaging element 104 is displayed on the image display element 103 and observed through the eyepiece optical system 102. For this reason, it is preferable that the entrance pupil position of the imaging optical system 105 and the exit pupil position of the eyepiece optical system 102 are close to each other. If the entrance pupil position of the imaging optical system 105 and the exit pupil position of the eyepiece optical system 102 are far from each other, when the observer wears the HMD 111, they will observe the external world from the entrance pupil position of the imaging optical system 105, which is located in front of them. As a result, there is a large difference between the image of the external world observed when the observer does not wear the HMD 111, which creates an uncomfortable feeling. Furthermore, even when performing seamless observation between video see-through observation and surrounding observation, it is preferable to reduce the difference in the pupils between the two to prevent discomfort from occurring between the video see-through observation and surrounding observation.

[0028] To miniaturize the imaging optical system 105 and reduce the amount of pupil shift, it is preferable to set the effective area of the imaging element 104 to 0.4 inches or less. If the effective area of the imaging element 104 is larger than 0.4 inches, the imaging optical system 105 will be enlarged to match the size of the imaging element 104, and the amount of pupil shift will increase. In addition, the HMD 111 will be enlarged, making it difficult to provide comfortable observation.

[0029] In the image display device 100 of this embodiment, the HMD 111 and the image processing unit 121 are separate entities, but they may be configured as an integrated unit by limiting the amount of image processing, such as image size and rendering, and by utilizing advances in semiconductors and improved performance. That is, the image processing unit 121 may be provided inside the HMD 111. Even in this case, it is preferable that the HMD 111 is small and lightweight.

[0030] In this embodiment, the imaging angle of view is larger than the display angle of view. Therefore, the image processing unit 121 extracts an angle of view corresponding to the display angle of view from the captured external image. Since the imaging angle of view is wider than the display angle of view, the positional accuracy of the imaging optical system 105 and the image sensor 104 can be relaxed.

[0031] In this embodiment, when observation is performed with the eye relief E in the preferred range of 5 mm to 30 mm, the distance D from the viewer's pupil to the entrance pupil of the imaging system is set to a range of 20 mm to 60 mm. Therefore, it is preferable to set the distance (eye relief E) from the most ocular surface 1024 of the eyepiece optical system 102 to the entrance pupil position of the imaging optical system 105 in the range of 5 mm to 30 mm. If this distance is less than 5 mm, the thickness of the imaging optical system 105 and the eyepiece optical system 102 becomes too thin, resulting in a narrow angle of view, a lack of realism, and a deterioration in image quality. On the other hand, if this distance exceeds 30 mm, there is a large difference between the external world observed through the HMD 111 and the external world observed without the HMD 111, creating an uncomfortable feeling. Furthermore, the HMD 11 becomes too large, making observation less comfortable.

[0032] In this embodiment, to achieve both the length of the eye relief E and a slimmer ocular optical system 102, it is preferable that the thickness L (mm) of the ocular optical system and the eye relief E (mm) satisfy the condition 0.6≦L / E≦1.3. If L / E is smaller than 0.6, the eye relief E becomes too long, which increases the outer diameter of the display lens and the size of the HMD 111, which is undesirable. On the other hand, if L / E is larger than 1.3, the eyepiece optical system 102 becomes thicker, which increases the size of the HMD 111, and the eye relief E becomes too short, which creates a feeling of oppression for the viewer and makes it impossible for a viewer who wears glasses to wear the HMD.

[0033] Furthermore, in this embodiment, when the maximum half angle of view of the eyepiece optical system 102 is θ, it is preferable to satisfy the condition 6≦E×tanθ≦20 in order to achieve both the length of the eye relief E and a wide angle of view of the eyepiece optical system 102. If E×tanθ is less than 6 mm, the eye relief E will be too short, causing a sense of oppression to the viewer, and viewers who wear eyeglasses will not be able to wear the eyepiece optical system 102, which is undesirable. Furthermore, the display angle of view of the eyepiece optical system 102 will be too narrow, making it impossible to observe a realistic, natural image. On the other hand, if E×tanθ is greater than 20 mm, the eye relief E will be too long, increasing the outer diameter of the display lens and the size of the HMD 111, which is undesirable.

[0034] (Second embodiment) Next, an eyepiece optical system 202 according to a second embodiment of the present invention will be described with reference to Fig. 4. Fig. 4 is a detailed explanatory diagram of the eyepiece optical system 202 according to this embodiment, showing the optical path including the cross section of the eyepiece optical system 202. The focal length F2 of the eyepiece optical system is 15.2 mm, and the display angle of view is 36.8° horizontally, 28° vertically, and 45.1° diagonally. The eyepiece optical system 202 according to this embodiment is a prism in which the space between three optical surfaces 2021, 2022, and 2023 is filled with a medium having a refractive index nd = 1.53. 202S denotes the exit pupil of the eyepiece optical system 202, and 2020 denotes the optical axis of the eyepiece optical system 202.

[0035] The cross section of Figure 4 is a y-z cross section in a coordinate system in which the z-axis is parallel to the optical axis 2020, the y-axis is perpendicular to the z-axis on the cross section, and the x-axis is in the depth direction of the page. In this embodiment, too, the three optical surfaces 2021, 2022, and 2023 of the decentered prism that constitutes the eyepiece optical system 202 are asymmetrical, plane-symmetric surfaces with the y-z cross section as their only plane of symmetry. This allows the central angle of view chief ray to exist on the y-z cross section even after refracting or reflecting, making it easier to define and measure the optical system.

[0036] Next, we will explain the optical path in the eyepiece optical system 202. Light from an image displayed on display surface 2031 of image display element 203 enters prism 202 from surface 2023, is totally internally reflected by surface 2021, is reflected by reflecting surface 2022 which is coated with a reflective film, passes through surface 2021, and is guided to exit pupil 202S.

[0037] Reference numeral 2024 denotes a plane perpendicular to the optical axis 2020, including the point at which the effective light beam reaching the exit pupil 202S, which is the closest to the pupil 202S through total internal reflection or transmission at the surface 2021, intersects with the surface, i.e., the light ray passing through at the minimum z position. Reference numeral 2025 denotes a plane perpendicular to the optical axis 2020, including the point at which the effective light beam reaching the exit pupil 202S from the display surface 2031 passes through the maximum z position on any surface. The exit pupil 202S is located 18 mm away from the plane 2024, and has a pupil diameter of 5 mm. In this embodiment, it is assumed that the center of the viewer's pupil is preferably located at the center of the exit pupil 202S, i.e., the eye relief is 18 mm.

[0038] When an observer with the center of the observer's pupil positioned at the center of the exit pupil 202S views the central field of view, the entire display field of view (36.8° horizontally, 28° vertically, 45.1° diagonally) is visible to the observer's eye 201. However, if the observer attempts to gaze at the periphery, vignetting occurs at the periphery. When the observer's pupil is positioned at the center of the exit pupil 202S and attempts to gaze at the periphery, vignetting occurs at a vignetting field of view of approximately 34.2° horizontally and 26° vertically, where the amount of light entering the pupil is approximately half that at the central field of view. Therefore, it is preferable to position the observer's pupil approximately 18 mm from the plane 2024. Under these conditions, it is preferable that the distance from the observer's pupil to the entrance pupil of the imaging system be 20 mm to 60 mm. Furthermore, in this embodiment, it is preferable that the distance from the observer's pupil to the entrance pupil of the imaging system be 20 mm to 45 mm. If the distance from the observer's pupil to the entrance pupil of the imaging system is greater than 60 mm, the difference in the observed image of the outside world when the HMD is worn and when it is not is large, resulting in a sense of discomfort.Furthermore, if the distance from the observer's pupil to the entrance pupil of the imaging system is less than 20 mm, the eye relief will be too short, causing a feeling of oppression for the observer, or the imaging system and eyepiece system will be too thin, resulting in a narrow angle of view, a loss of realism, and a deterioration in image quality.

[0039] In this embodiment, the thickness of the eyepiece optical system 202 is 12.1 mm when it is defined as the distance between the two planes 2024 and 2025. Therefore, it is preferable to set the distance from the viewer's pupil to the entrance pupil of the imaging system in the range of 20 mm to 60 mm. More preferably, it is set to the range of 20 mm to 45 mm.

[0040] Furthermore, even at an eye relief of 18 mm, if the observer rotates his or her eyeball to focus on the periphery, some peripheral vision will be blocked and invisible, thereby achieving a slimmer eyepiece optical system 202. In this way, the eyepiece optical system 202 achieves a thickness of 12.1 mm.

[0041] Furthermore, the above configuration reduces the size of the eyepiece optical system 202, suppressing the amount of discontinuity at the transition between video see-through observation and peripheral observation without an HMD, enabling seamless observation between video see-through observation and peripheral observation. In particular, the eyepiece optical system 202 is configured to more easily satisfy the preferable upper limit of 45 mm or less from the observer's pupil to the entrance pupil of the imaging system, making it less likely that discontinuity will occur at the transition between video see-through observation and peripheral observation without an HMD. In this embodiment, although some vignetting occurs around the periphery of the field of view when the eyeball is rotated, the observer can view the external world directly without using an HMD unless there is a component blocking light from the external world at that position.

[0042] In addition, by setting the eye relief to around 18 mm, sufficient eye relief is ensured even for observers wearing eyeglasses, enabling video see-through observation with little discomfort. Furthermore, this HMD allows observation at a wider angle than in the first embodiment.

[0043] (Third embodiment) Next, an eyepiece optical system 302 according to a third embodiment of the present invention will be described with reference to Fig. 5. Fig. 5 is a detailed explanatory diagram of the eyepiece optical system 302 according to this embodiment, showing the optical path including the cross section of the eyepiece optical system 302. The focal length F3 of the eyepiece optical system 302 is 15.7 mm, and the display angle of view is 35.5° horizontally, 27° vertically, and 43.6° diagonally. The eyepiece optical system 302 according to this embodiment is a prism in which the space between three optical surfaces 3021, 3022, and 3023 is filled with a medium having a refractive index nd = 1.53. 302S denotes the exit pupil of the eyepiece optical system 302, and 3020 denotes the optical axis of the eyepiece optical system 302.

[0044] The cross section of Figure 5 is a yz cross section in a coordinate system in which the z axis is parallel to the optical axis 3020, the y axis is perpendicular to the z axis on the cross section, and the x axis is in the depth direction of the page. In this embodiment, the three optical surfaces 3021, 3022, and 3023 of the decentered prism 302, which is the eyepiece optical system, are asymmetrical, plane-symmetric surfaces with the yz cross section as their only plane of symmetry. This allows the central angle of view chief ray to exist on the yz cross section even after refracting or reflecting, making it easier to define and measure the optical system.

[0045] Next, we will explain the optical path in the eyepiece optical system 302. Light from an image displayed on display surface 3031 of image display element 303 enters prism 302 from surface 3023, is totally internally reflected by surface 3021, is reflected by reflecting surface 3022 which is coated with a reflective film, passes through surface 3021, and is guided to exit pupil 302S.

[0046] Reference numeral 3024 denotes a plane perpendicular to the optical axis 3020, including the point at which the effective light beam reaching the pupil 302S, which is the closest to the pupil 302S through total internal reflection or transmission at surface 3021, intersects with the surface, i.e., the light ray passing through at the minimum z position. Reference numeral 3025 denotes a plane perpendicular to the optical axis 3020, including the point at which the effective light beam reaching the pupil 302S from the display surface 3031 passes through the maximum z position on any surface. The exit pupil 302S is located 20 mm away from the plane 3024, and has a pupil diameter of 5 mm. In this embodiment, it is assumed that the viewer's pupil is preferably positioned 10 mm off the center of the exit pupil 302S in the z-axis direction, i.e., the eye relief E is 10 mm.

[0047] However, the viewer's pupil is not necessarily positioned at a position where the eye relief E is 10 mm; it is preferable that the pupil be positioned approximately 5 mm to 20 mm from plane 3024. Under these conditions, it is preferable to set the distance D from the viewer's pupil to the entrance pupil of the imaging system to satisfy a range of 20 mm to 60 mm. If the distance D from the viewer's pupil to the entrance pupil of the imaging system is greater than 60 mm, the difference between the image of the outside world observed when wearing the HMD and when not wearing it will be significant, creating a sense of discomfort. On the other hand, if the distance D from the viewer's pupil to the entrance pupil of the imaging system is less than 20 mm, the eye relief will be too short, causing a feeling of oppression for the viewer, or the imaging system and eyepiece system will be too thin, resulting in a narrow angle of view, a loss of realism, and potentially degraded image quality.

[0048] In this embodiment, the thickness of the eyepiece optical system 202 is the distance between the two planes 3024 and 3025, and is set to 12.1 mm, and the distance from the viewer's pupil to the entrance pupil of the imaging system is preferably set in the range of 20 mm to 60 mm, and more preferably in the range of 20 mm to 45 mm.

[0049] Even at a position of 20 mm, which is the longest of the preferred eye relief range of 5 mm to 20 mm, when observing in the direction of the central field angle, the entire display field angle of the observed image is visible: 35.5° horizontally, 27° vertically, and 43.6° diagonally. However, when the observer rotates their eyeball to focus on the periphery, some areas are obscured and cannot be seen, thereby achieving a slimmer eyepiece optical system 302. As a result, the eyepiece optical system 302 of this embodiment achieves a thickness of 12.1 mm.

[0050] Furthermore, the above configuration reduces the size of the eyepiece optical system 302, suppressing the amount of discontinuity at the transition between video see-through observation and peripheral observation without an HMD, enabling seamless observation between video see-through observation and peripheral observation. In particular, the eyepiece optical system 302 is configured to easily satisfy the upper limit of 45 mm for the distance from the observer's pupil to the entrance pupil of the imaging system, making it less likely that discontinuity will occur at the transition between video see-through observation and peripheral observation without an HMD. In this embodiment, although some vignetting occurs around the periphery of the field of view when the eyeball is rotated, the observer can view the external world directly without using an HMD unless there is a component blocking light from the external world at that position.

[0051] Furthermore, by setting the eye relief to approximately 10 to 20 mm, an eye relief that is suitable for observers wearing eyeglasses is ensured, while enabling video see-through observation with little discomfort. Furthermore, the HMD of this embodiment allows observation at a wider angle than the first embodiment.

[0052] (Fourth embodiment) Next, an eyepiece optical system 402 according to a fourth embodiment of the present invention will be described with reference to Fig. 6. Fig. 6 is a detailed explanatory diagram of the eyepiece optical system 402 according to this embodiment, showing the optical path including the cross section of the eyepiece optical system 402. The focal length F1 of the eyepiece optical system 402 is 13.2 mm, and the display angle of view is 41.8° horizontally, 32° vertically, and 51.1° diagonally. The eyepiece optical system 402 according to this embodiment is a prism in which the space between three optical surfaces 4021, 4022, and 4023 is filled with a medium having a refractive index nd = 1.53. 402S denotes the exit pupil of the eyepiece optical system 402, and 4020 denotes the optical axis of the eyepiece optical system 402.

[0053] The cross section in Figure 6 is a y-z cross section in a coordinate system in which the z-axis is parallel to the optical axis 4020, the y-axis is perpendicular to the z-axis on the cross section, and the x-axis is in the depth direction of the page. In this embodiment, the three optical surfaces 4021, 4022, and 4023 of the decentered prism that constitutes the eyepiece optical system 402 are asymmetrical, plane-symmetric surfaces with the y-z cross section as their only plane of symmetry. This allows the central field chief ray to exist on the y-z cross section even after refracting or reflecting, making it easier to define and measure the optical system.

[0054] Next, we will explain the optical path in the eyepiece optical system 402. Light from an image displayed on a display surface 4031 of the image display element 403 enters the prism 402 from surface 4023, is totally internally reflected by surface 4021, is reflected by a reflecting surface 4022 that is coated with a reflective film, passes through surface 4021, and is guided to the exit pupil 402S.

[0055] Reference numeral 4024 denotes a plane perpendicular to the optical axis 4020, which includes the point at which the effective light beam reaching the exit pupil 402S, through total internal reflection or transmission at the surface 4021, intersects with the surface at the z minimum position. Reference numeral 4025 denotes a plane perpendicular to the optical axis 4020, which includes the point at which the effective light beam reaching the exit pupil 402S from the display surface 4031 passes through the z maximum position on any of the surfaces. The exit pupil 402S is located 10 mm away from the plane 4024, and has a pupil diameter of 5 mm. In this embodiment, it is assumed that the center of the viewer's pupil is preferably positioned at the center of the exit pupil 402S, i.e., the eye relief E is 10 mm.

[0056] When an observer, with the center of the observer's pupil positioned at the center of the exit pupil 202S, views the central field of view, the entire display field of view (41.8° horizontally, 32° vertically, 51.1° diagonally) is visible to the observer's eye 201. However, when the observer attempts to gaze at the periphery, vignetting occurs in the periphery. When the observer's pupil is positioned at the center of the exit pupil 202S and attempts to gaze at the periphery, vignetting occurs at a vignetting field of view of approximately 36.6° horizontally and 28° vertically, where the amount of light entering the pupil is approximately half that at the central field of view. Therefore, it is preferable that the observer's pupil be positioned approximately 10 mm away from the plane 4024. Under these conditions, it is preferable to set the distance from the observer's pupil to the entrance pupil of the imaging system in the range of 20 mm to 60 mm. More preferably, the distance from the observer's pupil to the entrance pupil of the imaging system is set in the range of 20 mm to 45 mm. If the distance from the observer's pupil to the entrance pupil of the imaging system is greater than 60 mm, the difference between the image of the outside world observed when wearing an HMD and when not is significant, creating a sense of discomfort. On the other hand, if the distance from the observer's pupil to the entrance pupil of the imaging system is less than 20 mm, the eye relief will be too short, causing a feeling of oppression for the observer, or the imaging system and eyepiece system will be too thin, resulting in a narrow angle of view, a loss of realism, and a deterioration in image quality.

[0057] In this embodiment, the thickness of the eyepiece optical system 402, when taken as the distance between the two planes 4024 and 4025, is 10.6 mm. Therefore, the distance from the viewer's pupil to the entrance pupil of the imaging system can be set in the range of 20 mm to 60 mm, preferably 20 mm to 45 mm. Furthermore, even when the eye relief E is 10 mm, if the viewer rotates their eyeball to focus on the periphery, some vignetting occurs in the periphery, thereby achieving a thin and wide-angle eyepiece optical system 402. In this way, the thickness of the eyepiece optical system 402 is 10.6 mm.

[0058] With the above configuration, the size of the eyepiece optical system 402 can be reduced, suppressing the amount of discontinuity at the transition between video see-through observation and peripheral observation without an HMD, enabling seamless observation between video see-through observation and peripheral observation. In particular, the eyepiece optical system 402 is configured to more easily satisfy the preferable upper limit of 45 mm or less from the observer's pupil to the entrance pupil of the imaging system, making it less likely that discontinuity will occur at the transition between video see-through observation and peripheral observation without an HMD. In this embodiment, although some vignetting occurs around the periphery of the field of view when the eyeball is rotated, the observer can view the external world directly without using an HMD unless there is a component blocking light from the external world at that position.

[0059] Furthermore, by setting the eye relief E to approximately 10 mm, the eye relief is insufficient for observers wearing eyeglasses, but video see-through observation is possible with less discomfort. Furthermore, the HMD of this embodiment allows observation at a wider angle than in the first embodiment. Furthermore, in this embodiment, the eye relief is short, making observation with eyeglasses difficult, but diopter adjustment is possible by moving the display surface 4031 in the direction of the central angle of view chief ray before it is incident on the surface 4023.

[0060] In each embodiment, it is preferable that the focal length F (mm) of the eyepiece optical system satisfies the condition 10≦F≦20. In each embodiment, the eyepiece optical system does not form an intermediate image on the optical path from the image display element to the viewer. In each embodiment, a portion of the light from the image display element may be blocked (vignetted) at the position of the eye relief E of the eyepiece optical system.

[0061] According to each embodiment, it is possible to provide an optical system and an image display device that are small in size and yet can reduce the sense of discomfort felt by the viewer.

[0062] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0063] 102, 202, 302, 402 Eye Optics Department 105 Department of Imaging Optics

Claims

1. An optical system having an imaging optical system that guides light from an object to an imaging element, and an eyepiece optical system that guides light from a display element to an observer, the imaging optical system is a coaxial optical system, and the eyepiece optical system is a decentered optical system; the optical axis of the imaging optical system and a part of the optical axis of the eyepiece optical system are positioned on the same straight line, When the distance on the straight line between the entrance pupil of the imaging optical system and the exit pupil of the eyepiece optical system is D (mm), and the focal length of the eyepiece optical system is F (mm), 20≦D≦60 10≦F≦18.6 An optical system characterized by satisfying the following conditional expression:

2. When the eye relief of the eyepiece optical system is E (mm), 5≦E≦30 2. The optical system according to claim 1, wherein the following condition is satisfied:

3. When the thickness of the eyepiece optical system on the straight line is L (mm) and the eye relief of the eyepiece optical system is E (mm), 0.6≦L / E≦1.3 3. The optical system according to claim 1, wherein the following condition is satisfied:

4. When the eye relief of the eyepiece optical system is E (mm) and the maximum half angle of view of the eyepiece optical system is θ, 6≦E×tanθ≦20 4. The optical system according to claim 1, wherein the following condition is satisfied:

5. 5. The optical system according to claim 1, wherein the eyepiece optical system does not form an intermediate image on the optical path from the display element to the viewer.

6. An image display device comprising: the optical system according to claim 1 ; the imaging element; and the display element.

7. 7. The image display device according to claim 6, further comprising an image processing unit that generates a display image to be displayed on the display element using the captured image acquired by the image sensor.

8. an imaging angle of view of the imaging optical system is larger than a display angle of view of the eyepiece optical system; The image display device according to claim 7 , wherein the image processing unit generates the display image by cutting out a range of an angle of view corresponding to the display angle of view in the captured image.

9. 9. The image display device according to claim 6, wherein the effective area of the image pickup element is 0.4 inches or less.

10. 10. The image display device according to claim 6, wherein the image pickup device and the eyepiece optical system are arranged on the straight line.

Images