Head-up display

Abstract

To provide a head-up display capable of downsizing.SOLUTION: The head-up display includes: a device for emitting light beams for converting an original image into a projected image; and a projection optical system that forms the projected image from the original image and projects the projected image to an observer as a virtual image. The projection optical system includes: a first lens that has a refractive surface that receives the light beam emitted from the device; a second mirror that reflects the light downwards; and a third mirror that reflects the light reflected by the second mirror onto a reflective member as the projected image.The first lens, the second mirror, and the third mirror are arranged in that order in an optical path to the reflective member. The projection optical system has a function that uses the light beams emitted from the device to form an intermediate image from the original image below the second mirror, and forms the projected image from the intermediate image.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present disclosure relates to head-up displays. [Background technology]

[0002] Patent Document 1 discloses a head-up display that projects a display image onto a windshield. This head-up display includes a display device having a display surface that displays an image on the display surface, a concave mirror, and a lens with a light-condensing effect that is positioned between the concave mirror and the display surface. The head-up display also includes a first optical system that focuses light rays emitted from the display surface via the lens and the concave mirror to form an enlarged intermediate image. The head-up display also includes a second optical system that projects the intermediate image onto the windshield. The intermediate image formed by the first optical system is larger than the display image displayed on the display surface of the display device. This allows for the miniaturization of the first and second optical systems. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2017-120388 Summary of the Invention

[0004] The present disclosure provides a head-up display that can be made compact.

[0005] The head-up display of the present disclosure projects a projection image formed from an original image onto a transparent reflecting member, allowing an observer to view a virtual image. The head-up display includes a device that emits light rays that convert the original image into a projection image, and a projection optical system that forms a projection image from the original image and projects the projection image as a virtual image to the observer. The projection optical system includes a first lens having a refractive surface that receives the light rays emitted from the device, a second mirror that reflects the light rays downward, and a third mirror that reflects the light reflected by the second mirror onto the reflecting member as a projection image. The first lens, second mirror, and third mirror are arranged in this order along the optical path to the reflecting member. The projection optical system functions to form an intermediate image of the original image below the second mirror using the light rays emitted from the device, and to form a projection image from the intermediate image.

[0006] The head-up display of the present disclosure presents a virtual image with little distortion and can be made compact. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram illustrating a vehicle equipped with a head-up display according to the first embodiment. [Figure 2] FIG. 2 is a schematic diagram showing the configuration of the head-up display according to the first embodiment. [Figure 3] FIG. 3 is a schematic diagram for explaining the telephoto arrangement according to the first embodiment. [Figure 4] FIG. 4 is a schematic diagram showing the configuration of the relay optical system according to the first embodiment. [Figure 5] FIG. 5 is a schematic diagram showing the configuration of a head-up display according to the second embodiment. [Figure 6] FIG. 6 is a schematic diagram showing the configuration of a head-up display according to the third embodiment. [Figure 7] FIG. 7 is a diagram illustrating the operation of the head-up display according to the fourth embodiment. [Figure 8] FIG. 8 is a schematic diagram showing the configuration of a head-up display according to the fifth embodiment. [Figure 9] FIG. 9 is a diagram illustrating the operation of the head-up display according to the sixth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. However, more detailed explanation than necessary may be omitted. For example, detailed explanation of well-known matters or redundant explanation of substantially the same configuration may be omitted. This is to avoid unnecessary redundancy in the following explanation and to facilitate understanding by those skilled in the art.

[0009] The inventor(s) provide the accompanying drawings and the following description to enable those skilled in the art to fully understand the present disclosure, and do not intend for them to limit the subject matter described in the claims.

[0010] (Embodiment 1) Hereinafter, the first embodiment will be described with reference to FIGS.

[0011] [1-1.Configuration] [1-1-1. Overall structure of head-up display] Specific embodiments and examples of the head-up display 100 of the present disclosure will be described below with reference to the drawings.

[0012] Fig. 1 is a diagram showing a cross section of a vehicle 200 equipped with a head-up display 100 according to the present disclosure. As shown in Fig. 1, the head-up display 100 is disposed inside a dashboard 210 below a windshield 220 of the vehicle 200. An observer D recognizes an image projected from the head-up display 100 as a virtual image I.

[0013] Fig. 2 is a schematic diagram showing the configuration of the head-up display 100 according to this embodiment. Fig. 3 is a schematic diagram for explaining the configuration of the head-up display 100 according to this embodiment.

[0014] As shown in FIG. 2, the head-up display 100 includes a display device 110 and a projection optical system 140. The head-up display 100 projects an image displayed by the display device 110 onto a windshield 220. The projected light is reflected by the windshield 220 and guided to a viewpoint region 300 of an observer D. In this way, the head-up display 100 allows the observer D to view a virtual image I. Here, the viewpoint is the principal point when the eyes of the observer D are considered to be lenses. The viewpoint region 300 is an area where the viewpoint of the observer D is located, where the virtual image I can be viewed without any loss.

[0015] Here, in the present disclosure, "forward" refers to the direction toward the windshield 220 of the vehicle 200 as viewed from the observer D. "Backward" refers to the opposite direction from "forward." "Downward" refers to the direction toward the ground on which the vehicle 200 is traveling. "Upward" refers to the opposite direction from "downward." "Inward" refers to the passenger seat side as viewed from the observer D in the driver's seat. "Outward" refers to the opposite direction from "inward." Furthermore, the viewpoint area 300 is an area in which the observer D can view the virtual image I without any loss.

[0016] Here, as shown in FIG. 2 , of the light rays emitted from the display device 110, a light ray that reaches the viewpoint region 300 is referred to as a light ray L. Furthermore, of the light rays emitted from the display device 110, a light ray that passes through the center of the virtual image I and reaches the center of the viewpoint region 300 is referred to as a reference light ray Lc. That is, when viewed from the observer D, the reference light ray Lc corresponds to the optical path from the center of the virtual image I to the viewpoint of the observer D. The reference light ray Lc visually recognized by the observer D actually reaches the observer D from the display device 110 via the optical system. Therefore, the light ray that corresponds to the reference light ray Lc emitted from the center of the virtual image I and travels from the display device 110 to the observer D is also referred to as the reference light ray Lc. Furthermore, the optical paths corresponding to these light rays are also similarly referred to as the reference light ray Lc. However, it is assumed that the viewpoint of the observer D is at the center of the viewpoint region 300.

[0017] The display device 110 displays a display image on a diffusing surface or the like under the control of a control unit such as a CPU (not shown). The display device 110 may be, for example, a backlit liquid crystal display (LCD), an organic light-emitting diode (OLED), or a plasma display. Alternatively, the display device 110 may generate an image using a screen that diffuses or reflects light, a projector, or a scanning laser. The display device 110 may display various information such as road navigation guidance, the distance to the vehicle ahead, the remaining battery level of the vehicle, and the current vehicle speed. The display device 110 may electronically distort the image in advance depending on distortions occurring in the projection optical system 130 or the windshield 220, or the position of the viewer D captured by a camera (not shown). This allows the viewer D to view a good virtual image I. The display device 110 may also shift display pixels of multiple wavelengths in advance for each display position depending on chromatic aberration occurring in the projection optical system 130. This allows the viewer D to view a good virtual image I.

[0018] The projection optical system 140 includes a relay optical system 120 and a projection optical system 130. The relay optical system 120 includes a second lens 121, a first mirror 122 serving as a second optical element, a first lens 123, and a second mirror 124 serving as a first optical element. The relay optical system 120 focuses light rays emitted from the display device 110 to form an intermediate image M, which is an enlarged version of the displayed image. The intermediate image M is enlarged more than the displayed image displayed on the screen of the display device 110. In other words, even if the displayed image displayed on the screen of the display device 110 is small, a large intermediate image M can be obtained. This allows the screen size of the display device 110 to be reduced. Furthermore, because the intermediate image M is large, the magnification of the projection optical system 130 can be reduced. This allows the positive power of the third mirror 125 of the projection optical system 130 to be weakened, thereby suppressing image distortion.

[0019] The intermediate image M does not need to be formed as a good point at the intermediate image position, and spherical aberration, coma, curvature of field, and astigmatism may occur.

[0020] The projection optical system 130 includes a third mirror 125. The projection optical system 130 reflects the intermediate image M formed by the relay optical system 120 via the third mirror 125. As a result, the projection optical system 130 projects the intermediate image M onto the windshield 220. Note that the intermediate image M is an aerial image formed in the air, and is not formed on a diffusely reflecting projection surface. The third mirror 125 is disposed on the optical path from the intermediate image M to the windshield 220.

[0021] [1-1-2. Arrangement of the projection optical system, relay optical system, and display device] As shown in Fig. 2, the second lens 121 is located further forward of the vehicle 200 than the display device 110. As shown in Fig. 2, the second lens 121 is disposed tilted counterclockwise with respect to the reference light ray Lc when viewed in the XZ plane in Fig. 2. This makes it possible to prevent stray light caused by external light entering the housing and being reflected by the display surface of the display device 110 or the first mirror 122.

[0022] Second lens 121 is a free-form lens with different curvatures in the X-axis and Y-axis directions. The surface of second lens 121 facing display device 110 (incident surface) has a shape in which the plane faces display device 110 in the X-axis and Y-axis directions. The surface of second lens 121 facing first mirror 122 (exit surface) has a convex shape that is convex toward first mirror 122 in the X-axis and Y-axis directions.

[0023] First mirror 122 is located further forward of vehicle 200 than second lens 121. First mirror 122 collects light rays emitted from second lens 121 and reflects them toward first lens 123. The reflective surface of first mirror 122 is disposed eccentrically so as to reflect the image displayed on display device 110 in a direction in which it is reflected on second mirror 124. Here, the reflective surface of first mirror 122 has a concave shape. That is, first mirror 122 magnifies the light incident from second lens 121 and projects it onto first lens 123. Furthermore, first mirror 122 has a free-form surface shape. This is in order to correct distortion of the virtual image caused by reflection.

[0024] As shown in FIG. 2, the first lens 123 is located further rearward of the vehicle 200 than the first mirror 122. As shown in FIG. 2, the first lens 123 is disposed tilted clockwise with respect to the reference light ray Lc when viewed in the XZ plane of FIG. 2. The tilt angle of the first lens 123 with respect to the reference light ray Lc is, for example, between 15 degrees and 30 degrees. This makes it possible to prevent stray light caused by external light entering the housing and being reflected by the first mirror 122 or the second mirror 124.

[0025] Furthermore, first lens 123 is a free-form lens with different curvatures in the X-axis and Y-axis directions. The surface of first lens 123 on the first mirror 122 side (incident surface) has a convex shape that is convex toward first mirror 122 in the X-axis and Y-axis directions. Furthermore, the surface of first lens 123 on the second mirror 124 side (exit surface) has a shape that faces a flat surface toward display device 110 in the X-axis and Y-axis directions.

[0026] The second mirror 124 is located further rearward of the vehicle 200 than the first lens 123. The second mirror 124 diverges the light rays emitted from the first lens 123 and forms an intermediate image M, which is an enlarged version of the displayed image, on the optical path between the second mirror 124 and the third mirror 125. The reflective surface of the second mirror 124 is disposed decentered so as to enlarge the displayed image projected by the first lens 123 and form the intermediate image M on the optical path between the second mirror 124 and the third mirror 125. Here, the reflective surface of the second mirror 124 has a convex shape. The second mirror 124 has a free-form shape. This is to correct distortion of the virtual image caused by reflection.

[0027] The projection optical system 130 includes a third mirror 125 as a third optical element. The third mirror 125 is located further forward of the vehicle 200 than the second mirror 124. The third mirror 125 collects the light rays diverged by the second mirror 124 and projects an intermediate image M onto the windshield 220. The reflective surface of the third mirror 125 is disposed eccentrically so as to project the intermediate image M onto the windshield 220. Here, the reflective surface of the third mirror 125 has a concave shape. The third mirror 125 has a free-form surface shape. This is to correct distortion of the virtual image caused by reflection.

[0028] In the projection optical system 140 of this embodiment, a first mirror 122, a first lens 123 having a converging effect, and a second mirror 124 as a first optical element having a diverging effect and forming an intermediate image M are arranged in this order on the optical path from the display device 110. By arranging the first lens 123 and the second mirror 124 that forms the intermediate image M in this order on the optical path, the intermediate image M can be formed at a position close to the exit side of the first lens 123. As a result, the first lens 123 itself can be made smaller, and the head-up display 100 can be made smaller as well.

[0029] Furthermore, in the relay optical system 120 of this embodiment, a first lens 123 having positive power and a second mirror 124 having negative power are arranged from the display device 110 toward the intermediate image M. That is, the relay optical system 120 has a so-called telephoto arrangement. By adopting this telephoto arrangement, the first lens 123 enhances the negative power of the second mirror 124, and the second mirror 124 enhances the positive power of the first lens 123. That is, the first lens 123 and the second mirror 124 enhance each other's power. As a result, the overall length of the relay optical system 120 can be shortened, and the head-up display 100 can be made more compact.

[0030] Fig. 3 is a diagram for explaining the effect of the telephoto arrangement. In Fig. 3, for ease of understanding, the relay optical system 120 and the projection optical system 130 are arranged on a straight line. As can be seen from Fig. 3, compared to the comparative example shown in Fig. 3A which does not have the first lens 123, in this embodiment shown in Fig. 3B in which the first lens 123 and the second mirror 124 are arranged in a telephoto arrangement, the overall length of the relay optical system 120 is shorter.

[0031] Furthermore, the light rays that form intermediate image M are narrowed near second mirror 124, which has negative power and forms intermediate image M. By arranging first lens 123 with positive power near second mirror 124 with such negative power to achieve a telephoto arrangement, first lens 123 itself can be made smaller.

[0032] In this embodiment, as shown in FIG. 4, the incident surface and the exit surface of second lens 121 are inclined counterclockwise with respect to reference ray Lc in the XZ plane view of FIG. 4. Furthermore, the incident surface and the exit surface of first lens 123 are inclined clockwise with respect to reference ray Lc in the XZ plane view of FIG. 4. As a result, external light reflected by first lens 123 is reflected upward from first mirror 122, and external light reflected by second lens 121 is reflected downward from first mirror 122. In other words, external light can be prevented from entering viewpoint area 300. Here, it is desirable that the inclination of second lens 121 and first lens 123 with respect to reference ray Lc is an angle such that when external light incident along reference ray Lc is reflected by the incident surface or the exit surface, the reflected light does not enter first mirror 122. More preferably, the tilt is set at an angle such that when external light incident on second lens 121 or first lens 123 from first mirror 122 is reflected on the entrance surface or exit surface of second lens 121 or first lens 123, the reflected light does not enter first mirror 122. Note that when second lens 121 and first lens 123 are tilted with respect to reference ray Lc, the points on the optical refractive surfaces of second lens 121 and first lens 123 where the reference ray Lc intersects are not horizontal with respect to a plane perpendicular to the reference ray Lc.

[0033] In this embodiment, the second lens 121 has a wedge shape with a lens thickness that decreases downward relative to the reference light ray Lc. The first lens 123 has a wedge shape with a lens thickness that decreases upward relative to the reference light ray Lc. As described above, when the second lens 121 is tilted with respect to the reference light ray Lc, if the exit surface of the second lens 121 has a convex shape symmetrical with respect to the reference light ray Lc, the optical path lengths of the light rays that pass through the upper side of the second lens 121 relative to the reference light ray Lc and the light path lengths of the light rays that pass through the lower side are different. Similarly, when the first lens 123 is tilted with respect to the reference light ray Lc, if the entrance surface of the first lens 123 has a convex shape symmetrical with respect to the reference light ray Lc, the optical path lengths of the light rays that pass through the upper side of the first lens 123 relative to the reference light ray Lc are different from the optical path lengths of the light rays that pass through the lower side.

[0034] Therefore, in this embodiment, the second lens 121 has a wedge shape in which the lens thickness decreases toward the lower side with respect to the reference light ray Lc. The first lens 123 also has a wedge shape in which the lens thickness decreases toward the upper side with respect to the reference light ray Lc. With this configuration, a light ray emitted from the display device 110 and transmitted through the upper side of the second lens 121 with respect to the reference light ray Lc (i.e., a portion of the second lens 121 where the lens thickness is thick) is reflected by the first mirror 122. The reflected light ray then transmits through the upper side of the first lens 123 with respect to the reference light ray Lc (i.e., a portion of the first lens 123 where the lens thickness is thin). The light ray emitted from the display device 110 and transmitted through the lower side of the second lens 121 with respect to the reference light ray Lc (i.e., a portion of the second lens 121 where the lens thickness is thin) is reflected by the first mirror 122. The reflected light ray then passes through the lower side of first lens 123 relative to reference light ray Lc (i.e., the thicker portion of first lens 123). In this way, the optical path lengths of the light rays passing through second lens 121 and first lens 123 can be adjusted to make the optical path lengths of the light rays uniform regardless of the portions of second lens 121 and first lens 123 through which they pass.

[0035] In this embodiment, the exit surface of second lens 121 is provided facing downward relative to the entrance surface. That is, the shape of second lens 121 in the Y-axis direction is wedge-shaped. By making the cross-sectional shape of second lens 121 along the Y-axis direction wedge-shaped, the optical path length of light passing above second lens 121 is longer than the optical path length of light passing below second lens 121. That is, the optical path length of the image light emitted from display device 110 until it reaches first mirror 122 can be changed depending on the position in the Y-axis direction. This makes it possible to satisfactorily correct decentered curvature of field occurring in first mirror 122.

[0036] [1-2. Effects, etc.] A head-up display 100 as an example of a head-up display according to the first embodiment is a head-up display that projects an image onto a windshield 220 (an example of a transmissive reflecting member) to allow an observer D to view a virtual image I. The head-up display 100 includes a display device 110 as an example of a display device, and a projection optical system 140. The display device 110 displays an image. The projection optical system 140 functions to form the image displayed by the display device 110 as an intermediate image M. A first lens 123 included in the projection optical system 140 is disposed at an angle with respect to a reference light ray Lc. Therefore, even when external light enters the projection optical system 140, stray light caused by the external light being reflected by the first lens 123 or the like can be suppressed. The projection optical system 140 also includes, in this order along the optical path from the display device 110, the first lens 123 having a converging effect and a second mirror 124 as an example of a first optical element having a diverging effect. As described above, in the head-up display 100 according to the first embodiment, a telephoto arrangement is achieved in which the first lens 123 having positive power is arranged before the second mirror 124 having negative power and forming the intermediate image M in the order of the optical path from the display device 110. Therefore, by shortening the overall length of the relay optical system 120 and reducing the size of the first lens 123 itself, the head-up display 100 can be made smaller.

[0037] The second mirror 124 is used as an example of the first optical element according to the embodiment 1. Therefore, it is possible to enlarge the image displayed on the small display device 110 to create an intermediate image M, and further enlarge the intermediate image M and project it onto the observer D.

[0038] In the head-up display 100 according to the first embodiment, at least one surface of the first lens 123 has a free-form surface shape. Therefore, in an imaging optical system such as the head-up display 100, it is possible to suppress reflection of external light and achieve good optical characteristics.

[0039] In the head-up display 100 according to the first embodiment, the first lens 123 has a wedge shape. Therefore, even if the first lens 123 is tilted with respect to the reference light ray Lc, the optical path length of the light ray passing through the first lens 123 can be adjusted.

[0040] The head-up display 100 according to the first embodiment includes a first mirror 122 as an example of a second optical element and a second lens 121. The first mirror 122 is disposed between the display device 110 and the first lens 123. The second lens 121 is disposed between the display device 110 and the first mirror 122. The second lens 121 has a wedge shape, and at least one surface thereof has a free-form curved surface shape. Furthermore, in the head-up display 100 according to the first embodiment, the first lens 123 and the second lens 121 are disposed such that a light ray passing through a portion where one lens is thin passes through a portion where the other lens is thick, and a light ray passing through a portion where one lens is thick passes through a portion where the other lens is thin. Therefore, even when the first lens 123 and the second lens 121 are tilted with respect to the reference light ray Lc, the optical path lengths of the light rays passing through the first lens 123 and the second lens 121 can be made uniform.

[0041] In the head-up display 100 according to the first embodiment, the intermediate image M is an aerial image formed in the air on the optical path from the display device 110 to the virtual image I. Therefore, without adding a component for forming the intermediate image M, it is possible to enlarge the image displayed on the small display device 110 to form the intermediate image M, and further enlarge the intermediate image M and project it onto the observer D.

[0042] Vehicle 200, which is an example of a moving object according to the first embodiment, includes head-up display 100 and windshield 220 as a transparent reflecting member. As a result, observer D driving vehicle 200 can visually recognize the image projected on windshield 220 as a virtual image I.

[0043] (Embodiment 2) Next, a second embodiment will be described with reference to FIG.

[0044] [2-1.Configuration] Fig. 5 is a schematic diagram illustrating an optical path for explaining a head-up display 100 according to embodiment 2. As shown in Fig. 5, the head-up display 100 according to this embodiment includes a third lens 126 in which a first lens portion 126a and a second lens portion 126b, which correspond to the first lens and the second lens in embodiment 1, are integrally formed.

[0045] As shown in Fig. 5, third lens 126 is located further forward of vehicle 200 than display device 110 and second mirror 124. As shown in Fig. 5, the surface of third lens 126 facing first mirror 122 has a convex shape that is convex toward first mirror 122 in the X-axis direction and the Y-axis direction. Also, as shown in Fig. 5, the surface of third lens 126 facing display device 110 and second mirror 124 has a flat shape with the flat surface facing display device 110 and second mirror 124. Third lens 126 is a free-form lens in which the curvature of the convex surface differs in the X-axis direction and the Y-axis direction.

[0046] In the optical path from display device 110 to first mirror 122, the flat surface of second lens unit 126b is the incident surface, and the convex surface is the exit surface. In second lens unit 126b, the incident surface and the exit surface are tilted counterclockwise with respect to reference light ray Lc in the XZ plane view shown in FIG. 5. This makes it possible to prevent stray light caused by external light entering the housing and being reflected by the display surface of display device 110 and first mirror 122.

[0047] In the optical path from first mirror 122 to second mirror 124, the flat surface of first lens unit 126a is the emission surface, and the convex surface is the incidence surface. First lens unit 126a is tilted clockwise with respect to reference light ray Lc in the XZ plane view shown in FIG. 5. This makes it possible to prevent stray light caused by external light entering the housing and being reflected by the display surface of display device 110 and first mirror 122.

[0048] In addition, in the relay optical system 120 of this embodiment, a first lens unit 126a having positive power and a second mirror 124 having negative power are arranged from the display device 110 toward the intermediate image M. That is, the relay optical system 120 has a so-called telephoto arrangement. With this telephoto arrangement, the first lens unit 126a enhances the negative power of the second mirror 124, and the second mirror 124 enhances the positive power of the first lens unit 126a. That is, the first lens unit 126a and the second mirror 124 enhance each other's power. As a result, the overall length of the relay optical system 120 can be shortened, and the head-up display 100 can be made more compact.

[0049] As described above, in this embodiment, first lens unit 126a is disposed between first mirror 122 as the second optical element and third mirror 125 that projects intermediate image M. In particular, in the order of the optical path from display device 110, third lens 126 having positive power is disposed before second mirror 124 as the first optical element that has negative power and forms intermediate image M. Therefore, by shortening the overall length of relay optical system 120 and reducing the size of first lens unit 126a itself, it is possible to reduce the size of head-up display 100.

[0050] In the present embodiment, third lens 126 is a lens formed by integrating first lens portion 126a and second lens portion 126b, which correspond to second lens 121 and first lens 123 in the first embodiment. First lens portion 126a and second lens portion 126b have a wedge shape in which the lens thickness decreases from the center of third lens 126 toward the ends. When third lens 126 is tilted with respect to reference ray Lc as described above, in the optical path from display device 110 to first mirror 122, the optical path length of a light ray passing above second lens portion 126b relative to reference ray Lc differs from the optical path length of a light ray passing below second lens portion 126b. Similarly, in the optical path from first mirror 122 to second mirror 124, the optical path length of a light ray passing above second lens portion 126b relative to reference ray Lc differs from the optical path length of a light ray passing below second lens portion 126b.

[0051] Therefore, in the present embodiment, second lens portion 126b has a wedge shape in which the lens thickness decreases downward with respect to reference light ray Lc, and first lens portion 126a has a wedge shape in which the lens thickness decreases upward with respect to reference light ray Lc. With this configuration, a light ray that is emitted from display device 110 and passes through the upper side of second lens portion 126b with respect to reference light ray Lc (i.e., a portion of second lens portion 126b where the lens thickness is thick) is reflected by first mirror 122. Then, the reflected light ray passes through the upper side of first lens portion 126a with respect to reference light ray Lc (i.e., a portion of first lens portion 126a where the lens thickness is thin).

[0052] Furthermore, the light beam emitted from display device 110 and transmitted through the lower side of second lens portion 126b relative to reference light beam Lc (i.e., the portion of second lens portion 126b where the lens thickness is thin) is reflected by first mirror 122. Then, the reflected light beam is transmitted through first lens portion 126a relative to reference light beam Lc (i.e., the portion of first lens portion 126a where the lens thickness is thick).

[0053] In this embodiment, the optical path length of the light beam passing through the second lens portion 126b and the first lens portion 126a of the third lens 126 can be adjusted in this manner, thereby making the optical path length of the light beam uniform regardless of the location where it passes through the third lens 126.

[0054] Here, it is desirable that the inclination of third lens 126 with respect to reference ray Lc is set at an angle such that when external light incident along reference ray Lc is reflected on the entrance surface or exit surface of third lens 126, the reflected light does not enter first mirror 122. Note that "third lens 126 is inclined with respect to reference ray Lc" means that the point on the optical refractive surface of third lens 126 where it intersects with reference ray Lc is not horizontal with respect to a plane perpendicular to reference ray Lc.

[0055] Furthermore, in the optical path from display device 110 to first mirror 122, the exit surface of second lens unit 126b is provided facing downward relative to the entrance surface. The shape of second lens unit 126b in the Y-axis direction is wedge-shaped. By making the cross-sectional shape of second lens unit 126b along the Y-axis direction wedge-shaped, the optical path length of light passing above second lens unit 126b in the optical path from display device 110 to first mirror 122 is longer than the optical path length of light passing below second lens unit 126b. In other words, the optical path length of the image light emitted from display device 110 to reach first mirror 122 can be changed depending on the position in the Y-axis direction. This allows for excellent correction of decentered curvature of field occurring in first mirror 122.

[0056] As described above, the present embodiment includes third lens 126 that integrates first lens portion 126a and second lens portion 126b, which correspond to second lens 121 and first lens 123 in Embodiment 1. This reduces the number of parts, and can reduce the manufacturing cost of head-up display 100.

[0057] [2-2. Effects, etc.] A head-up display 100 as an example of a head-up display according to the second embodiment is a head-up display that allows an observer D to visually recognize a virtual image I. The head-up display 100 includes a display device 110 as an example of a display device, and a projection optical system 140. The display device 110 displays an image. The projection optical system 140 functions to form the image displayed by the display device 110 as an intermediate image M. A third lens 126 included in the projection optical system 140 is disposed at an angle with respect to the reference light ray Lc. Therefore, even when external light enters the projection optical system 140, stray light caused by the external light being reflected by the third lens 126 or the like can be suppressed. The projection optical system 140 also includes, in this order along the optical path from the display device 110, the third lens 126 having a converging effect and a second mirror 124 as an example of a first optical element having a diverging effect. The third lens 126 is a lens in which the first lens portion 126a and the second lens portion 126b, which correspond to the first lens 123 and the second lens 121 in the first embodiment, are integrally formed. As described above, in the head-up display 100 according to the second embodiment, the third lens 126 and the second mirror 124 are arranged in this order along the optical path from the display device 110. Therefore, the intermediate image M can be formed at a position close to the exit side of the first lens portion 126a, and the first lens portion 126a itself can be made compact. As a result, the head-up display 100 can be made compact. Furthermore, the third lens 126 is integrally formed with the second lens 121 and the first lens 123 in the first embodiment. This reduces the number of parts and reduces the manufacturing cost of the head-up display 100.

[0058] In the projection optical system 140 according to the second embodiment, the third lens 126 and the second mirror 124 having a diverging effect are arranged in this order on the optical path from the display device 110. Therefore, in the order on the optical path from the display device 110, the first lens unit 126a having positive power is arranged before the second mirror 124 having negative power and forming the intermediate image M, thereby realizing a telephoto arrangement. Therefore, by shortening the overall length of the relay optical system 120 and reducing the size of the first lens unit 126a, the head-up display 100 can be made smaller.

[0059] In this embodiment, the light beam emitted from the display device 110 passes through the third lens 126 twice, once on the optical path from the display device 110 to the first mirror 122 and once on the optical path from the first mirror 122 to the second mirror 124. In this case, the projection optical system 140 still includes, in this order on the optical path from the display device 110, the first mirror 122 having a light-condensing effect, the third lens 126 having a light-condensing effect, the second mirror 124 having a diverging effect, and the third mirror 125 that projects the intermediate image M. Furthermore, the light beam emitted from the display device 110 still travels through the first mirror 122, the third lens 126, the second mirror 124, and the third mirror 125 in this order, causing the observer D to view the virtual image I.

[0060] In the head-up display 100 according to the second embodiment, at least one surface of the third lens 126 has a free-form surface shape. Therefore, in an imaging optical system such as the head-up display 100, it is possible to suppress reflection of external light and achieve good optical characteristics.

[0061] In the head-up display 100 according to the second embodiment, the first lens portion 126a and the second lens portion 126b of the third lens 126 have a wedge shape. Therefore, even when the third lens 126 is tilted with respect to the reference light ray Lc, the optical path length of the light ray passing through the third lens 126 can be adjusted.

[0062] In head-up display 100 according to embodiment 2, third lens 126, which is formed integrally with first lens unit 126a and second lens unit 126b corresponding to first lens 123 and second lens 121 according to embodiment 1, has a wedge shape. Therefore, a light ray that passes through a portion of second lens unit 126b where the lens thickness is thin on the optical path from display device 110 to first mirror 122 passes through a portion of first lens unit 126a where the lens thickness is thick on the optical path from first mirror 122 to second mirror 124. Similarly, a light ray that passes through a portion of second lens unit 126b where the lens thickness is thick on the optical path from display device 110 to first mirror 122 passes through a portion of first lens unit 126a where the lens thickness is thin on the optical path from first mirror 122 to second mirror 124. Therefore, even if the third lens 126 is tilted with respect to the reference light ray Lc, the optical path length of the light ray passing through the third lens 126 can be made uniform.

[0063] In the head-up display 100 according to the second embodiment, the intermediate image M is an aerial image formed in the air on the optical path from the display device 110 to the virtual image I. Therefore, without adding a component for forming the intermediate image M, it is possible to enlarge the image displayed on the small display device 110 to form the intermediate image M, and further enlarge the intermediate image M and project it onto the observer D.

[0064] (Embodiment 3) Next, a third embodiment will be described with reference to FIG.

[0065] [3-1.Configuration] Fig. 6 is a schematic diagram illustrating an optical path for explaining the head-up display 100 according to embodiment 3. As shown in Fig. 6, the head-up display 100 of the present embodiment includes a fourth lens 127 as another example of the second optical element.

[0066] Display device 110 and second lens 121 of the present embodiment have the same configuration as display device 110 and second lens 121 in each of the above-described embodiments. However, their positions are different from those of the above-described embodiments. In the present embodiment, display device 110 and second lens 121 are located further forward of vehicle 200 than fourth lens 127, which serves as the second optical element, as shown in FIG. 6 .

[0067] 6, fourth lens 127 has an entrance surface facing second lens 121 and an exit surface facing first lens 123, both of which have a convex shape that is convex toward second lens 121 and first lens 123 in the X-axis direction and the Y-axis direction, respectively. Fourth lens 127 is a free-form lens in which the curvature of the convex surface differs in the X-axis direction and the Y-axis direction.

[0068] In the present embodiment, second lens 121, fourth lens 127, and first lens 123 are arranged to be tilted clockwise with respect to reference ray Lc in the XZ plane view shown in Fig. 6. This makes it possible to prevent stray light caused by external light entering the housing and being reflected by second lens 121, fourth lens 127, or first lens 123.

[0069] As described above, in this embodiment, the fourth lens 127 is used as the second optical element. The first lens 123 is disposed between the fourth lens 127 and the third mirror 125 that projects the intermediate image M. In particular, in the order of the optical path from the display device 110, the first lens 123 having positive power is disposed before the second mirror 124 that serves as the first optical element and has negative power to form the intermediate image M. Therefore, the overall length of the relay optical system 120 can be shortened and the first lens 123 itself can be made smaller, thereby making it possible to make the head-up display 100 more compact.

[0070] In the present embodiment, the positional relationship between first lens 123 and second lens 121 is different from that in the first embodiment, but the positions of the thick and thin lens portions relative to reference light ray Lc are opposite to each other. Therefore, similar to the first embodiment, the optical path lengths of the light rays passing through second lens 121 and first lens 123 can be adjusted to make the optical path lengths of the light rays uniform regardless of the portions passing through second lens 121 and first lens 123.

[0071] [3-2. Effects, etc.] A head-up display 100 as an example of a head-up display according to the third embodiment is a head-up display that allows an observer D to visually recognize a virtual image I. The head-up display 100 includes a display device 110 as an example of a display device, and a projection optical system 140. The display device 110 displays an image. The projection optical system 140 forms an intermediate image M from the image displayed by the display device 110. A first lens 123 included in the projection optical system 140 is disposed at an angle with respect to a reference ray Lc. Therefore, even when external light enters the projection optical system 140, stray light caused by the external light being reflected by the first lens 123, the second lens 121, or the fourth lens 127 can be suppressed. The projection optical system 140 also includes, in this order on an optical path from the display device 110, a fourth lens 127 as an example of a second optical element, the first lens 123 having a converging effect, and a second mirror 124 as an example of a first optical element having a diverging effect. As described above, in the head-up display 100 according to the third embodiment, a telephoto arrangement is realized by arranging the first lens 123 having positive power before the second mirror 124 having negative power and forming the intermediate image M in the order of the optical path from the display device 110. Therefore, by shortening the overall length of the relay optical system 120 and reducing the size of the first lens 123 itself, the head-up display 100 can be made smaller.

[0072] In the head-up display 100 according to the third embodiment, at least one surface of the first lens 123, the second lens 121, and the fourth lens 127 has a free-form surface shape. Therefore, in an imaging optical system such as the head-up display 100, it is possible to suppress reflection of external light and achieve good optical characteristics.

[0073] In the head-up display 100 according to the third embodiment, the first lens 123 and the second lens 121 have a wedge shape. Therefore, even if the first lens 123 and the second lens 121 are tilted with respect to the reference light ray Lc, the optical path lengths of the light rays passing through the first lens 123 and the second lens 121 can be adjusted.

[0074] In the head-up display 100 according to the third embodiment, the first lens 123 and the second lens 121 are arranged such that the positions of the thick and thin lens portions relative to the reference light ray Lc are opposite to each other. Therefore, similar to the first embodiment, the optical path lengths of the light rays passing through the second lens 121 and the first lens 123 can be adjusted to make the optical path lengths of the light rays uniform regardless of the portions through which the light rays pass through the second lens 121 and the first lens 123.

[0075] In the head-up display 100 according to the third embodiment, the intermediate image M is an aerial image formed in the air on the optical path from the display device 110 to the virtual image I. Therefore, without adding a component for forming the intermediate image M, it is possible to enlarge the image displayed on the small display device 110 to form the intermediate image M, and further enlarge the intermediate image M and project it onto the observer D.

[0076] (Fourth embodiment) Next, a fourth embodiment will be described with reference to FIG.

[0077] [4-1.Configuration] Fig. 7 is a schematic diagram illustrating an optical path for explaining a head-up display 100 according to embodiment 4. As shown in Fig. 7, the head-up display 100 according to this embodiment includes a fifth lens 128 in front of the first lens 123 in the optical path from the first mirror 122 to the second mirror 124.

[0078] Fifth lens 128 is a free-form lens whose curvature differs in the X-axis direction and the Y-axis direction. In fifth lens 128, the surface facing first mirror 122 is a flat incident surface, and the surface facing first lens 123 is a concave exit surface that is concave toward first lens 123 in the X-axis direction. The curvature of the exit surface of fifth lens 128 in the Y-axis direction is smaller than the curvature in the X-axis direction. In other words, the shape of fifth lens 128 in the Y-axis direction is a concave shape, convex shape, or flat shape with a smaller curvature than the X-axis direction.

[0079] In this embodiment, as shown in FIG. 7, the entrance surface and exit surface of fifth lens 128 are tilted clockwise with respect to reference ray Lc in the XZ plane view in FIG. 7. As a result, reflected light is reflected upward from fifth lens 128. This prevents the reflected light from entering viewpoint area 300. Here, the inclination of fifth lens 128 with respect to reference ray Lc is desirably an angle at which, when external light incident along reference ray Lc is reflected at the entrance surface or exit surface, the reflected light does not enter first mirror 122 or second mirror 124. More desirably, the above-mentioned inclination is desirably an angle at which, when external light incident on fifth lens 128 from first mirror 122 is reflected at the entrance surface or exit surface of fifth lens 128, the reflected light does not enter first mirror 122. The fifth lens 128 being tilted with respect to the reference ray Lc means that the point of intersection of the optical refractive surface of the fifth lens 128 with the reference ray Lc is not horizontal with respect to a plane perpendicular to the reference ray Lc.

[0080] The fifth lens 128 is a lens element having negative refractive power. By disposing the fifth lens 128 in front of the first lens 123 in the optical path from the first mirror 122 to the second mirror 124, chromatic aberration occurring in the first lens 123 can be suppressed.

[0081] In the projection optical system 140 of this embodiment, a fifth lens 128, a first mirror 122 as a second optical element having a light-collecting effect, and a second mirror 124 as a first optical element that forms an intermediate image M are arranged in this order on the optical path from the display device 110. By arranging the first lens 123 in front of the second mirror 124 that forms the intermediate image M in this order on the optical path from the display device 110, the intermediate image M can be formed at a position close to the exit side of the first lens 123. This allows the first lens 123 itself to be made smaller. As a result, the head-up display 100 can be made smaller. Furthermore, the negative refractive power of the fifth lens 128 makes it possible to suppress chromatic aberration that occurs in the first lens 123.

[0082] In addition, in the relay optical system 120 of this embodiment, a first lens 123 having positive power and a second mirror 124 having negative power are arranged from the display device 110 toward the intermediate image M. That is, the relay optical system 120 has a so-called telephoto arrangement. By adopting this telephoto arrangement, the first lens 123 enhances the negative power of the second mirror 124, and the second mirror 124 enhances the positive power of the first lens 123. That is, the first lens 123 and the second mirror 124 enhance each other's power. As a result, the overall length of the relay optical system 120 can be shortened, and the head-up display 100 can be made more compact.

[0083] In the present embodiment, as shown in FIG. 7, the incident surface and the exit surface of second lens 121 are inclined counterclockwise with respect to reference ray Lc in the XZ plane view of FIG. 7. The incident surface and the exit surface of first lens 123 are inclined clockwise with respect to reference ray Lc in the XZ plane view of FIG. 7. As a result, external light reflected by first lens 123 is reflected downward by second mirror 124, and external light reflected by second lens 121 is reflected downward by first mirror 122. This prevents reflected light from entering viewpoint area 300. Here, it is desirable that the inclination of second lens 121 and first lens 123 with respect to reference ray Lc is an angle such that when external light incident along reference ray Lc is reflected by the incident surface or the exit surface, the reflected light does not enter first mirror 122 or second mirror 124. More preferably, the tilt is set at an angle such that when external light incident on second lens 121 or first lens 123 from first mirror 122 is reflected on the entrance surface or exit surface of second lens 121 or first lens 123, the reflected light does not enter first mirror 122. Note that when second lens 121 and first lens 123 are tilted with respect to reference ray Lc, the points on the optical refractive surfaces of second lens 121 and first lens 123 where the reference ray Lc intersects are not horizontal with respect to a plane perpendicular to the reference ray Lc.

[0084] In the present embodiment, similarly to Embodiment 1, first lens 123 and second lens 121 are arranged such that the positions of the thick and thin lens portions relative to reference light ray Lc are opposite to each other. Therefore, similarly to Embodiment 1, the optical path lengths of light rays passing through second lens 121 and first lens 123 can be adjusted to make the optical path lengths of light rays uniform regardless of the portions through which they pass through second lens 121 and first lens 123.

[0085] [4-2. Effects, etc.] A head-up display 100 as an example of a head-up display according to the fourth embodiment is a head-up display that allows an observer D to visually recognize a virtual image I. The head-up display 100 includes a display device 110 as an example of a display device, and a projection optical system 140. The display device 110 displays an image. The projection optical system 140 functions to form the image displayed by the display device 110 as an intermediate image M. A first lens 123 included in the projection optical system 140 is disposed at an angle with respect to the reference ray Lc. Therefore, even when external light enters the projection optical system 140, stray light caused by the external light being reflected by the fifth lens 128 or the like can be suppressed. The projection optical system 140 also includes, in this order along the optical path from the display device 110, the first lens 123 having a converging effect and a second mirror 124 as an example of a first optical element having a diverging effect. As described above, in the head-up display 100 according to the fourth embodiment, the first lens 123 having positive power is arranged in front of the second mirror 124 having negative power and forming the intermediate image M, in the order of the optical path from the display device 110, to form a telephoto arrangement. Therefore, the overall length of the relay optical system 120 is shortened and the first lens 123 itself is made smaller, thereby making it possible to make the head-up display 100 more compact. Furthermore, in the order of the optical path from the display device 110, the fifth lens 128 is arranged in front of the first lens 123. Therefore, the negative refractive power of the fifth lens 128 can suppress chromatic aberration occurring in the first lens 123.

[0086] In the head-up display 100 according to the fourth embodiment, the first mirror 122 is used as an example of the second optical element, and the second mirror 124 is used as an example of the first optical element. Therefore, it is possible to sufficiently enlarge the image displayed on the small display device 110 to create an intermediate image M, and to further enlarge the intermediate image M and project it onto the observer D.

[0087] In the head-up display 100 according to the fourth embodiment, at least one surface of the second lens 121, the first lens 123, and the fifth lens 128 has a free-form surface shape. Therefore, in an imaging optical system such as the head-up display 100, it is possible to suppress reflection of external light and achieve good optical characteristics.

[0088] In the head-up display 100 according to the fourth embodiment, the first lens 123 and the second lens 121 have a wedge shape. Therefore, even when the first lens 123 and the second lens 121 are tilted with respect to the reference light ray Lc, the optical path lengths of the light rays passing through the first lens 123 and the second lens 121 can be adjusted.

[0089] The head-up display 100 according to the fourth embodiment includes a second lens 121 between the display device 110 and the first mirror 122. The second lens 121 has a wedge shape, and at least one surface thereof is a free-form surface. In the head-up display 100 according to the fourth embodiment, the first lens 123 and the second lens 121 are arranged such that a light ray passing through a portion where one lens is thin passes through a portion where the other lens is thick, and a light ray passing through a portion where one lens is thick passes through a portion where the other lens is thin. Therefore, even when the first lens 123 and the second lens 121 are tilted with respect to the reference light ray Lc, the optical path lengths of the light rays passing through the first lens 123 and the second lens 121 can be made uniform.

[0090] In the head-up display 100 according to the fourth embodiment, the intermediate image M is an aerial image formed in the air on the optical path from the display device 110 to the virtual image I. Therefore, without adding a component for forming the intermediate image M, it is possible to enlarge the image displayed on the small display device 110 to form the intermediate image M, and further enlarge the intermediate image M and project it onto the observer D.

[0091] (Embodiment 5) Next, a fifth embodiment will be described with reference to FIG.

[0092] [5-1.Configuration] Fig. 8 is a schematic diagram illustrating an optical path for explaining a head-up display 100 according to embodiment 5. As shown in Fig. 8, the head-up display 100 according to this embodiment includes a sixth lens 129 located after the intermediate image M in the order of the optical path from the second mirror 124 to the third mirror 125.

[0093] Sixth lens 129 is a free-form lens whose curvature differs in the X-axis direction and the Y-axis direction. In sixth lens 129, the surface facing third mirror 125 is a flat exit surface, and the surface facing intermediate image M is a concave entrance surface that is concave toward first lens 123 in the X-axis direction. The curvature of the entrance surface of second mirror 124 in the Y-axis direction is smaller than the curvature in the X-axis direction. In other words, the shape of sixth lens 129 in the Y-axis direction is a concave shape, convex shape, or flat shape with a smaller curvature than the X-axis direction.

[0094] In this embodiment, as shown in FIG. 8 , the entrance surface and exit surface of sixth lens 129 are inclined counterclockwise with respect to reference ray Lc in the XZ plane view in FIG. 8 . As a result, reflected light is reflected downward from sixth lens 129. This prevents the reflected light from entering viewpoint area 300. Here, the inclination of sixth lens 129 with respect to reference ray Lc is desirably an angle such that, when external light incident along reference ray Lc is reflected on the entrance surface or exit surface, the reflected light does not enter third mirror 125 and second mirror 124. More desirably, the inclination is desirably an angle such that, when external light incident on sixth lens 129 from second mirror 124 is reflected on the entrance surface or exit surface of sixth lens 129, the reflected light does not enter second mirror 124 and third mirror 125. Note that the sixth lens 129 being tilted with respect to the reference ray Lc means that the point of intersection of the optical refractive surface of the sixth lens 129 with the reference ray Lc is not horizontal with respect to a plane perpendicular to the reference ray Lc.

[0095] The sixth lens 129 is a lens element having negative refractive power. In the optical path from the display device 110 to the third mirror 125, the sixth lens 129 is disposed after the optical elements of the relay optical system 120. This reduces the burden of aberration correction on the optical elements, enabling higher image quality to be achieved.

[0096] In the projection optical system 140 of this embodiment, a first mirror 122 serving as a second optical element having a light-collecting effect and a second mirror 124 serving as a first optical element that forms an intermediate image M are arranged in this order along the optical path from the display device 110. By arranging the first lens 123 in front of the second mirror 124 that forms the intermediate image M in this order along the optical path from the display device 110, the intermediate image M can be formed at a position close to the exit side of the first lens 123. This allows the first lens 123 itself to be made smaller. As a result, the head-up display 100 can be made smaller. In addition, a sixth lens 129 is arranged behind the intermediate image M. This reduces the burden of aberration correction on the optical elements in the relay optical system 120, thereby improving image quality.

[0097] In addition, in the relay optical system 120 of this embodiment, a first lens 123 having positive power and a second mirror 124 having negative power are arranged from the display device 110 toward the intermediate image M. That is, the relay optical system 120 has a so-called telephoto arrangement. By adopting this telephoto arrangement, the first lens 123 enhances the negative power of the second mirror 124, and the second mirror 124 enhances the positive power of the first lens 123. That is, the first lens 123 and the second mirror 124 enhance each other's power. As a result, the overall length of the relay optical system 120 can be shortened, and the head-up display 100 can be made more compact.

[0098] In the present embodiment, as shown in FIG. 8 , the incident surface and the exit surface of second lens 121 are inclined counterclockwise with respect to reference ray Lc in the XZ plane view of FIG. 8 . The incident surface and the exit surface of first lens 123 are inclined clockwise with respect to reference ray Lc in the XZ plane view of FIG. 8 . As a result, external light reflected by first lens 123 is reflected downward by second mirror 124, and external light reflected by second lens 121 is reflected downward by first mirror 122. This prevents reflected light from entering viewpoint area 300. Here, it is desirable that the inclination of second lens 121 and first lens 123 with respect to reference ray Lc be an angle such that when external light incident along reference ray Lc is reflected by the incident surface or the exit surface, the reflected light does not enter first mirror 122 or second mirror 124. More preferably, the tilt is set at an angle such that when external light incident on second lens 121 or first lens 123 from first mirror 122 is reflected on the entrance surface or exit surface of second lens 121 or first lens 123, the reflected light does not enter first mirror 122. Note that when second lens 121 and first lens 123 are tilted with respect to reference ray Lc, the points on the optical refractive surfaces of second lens 121 and first lens 123 where the reference ray Lc intersects are not horizontal with respect to a plane perpendicular to the reference ray Lc.

[0099] In the present embodiment, similarly to Embodiment 1, first lens 123 and second lens 121 are arranged such that the positions of the thick and thin lens portions relative to reference light ray Lc are opposite to each other. Therefore, similarly to Embodiment 1, the optical path lengths of light rays passing through second lens 121 and first lens 123 can be adjusted to make the optical path lengths of light rays uniform regardless of the portions through which they pass through second lens 121 and first lens 123.

[0100] [5-2. Effects, etc.] A head-up display 100 as an example of a head-up display according to the fifth embodiment is a head-up display that allows an observer D to visually recognize a virtual image I. The head-up display 100 includes a display device 110 as an example of a display device, and a projection optical system 140. The display device 110 displays an image. The projection optical system 140 has a function of forming the image displayed by the display device 110 as an intermediate image M. A first lens 123 included in the projection optical system 140 is disposed at an angle with respect to the reference light ray Lc. Therefore, even when external light enters the projection optical system 140, stray light caused by the external light being reflected by the sixth lens 129 and the like can be suppressed. The projection optical system 140 also includes, in this order along the optical path from the display device 110, the first lens 123 having a converging effect and a second mirror 124 as an example of a first optical element having a diverging effect. As described above, in the head-up display 100 according to the fifth embodiment, the first lens 123 having positive power is arranged in front of the second mirror 124 having negative power and forming the intermediate image M, in the order of the optical path from the display device 110, to form a telephoto arrangement. Therefore, the overall length of the relay optical system 120 is shortened and the first lens 123 itself is made smaller, thereby making it possible to make the head-up display 100 more compact. Furthermore, in the order of the optical path from the display device 110, the sixth lens 129 is arranged behind the relay optical system 120. Therefore, the burden of aberration correction on the optical elements of the relay optical system 120 is reduced, and high image quality can be achieved.

[0101] In the head-up display 100 according to the fifth embodiment, the first mirror 122 is used as an example of the second optical element, and the second mirror 124 is used as an example of the first optical element. Therefore, it is possible to sufficiently enlarge the image displayed on the small display device 110 to create an intermediate image M, and to further enlarge the intermediate image M and project it onto the observer D.

[0102] In the head-up display 100 according to the fifth embodiment, at least one surface of the second lens 121, the first lens 123, and the sixth lens 129 has a free-form surface shape. Therefore, in an imaging optical system such as the head-up display 100, it is possible to suppress reflection of external light and achieve good optical characteristics.

[0103] In the head-up display 100 according to the fifth embodiment, the first lens 123 and the second lens 121 have a wedge shape. Therefore, even if the first lens 123 and the second lens 121 are tilted with respect to the reference light ray Lc, the optical path lengths of the light rays passing through the first lens 123 and the second lens 121 can be adjusted.

[0104] The head-up display 100 according to the fifth embodiment includes a second lens 121 between the display device 110 and the first mirror 122. The second lens 121 has a wedge shape, and at least one surface thereof is a free-form surface. In the head-up display 100 according to the fourth embodiment, the first lens 123 and the second lens 121 are arranged such that a light ray passing through a portion where one lens is thin passes through a portion where the other lens is thick, and a light ray passing through a portion where one lens is thick passes through a portion where the other lens is thin. Therefore, even when the first lens 123 and the second lens 121 are tilted with respect to the reference light ray Lc, the optical path lengths of the light rays passing through the first lens 123 and the second lens 121 can be made uniform.

[0105] In the head-up display 100 according to the fifth embodiment, the intermediate image M is an aerial image formed in the air on the optical path from the display device 110 to the virtual image I. Therefore, without adding a component for forming the intermediate image M, it is possible to enlarge the image displayed on the small display device 110 to form the intermediate image M, and further enlarge the intermediate image M and project it onto the observer D.

[0106] (Sixth embodiment) Next, a sixth embodiment will be described with reference to FIG.

[0107] [6-1.Configuration] Fig. 9 is a schematic diagram illustrating an optical path for explaining a head-up display 100 according to embodiment 6. As shown in Fig. 9, the head-up display 100 of the present embodiment includes a seventh lens 150 as another example of the first optical element.

[0108] The first mirror 122 of the present embodiment has the same configuration as the first mirror 122 in the first and second embodiments. However, the arrangement position is different from that of the above-described embodiments. The first mirror 122 in the present embodiment is arranged at the rearmost position of the vehicle 200 within the head-up display 100, as shown in FIG. 9. The display device 110 and the second lens 121 in the present embodiment have the same configuration as the display device 110 and the second lens 121 in the above-described embodiments. However, the arrangement position is different from that of the above-described embodiments. In the present embodiment, the display device 110 and the second lens 121 are arranged further forward of the vehicle 200 than the first mirror 122, as shown in FIG. 9.

[0109] First lens 123 of the present embodiment has the same configuration as first lens 123 in Embodiments 1 and 3. However, the arrangement position is different. First lens 123 in the present embodiment is located further rearward of vehicle 200 than seventh lens 150, which serves as the first optical element.

[0110] Seventh lens 150 is a free-form lens whose curvature differs in the X-axis direction and the Y-axis direction. In seventh lens 150, the surface facing first lens 123 is a flat incident surface, and the surface facing third mirror 125 is a concave exit surface that is concave toward third mirror 125 in the X-axis direction. The curvature of the exit surface of seventh lens 150 in the Y-axis direction is smaller than the curvature in the X-axis direction. In other words, the shape of seventh lens 150 in the Y-axis direction is a concave, convex, or flat shape with a smaller curvature than the X-axis direction.

[0111] In this embodiment, as shown in FIG. 9 , the entrance surface and exit surface of seventh lens 150 are tilted counterclockwise with respect to reference ray Lc in the XZ plane view in FIG. 9 . As a result, reflected light is reflected downward from seventh lens 150. This prevents the reflected light from entering viewpoint area 300. Here, the tilt of seventh lens 150 with respect to reference ray Lc is desirably set to an angle such that, when external light incident along reference ray Lc is reflected at the entrance surface or exit surface, the reflected light does not enter first mirror 122 or third mirror 125. More desirably, the tilt is desirably set to an angle such that, when external light incident on seventh lens 150 from first mirror 122 is reflected at the entrance surface or exit surface of seventh lens 150, the reflected light does not enter first mirror 122. The seventh lens 150 being tilted with respect to the reference ray Lc means that the point of intersection of the optical refractive surface of the seventh lens 150 with the reference ray Lc is not horizontal with respect to a plane perpendicular to the reference ray Lc.

[0112] Furthermore, the exit surface of the seventh lens 150 is wedge-shaped when viewed in the XZ plane of Fig. 9. By making the cross-sectional shape of the seventh lens 150 along the Y-axis direction wedge-shaped, the optical path length of light passing above the seventh lens 150 becomes longer than the optical path length of light passing below the seventh lens 150. In other words, the optical path length of the image light emitted from the display device 110 until it is focused as the intermediate image M can be changed depending on the position in the Y-axis direction. This makes it possible to satisfactorily correct the decentered curvature of field that occurs in the first mirror 122.

[0113] In the projection optical system 140 of this embodiment, a first mirror 122 as a second optical element having a light-collecting effect and a seventh lens 150 as a first optical element that forms an intermediate image M are arranged in this order on the optical path from the display device 110. A first lens 123 having a light-collecting effect is arranged between the first mirror 122 and the seventh lens 150. In this way, by arranging the first lens 123 between the first mirror 122 that forms the intermediate image M and the seventh lens 150 that forms the intermediate image M, the intermediate image M can be formed at a position close to the exit side of the first lens 123. Therefore, the first lens 123 itself can be made smaller. As a result, the head-up display 100 can be made smaller.

[0114] In addition, in the relay optical system 120 of this embodiment, a first lens 123 having positive power and a seventh lens 150 having negative power are arranged from the display device 110 toward the intermediate image M. That is, the relay optical system 120 has a so-called telephoto arrangement. By adopting this telephoto arrangement, the first lens 123 enhances the negative power of the seventh lens 150, and the seventh lens 150 enhances the positive power of the first lens 123. That is, the first lens 123 and the seventh lens 150 enhance each other's power. As a result, the overall length of the relay optical system 120 can be shortened, and the head-up display 100 can be made more compact.

[0115] In the present embodiment, as shown in FIG. 9, the incident surface and the exit surface of second lens 121 are inclined clockwise with respect to reference ray Lc in the XZ plane view of FIG. 9. The incident surface and the exit surface of first lens 123 are inclined counterclockwise with respect to reference ray Lc in the XZ plane view of FIG. 9. As a result, external light reflected by first lens 123 is reflected upward from first mirror 122, and external light reflected by second lens 121 is reflected downward from first mirror 122. This prevents reflected light from entering viewpoint area 300. Here, it is desirable that the inclination of second lens 121 and first lens 123 with respect to reference ray Lc is an angle such that when external light incident along reference ray Lc is reflected by the incident surface or the exit surface, the reflected light does not enter first mirror 122. More preferably, the tilt is set at an angle such that when external light incident on second lens 121 or first lens 123 from first mirror 122 is reflected on the entrance surface or exit surface of second lens 121 or first lens 123, the reflected light does not enter first mirror 122. Note that when second lens 121 and first lens 123 are tilted with respect to reference ray Lc, the points on the optical refractive surfaces of second lens 121 and first lens 123 where the reference ray Lc intersects are not horizontal with respect to a plane perpendicular to the reference ray Lc.

[0116] In the present embodiment, similarly to Embodiment 1, first lens 123 and second lens 121 are arranged such that the positions of the thick and thin lens portions relative to reference light ray Lc are opposite to each other. Therefore, similarly to Embodiment 1, the optical path lengths of light rays passing through second lens 121 and first lens 123 can be adjusted to make the optical path lengths of light rays uniform regardless of the portions through which they pass through second lens 121 and first lens 123.

[0117] [6-2. Effects, etc.] A head-up display 100 as an example of a head-up display according to the sixth embodiment is a head-up display that allows an observer D to visually recognize a virtual image I. The head-up display 100 includes a display device 110 as an example of a display device, and a projection optical system 140. The display device 110 displays an image. The projection optical system 140 has a function of forming the image displayed by the display device 110 as an intermediate image M. A first lens 123 included in the projection optical system 140 is disposed at an angle with respect to the reference light ray Lc. Therefore, even when external light enters the projection optical system 140, stray light caused by the external light being reflected by the seventh lens 150 and the like can be suppressed. The projection optical system 140 also includes, in this order along the optical path from the display device 110, the first lens 123 having a light-condensing function and the seventh lens 150 as an example of a first optical element. As described above, in the head-up display 100 according to the sixth embodiment, the first lens 123 having positive power is arranged in front of the seventh lens 150 having negative power and forming the intermediate image M in the order of the optical path from the display device 110, thereby forming a telephoto arrangement. Therefore, by shortening the overall length of the relay optical system 120 and reducing the size of the first lens 123 itself, the head-up display 100 can be made smaller.

[0118] The first mirror 122 is used as an example of the second optical element according to the sixth embodiment, and the third mirror 125 is used in the projection optical system 130. Therefore, it is possible to sufficiently enlarge the image displayed on the small display device 110 to create an intermediate image M, and to further enlarge the intermediate image M and project it onto the observer D.

[0119] The head-up display 100 according to the sixth embodiment uses a seventh lens 150 having negative power as an example of a first optical element near the intermediate image M. This allows the seventh lens 150 to function as a so-called field lens. This allows the first lens 123, the first mirror 122, and the second lens 121 to be made smaller.

[0120] In the head-up display 100 according to the sixth embodiment, at least one surface of the first lens 123, the second lens 121, and the seventh lens 150 has a free-form surface shape. Therefore, in an imaging optical system such as the head-up display 100, it is possible to suppress reflection of external light and achieve good optical characteristics.

[0121] In the head-up display 100 according to the sixth embodiment, the first lens 123, the second lens 121, and the seventh lens 150 have a wedge shape. Therefore, even if the first lens 123, the second lens 121, and the seventh lens 150 are tilted with respect to the reference light ray Lc, the optical path lengths of the light rays passing through the first lens 123, the second lens 121, and the seventh lens 150 can be adjusted.

[0122] The head-up display 100 according to the sixth embodiment includes a second lens 121 between the display device 110 and a first mirror 122 serving as an example of a second optical element. The second lens 121 has a wedge shape, and at least one surface thereof has a free-form curved shape. In the head-up display 100 according to the sixth embodiment, the first lens 123 and the second lens 121 are arranged such that a light ray passing through a portion of one lens where the lens thickness is thin passes through a portion of the other lens where the lens thickness is thick, and a light ray passing through a portion of one lens where the lens thickness is thick passes through a portion of the other lens where the lens thickness is thin. Therefore, even when the first lens 123 and the second lens 121 are tilted with respect to the reference light ray Lc, the optical path lengths of the light rays passing through the first lens 123 and the second lens 121 can be made uniform.

[0123] In the head-up display 100 according to the sixth embodiment, the intermediate image M is an aerial image formed in the air on the optical path from the display device 110 to the virtual image I. Therefore, without adding a component for forming the intermediate image M, it is possible to enlarge the image displayed on the small display device 110 to form the intermediate image M, and further enlarge the intermediate image M and project it onto the observer D.

[0124] (Other embodiments) As described above, the first to sixth embodiments have been described as examples of the technology disclosed in the present application. However, the technology in the present disclosure is not limited to these, and can be applied to embodiments in which modifications, substitutions, additions, omissions, etc. are made. Furthermore, it is also possible to combine the components described in the first to sixth embodiments to create new embodiments.

[0125] In the first to sixth embodiments, second lens 121 is shown as an example of a refractive optical system provided between display device 110 and first mirror 122. However, the refractive optical system is not limited to second lens 121, which is a single lens element. For example, the refractive optical system may be one in which multiple lens elements are arranged between display device 110 and first mirror 122. When multiple lens elements are present, it is desirable that the lens element onto which light emitted from the display device first enters has positive power.

[0126] In the first to sixth embodiments, one third mirror 125 is provided as the projection optical system 140. However, two or more mirrors may be provided. The additional mirror may be provided further forward on the vehicle than the third mirror 125, or may be provided inward or outward from the vehicle, that is, in a direction perpendicular to the plane of the paper in FIGS. 1, 2, and 4 to 9.

[0127] In the first to sixth embodiments, a lens element is used in the relay optical system 120. However, the configuration of the head-up display 100 is not limited to this. For example, a lens element may be additionally disposed between the third mirror 125 and the windshield 220.

[0128] The first mirror 122, the second mirror 124, and the third mirror 125 in the head-up display 100 of the first to sixth embodiments have been described as mirrors with rotationally asymmetric shapes. However, these mirrors are not limited to this. For example, these mirrors may have a so-called saddle-shaped surface shape in which the signs of curvature in the X-axis direction and the Y-axis direction are different.

[0129] The surface shape of the lens elements used in the first to sixth embodiments is not limited to a free-form surface shape. For example, the surface shape of the lens elements may be toroidal, anamorphic, or cylindrical. Furthermore, lenses of these shapes may be disposed decentered with respect to the reference ray Lc.

[0130] The exit surface of fifth lens 128 in embodiment 4, the entrance surface of sixth lens 129 in embodiment 5, and the exit surface in embodiment 6 do not need to be entirely concave in the X-axis direction, and may have locally convex shapes.

[0131] The planar surface of the lens elements used in the first to sixth embodiments may be a convex or concave surface, or may have a locally curved surface shape.

[0132] The shapes of the reflecting surfaces of first mirror 122, second mirror 124, and third mirror 125 in the first to fifth embodiments are not limited to free-form shapes. The reflecting surfaces of these mirrors may be spherical, aspherical, toroidal, or anamorphic. Mirrors of these shapes may also be positioned decentered with respect to the reference light ray Lc.

[0133] In the first to sixth embodiments, the head-up display 100 is disposed below the dashboard 210, but it may be disposed above the dashboard 210.

[0134] As described above, the embodiments have been described as examples of the technology of the present disclosure. For this purpose, the accompanying drawings and detailed description have been provided. Therefore, the components described in the accompanying drawings and detailed description may include not only components essential for solving the problem, but also components that are not essential for solving the problem in order to exemplify the above technology. Therefore, the fact that these non-essential components are described in the accompanying drawings or detailed description should not be interpreted as immediately indicating that these non-essential components are essential.

[0135] Furthermore, since the above-described embodiments are intended to illustrate the technology of the present disclosure, various modifications, substitutions, additions, omissions, etc. may be made within the scope of the claims or their equivalents.

[0136] (Outline of the embodiment) (1) A head-up display according to the present disclosure projects an image onto a transparent reflecting member to allow an observer to view a virtual image, and includes a display device that displays the image and a projection optical system that projects the image displayed on the display device as a virtual image to the observer. The projection optical system has a function of forming the image as an intermediate image and includes a first lens having a converging function and a first optical element having a diverging function. The first lens and the first optical element are arranged in this order on an optical path from the display device. When a light ray that reaches the center of the observer's viewpoint area and corresponds to the center of the virtual image is defined as a reference light ray, the first lens is arranged at an angle with respect to the reference light ray.

[0137] In this way, the projection optical system is configured by arranging, in the order of the optical path from the display device, a first lens having a converging effect and a first optical element having a diverging effect, with the first lens tilted with respect to the reference light ray. Therefore, even when external light enters the projection optical system, stray light caused by the external light being reflected by the first lens or the like can be suppressed. Furthermore, the projection optical system has a telephoto arrangement in which, in the order of the optical path from the display device, the first lens having a positive power is arranged before the first optical element having a negative power that forms an intermediate image. Therefore, by shortening the overall length of the relay optical system and miniaturizing the first lens itself, the head-up display can be made more compact.

[0138] (2) In the head-up display of (1), the first optical element is a mirror. Therefore, an image displayed on a small display device can be sufficiently enlarged to create an intermediate image, which can then be further enlarged and projected to the viewer.

[0139] (3) In the head-up display of (1) or (2), at least one surface of the first lens has a free-form surface shape. Therefore, in an imaging optical system such as a head-up display, reflection of external light can be suppressed and good optical characteristics can be achieved.

[0140] (4) In the head-up display of any one of (1) to (3), the first lens has a wedge shape. Therefore, even if the first lens is tilted with respect to a reference ray, the optical path length of the ray passing through the first lens can be adjusted.

[0141] (5) In the head-up display of (4), the projection optical system includes a second optical element having a light-collecting effect and a second lens having a light-collecting effect. The second lens, the second optical element, and the first lens are arranged in this order on the optical path from the display device. The second lens has a wedge shape. At least one surface of the second lens has a free-form surface shape. The first lens and the second lens are arranged so that a light ray passing through a thin portion of the first lens passes through a thick portion of the second lens, and a light ray passing through a thick portion of the first lens passes through a thin portion of the second lens. Therefore, even if the first lens and the second lens are tilted with respect to a reference light ray, the optical path lengths of the light rays passing through the first lens and the second lens can be made uniform.

[0142] (6) In the head-up display of (5), the first lens and the second lens are integrally formed, which reduces the number of parts and reduces the manufacturing cost of the head-up display.

[0143] (7) In the head-up display of (5), the projection optical system includes a lens having negative refractive power, which is disposed in front of the first lens and tilted with respect to the reference ray in the optical path from the second optical element to the first optical element, thereby reducing the burden of aberration correction on the optical element and achieving high image quality.

[0144] (8) In the head-up display of (5), the projection optical system includes a lens having negative refractive power, which is disposed inclined with respect to the reference ray after the intermediate image in the optical path from the first optical element to the virtual image. This reduces the burden of aberration correction on the optical element, thereby achieving high image quality.

[0145] (9) In the head-up display of any one of (1) to (8), the intermediate image is an aerial image formed in the air on the optical path. Therefore, without adding a component for forming the intermediate image, it is possible to enlarge an image displayed on a small display device to form an intermediate image, and further enlarge the intermediate image and project it to the observer. [Industrial Applicability]

[0146] The present disclosure is applicable to head-up displays that use refractive optical systems such as lenses, etc. Specifically, the present disclosure is applicable to head-up displays for vehicles, etc. [Explanation of symbols]

[0147] 100 Head-Up Display 110 Display Devices 120 Relay Optical System 121 Second lens 122 1st Mirror 123 First lens 124 Second Mirror 125 3rd Mirror 126 Third Lens 127 4th lens 128 5th lens 129 6th lens 130 Projection optical system 140 Projection optical system 150 7th lens 200 vehicles 210 Dashboard 220 Windshield 300 Viewpoint Area D. Observer I Virtual Image M intermediate image L ray Lc reference ray

Claims

1. A head-up display that projects a projection image formed from an original image onto a transparent reflecting member to allow an observer to view a virtual image, a device for emitting a light beam that converts the original image into the projected image; a projection optical system that forms the projected image from the original image and projects the projected image to the viewer as a virtual image, The projection optical system includes: a first lens having a refractive surface onto which the light beam emitted from the device is incident; a second mirror that reflects the light beam downward; a third mirror that reflects the light reflected by the second mirror to the reflecting member as the projection image, the first lens, the second mirror, and the third mirror are arranged in this order on an optical path to the reflecting member; the projection optical system has a function of forming the original image as an intermediate image below the second mirror by using light rays emitted from the device, and forming the projected image from the intermediate image; Head-up display.

2. When a light ray that reaches the center of the viewpoint area of ​​the observer and corresponds to the center of the virtual image is defined as a reference light ray, the first lens is disposed so as to be inclined with respect to the reference light ray. The head-up display according to claim 1 .

3. the first lens is disposed at an angle with respect to the reference light ray so that an upper side thereof is closer to the second mirror than a lower side thereof; The head-up display according to claim 2 .

4. The first lens is disposed at an angle between 15 degrees and 30 degrees with respect to a plane perpendicular to the reference light beam. The head-up display according to claim 3 .

5. an optical path between the second mirror and the third mirror is in air; the intermediate image is an aerial image formed in the air on the optical path between the second mirror and the third mirror. The head-up display according to claim 1 .

6. the intermediate image is formed at a position closer to the second mirror than to the third mirror; The head-up display according to claim 5 .

7. the second mirror is a convex mirror; The head-up display according to claim 1 .

8. the third mirror is a concave mirror; The head-up display according to claim 1 .

9. the third mirror has a free-form surface shape; The head-up display according to claim 7.

Images