Head-up display

Abstract

To provide a head-up display that can be miniaturized and is effective in suppression of stray light because of external light.SOLUTION: A head-up display includes: a device for emitting rays for turning an original image into a projection image; and a projection optical system for forming a projection image from an original image and projecting the projection image as a virtual image to an observer. The projection optical system includes: a first lens having a refractive surface that rays emitted from the device enter; a fifth lens having negative refractive power while a surface in the first lens side is in a concave shape; a second mirror for reflecting rays; and a third mirror for reflecting light reflected by the second mirror to a reflection member as a projection image. The fifth lens, the first lens, the second mirror, and the third mirror are disposed in the order of an optical path to the reflection member.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present disclosure relates to a head-up display.

Background Art

[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 for displaying an image on the display surface, a concave mirror, and a lens having a condensing action disposed between the concave mirror and the display surface. Further, this head-up display includes a first optical system that forms an intermediate image in which the image is enlarged by causing light rays emitted from the display surface to form an image through the lens and the concave mirror. Furthermore, this head-up display 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 by the display device on the display surface. Thereby, miniaturization of the first optical system and the second optical system is achieved.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

[0004] The present disclosure provides a head-up display that can be miniaturized and is effective in suppressing stray light caused by external light.

[0005] The head-up display of the present disclosure is a head-up display that projects a projected image formed from an original image onto a transmissive reflective member to allow an observer to visually recognize a virtual image, and includes a device that emits light rays that form the projected image from the original image, and a projection optical system that forms a projected image from the original image and projects the projected image as a virtual image onto the observer. The projection optical system includes a first lens having a refractive surface that receives the light rays emitted from the device, a fifth lens having a concave surface on the side of the first lens and having a negative refractive power, a second mirror that reflects the light rays, and a third mirror that reflects the light reflected by the second mirror as a projected image onto the reflective member. The fifth lens, the first lens, the second mirror, and the third mirror are arranged in the order of the optical path to the reflective member.

[0006] The head-up display in the present disclosure presents a virtual image with little distortion, can be miniaturized, and is effective in suppressing stray light caused by external light.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiments for Carrying out the Invention

[0008] Hereinafter, the embodiments will be described in detail with reference to the drawings as appropriate. However, a more detailed description than necessary may be omitted. For example, a detailed description of well-known matters and a redundant description of substantially the same configuration may be omitted. This is to avoid making the following description unnecessarily redundant and to facilitate the understanding of those skilled in the art.

[0009] It should be noted that the inventor(s) provide the accompanying drawings and the following description so that those skilled in the art can fully understand the present disclosure, and do not intend to limit the subject matter described in the claims thereby.

[0010] (Embodiment 1) Hereinafter, Embodiment 1 will be described with reference to FIGS. 1 to 4.

[0011] [1-1. Configuration] [1-1-1. Overall Configuration of the 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 the head-up display 100 according to the present disclosure. As shown in FIG. 1, the head-up display 100 is disposed inside the dashboard 210 below the windshield 220 of the vehicle 200. The observer D recognizes the 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 the present embodiment. FIG. 3 is a schematic diagram for explaining the configuration of the head-up display 100 according to the present 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 the windshield 220. The projected light is reflected by the windshield 220 and guided to the viewing area 300 of the observer D. Thereby, the head-up display 100 allows the observer D to visually recognize the virtual image I. Here, the viewing point is the principal point when considering the eyes of the observer D as a lens. Also, the viewing area 300 is an area where the virtual image I can be visually recognized without omission, and is the area where the viewing point of the observer D is located.

[0015] Here, in the present disclosure, the front is the direction in which the windshield 220 of the vehicle 200 is located as seen from the observer D. The rear is the direction opposite to the front. Also, the downward direction is the direction of the ground on which the vehicle 200 travels. The upward direction is the direction opposite to the downward direction. The inner side is the passenger seat side as seen from the observer D in the driver's seat. The outer side is the direction opposite to the inner side. Also, the viewing area 300 is an area where the observer D can visually recognize the virtual image I without omission.

[0016] Here, as shown in FIG. 2, among the light rays emitted from the display device 110, the light ray that reaches the viewing area 300 is defined as the light ray L. Also, among the light rays emitted from the display device 110, the light ray that passes through the center of the virtual image I and reaches the center of the viewing area 300 is defined as the 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 viewing point of the observer D. The reference light ray Lc visually recognized by the observer D is actually the one that has reached the observer D from the display device 110 through the optical system. Therefore, the light ray from the display device 110 to the observer D corresponding to the reference light ray Lc emitted from the center of the virtual image I is also expressed as the reference light ray Lc. Also, the optical paths corresponding to these light rays are similarly expressed as the reference light ray Lc. However, it is assumed that the viewing point of the observer D is at the center of the viewing area 300.

[0017] The display device 110 displays a display image on a diffusing surface or the like based on control by a control unit such as a CPU (not shown). As the display device 110, for example, a liquid crystal display (LCD) with a backlight, an organic light-emitting diode (OLED), a plasma display, or the like can be used. Also, as the display device 110, a screen that diffuses or reflects light and a projector or a scanning laser may be used to generate an image. The display device 110 can display various types of information such as road navigation display, the distance to the vehicle ahead, the remaining battery level of the vehicle, and the current vehicle speed. Further, the display device 110 may electronically distort the image in advance according to the distortion generated in the projection optical system 130 or the windshield 220 and the position of the observer D obtained by a camera (not shown). Thereby, a good virtual image I can be visually recognized by the observer D. Also, the display device 110 may display display pixels of a plurality of wavelengths shifted for each display position in advance according to the chromatic aberration generated in the projection optical system 130. Thereby, a good virtual image I can be visually recognized by the observer D.

[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 as a second optical element, a first lens 123, and a second mirror 124 as a first optical element. The relay optical system 120 forms an intermediate image M that magnifies the display image by imaging the light rays emitted from the display device 110. The intermediate image M is formed to be larger than the display image displayed on the screen of the display device 110. That is, even if the display image displayed on the screen of the display device 110 is small, a large intermediate image M can be obtained. Thereby, the size of the screen of the display device 110 can be reduced. Also, because the intermediate image M is large, the magnification in the projection optical system 130 can be lowered. Thereby, the positive power of the third mirror 125 of the projection optical system 130 can be weakened, and screen distortion can be suppressed.

[0019] The intermediate image M does not need to be imaged as a good point at the intermediate image position. Spherical aberration, coma aberration, field curvature, 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. Thereby, the projection optical system 130 projects the intermediate image M onto the windshield 220. Note that the intermediate image M is an aerial image that is formed in the air and does not form an image on a projection surface that diffusely reflects. The third mirror 125 is disposed on the optical path from the intermediate image M to the windshield 220.

[0021] [1-1-2. Arrangement Configuration of Projection Optical System, Relay Optical System, and Display Device] As shown in FIG. 2, the second lens 121 is located in front of the vehicle 200 in the forward direction with respect to the display device 110. As shown in FIG. 2, the second lens 121 is disposed so as to be inclined counterclockwise with respect to the reference ray Lc in a view along the XZ plane of FIG. 2. Thereby, it is possible to prevent stray light caused by external light entering the housing and reflecting off the display surface of the display device 110 or the first mirror 122.

[0022] Further, the second lens 121 is a free-form surface lens having different curvatures in the X-axis direction and the Y-axis direction. The surface (incident surface) of the second lens 121 on the display device 110 side has a shape in which the X-axis direction and the Y-axis direction face the plane on the display device 110 side. Also, the surface (exit surface) of the second lens 121 on the first mirror 122 side has a convex surface shape that is convex in the X-axis direction and the Y-axis direction on the first mirror 122 side.

[0023] The first mirror 122 is located in front of the vehicle 200 in the forward direction compared to the second lens 121. The first mirror 122 condenses the light rays emitted from the second lens 121 and reflects them toward the first lens 123. The reflecting surface of the first mirror 122 is eccentrically arranged so as to reflect the display image displayed on the display device 110 in the direction of being reflected on the second mirror 124. Here, the reflecting surface of the first mirror 122 is concave. That is, the first mirror 122 enlarges the light incident from the second lens 121 and projects it onto the first lens 123. Also, the first mirror 122 has a free-form surface shape. This is to correct the distortion of the virtual image caused by reflection.

[0024] The first lens 123 is located behind the vehicle 200 in the rearward direction compared to the first mirror 122 as shown in FIG. 2. The first lens 123 is arranged to be inclined clockwise with respect to the reference light ray Lc in the XZ plane view as shown in FIG. 2. The inclination of the first lens 123 with respect to the reference light ray Lc is, for example, an angle between 15 degrees and 30 degrees. Thereby, it is 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] Also, the first lens 123 is a free-form surface lens having different curvatures in the X-axis direction and the Y-axis direction. The surface (incident surface) of the first lens 123 on the first mirror 122 side has a convex shape that is convex in the X-axis direction and the Y-axis direction on the first mirror 122 side. Also, the surface (exit surface) of the first lens 123 on the second mirror 124 side has a shape in which the X-axis direction and the Y-axis direction face the plane on the display device 110 side.

[0026] The second mirror 124 is located in the rearward direction of the vehicle 200 with respect to the first lens 123. The second mirror 124 diverges the light rays emitted from the first lens 123 and forms an intermediate image M that magnifies the displayed image in the optical path between the second mirror 124 and the third mirror 125. The reflecting surface of the second mirror 124 is eccentrically arranged so as to magnify the displayed image projected by the first lens 123 and form the intermediate image M in the optical path between the second mirror 124 and the third mirror 125. Here, the reflecting surface of the second mirror 124 has a convex shape. The second mirror 124 has a free-form surface shape. This is to correct the 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 in the forward direction of the vehicle 200 with respect to the second mirror 124. The third mirror 125 condenses the light rays diverged by the second mirror 124 and projects the intermediate image M onto the windshield 220. The reflecting surface of the third mirror 125 is eccentrically arranged so as to project the intermediate image M onto the windshield 220. Here, the reflecting surface of the third mirror 125 has a concave shape. The third mirror 125 has a free-form surface shape. This is to correct the distortion of the virtual image caused by reflection.

[0028] In the projection optical system 140 in the present embodiment, in the order of the optical path from the display device 110, the first mirror 122, the first lens 123 having a condensing action, and the second mirror 124 as a first optical element having a diverging action and forming the intermediate image M are arranged. In this way, by arranging the first lens 123 and the second mirror 124 that forms the intermediate image M in this order of the optical path, the intermediate image M can be formed at a position close to the emission side of the first lens 123. As a result, the first lens 123 itself can be miniaturized, and the head-up display 100 can be miniaturized.

[0029] In the relay optical system 120 in the present embodiment, a first lens 123 having a positive power and a second mirror 124 having a negative power are arranged from the display device 110 toward the intermediate image M. That is, in the relay optical system 120, a so-called telephoto arrangement is adopted. By adopting such a 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 the power of each other. As a result, the overall length of the relay optical system 120 can be shortened, and the head-up display 100 can be miniaturized.

[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 with the comparative example without the first lens 123 shown in FIG. 3(A), in the present embodiment in which the first lens 123 and the second mirror 124 shown in FIG. 3(B) are in a telephoto arrangement, the overall length of the relay optical system 120 is shorter.

[0031] Also, in the vicinity of the second mirror 124 having a negative power for forming the intermediate image M, the light rays for forming the intermediate image M are converging. By arranging the first lens 123 having a positive power in the vicinity of the second mirror 124 having such a negative power to realize a telephoto arrangement, the first lens 123 itself can be miniaturized.

[0032] Also, in the present embodiment, as shown in FIG. 4, the incident surface and the exit surface of the second lens 121 are inclined counterclockwise with respect to the reference ray Lc in the XZ plane view of FIG. 4. Further, the incident surface and the exit surface of the first lens 123 are inclined clockwise with respect to the reference ray Lc in the XZ plane view of FIG. 4. As a result, the reflected light due to external light in the first lens 123 is reflected upward from the first mirror 122, and the reflected light due to external light in the second lens 121 is reflected downward from the first mirror 122. That is, it is possible to prevent external light from entering the viewpoint region 300. Here, the inclination of the second lens 121 and the first lens 123 with respect to the reference ray Lc is preferably set to an angle such that when external light incident along the reference ray Lc is reflected at the incident surface or the exit surface, the reflected light does not enter the first mirror 122. More preferably, the above inclination is set to an angle such that when external light incident from the first mirror 122 to the second lens 121 or the first lens 123 is reflected at the incident surface or the exit surface of the second lens 121 or the first lens 123, the reflected light does not enter the first mirror 122. Note that the fact that the second lens 121 and the first lens 123 are inclined with respect to the reference ray Lc means that the portion where the optical refracting surface of the second lens 121 and the first lens 123 intersects the reference ray Lc is not horizontal with respect to the plane perpendicular to the reference ray Lc.

[0033] In the present embodiment, the second lens 121 has a wedge shape in which the lens thickness becomes thinner toward the lower side with respect to the reference ray Lc. The first lens 123 has a wedge shape in which the lens thickness becomes thinner toward the upper side with respect to the reference ray Lc. When the second lens 121 is inclined with respect to the reference ray Lc as described above, if the exit surface of the second lens 121 has a convex surface shape symmetric with respect to the reference ray Lc, the optical path length of the light ray transmitted through the upper side of the second lens 121 with respect to the reference ray Lc is different from the optical path length of the light ray transmitted through the lower side. Similarly, when the first lens 123 is inclined with respect to the reference ray Lc, if the incident surface of the first lens 123 has a convex surface shape symmetric with respect to the reference ray Lc, the optical path length of the light ray transmitted through the upper side of the first lens 123 with respect to the reference ray Lc is different from the optical path length of the light ray transmitted through the lower side.

[0034] Therefore, in the present embodiment, the second lens 121 has a wedge shape in which the lens thickness becomes thinner toward the lower side with respect to the reference light beam Lc. Further, the first lens 123 has a wedge shape in which the lens thickness becomes thinner toward the upper side with respect to the reference light beam Lc. By configuring in this way, the light beam emitted from the display device 110 and transmitted through the upper side (i.e., the thick portion of the lens thickness of the second lens 121) with respect to the reference light beam Lc of the second lens 121 is reflected by the first mirror 122. Then, the reflected light beam is transmitted through the upper side (i.e., the thin portion of the lens thickness of the first lens 123) with respect to the reference light beam Lc of the first lens 123. Also, the light beam emitted from the display device 110 and transmitted through the lower side (i.e., the thin portion of the lens thickness of the second lens 121) with respect to the reference light beam Lc of the second lens 121 is reflected by the first mirror 122. Then, the reflected light beam is transmitted through the lower side (i.e., the thick portion of the lens thickness of the first lens 123) with respect to the reference light beam Lc of the first lens 123. In this way, the optical path lengths of the light beams transmitted through the second lens 121 and the first lens 123 are adjusted, and the optical path lengths of the light beams can be made uniform regardless of the portions passing through the second lens 121 and the first lens 123.

[0035] In the present embodiment, the exit surface of the second lens 121 is provided downward with respect to the entrance surface. That is, the shape of the second lens 121 in the Y-axis direction is a wedge shape. By making the cross-sectional shape of the second lens 121 along the Y-axis direction a wedge shape, the optical path length of the light passing through the upper side of the second lens 121 becomes longer than the optical path length of the light passing through the lower side of the second lens 121. That is, the optical path length until the image light emitted from the display device 110 reaches the first mirror 122 can be changed according to the position in the Y-axis direction. Thereby, the decentered image plane curvature generated in the first mirror 122 can be corrected favorably.

[0036] [1-2. Effects, etc.] As an example of the head-up display according to Embodiment 1, a head-up display 100 is a head-up display that projects an image onto a windshield 220 (an example of a transmissive reflective member) and 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 an image of 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 ray Lc. Therefore, even when external light enters the projection optical system 140, stray light caused by the reflection of the external light on the first lens 123 or the like can be suppressed. Further, the projection optical system 140 includes a first lens 123 having a condensing action and a second mirror 124 as an example of a first optical element having a diverging action in the order of the optical path from the display device 110. Thus, in the head-up display 100 according to Embodiment 1, in the order of the optical path from the display device 110, a first lens 123 having a positive power is disposed in front of a second mirror 124 having a negative power and forming an intermediate image M to form a telephoto arrangement. Therefore, the overall length of the relay optical system 120 can be shortened and the first lens 123 itself can be miniaturized, so that the head-up display 100 can be miniaturized.

[0037] A second mirror 124 was used as an example of the first optical element according to 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 Embodiment 1, 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, good optical characteristics can be realized while suppressing the reflection of external light.

[0039] In the head-up display 100 according to Embodiment 1, the first lens 123 has a wedge shape. Therefore, even when the first lens 123 is tilted with respect to the reference light beam Lc, the optical path length of the light beam passing through the first lens 123 can be adjusted.

[0040] The head-up display 100 according to Embodiment 1 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 has a free-form surface shape. Further, in the head-up display 100 according to Embodiment 1, the first lens 123 and the second lens 121 are arranged such that the light beam passing through the portion where one lens thickness is thin passes through the portion where the other lens thickness is thick, and the light beam passing through the portion where one lens thickness is thick passes through the portion where the other lens thickness is thin. Therefore, even when the first lens 123 and the second lens 121 are tilted with respect to the reference light beam Lc, the optical path lengths of the light beams passing through the first lens 123 and the second lens 121 can be made uniform.

[0041] In the head-up display 100 according to Embodiment 1, 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 member for forming the intermediate image M, the image displayed on the small display device 110 can be enlarged to form the intermediate image M, and the intermediate image M can be further enlarged and projected onto the observer D.

[0042] A vehicle 200, which is an example of a moving body according to Embodiment 1, includes a head-up display 100 and a windshield 220 as a transmissive reflection member. Thereby, the observer D driving the vehicle 200 can visually recognize the image projected on the windshield 220 as the virtual image I.

[0043] (Embodiment 2) Next, Embodiment 2 will be described with reference to FIG. 5.

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

[0045] The third lens 126 is located in front of the vehicle 200 with respect to the display device 110 and the second mirror 124 as shown in FIG. 5. In the third lens 126, as shown in FIG. 5, the surface on the side facing the first mirror 122 has a convex shape convex toward the first mirror 122 in the X-axis direction and the Y-axis direction. Further, in the third lens 126, as shown in FIG. 5, the surface on the side facing the display device 110 and the second mirror 124 has a planar shape facing the display device 110 and the second mirror 124. The third lens 126 is a free-form surface lens in which the curvature of the convex surface is different in the X-axis direction and the Y-axis direction.

[0046] In the optical path from the display device 110 to the first mirror 122, the planar surface of the second lens portion 126b is the incident surface, and the convex surface is the exit surface. In the second lens portion 126b, the incident surface and the exit surface are arranged to be inclined in the counterclockwise direction in the XZ plane view shown in FIG. 5 with respect to the reference light beam Lc. Thereby, it is possible to prevent stray light caused by external light entering the housing and reflecting on the display surface of the display device 110 and the first mirror 122.

[0047] In the optical path from the first mirror 122 to the second mirror 124, the planar surface of the first lens portion 126a is the exit surface, and the convex surface is the incident surface. The first lens portion 126a is arranged to be inclined in the clockwise direction in the XZ plane view shown in FIG. 5 with respect to the reference light beam Lc. Thereby, it is possible to prevent stray light caused by external light entering the housing and reflecting on the display surface of the display device 110 and the first mirror 122.

[0048] Also, in the relay optical system 120 in the present embodiment, a first lens unit 126a having a positive power and a second mirror 124 having a negative power are arranged from the display device 110 toward the intermediate image M. That is, in the relay optical system 120, a so-called telephoto arrangement is adopted. By adopting such a 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 the power of each other. As a result, the overall length of the relay optical system 120 can be shortened, and the head-up display 100 can be miniaturized.

[0049] As described above, in the present embodiment, the first lens unit 126a is arranged between the first mirror 122 as the second optical element 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, a third lens 126 having a positive power is arranged in front of the second mirror 124 as the first optical element that has a negative power and forms the intermediate image M. Therefore, by shortening the overall length of the relay optical system 120 and miniaturizing the first lens unit 126a itself, the head-up display 100 can be miniaturized.

[0050] In this embodiment, the third lens 126 is a lens formed by integrally configuring a first lens portion 126a and a second lens portion 126b corresponding to the second lens 121 and the first lens 123 in Embodiment 1. The first lens portion 126a and the second lens portion 126b have a wedge shape in which the lens thickness becomes thinner toward the end portion with respect to the central portion of the third lens 126. When the third lens 126 is tilted with respect to the reference light beam Lc as described above, in the optical path from the display device 110 to the first mirror 122, the optical path length of the light beam passing through the upper side of the second lens portion 126b with respect to the reference light beam Lc is different from the optical path length of the light beam passing through the lower side. Similarly, in the optical path from the first mirror 122 to the second mirror 124, the optical path length of the light beam passing through the upper side of the second lens portion 126b with respect to the reference light beam Lc is different from the optical path length of the light beam passing through the lower side.

[0051] Therefore, in this embodiment, the second lens portion 126b has a wedge shape in which the lens thickness becomes thinner toward the lower side with respect to the reference light beam Lc, and the first lens portion 126a has a wedge shape in which the lens thickness becomes thinner toward the upper side with respect to the reference light beam Lc. By configuring in this way, the light beam emitted from the display device 110 and transmitted through the upper side with respect to the reference light beam Lc of the second lens portion 126b (that is, the portion where the lens thickness of the second lens portion 126b is thick) is reflected by the first mirror 122. Then, the reflected light beam is transmitted through the upper side with respect to the reference light beam Lc of the first lens portion 126a (that is, the portion where the lens thickness of the first lens portion 126a is thin).

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

[0053] In this embodiment, in this way, 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 is adjusted, so that the optical path length of the light beam can be made uniform regardless of the location where the light beam passes through the third lens 126.

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

[0055] Furthermore, in the optical path from the display device 110 to the first mirror 122, the exit surface of the second lens portion 126b is provided downward from the incident surface. The shape of the second lens portion 126b in the Y-axis direction is a wedge shape. By making the cross-sectional shape along the Y-axis direction of the second lens portion 126b a wedge shape, in the optical path from the display device 110 to the first mirror 122, the optical path length of the light passing above the second lens portion 126b becomes longer than the optical path length of the light passing below the second lens portion 126b. That is, the optical path length until the video light emitted from the display device 110 reaches the first mirror 122 can be changed according to the position in the Y-axis direction. Thereby, decentered image plane curvature generated at the first mirror 122 can be corrected well.

[0056] In this embodiment, as described above, the third lens 126 is provided, which integrates the first lens portion 126a and the second lens portion 126b corresponding to the second lens 121 and the first lens 123 in Embodiment 1. Thereby, the number of components can be reduced, and the manufacturing cost of the head-up display 100 can be reduced.

[0057] [2-2. Effects, etc.] As an example of the head-up display according to Embodiment 2, the head-up display 100 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 an image of the image displayed by the display device 110 as an intermediate image M. The third lens 126 included in the projection optical system 140 is arranged to be inclined with respect to the reference light beam 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. Further, the projection optical system 140 includes, in the order of the optical path from the display device 110, a third lens 126 having a condensing action and a second mirror 124 as an example of a first optical element having a diverging action. The third lens 126 is a lens in which a first lens portion 126a and a second lens portion 126b corresponding to the first lens 123 and the second lens 121 in Embodiment 1 are integrally formed. Thus, in the head-up display 100 according to Embodiment 2, the third lens 126 and the second mirror 124 are arranged in the order of 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 downsized. As a result, the head-up display 100 can be downsized. Further, in the third lens 126, the second lens 121 and the first lens 123 in Embodiment 1 are integrally formed. Therefore, the number of parts can be reduced, and the manufacturing cost of the head-up display 100 can be reduced.

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

[0059] In this embodiment, the light beam emitted from the display device 110 passes through the third lens 126 twice in the optical path from the display device 110 to the first mirror 122 and in the optical path from the first mirror 122 to the second mirror 124. Also in this case, the projection optical system 140 includes, in the order of the optical path from the display device 110, the first mirror 122 having a condensing action, the third lens 126 having a condensing action, the second mirror 124 having a diverging action, and the third mirror 125 projecting the intermediate image M. Further, the light beam emitted from the display device 110 travels in the order of the first mirror 122, the third lens 126, the second mirror 124, and the third mirror 125, and there is no change in that the observer D visually recognizes 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, good optical characteristics can be realized while suppressing reflection of external light.

[0061] In the head-up display 100 according to the second embodiment, the first lens unit 126a and the second lens unit 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 beam Lc, the optical path length of the light beam passing through the third lens 126 can be adjusted.

[0062] In the head-up display 100 according to the second embodiment, a third lens 126 formed by integrally forming a first lens portion 126a and a second lens portion 126b corresponding to the first lens 123 and the second lens 121 in the first embodiment has a wedge shape. Therefore, in the optical path from the display device 110 to the first mirror 122, the light rays passing through the portion where the lens thickness of the second lens portion 126b is thin pass through the portion where the lens thickness of the first lens portion 126a is thick in the optical path from the first mirror 122 to the second mirror 124. Similarly, in the optical path from the display device 110 to the first mirror 122, the light rays passing through the portion where the lens thickness of the second lens portion 126b is thick pass through the portion where the lens thickness of the first lens portion 126a is thin in the optical path from the first mirror 122 to the second mirror 124. Therefore, even when the third lens 126 is tilted with respect to the reference ray Lc, the optical path lengths of the light rays 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 member 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] (Third Embodiment) Next, the third embodiment will be described with reference to FIG. 6.

[0065] [3-1. Configuration] FIG. 6 is a schematic diagram for explaining the optical path for explaining the head-up display 100 according to the third embodiment. 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] The display device 110 and the second lens 121 of the present embodiment have the same configuration as the display device 110 and the second lens 121 in each of the above-described embodiments. However, the arrangement positions are different from those in each of the above-described embodiments. In the present embodiment, as shown in FIG. 6, the display device 110 and the second lens 121 are located in front of the vehicle 200 rather than the fourth lens 127 as the second optical element.

[0067] As shown in FIG. 6, both the incident surface on the side facing the second lens 121 and the exit surface on the side facing the first lens 123 of the fourth lens 127 are convex surface shapes convex to the respective sides of the second lens 121 and the first lens 123 in the X-axis direction and the Y-axis direction. The fourth lens 127 is a free-form surface lens in which the curvature of the convex surface shape is different in the X-axis direction and the Y-axis direction.

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

[0069] As described above, in the present embodiment, the fourth lens 127 as the second optical element is used. The first lens 123 is arranged 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 a positive power is arranged in front of the second mirror 124 as the first optical element having a negative power and forming the intermediate image M. Therefore, by shortening the overall length of the relay optical system 120 and miniaturizing the first lens 123 itself, the head-up display 100 can be miniaturized.

[0070] In this embodiment, although the positional relationship between the first lens 123 and the second lens 121 is different from that in Embodiment 1, the positions of the thick and thin portions of the lens thickness with respect to the reference ray Lc are arranged to be opposite to each other. Therefore, similar to Embodiment 1, the optical path lengths of the rays passing through the second lens 121 and the first lens 123 can be adjusted so that the optical path lengths of the rays are made uniform regardless of the portions passing through the second lens 121 and the first lens 123.

[0071] [3-2. Effects, etc.] A head-up display 100 as an example of the head-up display according to Embodiment 3 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 an image of the image displayed by the display device 110 as an intermediate image M. The first lens 123 included in the projection optical system 140 is arranged to be inclined 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 first lens 123, the second lens 121, or the fourth lens 127 can be suppressed. Further, the projection optical system 140 includes a fourth lens 127 as an example of a second optical element, a first lens 123 having a condensing action, and a second mirror 124 as an example of a first optical element having a diverging action in the order of the optical path from the display device 110. Thus, in the head-up display 100 according to Embodiment 3, in the order of the optical path from the display device 110, a first lens 123 having a positive power is arranged in front of a second mirror 124 having a negative power and forming the intermediate image M to realize a telephoto arrangement. Therefore, the overall length of the relay optical system 120 can be shortened and the first lens 123 itself can be miniaturized, so that the head-up display 100 can be miniaturized.

[0072] The head-up display 100 according to Embodiment 3 has at least one surface of the first lens 123, the second lens 121, and the fourth lens 127 having a free-form surface. Therefore, in an imaging optical system such as the head-up display 100, good optical characteristics can be realized while suppressing reflection of external light.

[0073] In the head-up display 100 according to Embodiment 3, 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 beam Lc, the optical path length of the light beam passing through the first lens 123 and the second lens 121 can be adjusted.

[0074] In the head-up display 100 according to Embodiment 3, the positions of the thick and thin portions of the lens thickness in the first lens 123 and the second lens 121 with respect to the reference light beam Lc are arranged to be opposite to each other. Therefore, similar to Embodiment 1, the optical path length of the light beam passing through the second lens 121 and the first lens 123 can be adjusted to make the optical path length of the light beam uniform regardless of the portions passing through the second lens 121 and the first lens 123.

[0075] In the head-up display 100 according to Embodiment 3, 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 member for forming the intermediate image M, the image displayed on the small display device 110 can be enlarged to form the intermediate image M, and the intermediate image M can be further enlarged and projected onto the observer D.

[0076] (Embodiment 4) Next, Embodiment 4 will be described with reference to FIG. 7.

[0077] [4-1. Configuration] FIG. 7 is a schematic diagram for explaining an optical path for explaining the head-up display 100 according to Embodiment 4. As shown in FIG. 7, the head-up display 100 of the present 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] The fifth lens 128 is a free-form surface lens having different curvatures in the X-axis direction and the Y-axis direction. In the fifth lens 128, the surface on the first mirror 122 side is a flat incident surface, and the surface on the first lens 123 side is an exit surface having a concave shape that is concave toward the first lens 123 side in the X-axis direction. The curvature of the exit surface of the fifth lens 128 in the Y-axis direction is smaller than the curvature in the X-axis direction. That is, the shape of the fifth lens 128 in the Y-axis direction is a concave shape, a convex shape, or a flat shape with a curvature smaller than that in the X-axis direction.

[0079] In the present embodiment, as shown in FIG. 7, the incident surface and the exit surface of the fifth lens 128 are inclined in the clockwise direction with respect to the reference light beam Lc in the XZ plane view in FIG. 7. Thereby, the reflected light is reflected upward from the fifth lens 128. Therefore, the reflected light can be prevented from entering the viewpoint region 300. Here, the inclination of the fifth lens 128 with respect to the reference light beam Lc is desirably an angle such that the reflected light does not enter the first mirror 122 and the second mirror 124 when the external light incident along the reference light beam Lc is reflected at the incident surface or the exit surface. More desirably, the above inclination is an angle such that the reflected light does not enter the first mirror 122 when the external light incident from the first mirror 122 to the fifth lens 128 is reflected at the incident surface or the exit surface of the fifth lens 128. Note that the fifth lens 128 being inclined with respect to the reference light beam Lc means that the portion where the optical refracting surface of the fifth lens 128 intersects the reference light beam Lc is not horizontal with respect to the plane perpendicular to the reference light beam Lc.

[0080] The fifth lens 128 is a lens element having a negative refractive power. By disposing such 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, chromatic aberration generated in the first lens 123 can be suppressed.

[0081] In the projection optical system 140 according to the present embodiment, in the order of the optical path from the display device 110, a fifth lens 128, a first mirror 122 as a second optical element having a condensing action, and a second mirror 124 as a first optical element that forms an intermediate image M are arranged. In this way, by arranging the first lens 123 in front of the second mirror 124 that forms the intermediate image M in the order of 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. Therefore, the first lens 123 itself can be miniaturized. As a result, the head-up display 100 can be miniaturized. Further, due to the negative refractive power of the fifth lens 128, chromatic aberration generated in the first lens 123 can be suppressed.

[0082] Further, in the relay optical system 120 according to the present embodiment, a first lens 123 having a positive power and a second mirror 124 having a 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 such a telephoto arrangement, the first lens 123 increases the negative power of the second mirror 124, and the second mirror 124 increases the positive power of the first lens 123. That is, the first lens 123 and the second mirror 124 enhance the power of each other. As a result, the overall length of the relay optical system 120 can be shortened, and the head-up display 100 can be miniaturized.

[0083] Also, in the present embodiment, as shown in FIG. 7, the incident surface and the exit surface of the second lens 121 are inclined counterclockwise with respect to the reference light beam Lc in the XZ plane view of FIG. 7. Further, the incident surface and the exit surface of the first lens 123 are inclined clockwise with respect to the reference light beam Lc in the XZ plane view of FIG. 7. Thereby, the reflected light due to external light in the first lens 123 is reflected downward from the second mirror 124, and the reflected light due to external light in the second lens 121 is reflected downward from the first mirror 122. Therefore, it is possible to prevent the reflected light from entering the viewpoint region 300. Here, the inclination of the second lens 121 and the first lens 123 with respect to the reference light beam Lc is desirably set to an angle such that when the external light incident along the reference light beam Lc is reflected at the incident surface or the exit surface, the reflected light does not enter the first mirror 122 or the second mirror 124. More desirably, the above inclination is set to an angle such that when the external light incident from the first mirror 122 to the second lens 121 or the first lens 123 is reflected at the incident surface or the exit surface of the second lens 121 or the first lens 123, the reflected light does not enter the first mirror 122. Note that the fact that the second lens 121 and the first lens 123 are inclined with respect to the reference light beam Lc means that the location where the optical refracting surface of the second lens 121 and the first lens 123 intersects the reference light beam Lc is not horizontal with respect to the plane perpendicular to the reference light beam Lc.

[0084] In the present embodiment, similar to the first embodiment, the positions of the thick and thin portions of the lens thickness in the first lens 123 and the second lens 121 with respect to the reference light beam Lc are arranged to be opposite to each other. Therefore, similar to the first embodiment, the optical path lengths of the light beams passing through the second lens 121 and the first lens 123 can be adjusted to make the optical path lengths of the light beams uniform regardless of the portions passing through the second lens 121 and the first lens 123.

[0085] [4-2. Effects, etc.] As an example of the head-up display according to Embodiment 4, a head-up display 100 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 an image of 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 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. Further, the projection optical system 140 includes a first lens 123 having a condensing action and a second mirror 124 as an example of a first optical element having a diverging action in the order of the optical path from the display device 110. Thus, in the head-up display 100 according to Embodiment 4, in the order of the optical path from the display device 110, a first lens 123 having a positive power is disposed in front of a second mirror 124 having a negative power and forming an intermediate image M, so as to form a telephoto arrangement. Therefore, the overall length of the relay optical system 120 can be shortened, and the head-up display 100 can be downsized by downsizing the first lens 123 itself. Further, a fifth lens 128 is disposed in front of the first lens 123 in the order of the optical path from the display device 110. Therefore, chromatic aberration generated by the first lens 123 can be suppressed by the negative refractive power of the fifth lens 128.

[0086] In the head-up display 100 according to Embodiment 4, a first mirror 122 is used as an example of a second optical element, and a second mirror 124 is used as an example of a 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 further enlarge the intermediate image M and project it onto the observer D.

[0087] In the head-up display 100 according to Embodiment 4, 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, good optical characteristics can be realized while suppressing reflection of external light.

[0088] In the head-up display 100 according to Embodiment 4, 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 beam Lc, the optical path length of the light beam passing through the first lens 123 and the second lens 121 can be adjusted.

[0089] The head-up display 100 according to Embodiment 4 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 has a free-form surface shape. Further, in the head-up display 100 according to Embodiment 4, the first lens 123 and the second lens 121 are arranged such that the light beam passing through the portion where one lens thickness is thin passes through the portion where the other lens thickness is thick, and the light beam passing through the portion where one lens thickness is thick passes through the portion where the other lens thickness is thin. Therefore, even when the first lens 123 and the second lens 121 are tilted with respect to the reference light beam Lc, the optical path lengths of the light beams passing through the first lens 123 and the second lens 121 can be made uniform.

[0090] In the head-up display 100 according to Embodiment 4, 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 member 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, Embodiment 5 will be described with reference to FIG. 8.

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

[0093] The sixth lens 129 is a free-form surface lens having different curvatures in the X-axis direction and the Y-axis direction. In the sixth lens 129, the surface on the third mirror 125 side is a flat emission surface, and the surface on the intermediate image M side is an incident surface having a concave shape that is concave toward the first lens 123 side in the X-axis direction. The curvature of the incident surface of the second mirror 124 in the Y-axis direction is smaller than the curvature in the X-axis direction. That is, the shape of the sixth lens 129 in the Y-axis direction is a concave shape, a convex shape, or a flat shape smaller than the curvature in the X-axis direction.

[0094] In the present embodiment, as shown in FIG. 8, the incident surface and the emission surface of the sixth lens 129 are inclined counterclockwise with respect to the reference light beam Lc in a view from the XZ plane in FIG. 8. Thereby, the reflected light is reflected downward from the sixth lens 129. Therefore, the reflected light can be prevented from entering the viewpoint region 300. Here, the inclination of the sixth lens 129 with respect to the reference light beam Lc is desirably an angle at which external light incident along the reference light beam Lc is not incident on the third mirror 125 and the second mirror 124 when reflected at the incident surface or the emission surface. More desirably, the above inclination is an angle at which external light incident from the second mirror 124 to the sixth lens 129 is not incident on the second mirror 124 and the third mirror 125 when reflected at the incident surface or the emission surface of the sixth lens 129. Note that the fact that the sixth lens 129 is inclined with respect to the reference light beam Lc means that the portion where the optical refractive surface of the sixth lens 129 intersects the reference light beam Lc is not horizontal with respect to the plane perpendicular to the reference light beam Lc.

[0095] The sixth lens 129 is a lens element having a negative refractive power. In the optical path from the display device 110 to the third mirror 125, such a sixth lens 129 is arranged behind the optical elements of the relay optical system 120. Thereby, the burden of aberration correction of the optical elements can be reduced, and high image quality can be achieved.

[0096] In the projection optical system 140 of the present embodiment, in the order of the optical path from the display device 110, a first mirror 122 as a second optical element having a condensing action and a second mirror 124 as a first optical element that forms an intermediate image M are arranged. In this way, by arranging the first lens 123 in front of the second mirror 124 that forms the intermediate image M in the order of 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. Therefore, the first lens 123 itself can be miniaturized. As a result, the head-up display 100 can be miniaturized. Further, a sixth lens 129 is arranged behind the intermediate image M. Therefore, the burden of aberration correction of the optical elements in the relay optical system 120 can be reduced, and high image quality can be achieved.

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

[0098] Also, in the present embodiment, as shown in FIG. 8, the incident surface and the exit surface of the second lens 121 are inclined counterclockwise with respect to the reference ray Lc in the XZ plane view of FIG. 8. Further, the incident surface and the exit surface of the first lens 123 are inclined clockwise with respect to the reference ray Lc in the XZ plane view of FIG. 8. As a result, the reflected light due to external light in the first lens 123 is reflected downward from the second mirror 124, and the reflected light due to external light in the second lens 121 is reflected downward from the first mirror 122. Therefore, it is possible to prevent the reflected light from entering the viewpoint region 300. Here, the inclination of the second lens 121 and the first lens 123 with respect to the reference ray Lc is desirably set to an angle such that when the external light incident along the reference ray Lc is reflected at the incident surface or the exit surface, the reflected light does not enter the first mirror 122 or the second mirror 124. More desirably, the above inclination is set to an angle such that when the external light incident from the first mirror 122 to the second lens 121 or the first lens 123 is reflected at the incident surface or the exit surface of the second lens 121 or the first lens 123, the reflected light does not enter the first mirror 122. Note that the fact that the second lens 121 and the first lens 123 are inclined with respect to the reference ray Lc means that the point where the optical refracting surface of the second lens 121 and the first lens 123 intersects the reference ray Lc is not horizontal with respect to the plane perpendicular to the reference ray Lc.

[0099] In the present embodiment, as in the first embodiment, the positions of the thick and thin portions of the lens thickness in the first lens 123 and the second lens 121 with respect to the reference ray Lc are arranged to be opposite to each other. Therefore, as in the first embodiment, the optical path length of the light rays passing through the second lens 121 and the first lens 123 can be adjusted to make the optical path length of the light rays uniform regardless of the portions passing through the second lens 121 and the first lens 123.

[0100] [5-2. Effects, etc.] As an example of the head-up display according to Embodiment 5, the head-up display 100 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 an image of the image displayed by the display device 110 as an intermediate image M. The first lens 123 included in the projection optical system 140 is disposed at an angle with respect to the reference light beam 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 or the like can be suppressed. Further, the projection optical system 140 includes a first lens 123 having a condensing action and a second mirror 124 as an example of a first optical element having a diverging action in the order of the optical path from the display device 110. Thus, in the head-up display 100 according to Embodiment 5, in the order of the optical path from the display device 110, the first lens 123 having a positive power is disposed in front of the second mirror 124 having a negative power and forming the intermediate image M to form a telephoto arrangement. Therefore, the overall length of the relay optical system 120 can be shortened and the first lens 123 itself can be miniaturized, so that the head-up display 100 can be miniaturized. Further, in the order of the optical path from the display device 110, the sixth lens 129 is disposed behind the relay optical system 120. Therefore, the aberration correction burden of the optical elements of the relay optical system 120 can be reduced, and high image quality can be achieved.

[0101] In the head-up display 100 according to Embodiment 5, a first mirror 122 is used as an example of a second optical element, and a second mirror 124 is used as an example of a first optical element. Therefore, it is possible to sufficiently enlarge the image displayed on the small display device 110 to create the intermediate image M, and further enlarge the intermediate image M and project it onto the observer D.

[0102] In the head-up display 100 according to Embodiment 5, 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, good optical characteristics can be realized while suppressing reflection of external light.

[0103] In the head-up display 100 according to Embodiment 5, 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 beam Lc, the optical path length of the light beam passing through the first lens 123 and the second lens 121 can be adjusted.

[0104] The head-up display 100 according to Embodiment 5 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 has a free-form surface shape. Further, in the head-up display 100 according to Embodiment 4, the first lens 123 and the second lens 121 are arranged such that the light beam passing through the portion where one lens thickness is thin passes through the portion where the other lens thickness is thick, and the light beam passing through the portion where one lens thickness is thick passes through the portion where the other lens thickness is thin. Therefore, even when the first lens 123 and the second lens 121 are tilted with respect to the reference light beam Lc, the optical path lengths of the light beams transmitted through the first lens 123 and the second lens 121 can be made uniform.

[0105] In the head-up display 100 according to Embodiment 5, 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, 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 without adding a member for forming the intermediate image M.

[0106] (Embodiment 6) Next, Embodiment 6 will be described with reference to FIG. 9.

[0107] [6-1. Configuration] FIG. 9 is a schematic diagram for explaining an optical path for explaining the 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 Embodiment 1 and Embodiment 2. However, the arrangement position is different from each 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. Further, 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 each of the above-described embodiments. However, the arrangement position is different from each of the above-described embodiments. In the present embodiment, the display device 110 and the second lens 121 are located in the forward direction of the vehicle 200 rather than the first mirror 122 as shown in FIG. 9.

[0109] The first lens 123 of the present embodiment has the same configuration as the first lens 123 in Embodiment 1 and Embodiment 3. However, the arrangement position is different. The first lens 123 in the present embodiment is located in the rearward direction of the vehicle 200 rather than the seventh lens 150 as the first optical element.

[0110] The seventh lens 150 is a free-form surface lens having different curvatures in the X-axis direction and the Y-axis direction. In the seventh lens 150, the surface on the first lens 123 side is a flat incident surface, and the surface on the third mirror 125 side is an exit surface having a concave shape that is concave toward the third mirror 125 side in the X-axis direction. The curvature of the exit surface of the seventh lens 150 in the Y-axis direction is smaller than the curvature in the X-axis direction. That is, the shape of the seventh lens 150 in the Y-axis direction is a concave shape, a convex shape, or a flat shape having a curvature smaller than the curvature in the X-axis direction.

[0111] In the present embodiment, as shown in FIG. 9, the incident surface and the exit surface of the seventh lens 150 are inclined counterclockwise with respect to the reference light beam Lc in the XZ plane view in FIG. 9. Thereby, the reflected light is reflected downward from the seventh lens 150. Therefore, it is possible to prevent the reflected light from entering the viewpoint region 300. Here, the inclination of the seventh lens 150 with respect to the reference light beam Lc is desirably set to an angle such that when external light incident along the reference light beam Lc is reflected at the incident surface or the exit surface, the reflected light does not enter the first mirror 122 and the third mirror 125. More desirably, the above inclination is set to an angle such that when external light incident from the first mirror 122 to the seventh lens 150 is reflected at the incident surface or the exit surface of the seventh lens 150, the reflected light does not enter the first mirror 122. Note that the fact that the seventh lens 150 is inclined with respect to the reference light beam Lc means that the portion where the optical refractive surface of the seventh lens 150 intersects the reference light beam Lc is not horizontal with respect to the plane perpendicular to the reference light beam Lc.

[0112] Furthermore, the exit surface of the seventh lens 150 has a wedge shape in the XZ plane view of FIG. 9. By making the cross-sectional shape along the Y-axis direction of the seventh lens 150 wedge-shaped, the optical path length of the light passing above the seventh lens 150 becomes longer than the optical path length of the light passing below the seventh lens 150. That is, the optical path length until the video light emitted from the display device 110 forms an intermediate image M can be changed according to the position in the Y-axis direction. Thereby, the decentered image plane curvature generated in the first mirror 122 can be corrected favorably.

[0113] In the projection optical system 140 according to the present embodiment, in the order of the optical path from the display device 110, a first mirror 122 as a second optical element having a condensing action and a seventh lens 150 as a first optical element that forms an intermediate image M are arranged. A first lens 123 having a condensing action is arranged between the first mirror 122 and the seventh lens 150. Thus, 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 miniaturized. As a result, the head-up display 100 can be miniaturized.

[0114] Further, in the relay optical system 120 according to the present embodiment, a first lens 123 having a positive power and a seventh lens 150 having a 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 such a telephoto arrangement, the first lens 123 increases the negative power of the seventh lens 150, and the seventh lens 150 increases the positive power of the first lens 123. That is, the first lens 123 and the seventh lens 150 enhance the power of each other. As a result, the overall length of the relay optical system 120 can be shortened, and the head-up display 100 can be miniaturized.

[0115] Also, in the present embodiment, as shown in FIG. 9, the incident surface and the exit surface of the second lens 121 are inclined in the clockwise direction with respect to the reference ray Lc in the XZ plane view of FIG. 9. Further, the incident surface and the exit surface of the first lens 123 are inclined in the counterclockwise direction with respect to the reference ray Lc in the XZ plane view of FIG. 9. Thereby, the reflected light due to external light in the first lens 123 is reflected upward from the first mirror 122, and the reflected light due to external light in the second lens 121 is reflected downward from the first mirror 122. Therefore, it is possible to prevent the reflected light from entering the viewpoint region 300. Here, the inclination of the second lens 121 and the first lens 123 with respect to the reference ray Lc is desirably set to an angle such that when the external light incident along the reference ray Lc is reflected at the incident surface or the exit surface, the reflected light does not enter the first mirror 122. More desirably, the above inclination is set to an angle such that when the external light incident from the first mirror 122 to the second lens 121 or the first lens 123 is reflected at the incident surface or the exit surface of the second lens 121 or the first lens 123, the reflected light does not enter the first mirror 122. Note that the fact that the second lens 121 and the first lens 123 are inclined with respect to the reference ray Lc means that the portion where the optical refracting surface of the second lens 121 and the first lens 123 intersects the reference ray Lc is not horizontal with respect to the plane perpendicular to the reference ray Lc.

[0116] In the present embodiment, similar to the first embodiment, the positions of the thick and thin portions of the lens thickness in the first lens 123 and the second lens 121 with respect to the reference ray Lc are arranged to be opposite to each other. Therefore, similar to the first embodiment, it is possible to adjust the optical path lengths of the light rays passing through the second lens 121 and the first lens 123, and to make the optical path lengths of the light rays uniform regardless of the portions passing through the second lens 121 and the first lens 123.

[0117] [6-2. Effects, etc.] The head-up display 100 as an example of the head-up display according to Embodiment 6 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 an image of the image displayed by the display device 110 as an intermediate image M. The first lens 123 included in the projection optical system 140 is disposed at an angle with respect to the reference light beam 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 or the like can be suppressed. Further, the projection optical system 140 includes a first lens 123 having a condensing action and a seventh lens 150 as an example of a first optical element in the order of the optical path from the display device 110. Thus, in the head-up display 100 according to Embodiment 6, in the order of the optical path from the display device 110, a first lens 123 having a positive power is disposed in front of the seventh lens 150 having a negative power and forming the intermediate image M to form a telephoto arrangement. Therefore, the overall length of the relay optical system 120 can be shortened and the first lens 123 itself can be miniaturized, so that the head-up display 100 can be miniaturized.

[0118] A first mirror 122 is used as an example of the second optical element according to Embodiment 6, and a third mirror 125 is used for 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 further enlarge the intermediate image M and project it onto the observer D.

[0119] The head-up display 100 according to Embodiment 6 uses a seventh lens 150 having a negative power as an example of the first optical element near the intermediate image M. Thereby, the seventh lens 150 functions as a so-called field lens. Therefore, the first lens 123, the first mirror 122, and the second lens 121 can be miniaturized.

[0120] In the head-up display 100 according to Embodiment 6, 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, good optical characteristics can be realized while suppressing reflection of external light.

[0121] In the head-up display 100 according to Embodiment 6, the first lens 123, the second lens 121, and the seventh lens 150 have a wedge shape. Therefore, even when the first lens 123, the second lens 121, and the seventh lens 150 are tilted with respect to the reference light beam Lc, the optical path length of the light beam 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 Embodiment 6 includes a second lens 121 between the display device 110 and the first mirror 122 as an example of the second optical element. The second lens 121 has a wedge shape and at least one surface has a free-form surface shape. Further, in the head-up display 100 according to Embodiment 6, the first lens 123 and the second lens 121 are arranged such that the light beam passing through the portion where one lens thickness is thin passes through the portion where the other lens thickness is thick, and the light beam passing through the portion where one lens thickness is thick passes through the portion where the other lens thickness is thin. Therefore, even when the first lens 123 and the second lens 121 are tilted with respect to the reference light beam Lc, the optical path lengths of the light beams passing through the first lens 123 and the second lens 121 can be made uniform.

[0123] In the head-up display 100 according to Embodiment 6, 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, it is possible to enlarge the image displayed on the small display device 110 to obtain the intermediate image M and further enlarge the intermediate image M and project it onto the observer D without adding a member for forming the intermediate image M.

[0124] (Other Embodiments) As described above, as examples of the technologies disclosed in the present application, Embodiments 1 to 6 have been described. However, the technology in the present disclosure is not limited to this, and can also be applied to embodiments with changes, replacements, additions, omissions, etc. Further, it is also possible to form a new embodiment by combining the respective components described in the above Embodiments 1 to 6.

[0125] In Embodiments 1 to 6, the second lens 121 was shown as an example of the refractive optical system provided between the display device 110 and the first mirror 122. However, the refractive optical system is not limited to the second lens 121 which is a single lens element. For example, the refractive optical system may be one in which a plurality of lens elements are arranged between the display device 110 and the first mirror 122. When there are a plurality of lens elements, it is desirable that the lens element which the light emitted from the display device first enters has a positive power.

[0126] In Embodiments 1 to 6, one third mirror 125 is arranged as the projection optical system 140. However, two or more mirrors may be arranged. Further, the additional mirror may be arranged in front of the vehicle more than the third mirror 125, or may be arranged in the inner or outer direction of the vehicle, that is, in the direction perpendicular to the paper surface in FIGS. 1, 2, and 4 to 9.

[0127] In Embodiments 1 to 6, lens elements are 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 arranged between the third mirror 125 and the windshield 220.

[0128] In the head-up display 100 of Embodiments 1 to 6, the first mirror 122, the second mirror 124, and the third mirror 125 have been described using mirrors having a rotationally asymmetric shape. 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 the curvature are different in the X-axis direction and the Y-axis direction.

[0129] In Embodiments 1 to 6, the surface shape of the lens element used is not limited to a free-form surface shape. For example, the surface shape of the lens element may be a toroidal shape, an anamorphic shape, or a cylindrical shape. Further, lenses having these shapes may be arranged eccentrically with respect to the reference ray Lc.

[0130] In Embodiment 4, for the exit surface of the fifth lens 128, in Embodiment 5, for the entrance surface of the sixth lens 129, and in Embodiment 6, for the exit surface, the entire surface in the X-axis direction does not have to be concave, and may locally have a convex shape.

[0131] In Embodiments 1 to 6, the plane shape surface of the lens element used may be convex or concave, or may locally have a curved surface shape.

[0132] In Embodiments 1 to 5, the shape of the reflection surfaces of the first mirror 122, the second mirror 124, and the third mirror 125 is not limited to a free-form surface shape. The reflection surfaces of these mirrors may be a spherical shape, an aspherical shape, a toroidal shape, or an anamorphic shape. Further, mirrors having these shapes may be arranged eccentrically with respect to the reference ray Lc.

[0133] In Embodiments 1 to 6, the head-up display 100 is arranged below the dashboard 210, but it may also be arranged above the dashboard 210.

[0134] As described above, the embodiments have been described as examples of the technology in the present disclosure. For that purpose, the accompanying drawings and the detailed description have been provided. Therefore, among the components described in the accompanying drawings and the detailed description, not only the components essential for solving the problems but also the components not essential for solving the problems for exemplifying the above technology may be included. Therefore, just because those non-essential components are described in the accompanying drawings and the detailed description, it should not be immediately determined that those non-essential components are essential.

[0135] In addition, since the above-described embodiments are for exemplifying the technology in the present disclosure, various changes, replacements, additions, omissions, etc. can be made within the scope of the claims or the equivalent scope thereof.

[0136] (Summary of Embodiment) (1) The head-up display of the present disclosure is a head-up display that projects an image onto a transmissive reflective member and allows an observer to visually recognize 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 onto the observer. The projection optical system has a function of forming an intermediate image of the image, and includes a first lens having a condensing action and a first optical element having a diverging action. The first lens and the first optical element are arranged in the order of the optical path from the display device. When a reference ray that reaches the center of the observer's viewpoint region and corresponds to the center of the virtual image is used as a reference ray, the first lens is arranged at an angle with respect to the reference ray.

[0137] In this way, a projection optical system is configured by arranging a first lens having a condensing action and a first optical element having a diverging action in the order of the optical path from the display device, and the first lens is arranged at an angle with respect to the reference ray. Therefore, even when external light enters the projection optical system, stray light caused by the reflection of the external light on the first lens or the like can be suppressed. Further, the projection optical system is arranged in a telephoto arrangement with a first lens having a positive power in front of a first optical element having a negative power and forming an intermediate image in the order of the optical path from the display device. Therefore, the overall length of the relay optical system can be shortened, and the head-up display can be miniaturized by miniaturizing the first lens itself.

[0138] (2) In the head-up display of (1), the first optical element is a mirror. Therefore, it is possible to sufficiently enlarge the image displayed on the small display device to create an intermediate image, and further enlarge the intermediate image and project it onto the observer.

[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, good optical characteristics can be realized while suppressing reflection of external light.

[0140] (4) In any one of the head-up displays from (1) to (3), the first lens has a wedge shape. Therefore, even when the first lens is tilted with respect to the reference light beam, the optical path length of the light beam 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 condensing action and a second lens having a condensing action. The second lens, the second optical element, and the first lens are arranged in the order of 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 such that light rays passing through a thin portion of the lens thickness of the first lens pass through a thick portion of the lens thickness of the second lens, and light rays passing through a thick portion of the lens thickness of the first lens pass through a thin portion of the lens thickness of the second lens. Therefore, even when the first lens and the second lens are tilted with respect to the reference light beam, 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. Therefore, the number of parts can be reduced and the manufacturing cost of the head-up display can be reduced.

[0143] (7) In the head-up display of (5), the projection optical system includes a lens having a negative refractive power, which is arranged to be tilted with respect to the reference light beam in front of the first lens in the optical path from the second optical element to the first optical element. Therefore, the burden of aberration correction of the optical element can be reduced and high image quality can be achieved.

[0144] (8) In the head-up display of (5), the projection optical system includes a lens that is disposed at an angle with respect to the reference light beam after the intermediate image in the optical path from the first optical element to the virtual image and has a negative refractive power. Therefore, the burden of aberration correction of the optical element can be reduced, and high image quality can be achieved.

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

Industrial Applicability

[0146] The present disclosure is applicable to a head-up display using a refractive optical system such as a lens. Specifically, the present disclosure is applicable to a head-up display for vehicles and the like.

Explanation of Signs

[0147] 100 Head-up display 110 Display device 120 Relay optical system 121 Second lens 122 First mirror 123 First lens 124 Second mirror 125 Third mirror 126 Third lens 127 Fourth lens 128 Fifth lens 129 Sixth lens 130 Projection optical system 140 Projection optical system 150 Seventh lens 200 Vehicle 210 Dashboard 220 Windshield 300 Viewpoint area D Observer I Virtual image M Intermediate image L Light ray Lc Reference light ray

Claims

1. A head-up display that projects a projected image formed from an original image onto a transmissive reflective member to allow an observer to visually recognize a virtual image, a device that emits a light beam that forms the projected image from the original image, and a projection optical system that forms the projected image from the original image and projects the projected image as a virtual image onto the observer, comprising: the projection optical system includes: a first lens having a refracting surface for incident light rays emitted from the device, a fifth lens having a concave surface on the side of the first lens and having a negative refractive power, a second mirror that reflects light rays, and a third mirror that reflects the light reflected by the second mirror as the projected image onto the reflective member, wherein the fifth lens, the first lens, the second mirror, and the third mirror are arranged in the order of the optical path to the reflective member, the surface of the fifth lens on the side of the first lens has a concave shape that is concave in the first axial direction, and the curvature in the second axial direction perpendicular to the first axial direction is a free-form surface shape smaller than the curvature in the first axial direction, a head-up display.

2. The fifth lens is arranged adjacent to the first lens in the optical path, and the surface opposite to the surface on the side of the first lens has a planar shape, The head-up display according to claim 1.

3. When the light ray that reaches the center of the observer's viewing area and corresponds to the center of the virtual image is used as a reference light ray, the fifth lens is arranged to be inclined with respect to the reference light ray, The head-up display according to claim 1.

4. The fifth lens is arranged to be inclined with respect to the reference light ray such that the upper side is closer to the second mirror than the lower side, The head-up display according to claim 3.

5. When the light ray that reaches the center of the observer's viewing area and corresponds to the center of the virtual image is used as a reference light ray, the first lens is arranged to be inclined with respect to the reference light ray, The head-up display according to claim 1.

6. The projection optical system has a function of forming the original image as an intermediate image by the light rays emitted from the device and forming the projected image from the intermediate image, The head-up display according to claim 5.

7. The first lens is arranged to be inclined with respect to the reference light ray such that the upper side is closer to the second mirror than the lower side, The head-up display according to claim 5. A head-up display that projects a projected image formed from an original image onto a transmissive reflective member to allow an observer to visually recognize a virtual image, A device that emits light rays for forming the projected image from the original image, A projection optical system that forms the projected image from the original image and projects the projected image as a virtual image onto the observer, comprising: The projection optical system includes: A first lens having a refracting surface for incident light rays emitted from the device, A fifth lens having a concave surface on the side of the first lens and having a negative refractive power, A second mirror that reflects light rays, A third mirror that reflects the light reflected by the second mirror as the projected image onto the reflective member, The fifth lens, the first lens, the second mirror, and the third mirror are arranged in the order of the optical path to the reflective member, When a reference light ray that reaches the center of the observer's viewing area and corresponds to the center of the virtual image is used, the first lens is arranged at an angle with respect to the reference light ray, The first lens is arranged at an angle with respect to the reference light ray such that the upper side is closer to the second mirror than the lower side, The first lens is arranged at an angle between 15 degrees and 30 degrees with respect to a plane perpendicular to the reference light ray. A head-up display. A head-up display that projects a projected image formed from an original image onto a transmissive reflective member to allow an observer to visually recognize a virtual image, A device that emits light rays for forming the projected image from the original image, A projection optical system that forms the projected image from the original image and projects the projected image as a virtual image onto the observer, comprising: The projection optical system includes: A first lens having a refracting surface for incident light rays emitted from the device, A fifth lens having a concave surface on the side of the first lens and having a negative refractive power, A second mirror that reflects light rays, A third mirror that reflects the light reflected by the second mirror as the projected image onto the reflective member, The fifth lens, the first lens, the second mirror, and the third mirror are arranged in the order of the optical path to the reflective member, When a reference light ray that reaches the center of the observer's viewing area and corresponds to the center of the virtual image is used, the first lens is arranged at an angle with respect to the reference light ray, The projection optical system has a function of forming the original image as an intermediate image by the light rays emitted from the device and forming the projected image from the intermediate image. The optical path between the second mirror and the third mirror is in the air, The intermediate image is an aerial image formed in the air on the optical path between the second mirror and the third mirror, Head-up display.

10. The intermediate image is formed at a position closer to the second mirror than the third mirror, The head-up display according to claim 9.

11. The third mirror is a concave mirror, The head-up display according to claim 1.

12. The third mirror has a free-form surface shape, The head-up display according to claim 11.

Images