Projection optical system, image projection device, and eyepiece device

Abstract

The present invention achieves both stabilization of operation of a deflection mirror and miniaturization of a device.　The present art provides a projection optical system, etc., comprising a first lens group that has at least one lens and condenses light projected from a light source to a position of a primary imaging point that is an image of the light source, a deflection mirror that causes light to scan from the first lens group, and a second lens group that has at least one lens and forms an image of light from the deflection mirror at a position of a secondary image formation point that is an image of the primary image formation point, the focal point of the second lens group on the light source side being positioned in the vicinity of the emission position of a principal ray of light on the deflection mirror.

Description

Projection optical system, image projection apparatus, and eyepiece device

[0001] The technology according to the present disclosure (hereinafter also referred to as "the technology") relates to a projection optical system, an image projection apparatus, and an eyepiece device.

[0002] A technology has been developed for projecting an image by two-dimensionally scanning a light beam from a light source using a deflection mirror.

[0003] For example, Patent Document 1 discloses a technology relating to "a projection optical system comprising, in order from the light source side to the projection side along the optical axis, a first lens group having at least one lens and a positive focal length, which focuses light from the light source onto a primary image point that is an image of the light source; a deflector which scans the light from the first lens group; and a second lens group having at least one lens and a positive focal length, which focuses light from the deflector onto a secondary image point that is an image of the primary image point, wherein the first lens group forms the primary image point between the first lens group and the second lens group along the optical axis."

[0004] This patent document explains that by shortening the distance between the deflection mirror and the primary image point, the effective diameter of the deflection mirror can be reduced, which has advantages such as making the device smaller and preventing costs from increasing.

[0005] International Publication No. 2018 / 110448

[0006] The size of the image projected by a projection optical system is generally larger than the lens group that makes up the projection optical system. As a result, the image light emitted from this lens group often diverges as it travels. Therefore, the smaller the image size to be projected, the smaller the deflection mirror's swing angle tends to be. If the deflection mirror's swing angle becomes extremely small, the operation of the deflection mirror may become unstable. For this reason, it is necessary to ensure a certain degree of swing angle.

[0007] To ensure a certain degree of deflection angle, for example, the image light emitted from the lens group that constitutes the projection optical system may be converged, in which case the deflection mirror deflection angle becomes relatively large.

[0008] In this case, however, the area through which the chief ray of each light beam passes on the exit surface of this lens group becomes larger than the size of the image to be projected, which may result in an increase in the size of the projection optical system.

[0009] Therefore, a main object of the present technology is to provide a projection optical system or the like that achieves both stabilization of the operation of the deflection mirror and miniaturization of the device.

[0010] The present technology provides a projection optical system including: a first lens group having at least one lens and converging light projected from a light source at a position of a primary image point, which is an image of the light source; a deflection mirror that scans the light from the first lens group; and a second lens group having at least one lens and focusing the light from the deflection mirror at a position of a secondary image point, which is an image of the primary image point, wherein a focal point of the second lens group on the light source side is located near an emission position of a chief ray of light on the deflection mirror. When a direction from the deflection mirror to the second lens group is defined as positive, a distance from the focal point of the second lens group on the light source side to an emission position of light on the deflection mirror may be between −1% and 2% of a focal length of the second lens group. The focal length of the first lens group may be 2.0 mm or more. The focal length of the second lens group may be 24 mm or less. The distance on the optical axis from the exit surface of the second lens group to the secondary image point may be 500 mm or less. Chief rays of each light beam projected from the second lens group may be approximately parallel. The first lens group may have a combined lens of a positive lens and a negative lens. The second lens group may have a combined lens of a positive lens and a negative lens. The light projected from the light source may be laser light. The light source may include: a first light source unit that projects emitted light in a first wavelength band; a second light source unit that projects emitted light in a second wavelength band; and a third light source unit that projects emitted light in a third wavelength band. The first wavelength band may be a wavelength band corresponding to red; the second wavelength band may be a wavelength band corresponding to green; and the third wavelength band may be a wavelength band corresponding to blue.The present technology also provides an image projection device including: a projection optical system; and an eyepiece device placed in front of an eye of an observer, wherein the projection optical system includes: a first lens group having at least one lens and converging light projected from a light source at a position of a primary image point which is an image of the light source; a deflection mirror that scans the light from the first lens group; and a second lens group having at least one lens and focusing the light from the deflection mirror at a position of a secondary image point which is an image of the primary image point, wherein a focal point of the second lens group on the light source side is located near an emission position of a chief ray of light from the deflection mirror, and the eyepiece device projects the light from the projection optical system onto the retina of the observer. The focal point of the eyepiece device on the light source side may be located at the position of the secondary image point. The eyepiece device may be a contact lens type device. The present technology also provides an eyepiece device that is placed in front of an eye of an observer and projects light from a projection optical system onto the retina of the observer, wherein the projection optical system comprises: a first lens group having at least one lens that focuses light projected from a light source at a position of a primary image point that is an image of the light source; a deflection mirror that scans the light from the first lens group; and a second lens group having at least one lens that focuses light from the deflection mirror at a position of a secondary image point that is an image of the primary image point, wherein the focal point of the second lens group on the light source side is located near the emission position of the chief ray of light on the deflection mirror.

[0011] According to the present technology, it is possible to achieve both stabilization of the operation of the deflection mirror and miniaturization of the device. Note that the effects described here are not necessarily limited to those described herein, and may be any of the effects described in this disclosure.

[0012] FIG. 1 is a schematic diagram showing an example of the configuration of a projection optical system 10 according to a comparative example of the present technology. FIG. 1 is a schematic diagram showing an example of the configuration of a projection optical system 10 according to a comparative example of the present technology. FIG. 2 is a schematic diagram showing an example of the configuration of a projection optical system 10 according to an embodiment of the present technology. FIG. 3 is a schematic diagram showing a state of a light beam in the comparative example shown in FIG. 1. FIG. 2 is a schematic diagram showing a state of a light beam in the comparative example shown in FIG. 3. FIG. 3 is a schematic diagram showing an example of the configuration of an eyepiece device 20 according to an embodiment of the present technology. FIG. 4 is a graph showing a correlation between a focal length f3 of the eyepiece device 20 according to an embodiment of the present technology and a numerical aperture θ of a light beam projected by the eyepiece device 20. FIG. 5 is a graph showing a correlation between a distance D2 from the second lens group 2 to a secondary image plane P2 according to an embodiment of the present technology and a numerical aperture θ of a light beam projected by the eyepiece device 20. FIG. 6 is a graph obtained by paraxially calculating the focal lengths of the first lens group 1 and the second lens group 2 according to an embodiment of the present technology. FIG. 7 is a graph showing an example of a simulation result of the projection optical system 10 according to an embodiment of the present technology. Fig. 1 is a graph showing an example of a simulation result of a projection optical system 10 according to an embodiment of the present technology. Fig. 2 is a schematic diagram showing a configuration example of a projection optical system 10 according to an embodiment of the present technology. Fig. 3 is a schematic diagram showing a configuration example of an image projection device 100 according to an embodiment of the present technology. Fig. 4 is a schematic diagram showing a configuration example of an image projection device 100 according to an embodiment of the present technology.

[0013] Hereinafter, preferred embodiments for implementing the present technology will be described with reference to the drawings. Note that the embodiment described below shows an example of a typical embodiment of the present technology, and does not limit the scope of the present technology. In addition, the present technology can be combined with any of the following examples and their modifications.

[0014] In the following description of the embodiments, configurations may be described using terms including "approximately," such as "approximately parallel" and "approximately perpendicular." For example, "approximately parallel" does not only mean completely parallel, but also means substantially parallel, i.e., including a state where the orientation is deviated from the completely parallel state by, for example, a few percent. The same applies to other terms including "approximately." Furthermore, each figure is a schematic diagram and is not necessarily an accurate depiction. The scale of the drawings has been exaggerated to make the features of the technology easier to understand. Therefore, it should be noted that the scale of the drawings and the scale of the actual device are not necessarily the same.

[0015] Unless otherwise specified, in the drawings, "top" means the top or upper side in the drawing, "bottom" means the bottom or lower side in the drawing, "left" means the left or left side in the drawing, and "right" means the right or right side in the drawing. Furthermore, in the drawings, the same or equivalent elements or members are given the same reference numerals, and redundant explanations will be omitted.

[0016] The description will be given in the following order: 1. First embodiment of the present technology (example 1 of projection optical system) (1) Comparative example (2) Overview of this embodiment (3) Passage area of ​​chief ray (4) Direct retinal imaging (5) Simulation 2. Second embodiment of the present technology (example 2 of projection optical system) 3. Third embodiment of the present technology (example of image projection device) 4. Fourth embodiment of the present technology (example of eyepiece device)

[0017] [1. First Embodiment of the Present Technology (Example 1 of Projection Optical System)] [(1) Comparative Example] In order to explain the problem to be solved by the present technology, first, a comparative example of the present technology will be described with reference to Fig. 1. Fig. 1 is a schematic diagram showing an example of the configuration of a projection optical system 10 according to the comparative example of the present technology.

[0018] 1, the projection optical system 10 includes a first lens group 12, a deflection mirror 3, and a second lens group 2. The projection optical system 10, together with a light source 4, constitutes an image projection device 100.

[0019] The light source 4 includes a light source section 41 and at least one lens (for example, a collimator lens) 42 .

[0020] The first lens group 12 has a positive focal length as a whole. The first lens group 12 includes at least one lens, and focuses light projected from the light source 4 onto a primary image point P1, which is an image of the light source 4.

[0021] When light is collected or diffused by an optical system, refraction and reflection of light rays occur. This can result in deviation (aberration) from the original ideal image point. Therefore, the first lens group 12 does not necessarily have to collect light at the position of the primary image point P1, and may collect light near the position of the primary image point P1. The same applies to the secondary image point P2 described below.

[0022] The deflection mirror 3 scans the light from the first lens group 12. The deflection mirror 3 rotates or tilts around an axis. When light that has passed through the primary image point P1 is irradiated onto the deflection mirror 3, the angle of the deflection mirror 3 is controlled to reflect the light in a specific direction. By controlling the angle of the deflection mirror 3, the light can be scanned. For example, when the light is scanned horizontally by rotating the deflection mirror 3, the position of the light moves from left to right. Similarly, scanning in the vertical direction is also possible by tilting the deflection mirror 3.

[0023] An example of the deflection mirror 3 is a MEMS (Micro-Electro-Mechanical Systems Mirror). The MEMS mirror has a microscopic mechanical structure, and can be vibrated and rotated minutely using an electric signal. This allows the emitted light to be scanned to form an image.

[0024] The elements constituting the deflection mirror 3 are not limited to MEMS mirrors, but may also be, for example, galvanometers. A galvanometer is a device that scans emitted light by minutely vibrating a mirror using an electrical signal. By controlling the position of the mirror, the direction of the light can be changed, allowing the emitted light to be scanned.

[0025] The second lens group 2 has a positive focal length as a whole and includes at least one lens (e.g., lens 21), which focuses the light from the deflection mirror 3 at a secondary image point (secondary image plane) P2, which is an image of the primary image point P1.

[0026] In this comparative example, a focal point P3 on the light source 4 side of the second lens group 2 is located apart from an emission position P4 of the chief ray L of light on the deflection mirror 3. Specifically, the emission position P4 of the chief ray L of light on the deflection mirror 3 is located closer to the second lens group 2 than the focal point P3 on the light source 4 side of the second lens group 2.

[0027] As a result, each of the chief rays of the multiple light beams projected from the second lens group 2 is in a divergent state, expanding as it travels. As a result, the size of the second lens group 2 constituting the projection optical system 10 is smaller than the size of the image projected by the projection optical system 10. As a result, it is possible to project a high-resolution image while miniaturizing the projection optical system 10.

[0028] The smaller the size of the image to be projected, the smaller the swing angle of the deflection mirror 3 tends to be. For example, when the image light from the projection optical system 10 is projected onto the retina of the observer, the image size becomes very small and the swing angle of the deflection mirror 3 also becomes very small.

[0029] In order to project a high-resolution image while stabilizing the operation of the deflection mirror 3, it is preferable to set a relatively large swing angle of the deflection mirror 3. If the swing angle of the deflection mirror 3 is smaller than, for example, ±3 degrees, the operation of the deflection mirror 3 may become unstable.

[0030] In order to make the deflection angle of the deflection mirror 3 relatively large, the optical system may be adjusted so that the chief rays of the multiple light beams projected by the projection optical system 10 converge as they travel. This will be described with reference to Fig. 2. Fig. 2 is a schematic diagram showing an example configuration of a projection optical system 10 according to a comparative example of the present technology.

[0031] 2, a focal point P3 on the light source 4 side of the second lens group 2 is located apart from a position P4 from which the chief ray of light emerges on the deflection mirror 3. Specifically, the position P4 from which the chief ray of light emerges on the deflection mirror 3 is located farther from the second lens group 2 than the focal point P3 on the light source 4 side of the second lens group 2.

[0032] This allows the chief rays of the multiple light beams projected from the second lens group 2 to converge as they travel, making it possible to project an image smaller in size than the second lens group 2 while ensuring a relatively large deflection angle of the deflection mirror 3.

[0033] However, in this configuration example, there is a risk that the area through which the chief ray of each light beam passes on the exit surface of the second lens group 2 may become larger than the image size on the secondary image plane P2, which may increase the size of the second lens group 2 and lead to an increase in the size of the projection optical system 10.

[0034] [(2) Overview of this embodiment] Therefore, the present technology provides a projection optical system in which the chief rays of each light beam projected from the second lens group are made substantially parallel by specifying the positional relationship between the focal point of the second lens group on the light source side and the emission position of the chief ray of light on the deflection mirror.

[0035] Specifically, the present technology provides a projection optical system comprising: a first lens group having at least one lens that focuses light projected from a light source at a position of a primary image point that is an image of the light source; a deflection mirror that scans the light from the first lens group; and a second lens group having at least one lens that focuses light from the deflection mirror at a position of a secondary image point that is an image of the primary image point, wherein the focal point of the second lens group on the light source side is located near the emission position of the chief ray of light on the deflection mirror.

[0036] An example of the configuration of a projection optical system 10 according to an embodiment of the present technology will be described with reference to Fig. 3. Fig. 3 is a schematic diagram showing an example of the configuration of a projection optical system 10 according to an embodiment of the present technology.

[0037] 3, the projection optical system 10 includes a first lens group 12, a deflection mirror 3, and a second lens group 2. Note that the contents of each component that have been explained above with reference to FIG. 1 etc. will not be explained again.

[0038] The first lens group 12 preferably has a combination of a positive lens and a negative lens. When the first lens group 12 collects light from the light source 4, the chromatic aberration of each wavelength of the light source 4 can be corrected by using a combination of a positive lens and a negative lens for correcting chromatic aberration as the lens on the light collecting side. To correct chromatic aberration, for example, a combination of glass lenses with different Abbe numbers can be used for the positive lens and the negative lens.

[0039] Alternatively, the first lens group 12 may be composed of only a plurality of positive single lenses, and axial chromatic aberration may be corrected by adjusting the distance between the light source 4 and the first lens group 12. In this case, costs can be reduced because a compound lens for correcting chromatic aberration is not used. In this case, the lenses in the first lens group 12 do not have to be made of glass; using plastic lenses, for example, can further reduce costs.

[0040] The second lens group 2 preferably has a combination of a positive lens and a negative lens. By using at least one combination of a positive lens and a negative lens, lateral chromatic aberration occurring off-axis can be corrected. With the preferred configuration of the first lens group 12 described above, it is possible to correct on-axis chromatic aberration, but it is difficult to correct chromatic aberration over the entire off-axis angle of view. Therefore, it is preferable to correct chromatic aberration in the second lens group 2. By using at least one combination of a positive lens and a negative lens in the second lens group 2, chromatic aberration for each wavelength of the light source 4 can be corrected.

[0041] It is also preferable that the second lens group 2 has at least one transmitting surface having a free-form curved shape. If an axisymmetric lens is used in the second lens group 2, distortion may occur in the two-dimensionally scanned image. By using a lens having a free-form curved shape, this distortion is optically corrected, resulting in a good image.

[0042] The projected image may also be adjusted in a direction perpendicular to the optical axis by moving at least one of the lenses in the first lens group 12 and the second lens group 2 in a direction perpendicular to the optical axis, thereby moving the projected image in a plane perpendicular to the optical axis.

[0043] The light source 4 emits light whose intensity is modulated based on image data. The light projected from the light source 4 is preferably laser light. Laser light has high light brightness and consistent wavelength characteristics, making it suitable for projecting clear, bright images onto the retina. Laser light has the advantages of a high contrast ratio, a wide color gamut, and high resolution.

[0044] In this configuration example, a focal point P3 on the light source 4 side of the second lens group 2 is located near an emission position P4 of the chief ray of light from the deflection mirror 3. As a result, the chief ray L of each light beam projected from the second lens group 2 becomes approximately parallel. The chief ray of each light beam that has become approximately parallel is collected by, for example, an eyepiece device (not shown) placed in front of the observer's eye, and projected onto the observer's retina.

[0045] According to the present technology, the chief rays of the light beams projected from the second lens group 2 are substantially parallel, so that a large swing angle of the deflection mirror 3 can be ensured even when the size of the projected image is small. This allows for stable operation of the deflection mirror 3. Furthermore, compared to a comparative example (see FIG. 2 ) in which the chief rays of the multiple light beams projected from the second lens group 2 converge as they travel, the device can be made more compact. In other words, it is possible to achieve both stable operation of the deflection mirror and a compact device. This effect also occurs in other embodiments described below. Therefore, repeated description of this effect may be omitted in the description of other embodiments.

[0046] (3) Area through which the Chief Ray Passes The state of the light beam in each of the comparative example and this embodiment will be described with reference to FIGS.

[0047] Fig. 4 is a schematic diagram showing the state of light beams in the comparative example shown in Fig. 1. Fig. 4A shows the state of the chief ray of the light beam that passes through the outermost part of the image light among the multiple light beams contained in the image light projected from the second lens group 2. As shown in Fig. 4A, the chief ray of each light beam projected from the second lens group 2 diverges as it travels. The chief ray of each light beam is then refracted by the eyepiece device 20 placed in front of the viewer's eye and directed to the eyeball E.

[0048] 4B shows by dashed lines the passage area A1 of the chief ray of each light beam on the exit surface of the second lens group 2. On the exit surface of the second lens group 2, the passage area of ​​each light beam is the sum of the passage area A1 of the chief ray of each light beam shown by the dashed lines and the spread of the light beam that passes through the outermost part of the image light. In other words, the length of the passage area of ​​each light beam is the sum of the length r1 of the diagonal of the passage area of ​​the chief ray shown by the dashed lines and the beam diameter r2 of the light beam that passes through the outermost part of the image light.

[0049] 4C shows the area A2 through which the chief ray of each light beam passes at the secondary image point (secondary image plane) P2 by a dashed line. At the secondary image plane P2, each light beam is in a condensed state. Therefore, the size of the area A2 through which the chief ray of each light beam passes is approximately the same as the size of the image projected by the projection optical system 10.

[0050] 4A, in this comparative example, the chief rays of the multiple light beams projected from the second lens group 2 spread as they travel. Therefore, as shown in Figures 4B and 4C, an area A1 through which the chief rays of each light beam pass on the exit surface of the second lens group 2 is smaller than an area A2 through which the chief rays of each light beam pass at the secondary image point (secondary image plane) P2.

[0051] As described above, the size of the passing area A2 is approximately the same as the size of the image projected by the projection optical system 10. As the size of the image to be projected becomes smaller, the size of the passing area A1 on the exit surface of the second lens group 2 tends to become smaller, and the swing angle of the deflection mirror 3 also tends to become smaller. If the swing angle of the deflection mirror 3 becomes smaller, the operation of the deflection mirror 3 may become unstable.

[0052] 5 is a schematic diagram showing the state of light beams in the comparative example shown in FIG. 2. As shown in FIG. 5A, in this comparative example, the chief rays of the multiple light beams projected from the second lens group 2 converge as they travel. Therefore, when the size of the image to be projected is fixed, as shown in FIGS. 5B and 5C, the area A1 through which the chief rays of each light beam pass on the exit surface of the second lens group 2 is larger than the area A2 through which the chief rays of each light beam pass at the secondary image point (secondary image plane) P2. This may result in an increase in the size of the projection optical system 10.

[0053] 6A and 6B are schematic diagrams showing the state of light beams in the embodiment shown in FIG. 3. As shown in FIG. 6A, in this embodiment, the chief rays of the multiple light beams projected from the second lens group 2 are substantially parallel to each other. Therefore, when the size of the image to be projected is fixed, as shown in FIGS. 6B and 6C, the area A1 through which the chief rays of each light beam pass on the exit surface of the second lens group 2 is substantially the same size as the area A2 through which the chief rays of each light beam pass at the secondary image point (secondary image plane) P2. This makes it possible to achieve both stable operation of the deflection mirror 3 and a compact device.

[0054] (4) Retinal Imaging The projection optical system 10 according to this embodiment can be used, for example, in a retinal imaging type image projection device, which is also called a Maxwellian image projection device.

[0055] When light enters the pupil and reaches the retina, photoreceptor cells inside the retina detect the light and convert it into nerve signals that are sent along the optic nerve to the brain, where they are interpreted to allow us to perceive the scenes and objects we see.

[0056] In order to allow an observer to view an image, a retinal projection image projector projects an image onto the observer's retina and forms an image on the retina. To form an image on the retina, an eyepiece device is often placed in front of the observer's eye. As shown in Figure 6A, when the chief rays of the respective light beams projected from the second lens group 2 are substantially parallel, the chief rays of the respective light beams are refracted to the focal position of the eyepiece device.

[0057] Examples of the eyepiece device 20 include a lens, a half mirror, a prism, an optical fiber, and a diffraction element. In this embodiment, the eyepiece device 20 can be a contact lens-type device. A contact lens-type device is a thin, transparent lens that is attached directly to the surface of the eyeball. A contact lens-type device has, for example, a diffraction grating or a hologram lens, and projects light from the projection optical system 10 onto the observer's retina by utilizing principles such as light diffraction and interference.

[0058] In particular, retinal projection image projection devices, unlike those that view objects directly, form an image on the viewer's retina using an eyepiece device. Therefore, the focal position on the retina side of the eyepiece device needs to be located near the crystalline lens. In other words, the focal length of the eyepiece device needs to be short, on the order of a few mm.

[0059] This eyepiece device will be described with reference to Fig. 7. Fig. 7 is a schematic diagram showing a configuration example of an eyepiece device 20 according to an embodiment of the present technology.

[0060] 7, each light beam projected from the second lens group 2 is focused at a secondary image point P2, and then projected while expanding onto the eyepiece device 20. The eyepiece device 20 functions as, for example, a lens, and guides each light beam to the pupil E1 and the retina E2.

[0061] In this case, it is preferable that the focal point on the light source side of the eyepiece device 20 is located at the position of the secondary image point P2. This allows the eyepiece device 20 to guide each light beam to the pupil E1 in a substantially parallel state. Each light beam guided to the pupil E1 is refracted by the crystalline lens and forms an image on the retina E2. Note that the position of the focal point of the eyepiece device 20 does not necessarily have to coincide with the position of the secondary image point P2, and some deviation is acceptable.

[0062] The resolution of an image is determined by the degree of convergence of each light beam that forms an image on the retina. By increasing the degree of convergence of each light beam, the image resolution can be increased. In order to increase the degree of convergence on the retina, it is preferable to increase the beam diameter (exit pupil) of each light beam projected onto the eyeball. In order to increase this beam diameter, it is preferable to increase the numerical aperture θ.

[0063] The beam diameter of each light beam projected onto the eyeball is determined by the numerical aperture θ of each light beam projected from the second lens group 2 and the focal length of the eyepiece device 20. If the focal length of the eyepiece is f, then the beam diameter of the light beam projected from the eyepiece device 20 is approximately 2fθ.

[0064] As described above, it is necessary to position the focal position on the retina side of the ocular device 20 near the crystalline lens. Therefore, if the ocular device 20 is, for example, a contact lens-type device, the distance from the ocular device 20 to the crystalline lens is short, and therefore the focal length of the ocular device 20 is necessarily short.

[0065] Here, the relationship between the focal length of the eyepiece device 20 and the numerical aperture θ of the light beam projected by the eyepiece device 20 will be described with reference to Fig. 8. Fig. 8 is a graph showing the correlation between the focal length f3 of the eyepiece device 20 according to an embodiment of the present technology and the numerical aperture θ of the light beam projected by the eyepiece device 20.

[0066] 8, the horizontal axis represents the focal length f3 of the eyepiece device 20. The vertical axis represents the numerical aperture θ of the light beam projected by the eyepiece device 20. The legend on the right side of the graph indicates the beam diameter (exit pupil) of the light beam projected by the eyepiece device 20.

[0067] If the beam diameter is 0.15 mm or less, the image resolution will be significantly reduced. Therefore, it is preferable that the beam diameter be 0.15 mm or more. If the eyepiece device 20 is a contact lens-type device, its focal length may be approximately 8 mm. In this case, it can be seen from this graph that in order for the observer to view a high-resolution image, the numerical aperture θ must be 0.01 or more.

[0068] In order to set the numerical aperture θ to 0.01 or greater, it is necessary to increase the beam diameter of each light beam projected from the second lens group 2. In particular, when the distance on the optical axis from the second lens group 2 to the secondary image plane P2 (projection distance) is set long, it is necessary to increase the beam diameter of each light beam projected from the second lens group 2 in order to project high-resolution image light. This will be described with reference to Fig. 9. Fig. 9 is a graph showing the correlation between the distance D2 from the second lens group 2 to the secondary image plane P2 and the numerical aperture θ of the light beam projected by the eyepiece device 20 according to an embodiment of the present technology.

[0069] 9, the horizontal axis represents the distance (projection distance) D2 on the optical axis from the second lens group 2 to the secondary image plane P2. The vertical axis represents the numerical aperture θ of the light beam projected by the eyepiece device 20. The legend on the right side of the graph represents the maximum value [mm] of the area through which the chief ray passes on the exit surface of the second lens group 2.

[0070] The projection optical system 10 according to this embodiment can be incorporated into, for example, a wristwatch-type device. The eyepiece device 20 according to this embodiment can be, for example, a contact lens-type device. Therefore, the distance on the optical axis (projection distance) D2 from the second lens group 2 constituting this wristwatch-type device to the secondary image plane P2 may exceed, for example, 500 mm. Furthermore, the size of the image observed by the observer must be smaller than the size of the contact lens-type device. In other words, the area through which the chief ray passes on the exit surface of the second lens group 2 must be smaller than the size of the contact lens-type device. As a specific example, the length of the area through which the chief ray passes on the exit surface of the second lens group 2 must be 10 mm or less.

[0071] 9, when the projection distance D2 exceeds 500 mm, it becomes difficult to set the numerical aperture θ on the vertical axis to 0.01 or more while keeping the area through which the chief ray passes on the exit surface of the second lens group 2 to 10 mm or less. Therefore, in order to achieve both stable operation of the deflection mirror and a compact device while allowing the viewer to view a high-resolution image, it is preferable that the distance on the optical axis from the exit surface of the second lens group 2 to the secondary image point P2 be 500 mm or less.

[0072] [(5) Simulation] As described above, the present technology specifies the positional relationship between the focal point of the second lens group 2 on the light source 4 side and the emission position of the chief ray of light on the deflection mirror 3. The inventors conducted a simulation to confirm a preferable arrangement position of the deflection mirror 3. First, to determine the preconditions for the simulation, a paraxial calculation was performed on the focal lengths of the first lens group 12 and the second lens group 2 when the numerical aperture θ of the light beam projected from the second lens group 2 was 0.010 and the projection distance was 200 mm or more and 500 mm or less. The calculation results will be described with reference to FIG. 10 . FIG. 10 is a graph showing the paraxial calculation of the focal lengths of the first lens group 12 and the second lens group 2 according to an embodiment of the present technology.

[0073] 10, the horizontal axis represents the focal length f1 of the first lens group 12. The vertical axis represents the focal length f2 of the second lens group 2. The legend on the right side of the graph indicates the projection distance [mm].

[0074] In this graph, the focal length f1 ranges from 1.5 to 6.5 mm. However, if the focal length f1 is reduced, the radius of curvature of each lens in the first lens group 12 must be reduced. However, if the radius of curvature of the lens is made extremely small, it becomes difficult to process each lens. To facilitate lens processing, it is preferable that the focal length f1 of the first lens group 12 be 2.0 mm or greater.

[0075] Based on the results of this paraxial calculation, the preconditions for the simulation were set as follows:

[0076] <Preconditions> (a) Distance D2 from the exit surface of the second lens group 2 to the secondary image plane P2: 500 mm (b) Numerical aperture θ of the light beam projected from the second lens group 2: 0.01 (c) Focal length f1 of the first lens group 12: 2.3 mm (d) Focal length f2 of the second lens group 2: 22.0 mm (e) Length of the area through which the chief ray passes at the secondary image plane P2: 5 mm (2.5 mm on each side) (f) No aberration occurs at the respective foci of the first lens group 12 and the second lens group 2

[0077] The results of a simulation based on this precondition will be described with reference to Fig. 11 and Fig. 12. Fig. 11 and Fig. 12 are graphs showing an example of the results of a simulation of the projection optical system 10 according to an embodiment of the present technology.

[0078] 11, the horizontal axis represents the distance D1 from the focal point of the second lens group 2 on the light source side to the emission position of the chief ray of light on the deflection mirror 3, normalized by the focal length f2 of the second lens group 2. The direction from the deflection mirror 3 toward the second lens group 2 is defined as positive. The vertical axis represents the deflection angle α (one side) [deg] of the deflection mirror 3.

[0079] When the value on the horizontal axis is positive (greater than 0), the chief ray of each light beam reflected by the deflection mirror 3 travels in a diverging direction when projected from the second lens group 2. In this case, in order to ensure the length (5 mm) of prerequisite condition (e), it is necessary to reduce the swing angle α of the deflection mirror 3.

[0080] On the other hand, when the value on the horizontal axis is negative (less than 0), the smaller the value on the horizontal axis, the greater the amount of change in the swing angle α of the deflection mirror 3 (the tilt of the swing angle α). This indicates that the change in the size of the projected image is large relative to the perturbation in the distance from the focal point on the light source side of the second lens group 2 to the emission position of the chief ray of light on the deflection mirror 3.

[0081] As described above, in order to achieve both stable operation of the deflection mirror 3 and compactness of the device, it is preferable that the chief rays of the respective light beams projected from the second lens group 2 are substantially parallel. In order for the chief rays of the respective light beams projected from the second lens group 2 to be substantially parallel, it is preferable that the focal point P3 on the light source 4 side of the second lens group 2 coincides with the emission position P4 of the chief ray of light on the deflection mirror 3, as shown in Fig. 3. In other words, it is preferable that the value on the horizontal axis in Fig. 11 is 0.

[0082] However, the focal point P3 of the second lens group 2 on the light source 4 side does not necessarily have to coincide with the emission position P4 of the chief ray of light on the deflection mirror 3. The focal point P3 of the second lens group 2 on the light source 4 side may be located near the emission position P4 of the chief ray of light on the deflection mirror 3.

[0083] 11 , when the direction from the deflection mirror 3 toward the second lens group 2 is defined as positive, a distance D1 from a focal point P3 of the second lens group 2 on the light source 4 side to an emission position P4 of the chief ray of light on the deflection mirror 3 may be between −1% and 2% of the focal length f2 of the second lens group 2. If the distance D1 can be kept within this range of between −1% and 2%, the change in the swing angle of the deflection mirror 3 can be kept within 1 degree from the swing angle when the focal point P3 of the second lens group 2 on the light source 4 side and the emission position P4 of the chief ray of light on the deflection mirror 3 are aligned. This allows the light beams projected from the second lens group 2 to be substantially parallel.

[0084] Next, Fig. 12 will be described. In Fig. 12, the horizontal axis, as in Fig. 11, represents the distance D1 from the focal point P3 of the second lens group 2 on the light source 4 side to the emission position P4 of the chief ray of light on the deflection mirror 3, normalized by the focal length f2 of the second lens group 2. The direction from the deflection mirror 3 toward the second lens group 2 is defined as positive. The vertical axis represents the maximum value W of the length of the area through which the chief ray passes on the emission surface of the second lens group 2, when the center of the emission surface is used as the reference.

[0085] 12, when the value on the horizontal axis is negative (less than 0), the chief ray of each light beam reflected by the deflection mirror 3 travels in a converging direction when projected from the second lens group 2. In this case, to ensure the prerequisite image length (5 mm), it is necessary to increase the area on the exit surface of the second lens group 2 through which the chief ray passes.

[0086] When the direction from the deflection mirror 3 toward the second lens group 2 is defined as positive, it is preferable that the distance from a focal point P3 of the second lens group 2 on the light source 4 side to an emission position P4 of the chief ray of light on the deflection mirror 3 be between −1% and 2% of the focal length of the second lens group 2. If the distance can be kept within this range of −1% to 2%, the value on the vertical axis can be kept to about +1 mm from the state in which the focal point P3 of the second lens group 2 on the light source 4 side and the emission position P4 of the chief ray of light on the deflection mirror 3 coincide. This makes it possible to make the chief rays of the respective light beams projected from the second lens group 2 approximately parallel.

[0087] Next, the correlation between the focal length f2 of the second lens group 2 and the swing angle α of the deflection mirror 3 in a state in which the focal point P3 on the light source 4 side of the second lens group 2 coincides with the emission position P4 of the chief ray of light on the deflection mirror 3 will be described with reference to Fig. 13. Fig. 13 is a graph showing an example of a simulation result of the projection optical system 10 according to an embodiment of the present technology.

[0088] The preconditions for this simulation are that the numerical aperture θ of the light beam projected from the second lens group 2 is 0.01, and the length of the area through which the chief ray passes on the secondary image plane P2 is 5 mm (2.5 mm on each side).

[0089] 13, the horizontal axis represents the focal length f2 [mm] of the second lens group 2. The vertical axis represents the deflection angle α (one side) [deg] of the deflection mirror 3. The legend on the right side of the graph indicates the projection distance [mm].

[0090] 13, the graph depicts almost the same curve regardless of the projection distance (200, 300, 400, 500, 600). In other words, it can be seen that the swing angle α of the deflection mirror 3 is almost unaffected by the projection distance, but is affected by the focal length f2 of the second lens group 2 shown on the horizontal axis.

[0091] Furthermore, in this simulation, the numerical aperture θ of the light beam projected from the second lens group 2 was assumed to be 0.01 as a prerequisite, but the swing angle α of the deflection mirror 3 is not affected by this numerical aperture θ either. In other words, the swing angle α of the deflection mirror 3 is affected by the focal length f2 of the second lens group 2 and the length of the area through which the chief ray passes on the secondary image plane P2. In this example, if the focal length f2 of the second lens group 2 is 24 mm or less, the swing angle α of the deflection mirror 3 will be ±3 degrees or more, and the operation of the deflection mirror 3 will be stable.

[0092] Of course, the length of the area through which the chief ray passes at the secondary image plane P2 varies depending on the focal length of the eyepiece device 20, the required angle of view, etc. However, if the focal length f2 of the second lens group 2 is 24 mm or less, it is possible to maintain the swing angle α of the deflection mirror 3 within a range that does not impede its operation.

[0093] The above description of the projection optical system according to the first embodiment of the present technology can be applied to other embodiments of the present technology unless there is a particular technical contradiction.

[0094] 2. Second Embodiment of the Present Technology (Example 2 of Projection Optical System)] To project a color image, the light source may include a first light source unit that projects emitted light in a first wavelength band, a second light source unit that projects emitted light in a second wavelength band, and a third light source unit that projects emitted light in a third wavelength band. This will be described with reference to Fig. 14. Fig. 14 is a schematic diagram showing an example configuration of a projection optical system 10 according to an embodiment of the present technology.

[0095] 14, the light source 4 may include a first light source unit 41R that projects output light in a first wavelength band, a second light source unit 41G that projects output light in a second wavelength band, and a third light source unit 41B that projects output light in a third wavelength band. Note that the number of light source units is not particularly limited.

[0096] More specifically, the first wavelength band may be a wavelength band corresponding to red, the second wavelength band may be a wavelength band corresponding to green, and the third wavelength band may be a wavelength band corresponding to blue. This allows the image projection device 100 to allow the viewer to view a full-color image. The wavelength band corresponding to red may be, for example, approximately 620 to 750 nm. The wavelength band corresponding to green may be, for example, approximately 500 to 550 nm. The wavelength band corresponding to blue may be, for example, approximately 430 to 500 nm.

[0097] The light source 4 further includes, for example, lenses 42R, 42G, and 42B. The lens 42R approximately collimates the light in the first wavelength band projected by the first light source unit 41R. Similarly, the lens 42G approximately collimates the light in the second wavelength band projected by the second light source unit 41G. The lens 42B approximately collimates the light in the third wavelength band projected by the third light source unit 41B.

[0098] In this embodiment, the mirror 51 and the dichroic mirrors 52 and 53 are used as a combining optical system that combines the emitted light of each wavelength band onto the same optical axis and outputs the combined light to the first lens group 12.

[0099] The mirror 51 is disposed on the optical axis of the first light source unit 41R and the lens 42R. The mirror 51 reflects the light of the first wavelength band projected from the first light source unit 41R.

[0100] The dichroic mirror 52 is disposed on the optical axis of the second light source unit 41G and the lens 42G. The dichroic mirror 52 transmits light of the first wavelength band projected from the first light source unit 41R and reflects light of the second wavelength band projected from the second light source unit 41G.

[0101] The dichroic mirror 53 is disposed on the optical axis of the third light source unit 41B and the lens 42B. The dichroic mirror 53 reflects light of the first wavelength band projected from the first light source unit 41R, reflects light of the second wavelength band projected from the second light source unit 41G, and transmits light of the third wavelength band projected from the third light source unit 41B.

[0102] The first lens group 12 focuses the substantially parallel light from the combining optical system at a primary image point P1. A focal point P3 on the light source 4 side of the second lens group 2 is located near an emission position P4 of the chief ray of light from the deflection mirror 3. The light from the lens 21 is scanned two-dimensionally by the deflection mirror 3, passes through the second lens group 2, and is focused at a secondary image plane P2.

[0103] The elements constituting the combining optical system are not limited to those mentioned above, and the combining optical system may be constituted by, for example, a dichroic prism, a polarizing beam splitter (PBS), a polarization beam combiner (PBC), a half mirror, an interference filter, or the like.

[0104] However, the technology for emitting light in multiple wavelength bands to project a color image is not necessarily limited to this configuration. For example, the light source may be a single light source unit that emits light in multiple wavelength bands. Specifically, a laser diode array can be used to emit light in multiple wavelength bands from a single chip. Alternatively, light in multiple wavelength bands can be generated from a single chip by introducing luminescent materials of different colors into a liquid or gas and exciting each of them to emit light.

[0105] The above description of the projection optical system according to the second embodiment of the present technology can be applied to other embodiments of the present technology unless there is a particular technical contradiction.

[0106] 3. Third Embodiment of the Present Technology (Example of Image Projection Device) An image projection device according to this embodiment will be described with reference to Fig. 15. Fig. 15 is a schematic diagram showing an example configuration of an image projection device 100 according to an embodiment of the present technology.

[0107] As shown in FIG. 15, the image projection device 100 includes a projection optical system 10 and an eyepiece device 20 placed in front of the viewer's eyes.

[0108] In this configuration example, the projection optical system 10 is built into a wristwatch-type device, which is an example of the image projection device 100. The viewer can change the image projected by the image projection device 100 via a display provided in the wristwatch-type device 100.

[0109] Each light beam projected from the projection optical system 10 is focused at a secondary image point, and then projected while expanding onto the eyepiece device 20. The eyepiece device 20 projects the light from the projection optical system 10 onto the observer's retina E1.

[0110] The eyepiece device 20 may be, for example, a glasses-type device, but is preferably a contact lens-type device. Glasses-type devices need to be adapted to the shape of each individual's face. On the other hand, contact lens-type devices do not require this and can provide a comfortable fit and feel to everyone.

[0111] Furthermore, the contact lens type eyepiece device 20 can project light more directly onto the retina because the lenses are worn directly on the eye, whereas in the case of eyeglasses, the thickness of the frame and lenses may interfere, limiting the light transmission.

[0112] When the eyepiece device 20 is an eyeglass-type device, the eyepiece device 20 may include, for example, a half mirror, a prism, a lens, an optical fiber, a diffraction element, etc. In particular, the eyepiece device 20 may include, for example, a diffraction element such as a holographic optical element, a Fresnel lens, a reflective diffraction grating, or a transmissive diffraction grating. A diffraction element can diffuse or converge light by utilizing the diffraction effect of light. The inclusion of a diffraction element can simplify the eyepiece device 20, for example. Compared to other optical elements with complex optical configurations, such as lens arrays, a diffraction element can realize a simple and compact device design.

[0113] An example of the configuration of the image projection device 100 according to this embodiment will be described with reference to Fig. 16. Fig. 16 is a schematic diagram showing an example of the configuration of the image projection device 100 according to an embodiment of the present technology.

[0114] As shown in FIG. 16, the image projection device 100 includes at least a projection optical system 10 , a light source 4 , and a control unit 30 .

[0115] The projection optical system 10 includes a first lens group 12 , a deflection mirror 3 , and a second lens group 2 .

[0116] The first lens group 12 has at least one lens, and focuses the light projected from the light source 4 onto the position of a primary image point P1 , which is the image of the light source 4 .

[0117] The deflection mirror 3 scans the light from the first lens group 12 .

[0118] The second lens group 2 has at least one lens (for example, lens 21), and focuses the light from the deflection mirror 3 at a secondary image point P2, which is an image of the primary image point P1.

[0119] At this time, the focal point of the second lens group 2 on the light source 4 side is located near the emission position of the chief ray of light on the deflection mirror 3 .

[0120] The control unit 30 has a light source control unit 31 and a scan control unit 32. The light source control unit 31 controls the light emission of the light source 4 based on image data. The scan control unit 32 controls the scanning direction and scanning timing of the deflection mirror 3 based on the image data. The control unit 30 can be, for example, a microcontroller, a driver integrated circuit (IC), a signal generation circuit, or the like.

[0121] The image projection device 100 incorporating the projection optical system 10 is not limited to the wristwatch type device shown in FIG.

[0122] The above description of the image projection device according to the third embodiment of the present technology can be applied to other embodiments of the present technology unless there is a particular technical contradiction.

[0123] 15 and other drawings, the present technology provides an eyepiece device 20 that is placed in front of an eye of a viewer and projects light from a projection optical system 10 onto the retina of the viewer.

[0124] The eyepiece device 20 may be, for example, a glasses-type device, but is preferably a contact lens-type device. Glasses-type devices need to be adapted to the shape of each individual's face. On the other hand, contact lens-type devices do not require this and can provide a comfortable fit and feel to everyone.

[0125] Furthermore, the contact lens type eyepiece device 20 can project light more directly onto the retina because the lenses are worn directly on the eye, whereas in the case of eyeglasses, the thickness of the frame and lenses may interfere, limiting the light transmission.

[0126] When the eyepiece device 20 is an eyeglass-type device, the eyepiece device 20 may include, for example, a half mirror, a prism, a lens, an optical fiber, a diffraction element, etc. In particular, the eyepiece device 20 may include, for example, a diffraction element such as a holographic optical element, a Fresnel lens, a reflective diffraction grating, or a transmissive diffraction grating. A diffraction element can diffuse or converge light by utilizing the diffraction effect of light. The inclusion of a diffraction element can simplify the eyepiece device 20, for example. Compared to other optical elements with complex optical configurations, such as lens arrays, a diffraction element can realize a simple and compact device design.

[0127] As shown in FIG. 16 and other figures, the projection optical system 10 that projects light onto the eyepiece device 20 includes a first lens group 12 , a deflection mirror 3 , and a second lens group 2 .

[0128] The first lens group 12 has at least one lens, and focuses the light projected from the light source 4 onto the position of a primary image point P1 , which is the image of the light source 4 .

[0129] The deflection mirror 3 scans the light from the first lens group 12 .

[0130] The second lens group 2 has at least one lens (for example, lens 21), and focuses the light from the deflection mirror 3 at a secondary image point P2, which is an image of the primary image point P1.

[0131] At this time, the focal point of the second lens group 2 on the light source 4 side is located near the emission position of the chief ray of light on the deflection mirror 3 .

[0132] The above description of the eyepiece device according to the fourth embodiment of the present technology can be applied to other embodiments of the present technology unless there is a particular technical contradiction.

[0133] It should be noted that the embodiments of the present technology are not limited to the above-described embodiments, and various modifications are possible within the scope of the present technology. The specific numerical values, shapes, materials (including compositions), etc. described in each embodiment are merely examples, and the present technology is not limited to these.

[0134] The present technology can also have the following configurations. [1] A projection optical system including: a first lens group having at least one lens and converging light projected from a light source at a position of a primary image point, which is an image of the light source; a deflection mirror that scans the light from the first lens group; and a second lens group having at least one lens and focusing the light from the deflection mirror at a position of a secondary image point, which is an image of the primary image point, wherein a focal point of the second lens group on the light source side is located near an emission position of a chief ray of light on the deflection mirror. [2] The projection optical system according to [1], wherein, when a direction from the deflection mirror toward the second lens group is defined as positive, a distance from the focal point of the second lens group on the light source side to an emission position of light on the deflection mirror is between −1% and 2% of a focal length of the second lens group. [3] The projection optical system according to [1] or [2], wherein a focal length of the first lens group is 2.0 mm or more. [4] The projection optical system according to any one of [1] to [3], wherein the focal length of the second lens group is 24 mm or less. [5] The projection optical system according to any one of [1] to [4], wherein the distance on the optical axis from the exit surface of the second lens group to the secondary image point is 500 mm or less. [6] The projection optical system according to any one of [1] to [5], wherein the chief rays of the light beams projected from the second lens group are approximately parallel. [7] The projection optical system according to any one of [1] to [6], wherein the first lens group has a combined lens of a positive lens and a negative lens. [8] The projection optical system according to any one of [1] to [7], wherein the second lens group has a combined lens of a positive lens and a negative lens. [9] The projection optical system according to any one of [1] to [8], wherein the light projected from the light source is laser light.

[10] The projection optical system according to any one of [1] to [9], wherein the light source includes: a first light source unit that projects output light in a first wavelength band; a second light source unit that projects output light in a second wavelength band; and a third light source unit that projects output light in a third wavelength band.

[11] The projection optical system according to

[10] , wherein the first wavelength band is a wavelength band corresponding to red, the second wavelength band is a wavelength band corresponding to green, and the third wavelength band is a wavelength band corresponding to blue.

[12] The projection optical system according to any one of [1] to [9], wherein the light source is a single light source unit that emits light of multiple wavelength bands.

[13] An image projection device comprising: a projection optical system; and an eyepiece device placed in front of an eye of an observer, wherein the projection optical system comprises: a first lens group having at least one lens for focusing light projected from a light source at a position of a primary image point which is an image of the light source; a deflection mirror for scanning the light from the first lens group; and a second lens group having at least one lens for focusing the light from the deflection mirror at a position of a secondary image point which is an image of the primary image point, wherein the focal point of the second lens group on the light source side is located near the emission position of a chief ray of light from the deflection mirror, and the eyepiece device projects the light from the projection optical system onto the retina of the observer.

[14] The image projection device according to

[13] , wherein the focal point of the eyepiece device on the light source side is located at the position of the secondary image point.

[15] The image projection device according to

[13] or

[14] , wherein the eyepiece device is a contact lens type device.

[16] An eyepiece device that is placed in front of an eye of an observer and projects light from a projection optical system onto the retina of the observer, wherein the projection optical system comprises: a first lens group having at least one lens that focuses light projected from a light source at a position of a primary image point that is an image of the light source; a deflection mirror that scans the light from the first lens group; and a second lens group having at least one lens that focuses light from the deflection mirror at a position of a secondary image point that is an image of the primary image point, wherein the focal point of the second lens group on the light source side is located near the emission position of the chief ray of light from the deflection mirror.

[0135] 100 Image projection device 10 Projection optical system 1 First lens group 2 Second lens group 3 Deflecting mirror 4 Light source 41R First light source section 41G Second light source section 41B Third light source section 20 Eyepiece device 30 Control section 31 Light source control section 32 Scanning control section P1 Primary image point P2 Secondary image point P3 Focus of second lens group on the light source side P4 Emission position of chief ray on deflecting mirror A1 Passage area of ​​chief ray on exit surface of second lens group A2 Passage area of ​​chief ray on secondary image plane θ Numerical aperture α Swing angle of deflecting mirror f1 Focal length of first lens group f2 Focal length of second lens group f3 Focal length of eyepiece device E Eyeball E1 Pupil E2 Retina

Claims

1. A projection optical system comprising: a first lens group having at least one lens for focusing light projected from a light source onto a primary image point which is an image of the light source; a deflection mirror for scanning the light from the first lens group; and a second lens group having at least one lens for focusing light from the deflection mirror onto a secondary image point which is an image of the primary image point, wherein the focal point of the second lens group on the light source side is located near the emission position of the chief ray of light on the deflection mirror.

2. The projection optical system according to claim 1, wherein, when the direction from the deflection mirror toward the second lens group is defined as positive, the distance from the focal point of the second lens group on the light source side to the light emission position on the deflection mirror is greater than or equal to -1% and less than 2% of the focal length of the second lens group.

3. The projection optical system according to claim 1, wherein the focal length of the first lens group is 2.0 mm or more.

4. The projection optical system according to claim 1, wherein the focal length of the second lens group is 24 mm or less.

5. The projection optical system according to claim 1, wherein the distance on the optical axis from the exit surface of the second lens group to the secondary image point is 500 mm or less.

6. The projection optical system according to claim 1, wherein the chief rays of the respective light beams projected from said second lens group are substantially parallel.

7. The projection optical system according to claim 1, wherein the first lens group has a combination of a positive lens and a negative lens.

8. The projection optical system according to claim 1, wherein the second lens group has a combination of a positive lens and a negative lens.

9. The projection optical system according to claim 1, wherein the light projected from the light source is laser light.

10. The projection optical system according to claim 1, wherein the light source includes: a first light source unit that projects output light in a first wavelength band; a second light source unit that projects output light in a second wavelength band; and a third light source unit that projects output light in a third wavelength band.

11. The projection optical system according to claim 10, wherein the first wavelength band is a wavelength band corresponding to red, the second wavelength band is a wavelength band corresponding to green, and the third wavelength band is a wavelength band corresponding to blue.

12. An image projection device comprising: a projection optical system; and an eyepiece device arranged in front of an eye of an observer, wherein the projection optical system comprises: a first lens group having at least one lens and concentrating light projected from a light source onto a position of a primary image point which is an image of the light source; a deflection mirror which scans the light from the first lens group; and a second lens group having at least one lens and focusing light from the deflection mirror onto a position of a secondary image point which is an image of the primary image point, wherein the focus of the second lens group on the light source side is located near the emission position of the chief ray of light on the deflection mirror, and the eyepiece device projects the light from the projection optical system onto the retina of the observer.

13. The image projection device according to claim 12, wherein a focal point on the light source side of the eyepiece device is positioned at the position of the secondary image point.

14. The image projection device according to claim 12, wherein the eyepiece device is a contact lens type device.

15. An eyepiece device that is placed in front of an eye of an observer and projects light from a projection optical system onto the observer's retina, wherein the projection optical system comprises: a first lens group having at least one lens that focuses light projected from a light source onto a position of a primary image point that is an image of the light source; a deflection mirror that scans the light from the first lens group; and a second lens group having at least one lens that focuses light from the deflection mirror onto a position of a secondary image point that is an image of the primary image point, wherein the light source side focus of the second lens group is located near the emission position of the chief ray of light on the deflection mirror.

Images