Optical system and image projection device

Abstract

To provide an optical system and image projection device that can improve adjustment accuracy. [Solution] The optical system 100 according to the embodiment comprises a first optical system 110 which is a refractive optical system including a plurality of lenses, and a second optical system 120 which includes one optical element 121 having a transmitting surface and a reflecting surface, and is an optical system 100 which magnifies and images an image displayed on an image display element 130 onto a projection surface as a conjugate surface of the image display element 130 through the first optical system 110 and the second optical system 120, and is an optical system 100 which images the image displayed by the first optical system 110 as an intermediate image 133, and magnifies the intermediate image 133 with the second optical system 120 and images it onto a projection surface 140, and the second optical system 120 includes a first transmitting surface T1, a first reflecting surface R1, a second reflecting surface R2 and a second transmitting surface T2 in the order in which the light of the image from the first optical system 110 passes, and the optical path between each surface is formed of one medium, and the first reflecting surface R1 and the second transmitting surface T2 are formed of one continuous surface.

Description

Technical Field

[0001] The present disclosure relates to an ultra-short focus projection optical system and a projector capable of projecting onto a screen with a short projection distance.

Background Art

[0002] Regarding an ultra-short focus projection optical system capable of projecting onto a projection surface such as a screen with a short projection distance, a catadioptric optical system including a refractive optical system and a reflective optical system is known.

[0003] Patent Document 1 describes a projection optical system of a catadioptric optical system in which a reflective optical system is composed of two mirrors. Patent Document 2 describes a catadioptric optical system to which a reflective mirror and a prism are applied. Patent Document 3 describes a catadioptric optical system to which a prism composed of a plurality of transmission surfaces and a plurality of reflection surfaces is applied.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] The projection optical system of the catadioptric optical system of Patent Document 1 has a problem in the accuracy of assembling and adjusting a plurality of mirrors. The catadioptric optical system of Patent Document 2 has a problem in the accuracy of assembling and adjusting a mirror and a prism. The catadioptric optical system of Patent Document 3 has a problem in the accuracy of assembly and adjustment because the surfaces constituting the prism and the optical axis are configured in a predetermined optical arrangement.

[0006] This disclosure was made to solve such problems and provides an optical system and an image projection device that can improve adjustment accuracy. [Means for solving the problem]

[0007] An optical system of one embodiment comprises a first optical system which is a refractive optical system including a plurality of lenses, and a second optical system which includes one optical element having a transmitting surface and a reflecting surface, and is an optical system which magnifies and images an image displayed on an image display element onto a projection surface as a conjugate surface of the image display element through the first optical system and the second optical system, and is an optical system which images the image displayed by the first optical system as an intermediate image, and magnifies the intermediate image with the second optical system and images it onto the projection surface, wherein the second optical system includes a first transmitting surface, a first reflecting surface, a second reflecting surface and a second transmitting surface in the order through which the light of the image from the first optical system passes, the optical path between each surface is formed of a single medium, the first reflecting surface and the second transmitting surface are formed of a single continuous surface, and the second reflecting surface has a concave shape.

[0008] In the optical system described above, the first reflective surface and the second transmissive surface may be smoothly connected.

[0009] In the optical system described above, the first reflective surface and the second transmissive surface are formed as a single continuous surface, and the first reflective surface region that fills the effective light-ray region of the first reflective surface may be formed separately from the first reflective surface region on which a reflective film is provided, and the second transmissive surface region that fills the effective light-ray region of the second transmissive surface.

[0010] In the optical system described above, the first reflective surface may be substantially planar in shape.

[0011] In the optical system described above, the first transmission surface may include a rotationally symmetric plane that is rotationally symmetric with respect to the first optical axis, which is the optical axis of the first optical system.

[0012] In the optical system described above, the first reflective surface may be formed such that it bends the optical axis of the first optical system by 90°.

[0013] In the above optical system, the second reflecting surface and the second transmitting surface may include a rotationally symmetric surface that is rotationally symmetric with respect to a second optical axis obtained by bending the optical axis of the first optical system by 90°.

[0014] In the above optical system, an intermediate image may be formed in the optical path between the first reflecting surface and the second reflecting surface.

[0015] An image projection device according to an embodiment includes the optical system described above.

Advantages of the Invention

[0016] According to the present disclosure, it is possible to provide an optical system and an image projection device capable of improving adjustment accuracy.

Brief Description of the Drawings

[0017] [Figure 1] It is a cross-sectional view illustrating the optical system according to Embodiment 1. [Figure 2] It is a cross-sectional view illustrating the image projection device according to Embodiment 1. [Figure 3] In the second optical system according to Embodiment 1, it is a cross-sectional view illustrating an optical element. [Figure 4] It is a diagram illustrating lens data of the optical system according to Embodiment 1. [Figure 5] It is a diagram illustrating lens data of the optical system according to Embodiment 1. [Figure 6] It is a diagram illustrating lens data of the optical system according to Embodiment 1. [Figure 7] It is a graph illustrating the MTF performance of the optical system according to Embodiment 1, where the horizontal axis represents the spatial frequency and the vertical axis represents the MTF performance. [Figure 8] It is a cross-sectional view illustrating the optical system according to Embodiment 2. [Figure 9] In the second optical system according to Embodiment 2, it is a cross-sectional view illustrating an optical element. [Figure 10] It is a diagram illustrating lens data of the optical system according to Embodiment 2. [Figure 11]A diagram illustrating lens data of the optical system according to Embodiment 2. [Figure 12] A diagram illustrating lens data of the optical system according to Embodiment 2. [Figure 13] A cross-sectional view illustrating the optical system according to Embodiment 2. [Figure 14] In the second optical system according to Embodiment 3, it is a cross-sectional view illustrating an optical element. [Figure 15] A diagram illustrating lens data of the optical system according to Embodiment 3. [Figure 16] A diagram illustrating lens data of the optical system according to Embodiment 3. [Figure 17] It is a graph illustrating the MTF performance of the optical system according to Embodiment 3, where the horizontal axis represents the spatial frequency and the vertical axis represents the MTF performance. [Figure 18] A cross-sectional view illustrating the optical system according to Embodiment 4. [Figure 19] In the second optical system according to Embodiment 4, it is a cross-sectional view illustrating an optical element. [Figure 20] A diagram illustrating lens data of the optical system according to Embodiment 4. [Figure 21] A diagram illustrating lens data of the optical system according to Embodiment 4.

Modes for Carrying Out the Invention

[0018] For clarity of explanation, the following descriptions and drawings are appropriately omitted and simplified. Also, in the drawings, in cases where it becomes cumbersome or the distinction from voids is clear, hatching etc. may be omitted even for cross-sections. In each drawing, the same elements are denoted by the same reference numerals, and duplicate explanations are omitted as necessary. Some reference numerals may be omitted so that the drawings do not become complicated.

[0019] <Embodiment 1> An overview of the optical system and image projection device of Embodiment 1 will be described. Figure 1 is a cross-sectional view illustrating the optical system 100 according to Embodiment 1. Figure 2 is a cross-sectional view illustrating the image projection device 101 according to Embodiment 1. Figure 3 is a cross-sectional view illustrating the optical element 121 in the second optical system 120 according to Embodiment 1. In Figure 1, the medium is not shown for the sake of displaying the optical cross-sectional view of the second optical system 120.

[0020] The optical system 100 and image projection device 101 of this embodiment are projection optical systems equipped with a first optical system 110 and a second optical system 120, which enable projection over a short projection distance. The second optical system 120 has an optical axis C1 common to the optical axis C1 of the first optical system 110, which is a refractive optical system, and another optical axis C2 after bending at the reflective surface. Each surface of the optical element 121, such as a prism, that constitutes the second optical system 120 is characterized by being a plane of rotational symmetry with respect to the optical axis C1 and the optical axis C2. This improves the ease of assembly and adjustment of the optical system 100.

[0021] Specifically, the optical element 121 includes a first transmission surface T1, a first reflection surface R1, a second reflection surface R2, and a second transmission surface T2. The first transmission surface T1 includes a rotationally symmetric surface having an optical axis C1 common to the optical axis C1 of the first optical system 110. The first reflection surface R1 includes a surface that bends the optical axis C1 by 90°. The second reflection surface R2 has a concave shape and includes a rotationally symmetric surface having one optical axis C2. The second transmission surface T2 has a convex shape and includes a rotationally symmetric surface having another optical axis C2. In this way, the second optical system 120 does not need to be formed from multiple optical elements, but can be integrally formed as a single optical element 121 having a transmission surface and a reflection surface. Furthermore, integral formation makes it easy to improve the alignment accuracy of each surface. The optical system 100 and image projection device 101 of this embodiment will be described in detail below.

[0022] As shown in Figures 1 to 3, the optical system 100 of this embodiment comprises a first optical system 110 and a second optical system 120. The optical system 100 magnifies and projects the image displayed on the image display element 130 onto the projection surface 140, which is the conjugate surface of the image display element 130, through the first optical system 110 and the second optical system 120. The projection surface 140 is, for example, a screen. Note that the projection surface 140 is not limited to a screen and may include a wall, the ground, a water surface, etc. The optical system 100 may further include a cover glass 131 and a prism 132 between the image display element 130 and the first optical system 110. The cover glass 131 can be provided between the prism 132 and the image display element 130, and between the prism 132 and the first optical system 110.

[0023] Here, for the sake of explaining the optical system 100, we introduce the XYZ Cartesian coordinate system. For example, the direction in which the optical axis C1 of the first optical system 110 extends is defined as the Z-axis direction. For the sake of explanation, the +Z-axis direction may be referred to as "up" and the -Z-axis direction as "down." Note that "up" and "down" are directions used for the sake of explanation and do not indicate the actual direction in which the optical system 100 is positioned.

[0024] The first optical system 110 is a refractive optical system including multiple lenses. The first optical system 110 may include lenses L1 to L12. The first optical system 110 may also be a refractive optical system composed of multiple lenses. The first optical system 110 may be composed of 12 refractive lenses, L1 to L12. Lenses L1 to L12 are arranged in this order along the +Z axis. The first optical system 110 has an optical axis C1.

[0025] The light from the image displayed on the image display element 130 travels such that it has a component in the +Z axis direction, for example. The light from the image displayed on the image display element 30 enters the lens L12 via the prism 132. The light that enters the lens L12 enters the lens L11-L1 and exits from lens L1. The light from the image that exits from lens L1 enters the second optical system 120.

[0026] The second optical system 120 includes one optical element 121 having transmission surfaces T1 and T2 and reflective surfaces R1 and R2. The second optical system 120 may consist of one optical element 121 having transmission surfaces T1 and T2 and reflective surfaces R1 and R2. The optical element 121 in the second optical system 120 includes a first transmission surface T1, a first reflective surface R1, a second reflective surface R2, and a second transmission surface T2. The optical element 121 in the second optical system 120 may consist of a first transmission surface T1, a first reflective surface R1, a second reflective surface R2, and a second transmission surface T2. The second optical system 120 includes a first transmission surface T1, a first reflective surface R1, a second reflective surface, and a second transmission surface in the order that the light of the image from the first optical system 110 passes through. The optical path between each surface of the second optical system 120 may be formed of a single optically transparent medium. The optically transparent medium includes, for example, glass and transparent resin.

[0027] The first transmission surface T1 faces in the direction of the -Z axis. Light emitted from the lens L12 in the first optical system 110 is incident on the first transmission surface T1. The first transmission surface T1 includes a rotationally symmetric plane with respect to the optical axis C1 of the first optical system 110. For example, the first transmission surface T1 may be a curved surface obtained by rotating the shape of the curve of the first transmission surface T1 shown in the cross-sectional view of Figure 3 by 180° from the -X axis side to the +X axis side, with respect to the optical axis C1 as the axis of rotation. In other words, the shape of the curve of the first transmission surface T1 shown in the cross-sectional view of Figure 3 is a function of the radius from the optical axis C1. Furthermore, the shape of the first transmission surface T1 at any position is also a function of the radius from the optical axis C1.

[0028] The first transmission surface T1 has a convex shape toward the side into which the light is incident. The first transmission surface T1 may also have an aspherical shape. Light that has passed through the first transmission surface T1 is incident on the first reflection surface R1.

[0029] The first reflective surface R1 reflects the incident light toward the second reflective surface R2. The first reflective surface R1 is formed to bend the optical axis C1 of the first optical system 10 by 90°. In other words, the first reflective surface R1 has the function of bending the optical axis C1 of the first optical system 10 by 90°. The direction in which the optical axis C1 is reflected by the first reflective surface R1 is called the optical axis C2. Thus, the optical axes C1 and C2 are orthogonal. Furthermore, the optical axes C1 and C2 intersect on the first reflective surface R1.

[0030] The first reflective surface R1 is substantially planar. "Substantially planar" means that it is planar to the extent that it includes unavoidable errors in manufacturing the first reflective surface R1. Light reflected by the first reflective surface R1 is incident on the second reflective surface R2. An intermediate image 133 may be formed in the optical path between the first reflective surface R1 and the second reflective surface R2. Therefore, the optical system 100 forms an image of the image displayed by the image display element 130, which is displayed by the first optical system 110, as an intermediate image 133, and then magnifies the intermediate image 133 with the second optical system 120 to project onto the surface 140.

[0031] The second reflective surface R2 reflects the incident light toward the second transmissive surface T2. The second reflective surface R2 includes a plane of rotational symmetry with respect to the optical axis C2, which is obtained by bending the optical axis C1 of the first optical system 110 by 90°. For example, the second reflective surface R2 may be a curved surface obtained by rotating the shape of the curve of the second reflective surface R2 shown in the cross-sectional view of Figure 3 by 180° from the -X axis side to the +X axis side, with respect to the optical axis C2 as the axis of rotation. In other words, the shape of the curve of the second reflective surface R2 shown in the cross-sectional view of Figure 3 is a function of the radius from the optical axis C2. Furthermore, the shape of the second reflective surface R2 at any position is also a function of the radius from the optical axis C2.

[0032] The second reflective surface R2 has a concave shape. Specifically, the surface on which the incident light is reflected has a concave shape. The second reflective surface R2 may also have an aspherical shape. The light reflected by the second reflective surface R2 is incident on the second transmissive surface T2.

[0033] The second transmission surface T2 transmits the incident light toward the projection surface 140 so as to project it onto the projection surface 140. The second transmission surface T2 includes a plane of rotational symmetry with respect to the optical axis C2. The shape of the curve of the second transmission surface T2 shown in the cross-sectional view of Figure 3 may be a curved surface obtained by rotating the optical axis C2 by 180° from the -X axis side to the +X axis side. In other words, the shape of the curve of the second transmission surface T2 shown in the cross-sectional view of Figure 3 is a function of the radius from the optical axis C2. Furthermore, the shape of the second transmission surface T2 at any position is also a function of the radius from the optical axis C2.

[0034] The second transmissive surface T2 has a convex shape toward the side from which light is emitted. The second transmissive surface T2 may also have an aspherical shape. Light transmitted through the second transmissive surface T2 is projected onto the projection surface 40.

[0035] The first reflective surface R1 and the second transmissive surface T2 may be formed as a single continuous surface. The first reflective surface R1 and the second transmissive surface T2 may be formed as a single surface that connects outside the effective light ray region. The first reflective surface region that fills the effective light ray region of the first reflective surface R1 may be formed separately from the first reflective surface region on which the reflective film is provided and the second transmissive surface region that fills the effective light ray region of the second transmissive surface T2.

[0036] The first reflective surface R1 and the second transmissive surface T2 may be smoothly connected. In other words, the first reflective surface R1 and the second transmissive surface T2 may be connected without forming a step. This makes manufacturing easier and thus reduces costs. However, this does not rule out the possibility of a step being formed between the first reflective surface R1 and the second transmissive surface T2.

[0037] In the cross-sectional view of Figure 3, the first reflective surface R1 and the second transmissive surface T2 are shown to be connected at an obtuse angle for convenience. However, the surface curvature can be appropriately extrapolated outside the effective ray region to match the shape of the processing tool of the surface manufacturing equipment. For this purpose, it is preferable that the optical path length D1 from the optical axis C2 reflected by the first reflective surface R1 to the second reflective surface R2 and the optical path length D2 from the optical axis C2 reflected by the second reflective surface R2 to the second transmissive surface T2 are approximately equal. If the optical path lengths D1 and D2 are not approximately equal, a step will occur at the connection surface between the first reflective surface R1 and the second transmissive surface T2. Therefore, the first reflective surface R1 and the second transmissive surface T2 may not be a single continuous surface. In Figure 2, the first reflective surface R1 and the second transmissive surface T2 are shown to be connected smoothly and continuously.

[0038] The surface between the first reflective surface R1 and the second transmissive surface T2 is called the connecting surface R1-T2. The surface between the first reflective surface R1 and the first transmissive surface T1 is called the connecting surface T1-R1. The surface between the first transmissive surface T1 and the second reflective surface R2 is called the connecting surface T1-R2. The surface between the second reflective surface R2 and the second transmissive surface T2 is called the connecting surface R2-T2. Each connecting surface may be a flat surface or a curved surface. Furthermore, each connecting surface may have a stepped shape. By using such shapes, it is made easier to attach the optical element 121 to the mechanism member for holding it. In addition, each connecting surface can be deformed considering the molding manufacturing process.

[0039] In this embodiment, the optical element 121 in the second optical system 120 may be surrounded by four surfaces including a first transmission surface T1, a first reflection surface R1, a second reflection surface R2, and a second transmission surface T2. The optical element 121 may also be provided as a single element whose interior is filled with a medium. This allows for mold molding in an appropriate shape, providing advantages in mass production and surface eccentricity accuracy control.

[0040] More preferably, when forming the first reflective surface R1 and the second transmitting surface T2 as a single surface, it is preferable that the optical axes C1 and C2 of the first reflective surface R1 remain on the first reflective surface R1. This ensures that the optical axes C1 and C2 are present on the optical element 121 of the second optical system 120, making it easier to ensure assembly and adjustment accuracy between the first optical system 110 and the projection surface 40.

[0041] In this embodiment, the first reflective surface R1 has a planar shape. The second reflective surface R2 has a concave shape on the magnification side. The second transmissive surface T2 has a convex shape on the magnification side. An intermediate image 133, conjugate to the image on the image display surface of the image display element 130 and the image on the projection surface, is formed between the first reflective surface R1 and the second reflective surface R2. The second reflective surface R2 has a concave shape as a reflective surface that magnifies and projects the intermediate image 133 onto the projection surface 140 such as a screen.

[0042] Furthermore, the second optical system 120 is equipped with a first transmission surface T1, a second reflection surface R2, and a second transmission surface T2 having optical power in the vicinity of the intermediate image 133, thereby enabling projection at a short projection distance while ensuring optical imaging performance. This optical power arrangement allows for the configuration to have an optical pupil between the second reflection surface R2 and the second transmission surface T2, thereby reducing the effective ray region of the second transmission surface T2. In addition, the boundary between the first reflection surface R1 and the second transmission surface T2 can be separated without overlapping with the effective ray region of the first reflection surface R1, which is configured as a continuous surface.

[0043] The first transmission surface T1 has an aspherical shape with different curvatures in the center and periphery, optimized for off-axis aberration correction together with the aspherical lens located closest to the second optical system 120 in the first optical system 110. Furthermore, the first reflection surface R1 bends the optical axis C1 of the first optical system 110 by 90° to form the optical axis C2, thereby enabling the image display surface of the image display element 130 and the projection surface 140, such as a screen, to be configured in a perpendicular relationship. In other words, the projection surface 140, such as a screen, and the optical axis C1 of the first optical system 110 can be configured in a parallel relationship. Therefore, the footprint of the image projection device 101 equipped with the optical system 100 can be minimized, improving user convenience such as flexibility in the installation environment.

[0044] Figures 4 to 6 illustrate the lens data of the optical system 100 according to Embodiment 1. Figure 4 shows the surface type, name, radius of curvature, spacing, nd (refractive index of the d line), and νd (Abbe number) for each optical element surface indicated by the surface number from the object surface, which is the image display surface of the image display element 130, to the image surface, which is the projection surface 140. Figures 5 and 6 show the design data of the aspherical surfaces of each optical element indicated by the surface number. The aspherical formula is also shown in Figures 5 and 6. The specifications are Fno 3.0, 70" projection, and the size of the object surface is 5.8 mm × 10.4 mm. The arrangement is shifted 3.79 mm from the center of the object surface.

[0045] Figure 7 is a graph illustrating the MTF (Modulation Transfer Function) performance of the optical system 100 according to Embodiment 1, where the horizontal axis represents spatial frequency and the vertical axis represents MTF. As shown in Figure 7, a spatial frequency of 90 lines / mm corresponds to a unit pixel of 5.6 μm on the image display element 130. The evaluation image heights on the image display element are Field1 (F1): Y=0.85 mm, Field2 (F2): Y=4.25 mm, and Field3 (F3): Y=8.5 mm. The evaluation wavelengths and weights are 643 nm: 525 nm: 440 nm = 1:1:1. As shown in Figure 7, the optical system 100 of this embodiment ensures an MTF performance of 0.6 or higher.

[0046] According to this embodiment, the optical system 100 includes the first optical system 110 and the second optical system 120 as described above, so that an ultra-short-focus projection optical system capable of projection at a short projection distance can be provided. The optical element 121 constituting the second optical system 120 is not formed from multiple optical elements, but is formed integrally as a single optical element 121 having a transmitting surface and a reflective surface. Therefore, projection at a short projection distance is possible while ensuring optical performance. Furthermore, by configuring the optical element with optical axes C1 and C2 on each surface, the alignment accuracy of each surface can be easily achieved.

[0047] <Embodiment 2> Next, the optical system according to Embodiment 2 will be described. This embodiment corresponds to a modification of the configuration of the first optical system 110 in the optical system 100 of Embodiment 1 described above. It also corresponds to a modification of the configuration of the second optical system 120 in the optical system 100 of Embodiment 1. Figure 8 is a cross-sectional view illustrating the optical system 200 according to Embodiment 2. As shown in Figure 8, the first optical system 110a of this embodiment includes lenses L1 to L13. Lens L1 is composed of an aspherical lens. The first optical system 110a further includes lens L13. The configuration of the first optical system 110a other than these is the same as the configuration of the first optical system 110 described above.

[0048] Figure 9 is a cross-sectional view illustrating an optical element 121a in the second optical system 120a according to Embodiment 2. As shown in Figure 9, in the second optical system 120a of this embodiment, the connection surfaces TI-R1, TI-R2, R2-T2, and R1-T2 may be flat or curved. Furthermore, each connection surface may have a stepped shape or a gradient angle. In addition, each connection surface may be deformed considering attachment to a mechanism member for holding the optical components including the optical system 200, or may be deformed considering the manufacturing of the optical components including the optical system 200 in a molding process.

[0049] Furthermore, each connection surface may be a sand-scraped surface or may be painted with black ink. In addition, a V-shaped groove may be provided on each connection surface. By adopting this configuration, the problem of unwanted light entering the optical components of the optical system 200 and reflecting off each connection surface, etc., resulting in ghost light on the projection surface can be avoided.

[0050] Figures 10 to 12 illustrate the lens data of the optical system 200 according to Embodiment 2. Figure 10 shows the surface type, name, radius of curvature, spacing, nd, and νd for each optical element surface indicated by the surface number from the object surface, which is the image display surface of the image display element 130, to the image surface, which is the projection surface 140. Figures 11 and 12 show the design data for the aspherical surfaces of each optical element indicated by the surface number. The specifications differ from Embodiment 1 in that Fno is 3.0 and the projection is 100”. The size of the object surface is 5.8 mm × 10.4 mm. The arrangement is shifted 3.79 mm from the center of the object surface.

[0051] According to this embodiment, the degree of design freedom for the optical element 121a in the second optical system 120a can be improved. Other configurations and effects are described in Embodiment 1.

[0052] <Embodiment 3> Next, an optical system according to Embodiment 3 will be described. This embodiment is an example of a configuration of an ultra-wide-angle projection optical system. Figure 13 is a cross-sectional view illustrating an optical system 300 according to Embodiment 3. Figure 14 is a cross-sectional view illustrating an optical element 121b in the second optical system 120b according to Embodiment 3. In Figures 13 and 14, projected light rays with a field of view of 11° to 120° are shown.

[0053] As shown in Figures 13 and 14, the optical system 300 of this embodiment includes a first optical system 110b and a second optical system 120b. The first transmission surface T1, first reflection surface R1, second reflection surface R2, and second transmission surface T2 in the second optical system 120b may have the same configuration as in Embodiment 1. However, the second optical system 120b of this embodiment is particularly characterized by the second transmission surface T2. That is, the exit pupil of the second optical system 120b is positioned shorter than the focal point of the second transmission surface T2. As a result, the second transmission surface T2 becomes a surface that acts in a direction that expands the light rays of each angle of view. With this configuration, the second optical system 120b can enable ultra-wide-angle projection. The connection surface T1-R1 between the first transmission surface T1 and the first reflection surface R1 is not shown in the figures, but the first transmission surface T1 and the first reflection surface R1 may be connected by extending them, or they may be connected by a planar or curved surface.

[0054] Figures 15 and 16 illustrate the lens data of the optical system 300 according to Embodiment 3. Figure 15 shows the surface type, name, radius of curvature, spacing, nd, and νd for each optical element surface indicated by surface number from the image plane, which is the image display surface of the image display element 130, to the object surface, which is the projection surface 140. Figure 16 shows the design data for the aspherical surface of each optical element indicated by surface number. The specifications differ from Embodiments 1 and 2 in that Fno is 3.0 and the projection is a maximum of 240° across the entire field of view. The size of the object surface is 5.8 mm × 10.4 mm. The arrangement is shifted 3.79 mm from the center of the object surface.

[0055] Figure 17 is a graph illustrating the MTF performance of the optical system 300 according to Embodiment 3, where the horizontal axis represents spatial frequency and the vertical axis represents MTF. As shown in Figure 17, a spatial frequency of 90 lines / mm corresponds to a unit pixel of 5.6 μm on the image display element 130. The evaluation image heights on the image display element are Field1(F1):Y=0.84mm, Field2(F2):Y=4.2mm, and Field3(F3):Y=8.4mm. Converted to field of view, this corresponds to Field1(F1):11°, Field2(F2):55°, and Field3(F3):110°. The evaluation wavelengths and weights are 643nm:525nm:440nm=1:1:1. As shown in Figure 17, the optical system 300 of this embodiment ensures an MTF performance of 0.7 or higher.

[0056] According to this embodiment, an optical system 300 for ultra-wide-angle projection can be provided. Other configurations and effects are described in Embodiments 1 and 2.

[0057] <Embodiment 4> Next, an optical system according to Embodiment 4 will be described. This embodiment is an example of a configuration of an ultra-wide-angle projection optical system, but the optical system is small in size. Figure 18 is a cross-sectional view illustrating the optical system 400 according to Embodiment 4. Figure 19 is a cross-sectional view illustrating the second optical system 120c in the optical system 400 according to Embodiment 4. In Figures 18 and 19, projected light rays with a field of view of 11° to 120° are shown.

[0058] As shown in Figures 18 and 19, the optical system 400 of this embodiment includes a first optical system 110c and a second optical system 120c. The first transmission surface T1, first reflection surface R1, second reflection surface R2, and second transmission surface T2 in the second optical system 120c of this embodiment may have the same configuration as in Embodiment 1. Also, in the second optical system 120c of this embodiment, similar to Embodiment 3 described above, the exit pupil of the second optical system 120c is positioned shorter than the focal point of the second transmission surface T2. The connection surface between the first transmission surface T1 and the first reflection surface R1 is not shown in the figures, but the first transmission surface T1 and the first reflection surface R1 may be connected by extending them, or they may be connected by a planar or curved surface.

[0059] Figures 20 and 21 illustrate the lens data of the optical system 400 according to Embodiment 4. Figure 20 shows the surface type, name, radius of curvature, spacing, nd, and νd for each optical element surface indicated by the surface number from the image plane, which is the image display surface of the image display element 130, to the object surface, which is the projection surface 140. Figure 21 shows the design data for the aspherical surface of each optical element indicated by the surface number. The specifications are the same as in Embodiment 3.

[0060] According to this embodiment, it is possible to provide an optical system 400 that is both an ultra-wide-angle projection optical system and has a small size. Other configurations and effects are described in Embodiments 1 to 3.

[0061] This disclosure is not limited to the embodiments described above, and can be modified as appropriate without departing from the spirit of the invention. For example, the configurations of Embodiments 1 to 4 can be combined with each other. [Explanation of symbols]

[0062] 100, 200, 300, 400 optics 101 Image projection device 110, 110a, 110b, 110c 1st optical system L1, L2, L3, L4, L5, L6, L7, L8, L9, L10 Lens L11, L12, L13 lenses 120, 120a, 120b, 120c 2nd optical system 121, 121a, 121b, 121c Optical elements 130 Image display elements 131 Cover glass 132 Prisms 133 Intermediate image 140 Projection surface C1, C2 optical axis R1 1st reflective surface R1-T2 connection surface R2 2nd reflective surface R2-T2 connection surface T1 1st transmission surface T1-R1 connection surface T1-R2 connection surface T2 2nd transparent surface

Claims

1. A first optical system of a refractive optical system including multiple lenses, A second optical system including one optical element having a transmissive surface and a reflective surface, Equipped with, An optical system that magnifies and images an image displayed on an image display element onto a projection surface as a conjugate surface of the image display element through the first optical system and the second optical system, An optical system that forms an image of the image displayed by the first optical system as an intermediate image, and then magnifies the intermediate image with the second optical system to form an image on the projection surface, The second optical system includes a first transmission surface, a first reflection surface, a second reflection surface, and a second transmission surface in the order through which the light of the image from the first optical system passes. The optical path between each surface is formed by a single medium. The first reflective surface and the second transmissive surface are formed as a single continuous surface. The second reflective surface has a concave shape. optical system.

2. The first reflective surface and the second transmissive surface are smoothly connected. The optical system according to claim 1.

3. The first reflective surface and the second transmissive surface are formed as a single continuous surface. A first reflective surface region that satisfies the light-effective region of the first reflective surface, wherein the first reflective surface region provided with a reflective film and the second transmissive surface region that satisfies the light-effective region of the second transmissive surface are formed separately. The optical system according to claim 1 or 2.

4. The first reflective surface has a substantially planar shape. The optical system according to claim 1 or 2.

5. The first transmission surface includes a rotationally symmetric plane that is rotationally symmetric with respect to the first optical axis, which is the optical axis of the first optical system. The optical system according to claim 1 or 2.

6. The first reflective surface is formed such that the optical axis of the first optical system is bent by 90°. The optical system according to claim 1 or 2.

7. The second reflective surface and the second transmitting surface include a rotationally symmetric plane that is rotationally symmetric with respect to a second optical axis obtained by bending the optical axis of the first optical system by 90°. The optical system according to claim 1 or 2.

8. An intermediate image is formed in the optical path between the first reflective surface and the second reflective surface. The optical system according to claim 1 or 2.

9. An image projection device comprising the optical system described in claim 1 or 2.

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