Projection optical systems and projectors

Abstract

A projection optical system and a projector, wherein the projection optical system is a short-focus projection optical system that can be miniaturized compared to conventional systems. The projection optical system comprises a first and a second optical system in order from the reduction side toward the magnification side. The second optical system comprises, in order from the reduction side toward the magnification side: an optical element having a concave reflection surface; and a first lens having a negative refractive power. When the axial interval from the image forming element to the reflection surface is OAL, the first distance from the optical axis to the maximum image height of the image forming element is imy, the maximum radius of the first lens is LL, the projection ratio obtained by dividing the projection distance by the second distance from the optical axis to the maximum image height of the magnified image is TR, and the numerical aperture of the image forming element is NA, all of the following conditional expressions (1) and (2) are satisfied. TR ≤ 0.3 (1) 35 ≤ (OAL / imy) × (LL / imy) × TR × (1 / NA) ≤ 60 (2).

Description

Technical Field

[0001] The invention relates to a projection optical system and a projector. Background Art

[0002] Patent document 1 describes a projector that uses a projection optical system to magnify a projection image displayed on an image display element and project the image onto a screen. The projection optical system includes a first refractive optical system, a reflective optical system, and a second refractive optical system in order from the reduction side toward the magnification side. The first refractive optical system includes a plurality of refractive lenses. The reflective optical system includes a concave mirror that reflects light from the first refractive optical system toward the image display element in a direction intersecting with the optical axis of the first refractive optical system. The second refractive optical system is composed of one refractive lens. The refractive lens is the magnification-side lens located closest to the magnification side in the projection optical system. Light from the concave mirror enters the magnification-side lens from a direction intersecting with the optical axis of the magnification-side lens.

[0003] In the embodiments of the projection optical system disclosed in Patent Document 1, the projection optical system with the shortest projection distance has a projection distance of 257.6 mm. The effective radius of the magnification-side lens of this projection optical system is 79.7 mm. In addition, the projection ratio of this projection optical system is 0.154.

[0004] Patent Document 1: Japanese Patent Application Laid-Open No. 2020-34690

[0005] In a projector, the smaller the throw ratio of the projection optical system, the shorter the projection distance required to project a magnified image of a given size. Therefore, for projectors used indoors, for example, the projection optical system equipped with a throw ratio of 0.3 or less is required to have a short focal length.

[0006] Here, when the projection optical system is shortened, aberrations generated on the magnification side tend to increase. Therefore, it is necessary to increase the effective radius of the magnification-side lens, through which the light rays from the concave mirror pass obliquely, so that light rays at each image height can be corrected within the magnification-side lens. However, when the magnification-side lens is enlarged to ensure a sufficient effective radius, the amount of radial protrusion of the magnification-side lens from the first optical axis of the first refractive optical system increases, making the projection optical system as a whole thicker. Consequently, miniaturization of projectors equipped with projection optical systems is hindered. Summary of the Invention

[0007] In order to solve the above-mentioned problems, the projection optical system of the present invention is used to magnify the projection image formed by the image forming element arranged on the reduction side conjugate surface and project the magnified image onto the magnification side conjugate surface. The projection optical system is characterized in that it has a first optical system and a second optical system in order from the reduction side toward the magnification side, the first optical system has an aperture, and the second optical system has, in order from the reduction side toward the magnification side: an optical element having a concave reflecting surface; and a first lens having a negative refractive power, and a lens is formed between the first optical system and the second optical system. The intermediate image conjugate with the reduction side conjugate surface and the magnification side conjugate surface is telecentric on the reduction side relative to the first optical system, and when the axial interval from the image forming element to the reflecting surface is set to OAL, the first distance from the optical axis to the maximum image height of the image forming element is set to imy, the maximum radius of the first lens is set to LL, the projection ratio obtained by dividing the projection distance by the second distance from the optical axis to the maximum image height of the magnified image is set to TR, and the numerical aperture of the image forming element is set to NA, all of the following conditional expressions (1) and (2) are satisfied.

[0008] TR≤0.3(1)

[0009] 35≤(OAL / imy)×(LL / imy)×TR×(1 / NA)≤60(2)

[0010] Next, the projector of the present invention is characterized in that the projector includes: the above-mentioned projection optical system; and the image forming element that forms a projection image on the reduction-side conjugate surface of the projection optical system. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a diagram showing a schematic configuration of a projector having the projection optical system of the present invention.

[0012] Figure 2 This is a ray diagram of the projection optical system of Example 1.

[0013] Figure 3 This is a diagram of the lateral aberration at the reference distance of the projection optical system of Example 1.

[0014] Figure 4 These are diagrams showing spherical aberration, astigmatism, and distortion at a reference distance of the projection optical system of Example 1.

[0015] Figure 5 These are diagrams showing spherical aberration, astigmatism, and distortion of the projection optical system of Example 1 at a close distance.

[0016] Figure 6These are diagrams showing spherical aberration, astigmatism, and distortion at long distances of the projection optical system of Example 1.

[0017] Figure 7 This is a ray diagram of the projection optical system of Example 2.

[0018] Figure 8 This is a diagram of the lateral aberration at the reference distance of the projection optical system of Example 2.

[0019] Figure 9 These are diagrams showing spherical aberration, astigmatism, and distortion at a reference distance of the projection optical system of Example 2.

[0020] Figure 10 These are diagrams showing spherical aberration, astigmatism, and distortion at close distances of the projection optical system of Example 2.

[0021] Figure 11 These are diagrams showing spherical aberration, astigmatism, and distortion at long distances of the projection optical system of Example 2.

[0022] Figure 12 This is a ray diagram of the projection optical system of Example 3.

[0023] Figure 13 This is a diagram of the lateral aberration at the reference distance of the projection optical system of Example 3.

[0024] Figure 14 These are diagrams showing spherical aberration, astigmatism, and distortion at a reference distance of the projection optical system of Example 3.

[0025] Figure 15 These are diagrams showing spherical aberration, astigmatism, and distortion at close distances of the projection optical system of Example 3.

[0026] Figure 16 These are diagrams showing spherical aberration, astigmatism, and distortion at long distances of the projection optical system of Example 3.

[0027] Figure 17 This is a ray diagram of the projection optical system of Example 4.

[0028] Figure 18 This is a diagram of the lateral aberration at the reference distance of the projection optical system of Example 4.

[0029] Figure 19 These are diagrams showing spherical aberration, astigmatism, and distortion at a reference distance of the projection optical system of Example 4.

[0030] Figure 20 These are diagrams showing spherical aberration, astigmatism, and distortion at close distances of the projection optical system of Example 4.

[0031] Figure 21 These are diagrams showing spherical aberration, astigmatism, and distortion at long distances of the projection optical system of Example 4.

[0032] Description of labels

[0033] 1: Projector; 2: Image forming unit; 3, 3A, 3B, 3C, 3D: Projection optical system; 4: Control unit; 6: Image processing unit; 7: Display driver; 10: Light source; 11: Integrating lens; 12: Integrating lens; 13: Polarization conversion element; 14: Overlapping lens; 15: Dichroic mirror; 16: Reflecting mirror; 17R: Field lens; 17G: Field lens; 17B: Field lens; 18 (18B, 18R, 18G): Liquid crystal panel; 19: Cross dichroic prism ; 21: dichroic mirror; 22: relay lens; 23: reflector; 24: relay lens; 25: reflector; 30: intermediate image; 31: first optical system; 32: second optical system; 33: optical element; 34: first lens; 36: first surface; 37: second surface; 40: reflecting surface; 41: first transmission surface; 42: reflecting surface; 43: second transmission surface; 51: aperture; L1~L17: lenses; L21~L24: junction lenses; N: optical axis; S: screen. DETAILED DESCRIPTION

[0034] Hereinafter, an optical system and a projector according to an embodiment of the present invention will be described with reference to the drawings.

[0035] (Projector)

[0036] Figure 1 1 is a diagram showing a schematic structure of a projector having a projection optical system 3 of the present invention. Figure 1 As shown, the projector 1 includes an image forming unit 2 that generates a projection image to be projected onto a screen S; a projection optical system 3 that magnifies the projection image and projects the magnified image onto the screen S; and a control unit 4 that controls the operation of the image forming unit 2 .

[0037] (Image Forming Unit and Control Unit)

[0038] The image forming unit 2 includes a light source 10, a first integrator lens 11, a second integrator lens 12, a polarization conversion element 13, and a superimposing lens 14. The light source 10 is composed of, for example, an ultra-high-pressure mercury lamp, a solid-state light source, or the like. The first integrator lens 11 and the second integrator lens 12 each include a plurality of lens elements arranged in an array. The first integrator lens 11 splits the light beam from the light source 10 into a plurality of lens elements. The lens elements of the first integrator lens 11 converge the light beam from the light source 10 near the lens elements of the second integrator lens 12.

[0039] The polarization conversion element 13 converts the light from the second integrator lens 12 into predetermined linearly polarized light. The superimposing lens 14 superimposes the images of the lens elements of the first integrator lens 11 via the second integrator lens 12 on the display areas of the liquid crystal panels 18R, 18G, and 18B described later.

[0040] The image forming unit 2 also includes a first dichroic mirror 15, a reflective mirror 16, a field lens 17R, and a liquid crystal panel 18R. The first dichroic mirror 15 reflects the R light, which is part of the light incident from the superimposing lens 14, and transmits the G and B light, which are part of the light incident from the superimposing lens 14. The R light reflected by the first dichroic mirror 15 passes through the reflective mirror 16 and the field lens 17R and enters the liquid crystal panel 18R. The liquid crystal panel 18R is a light modulator that serves as an image forming element. The liquid crystal panel 18R modulates the R light according to the image signal, thereby forming a red projected image.

[0041] The image forming unit 2 also includes a second dichroic mirror 21, a field lens 17G, and a liquid crystal panel 18G. The second dichroic mirror 21 reflects the G light, which is part of the light from the first dichroic mirror 15, and transmits the B light, which is part of the light from the first dichroic mirror 15. The G light reflected by the second dichroic mirror 21 enters the liquid crystal panel 18G via the field lens 17G. The liquid crystal panel 18G is a light modulator that serves as an image forming element. The liquid crystal panel 18G modulates the G light according to the image signal, thereby forming a green projected image.

[0042] The image forming unit 2 also includes a relay lens 22, a reflective mirror 23, a relay lens 24, a reflective mirror 25, a field lens 17B, a liquid crystal panel 18B, and a cross dichroic prism 19. The B light that has passed through the second dichroic mirror 21 passes through the relay lens 22, the reflective mirror 23, the relay lens 24, the reflective mirror 25, and the field lens 17B, and is incident on the liquid crystal panel 18B. The liquid crystal panel 18B is a light modulator that serves as an image forming element. The liquid crystal panel 18B modulates the B light according to the image signal, thereby forming a blue projection image.

[0043] The liquid crystal panels 18R, 18G, and 18B surround the cross dichroic prism 19 from three directions. The cross dichroic prism 19 is a light-combining prism that generates a projection image by combining light modulated by the liquid crystal panels 18R, 18G, and 18B.

[0044] The projection optical system 3 enlarges and projects the projection image synthesized by the cross dichroic prism 19 onto the screen S.

[0045] Control unit 4 includes image processing unit 6 to which external image signals such as video signals are input, and display driving unit 7 that drives liquid crystal panels 18R, 18G, and 18B based on the image signals output from image processing unit 6 .

[0046] Image processing unit 6 converts image signals input from an external device into image signals including grayscales of each color. Display driver 7 operates liquid crystal panels 18R, 18G, and 18B based on the projection image signals of each color output from image processing unit 6. As a result, image processing unit 6 displays projection images corresponding to the image signals on liquid crystal panels 18R, 18G, and 18B.

[0047] (Projection optical system)

[0048] Next, the projection optical system 3 will be described. Figure 1 As shown, a screen S is arranged on the magnification-side conjugate surface of the projection optical system 3. A liquid crystal panel 18R, a liquid crystal panel 18G, and a liquid crystal panel 18B are arranged on the reduction-side conjugate surface of the projection optical system 3.

[0049] Hereinafter, Examples 1 to 4 will be described as configuration examples of the projection optical system 3 mounted on the projector 1 .

[0050] (Example 1)

[0051] Figure 2 : is a ray diagram of the projection optical system 3A of Example 1. In the ray diagrams of the projection optical system 3 of Examples 1 to 4, the liquid crystal panel 18R, the liquid crystal panel 18G, and the liquid crystal panel 18B are represented as the liquid crystal panel 18. Figure 2 As shown, the projection optical system 3A of this example is composed of a first optical system 31 and a second optical system 32 in this order from the reduction side toward the magnification side. The second optical system 32 is arranged on the optical axis N of the first optical system 31.

[0052] For convenience, the following description refers to three mutually perpendicular axes as the X-axis, Y-axis, and Z-axis. The Z-axis coincides with the optical axis N of the first optical system 31. The Z-axis direction is along the optical axis N. In the Z-axis direction, the side where the first optical system 31 is located is referred to as the first direction Z1, and the side where the second optical system 32 is located is referred to as the second direction Z2. The Y-axis extends along the screen S. The Y-axis direction is vertical, with one side of the Y-axis direction being referred to as the upper direction Y1 and the other side being referred to as the lower direction Y2. The X-axis extends across the width of the screen.

[0053] The first optical system 31 is a refractive optical system. The first optical system 31 is composed of 17 lenses L1 to L17. The lenses L1 to L17 are arranged in order from the reduction side to the magnification side. An aperture 51 is arranged between the lens L7 and the lens L8.

[0054] Lens L6 has aspherical surfaces on both surfaces. Lens L9 has aspherical surfaces on both surfaces. Lens L16 (the third lens) has aspherical surfaces on both surfaces. Lens L17 (the second lens) has aspherical surfaces on both surfaces. Lens L2 and L3 form a cemented lens L21. Lens L4 and L5 form a cemented lens L22. Lens L11 and L12 form a cemented lens L23. Lens L14 and L15 form a cemented lens L24.

[0055] The second optical system 32 includes an optical element 33 and a first lens 34. The optical element 33 and the first lens 34 are arranged in order from the reduction side toward the magnification side. The optical element 33 includes a reflecting surface 40 facing the reduction side. The reflecting surface 40 has a concave shape that is concave in the second direction Z2. The reflecting surface 40 has an aspherical shape. Figure 2 As shown, the reflective surface 40 is located Y2 below the optical axis N. The reflective surface 40 is formed by providing a reflective coating (reflective layer) on the outer side surface in the first direction Z1 of the optical element 33. The reflective surface 40 reflects light on the surface of the optical element 33 in the Z1 direction.

[0056] The first lens 34 is located closer to the optical element 33 in the first direction Z1 and is positioned upward Y1 relative to the optical axis N. The first lens 34 has negative refractive power. The first lens 34 has a convex shape on its magnification-side surface and a concave shape on its reduction-side surface. Both surfaces of the first lens 34 have aspherical shapes.

[0057] Here, the liquid crystal panel 18 of the image forming unit 2 is arranged on the reduction-side conjugate surface of the projection optical system 3A. The screen S is arranged on the magnification-side conjugate surface of the projection optical system 3A.

[0058] The liquid crystal panel 18 forms a projected image on an image forming surface perpendicular to the optical axis N of the first optical system 31. The liquid crystal panel 18 is arranged at a position offset upward by Y1 relative to the optical axis N of the first optical system 31. Therefore, the projected image is formed at a position offset upward by Y1 relative to the optical axis N.

[0059] Light from the liquid crystal panel 18 passes through the first optical system 31 and the second optical system 32 in sequence. Between the first and second optical systems 31 and 32, the light passes below the optical axis N at position Y2. As a result, the light travels through the second optical system 32 toward the reflective surface 40. The light reaching the reflective surface 40 is then reflected in the first direction Z1 and upward at position Y1. The light reflected by the reflective surface 40 then crosses the optical axis N in a direction Y1 upward toward the first lens 34. The light passing through the first lens 34 is then expanded by the first lens 34 and reaches the screen S.

[0060] Here, the lens L17 of the first optical system 31 is arranged between the reflecting surface 40 and the first lens 34 in the direction of the optical axis N. The intermediate image 30 is formed between the lens L17 and the reflecting surface 40 .

[0061] The projection optical system 3A is telecentric on the reduction side relative to the first optical system 31. Telecentric means that the central ray of each light beam passing between the first optical system 31 and the liquid crystal panel 18 disposed on the conjugate surface on the reduction side is parallel or substantially parallel to the optical axis.

[0062] Here, the projection optical system 3A can change the projection distance. When the projection distance is changed, the eight lenses L10 to L17 of the first optical system 31 are moved along the optical axis N to perform focusing. During focusing, lenses L10, L11, and L12 are moved in unison. Additionally, lenses L13, L14, and L15 are moved in unison during focusing.

[0063] When the numerical aperture of the liquid crystal panel 18 is set to NA, the first distance from the optical axis N to the maximum image height of the liquid crystal panel 18 is set to imy, the second distance from the optical axis N to the maximum image height of the magnified image projected onto the screen S is set to scy, the distance from the first lens 34 to the screen S, i.e. the projection distance, is set to PD, the projection magnification obtained by dividing the second distance by the first distance is set to M, the projection ratio obtained by dividing the projection distance by the second distance is set to TR, the axial surface interval from the liquid crystal panel 18 to the reflecting surface 40 is set to OAL, and the maximum radius of the first lens 34 is set to LL, the data of the projection optical system 3A are as follows.

[0064]

[0065] The lens data for the projection optical system 3A is as follows. Surface numbers are assigned in order from the reduction side to the magnification side. The numbers are for the liquid crystal panel, dichroic prism, lens, optical element, first lens, and screen. Surface numbers that do not correspond to the liquid crystal panel, dichroic prism, lens, optical element, first lens, and screen are virtual data. R is the radius of curvature. D is the distance on the axis. C is the aperture radius, and twice the aperture radius is the diameter of the lens surface. The units of R, D, and C are mm.

[0066]

[0067]

[0068] Here, the projection optical system 3A of this example can change the projection distance between a reference distance, a short distance shorter than the reference distance, and a long distance longer than the reference distance. When the projection distance is changed, the eight lenses L10 to L17 of the first optical system 31 are moved along the optical axis N to perform focusing. In addition, when focusing in a manner such that the projection distance is changed from a short distance to a long distance, lens L10, lens L11, and lens L12 are moved toward the magnification side along the optical axis N. When focusing in the same manner, lens L13, lens L14, and lens L15 are moved toward the magnification side along the optical axis N. When focusing in the same manner, lens L16 is moved toward the magnification side along the optical axis N. When focusing in the same manner, lens L17 is moved toward the reduction side along the optical axis N.

[0069] The following shows variable spacing 1, variable spacing 2, variable spacing 3, variable spacing 4, variable spacing 5, and variable spacing 6 at various projection distances during focusing. Variable spacing 1 is the axial surface spacing between lens L9 and lens L10. Variable spacing 2 is the axial surface spacing between lens L12 and lens L13. Variable spacing 3 is the axial surface distance between lens L15 and lens L16. Variable spacing 4 is the axial surface distance between lens L16 and lens L17. Variable spacing 5 is the axial surface distance between lens L17 and reflective surface 40. Variable spacing 6 represents the projection distance.

[0070]

[0071] The aspheric coefficients are as follows.

[0072]

[0073]

[0074] Here, when the axial interval from the liquid crystal panel 18 to the reflecting surface 40 is set to OAL, the first distance from the optical axis N to the maximum image height of the liquid crystal panel 18 is set to imy, the maximum radius of the first lens 34 is set to LL, the projection ratio obtained by dividing the projection distance by the second distance from the optical axis N to the maximum image height of the magnified image projected onto the screen S is set to TR, and the numerical aperture of the liquid crystal panel 18 is set to NA, the projection optical system 3A of this example satisfies all of the following conditional expressions (1) and (2).

[0075] TR≤0.3(1)

[0076] 35≤(OAL / imy)×(LL / imy)×TR×(1 / NA)≤60(2)

[0077] Furthermore, it is more preferable that all of the following conditional expressions (1) and (2') are satisfied.

[0078] TR≤0.3(1)

[0079] 35≤(OAL / imy)×(LL / imy)×TR×(1 / NA)≤53(2')

[0080] In this example,

[0081]

[0082]

[0083] Therefore, TR = 0.194, which satisfies the conditional expression (1). (OAL / imy) × (LL / imy) × TR × (1 / NA) = 44, which satisfies the conditional expression (2).

[0084] (Effect)

[0085] The projection optical system 3A of this example magnifies the projection image formed by the liquid crystal panel 18 arranged on the reduction side conjugate surface and projects the magnified image onto the magnification side conjugate surface. The projection optical system 3A of this example has a first optical system 31 and a second optical system 32 in order from the reduction side toward the magnification side. The first optical system 31 has an aperture 51. The second optical system 32 has, in order from the reduction side toward the magnification side: an optical element 33 having a concave reflecting surface 40; and a first lens 34 having a negative refractive power. An intermediate image 30 conjugated with the reduction side conjugate surface and the magnification side conjugate surface is formed between the first optical system 31 and the second optical system 32. The reduction side is telecentric compared to the first optical system 31.

[0086] In addition, when the axial interval from the liquid crystal panel 18 to the reflecting surface 40 is set to OAL, the first distance from the optical axis N to the maximum image height of the liquid crystal panel 18 is set to imy, the maximum radius of the first lens 34 is set to LL, the projection ratio obtained by dividing the projection distance by the second distance from the optical axis N to the maximum image height of the magnified image projected onto the screen S is set to TR, and the numerical aperture of the liquid crystal panel 18 is set to NA, the projection optical system 3A of this example satisfies all of the following conditional expressions (1) and (2).

[0087] TR≤0.3(1)

[0088] 35≤(OAL / imy)×(LL / imy)×TR×(1 / NA)≤60(2)

[0089] The projection optical system 3A of this example satisfies conditional expression (1). Therefore, the projection optical system 3 is short-focused. Here, when the projection optical system is short-focused, the aberration generated on the magnification side tends to become larger. Therefore, it is necessary to increase the effective radius of the magnification side lens through which the light from the concave mirror passes obliquely, and to correct the light of each image height in the magnification side lens. However, when the magnification side lens is enlarged in order to ensure the effective radius, the amount of radial protrusion of the magnification side lens from the first optical axis of the first refractive optical system becomes larger, and the projection optical system as a whole becomes thicker.

[0090] To address this issue, the projection optical system 3A of this example satisfies conditional expression (2). Therefore, by suppressing the radial protrusion of the first lens 34 from the optical axis N, the overall thickness of the projection optical system can be suppressed, thereby miniaturizing the projector equipped with the projection optical system 3A. Furthermore, the radial protrusion of the first lens 34 from the optical axis N can be suppressed, and an effective diameter capable of correcting light rays at each image height can be ensured in the first lens 34. That is, when conditional expression (1) falls below the lower limit, the axial spacing from the liquid crystal panel 18 to the reflective surface 40 and the lens diameter of the first lens 34 become too small relative to TR and 1 / NA, making it difficult to correct light rays at each image height, and thus making it difficult to ensure the resolution performance of the projection optical system 3A. Furthermore, even if a lens capable of achieving resolution performance is designed, the lens requires molding precision during manufacturing, resulting in a problem of low mass production. When conditional expression (2) exceeds the upper limit, the axial spacing from the liquid crystal panel 18 to the reflective surface 40 and the lens diameter of the first lens 34 become too large. That is, the amount of radial projection of the first lens 34 from the optical axis N increases, and thus the entire projection optical system becomes thicker. Consequently, the projector equipped with the projection optical system increases in size.

[0091] Here, as a comparative example, Example 3 of Japanese Patent Gazette No. 2020-34690, which is a prior art document, is studied. The projection optical system of the comparative example has a first refractive optical system, a reflective optical system, and a second refractive optical system in order from the reduction side to the magnification side. The first refractive optical system has a plurality of refractive lenses. The reflective optical system has a concave mirror that reflects the light from the first refractive optical system toward the image display element side in a direction intersecting with the optical axis of the first refractive optical system. The second refractive optical system is composed of one refractive lens. The refractive lens is the magnifying side lens located closest to the magnifying side in the projection optical system. The light from the concave mirror is incident on the magnifying side lens from a direction intersecting with the optical axis of the magnifying side lens. The data of the comparative example are as follows.

[0092]

[0093] In the comparative example, TR = 0.154. Therefore, the projection optical system of the comparative example satisfies conditional formula (1). However, in the comparative example, (OAL / imy)×(LL / imy)×TR×(1 / NA)=72. Therefore, the projection optical system of the comparative example does not satisfy conditional formula (2). Therefore, when the projection ratio is equal, the lens radius of the magnification side lens of the projection optical system of the comparative example is larger than the effective radius of the first lens of the projection optical system 3A of this example. That is, the projection optical system of the comparative example as a whole is thicker than the projection optical system 3A of this example as a whole.

[0094] In the projection optical system 3A of this example, the reflective surface 40 has a reflective coating (reflective layer) on its surface. Here, in a structure in which the reflective surface is provided inside the optical element 33, the shape accuracy of the lens surface on the magnification side provided with the reflective surface depends on the shape accuracy of the optical element 33. That is, in order to improve the shape accuracy of the lens surface on the magnification side, it is also necessary to improve the shape accuracy of the lens surface on the reduction side. In contrast, the reflective surface 40 of the projection optical system 3A of this example is provided on the outer side surface of the optical element 33, so it is sufficient to improve the shape accuracy of the outer side surface of the optical element 33. Therefore, compared with a structure in which the reflective surface is provided inside the optical element 33, the reflective surface 40 of this example is easier to improve the shape accuracy of the reflective surface.

[0095] Furthermore, in a structure where the reflective surface is provided within the optical element 33, the reflective surface is formed by forming a reflective coating on the magnification-side lens surface of the optical element 33 after the optical element 33 is molded. However, in this case, a support film layer is required between the reflective coating layer and the magnification-side lens surface. While the support film layer prevents the reflective coating from peeling off the magnification-side lens surface, the interposition of the support film layer can easily degrade the optical performance of the reflective surface, leading to variations in the optical performance of the reflective surface during manufacturing. In contrast, in the projection optical system 3A of this example, the support film layer is provided on the side of the reflective coating layer opposite the reflective surface. Therefore, the optical performance of the reflective surface 40 is less likely to degrade. Consequently, the optical performance of the reflective surface 40 is more likely to be stabilized during manufacturing.

[0096] In the projection optical system 3A of this example, lens L17 (the second lens), which is located closest to the magnification side in the first optical system 31, is formed separately from the first lens 34. Lens L17 is located between the reflective surface 40 and the first lens 34 in the direction of the optical axis N. That is, lens L17, which is located closest to the magnification side in the first optical system 31, is located within the second optical system 32 in the direction of the optical axis N. This reduces the distance between lens L17 and the reflective surface 40. This shortens the axial distance between the liquid crystal panel 18 and the reflective surface 40, allowing for a more compact projection optical system 3A. Furthermore, the intermediate image 30 is formed between lens L17 of the first optical system 31 and the reflective surface 40 of the second optical system 32. Therefore, reducing the distance between lens L17 and the reflective surface 40 facilitates correction of various aberrations at different image heights of the intermediate image 30.

[0097] In addition, the first optical system 31 has a lens L17 (a second lens) and a lens L16 (a third lens) arranged adjacent to the reduction side of the lens L17. The lens L16 and the lens L17 have aspherical shapes. The projection optical system 3A of this example focuses as follows: by moving the lens L16 and the lens L17 toward the magnification side in the direction of the optical axis N, the projection distance is changed from a short distance to a long distance. Therefore, the projection optical system 3A moves the lens L16 and the lens L17 that correct the various aberrations of each image height in the direction of the optical axis N, so that the generation of various aberrations during focusing can be suppressed. In addition, in the case of a structure in which a lens that does not have an aspherical shape is moved in the direction of the optical axis N to perform focusing, it is necessary to have an aspherical lens that corrects the various aberrations. However, in this example, since the lens L16 and the lens L17 that move during focusing have aspherical shapes, the entire projection optical system can be miniaturized.

[0098] Furthermore, the first optical system 31 includes a cemented lens L23 and a cemented lens L24 on the magnification side relative to the aperture 51. Therefore, chromatic aberration can be corrected well.

[0099] Figure 3 It is a diagram of lateral aberration at the reference distance of the projection optical system 3A. Figure 4 It is a diagram showing spherical aberration, astigmatism, and distortion at a reference distance of the projection optical system 3A. Figure 5 It is a diagram showing spherical aberration, astigmatism, and distortion of the projection optical system 3A at a close distance. Figure 6 : is a diagram showing spherical aberration, astigmatism and distortion at a long distance of the projection optical system 3A. Figures 3 to 6 As shown, the projection optical system 3A of this example suppresses various aberrations in the magnified image.

[0100] (Example 2)

[0101] Figure 7This is the ray diagram of the projection optical system 3B of Example 2. Figure 7 As shown, the projection optical system 3B of this example is composed of a first optical system 31 and a second optical system 32 in this order from the reduction side toward the magnification side. The second optical system 32 is arranged on the optical axis N of the first optical system 31.

[0102] The first optical system 31 is a refractive optical system. The first optical system 31 is composed of 16 lenses L1 to L16. The lenses L1 to L16 are arranged in order from the reduction side to the magnification side. An aperture 51 is arranged between the lens L7 and the lens L8.

[0103] Lens L6 has aspherical surfaces on both surfaces. Lens L9 has aspherical surfaces on both surfaces. Lens L15 (the third lens) has aspherical surfaces on both surfaces. Lens L16 (the second lens) has aspherical surfaces on both surfaces. Lens L2 and L3 form a cemented lens L21. Lens L4 and L5 form a cemented lens L22. Lens L10 and L11 form a cemented lens L23. Lens L13 and L14 form a cemented lens L24.

[0104] The second optical system 32 includes an optical element 33 and a first lens 34. The optical element 33 and the first lens 34 are arranged in order from the reduction side toward the magnification side. The optical element 33 includes a reflecting surface 40 facing the reduction side. The reflecting surface 40 has a concave shape that is concave in the second direction Z2. The reflecting surface 40 has an aspherical shape. Figure 7 As shown, the reflective surface 40 is located Y2 below the optical axis N. The reflective surface 40 is formed by providing a reflective coating (reflective layer) on the outer side surface in the first direction Z1 of the optical element 33. The reflective surface 40 reflects light on the surface of the optical element 33 in the Z1 direction.

[0105] The first lens 34 is located closer to the optical element 33 in the first direction Z1 and is positioned upward Y1 relative to the optical axis N. The first lens 34 has negative refractive power. The first lens 34 has a convex shape on its magnification-side surface and a concave shape on its reduction-side surface. Both surfaces of the first lens 34 have aspherical shapes.

[0106] Here, the liquid crystal panel 18 of the image forming unit 2 is arranged on the reduction-side conjugate surface of the projection optical system 3B. The screen S is arranged on the magnification-side conjugate surface of the projection optical system 3B.

[0107] The liquid crystal panel 18 forms a projected image on an image forming surface perpendicular to the optical axis N of the first optical system 31. The liquid crystal panel 18 is arranged at a position offset upward by Y1 relative to the optical axis N of the first optical system 31. Therefore, the projected image is formed at a position offset upward by Y1 relative to the optical axis N.

[0108] Light from the liquid crystal panel 18 passes through the first optical system 31 and the second optical system 32 in sequence. Between the first and second optical systems 31 and 32, the light passes below the optical axis N at position Y2. As a result, the light travels through the second optical system 32 toward the reflective surface 40. The light reaching the reflective surface 40 is then reflected in the first direction Z1 and upward at position Y1. The light reflected by the reflective surface 40 then crosses the optical axis N in a direction Y1 upward toward the first lens 34. The light passing through the first lens 34 is then expanded by the first lens 34 and reaches the screen S.

[0109] Here, the lens L16 of the first optical system 31 is arranged between the reflecting surface 40 and the first lens 34 in the direction of the optical axis N. The intermediate image 30 is formed between the lens L16 and the reflecting surface 40 .

[0110] In the projection optical system 3B, the portion closer to the reduction side than the first optical system 31 is telecentric.

[0111] Here, the projection optical system 3B can change the projection distance. When the projection distance is changed, the seven lenses L10 to L16 of the first optical system 31 are moved along the optical axis N to perform focusing. During focusing, the lenses L12, L13, and L14 are moved integrally.

[0112] When the numerical aperture of the liquid crystal panel 18 is set to NA, the first distance from the optical axis N to the maximum image height of the liquid crystal panel 18 is set to imy, the second distance from the optical axis N to the maximum image height of the magnified image projected onto the screen S is set to scy, the distance from the first lens 34 to the screen S, i.e. the projection distance, is set to PD, the projection magnification obtained by dividing the second distance by the first distance is set to M, the projection ratio obtained by dividing the projection distance by the second distance is set to TR, the axial surface interval from the liquid crystal panel 18 to the reflecting surface 40 is set to OAL, and the maximum radius of the first lens 34 is set to LL, the data of the projection optical system 3B are as follows.

[0113]

[0114] The lens data for projection optical system 3B is as follows. Surface numbers are assigned in order from the reduction side to the magnification side. The numbers are for the liquid crystal panel, dichroic prism, lens, optical element, first lens, and screen. Surface numbers not corresponding to the liquid crystal panel, dichroic prism, lens, optical element, first lens, and screen are virtual data. R is the radius of curvature. D is the distance on the axis. C is the aperture radius, and twice the aperture radius is the diameter of the lens surface. The units of R, D, and C are mm.

[0115]

[0116]

[0117] Here, the projection optical system 3B of this example can change the projection distance between a reference distance, a short distance shorter than the reference distance, and a long distance longer than the reference distance. When the projection distance is changed, the seven lenses L10 to L16 of the first optical system 31 are moved along the optical axis N to perform focusing. In addition, when focusing in a manner such that the projection distance is changed from a short distance to a long distance, lens L10 and lens L11 are moved toward the reduction side along the optical axis N. When focusing in the same manner, lens L12, lens L13, and lens L14 are moved toward the magnification side along the optical axis N. When focusing in the same manner, lens L15 is moved toward the magnification side along the optical axis N. When focusing in the same manner, lens L16 is moved toward the magnification side along the optical axis N.

[0118] The following shows variable spacing 1, variable spacing 2, variable spacing 3, variable spacing 4, variable spacing 5, and variable spacing 6 at various projection distances during focusing. Variable spacing 1 is the axial surface spacing between lens L9 and lens L10. Variable spacing 2 is the axial surface spacing between lens L11 and lens L12. Variable spacing 3 is the axial surface distance between lens L14 and lens L15. Variable spacing 4 is the axial surface distance between lens L15 and lens L16. Variable spacing 5 is the axial surface distance between lens L16 and reflective surface 40. Variable spacing 6 represents the projection distance.

[0119]

[0120] The aspheric coefficients are as follows.

[0121]

[0122] Here, when the axial interval from the liquid crystal panel 18 to the reflecting surface 40 is set to OAL, the first distance from the optical axis N to the maximum image height of the liquid crystal panel 18 is set to imy, the maximum radius of the first lens 34 is set to LL, the projection ratio obtained by dividing the projection distance by the second distance from the optical axis N to the maximum image height of the magnified image projected onto the screen S is set to TR, and the numerical aperture of the liquid crystal panel 18 is set to NA, the projection optical system 3B of this example satisfies all of the following conditional expressions (1) and (2).

[0123] TR≤0.3(1)

[0124] 35≤(OAL / imy)×(LL / imy)×TR×(1 / NA)≤60(2)

[0125] Furthermore, it is more preferable that all of the following conditional expressions (1) and (2') are satisfied.

[0126] TR≤0.3(1)

[0127] 35≤(OAL / imy)×(LL / imy)×TR×(1 / NA)≤53(2')

[0128] In this example,

[0129]

[0130] Therefore, TR = 0.197, which satisfies the conditional expression (1). (OAL / imy) × (LL / imy) × TR × (1 / NA) = 35, which satisfies the conditional expression (2).

[0131] (Effect)

[0132] In the projection optical system 3B of this example, the reflection surface 40 has a reflection coating (reflection layer) on the surface. Therefore, the projection optical system 3B of this example can obtain the same effects as those of the first embodiment.

[0133] In the projection optical system 3B of this example, the lens L16 (second lens) located closest to the magnification side in the first optical system 31 is formed separately from the first lens 34. Lens L16 is located between the reflection surface 40 and the first lens 34 in the direction of the optical axis N. That is, lens L16 located closest to the magnification side in the first optical system 31 is located within the second optical system 32 in the direction of the optical axis N. This shortens the distance between lens L16 and the reflection surface 40. Consequently, the projection optical system 3B of this example can achieve the same effects as those of Example 1.

[0134] In addition, the first optical system 31 has a lens L16 (a second lens) and a lens L15 (a third lens) arranged adjacent to the reduction side of the lens L16. The lens L15 and the lens L16 have an aspherical shape. The projection optical system 3B of this example focuses as follows: by moving the lens L15 and the lens L16 toward the magnification side in the direction of the optical axis N, the projection distance is changed from a short distance to a long distance. Therefore, the projection optical system 3B moves the lens L15 and the lens L16 that correct the various aberrations of each image height in the direction of the optical axis N, so that the generation of various aberrations during focusing can be suppressed. In addition, in the case of a structure in which a lens that does not have an aspherical shape is moved in the direction of the optical axis N to perform focusing, it is necessary to have an aspherical lens that corrects the various aberrations. However, in this example, since the lens L15 and the lens L16 that move during focusing have an aspherical shape, the entire projection optical system can be miniaturized.

[0135] Furthermore, the first optical system 31 includes a cemented lens L23 and a cemented lens L24 on the magnification side relative to the aperture 51. Therefore, chromatic aberration can be corrected well.

[0136] Here, the projection optical system 3B of this example satisfies conditional expressions (1) and (2), and therefore, the same effects as those of the projection optical system 3A of Example 1 can be obtained. Figure 8 It is a diagram of lateral aberration at the reference distance of the projection optical system 3B. Figure 9 It is a diagram showing spherical aberration, astigmatism, and distortion at a reference distance of the projection optical system 3B.

[0137] Figure 10 It is a diagram showing spherical aberration, astigmatism, and distortion of the projection optical system 3B at a close distance. Figure 11 : is a diagram showing spherical aberration, astigmatism and distortion at a long distance of the projection optical system 3B. Figures 8 to 11 As shown, the projection optical system 3B of this example suppresses various aberrations in the magnified image.

[0138] (Example 3)

[0139] Figure 12 is the ray diagram of the projection optical system 3C of Example 3. Figure 12 As shown, the projection optical system 3C of this example is composed of a first optical system 31 and a second optical system 32 in this order from the reduction side toward the magnification side. The second optical system 32 is arranged on the optical axis N of the first optical system 31.

[0140] The first optical system 31 is a refractive optical system. The first optical system 31 is composed of 13 lenses L1 to L13. The lenses L1 to L13 are arranged in order from the reduction side to the magnification side. An aperture 51 is arranged between the lens L6 and the lens L7.

[0141] Lens L5 has aspherical surfaces on both surfaces. Lens L8 has aspherical surfaces on both surfaces. Lens L12 (the third lens) has aspherical surfaces on both surfaces. Lens L13 (the second lens) has aspherical surfaces on both surfaces. Lenses L3 and L4 form a cemented lens L21. Lenses L10 and L11 form a cemented lens L22.

[0142] The second optical system 32 includes an optical element 33 and a first lens 34. The optical element 33 and the first lens 34 are arranged in order from the reduction side toward the magnification side. The optical element 33 includes a reflecting surface 40 facing the reduction side. The reflecting surface 40 has a concave shape that is concave in the second direction Z2. The reflecting surface 40 has an aspherical shape. Figure 12 As shown, the reflective surface 40 is located Y2 below the optical axis N. The reflective surface 40 is formed by providing a reflective coating (reflective layer) on the outer side surface in the first direction Z1 of the optical element 33. The reflective surface 40 reflects light on the surface of the optical element 33 in the Z1 direction.

[0143] The first lens 34 is located closer to the optical element 33 in the first direction Z1 and is positioned upward Y1 relative to the optical axis N. The first lens 34 has negative refractive power. The first lens 34 has a convex shape on its magnification-side surface and a concave shape on its reduction-side surface. Both surfaces of the first lens 34 have aspherical shapes.

[0144] Here, the liquid crystal panel 18 of the image forming unit 2 is arranged on the reduction-side conjugate surface of the projection optical system 3C. The screen S is arranged on the magnification-side conjugate surface of the projection optical system 3C.

[0145] The liquid crystal panel 18 forms a projected image on an image forming surface perpendicular to the optical axis N of the first optical system 31. The liquid crystal panel 18 is arranged at a position offset upward by Y1 relative to the optical axis N of the first optical system 31. Therefore, the projected image is formed at a position offset upward by Y1 relative to the optical axis N.

[0146] Light from the liquid crystal panel 18 passes through the first optical system 31 and the second optical system 32 in sequence. Between the first and second optical systems 31 and 32, the light passes below the optical axis N at position Y2. As a result, the light travels through the second optical system 32 toward the reflective surface 40. The light reaching the reflective surface 40 is then reflected in the first direction Z1 and upward at position Y1. The light reflected by the reflective surface 40 then crosses the optical axis N in a direction Y1 upward toward the first lens 34. The light passing through the first lens 34 is then expanded by the first lens 34 and reaches the screen S.

[0147] Here, the lens L13 of the first optical system 31 is arranged between the reflecting surface 40 and the first lens 34 in the direction of the optical axis N. The intermediate image 30 is formed between the lens L13 and the reflecting surface 40 .

[0148] In the projection optical system 3C, the portion closer to the reduction side than the first optical system 31 is telecentric.

[0149] Here, the projection optical system 3C can change the projection distance. When the projection distance is changed, the four lenses L9 to L12 of the first optical system 31 are moved along the optical axis N to perform focusing. During focusing, the lens L10 and the lens L11 are moved integrally.

[0150] When the numerical aperture of the liquid crystal panel 18 is set to NA, the first distance from the optical axis N to the maximum image height of the liquid crystal panel 18 is set to imy, the second distance from the optical axis N to the maximum image height of the magnified image projected onto the screen S is set to scy, the distance from the first lens 34 to the screen S, i.e. the projection distance, is set to PD, the projection magnification obtained by dividing the second distance by the first distance is set to M, the projection ratio obtained by dividing the projection distance by the second distance is set to TR, the axial surface interval from the liquid crystal panel 18 to the reflecting surface 40 is set to OAL, and the maximum radius of the first lens 34 is set to LL, the data of the projection optical system 3C are as follows.

[0151]

[0152]

[0153] The lens data for projection optical system 3C is as follows. Surface numbers are assigned in order from the reduction side to the magnification side. The numbers are for the liquid crystal panel, dichroic prism, lens, optical element, first lens, and screen. Surface numbers not corresponding to the liquid crystal panel, dichroic prism, lens, optical element, first lens, or screen are fictitious data. R is the radius of curvature. D is the axial spacing. C is the aperture radius, which is twice the diameter of the lens surface. The units of R, D, and C are mm.

[0154]

[0155]

[0156] Here, the projection optical system 3C of this example can change the projection distance between a reference distance, a short distance shorter than the reference distance, and a long distance longer than the reference distance. When the projection distance is changed, the four lenses L9 to L12 of the first optical system 31 are moved along the optical axis N to perform focusing. In addition, when focusing in a manner such that the projection distance is changed from a short distance to a long distance, the lens L9 moves toward the magnification side along the optical axis N. When focusing in the same manner, the lens L10 and the lens L11 move toward the magnification side along the optical axis N. When focusing in the same manner, the lens L12 moves toward the magnification side along the optical axis N. In addition, in the projection optical system 3C of this example, the lens L13 is fixed.

[0157] The following shows variable spacing 1, variable spacing 2, variable spacing 3, variable spacing 4, and variable spacing 5 at various projection distances during focusing. Variable spacing 1 is the axial spacing between lenses L8 and L9. Variable spacing 2 is the axial spacing between lenses L9 and L10. Variable spacing 3 is the axial spacing between lenses L11 and L12. Variable spacing 4 is the axial spacing between lenses L12 and L13. Variable spacing 5 represents the projection distance.

[0158]

[0159]

[0160] The aspheric coefficients are as follows.

[0161]

[0162] Here, when the axial interval from the liquid crystal panel 18 to the reflecting surface 40 is set to OAL, the first distance from the optical axis N to the maximum image height of the liquid crystal panel 18 is set to imy, the maximum radius of the first lens 34 is set to LL, the projection ratio obtained by dividing the projection distance by the second distance from the optical axis N to the maximum image height of the magnified image projected onto the screen S is set to TR, and the numerical aperture of the liquid crystal panel 18 is set to NA, the projection optical system 3C of this example satisfies all of the following conditional expressions (1) and (2).

[0163] TR≤0.3(1)

[0164] 35≤(OAL / imy)×(LL / imy)×TR×(1 / NA)≤60(2)

[0165] In this example,

[0166]

[0167] Therefore, TR = 0.259, which satisfies the conditional expression (1). (OAL / imy) × (LL / imy) × TR × (1 / NA) = 59, which satisfies the conditional expression (2).

[0168] (Effect)

[0169] In the projection optical system 3C of this example, the reflection surface 40 has a reflection coating (reflection layer) on the surface. Therefore, the projection optical system 3C of this example can obtain the same effects as those of the first embodiment.

[0170] In the projection optical system 3C of this example, the lens L13 (second lens) located closest to the magnification side of the first optical system 31 is formed separately from the first lens 34. Lens L13 is located between the reflective surface 40 and the first lens 34 in the direction of the optical axis N. That is, the lens L13 located closest to the magnification side of the first optical system 31 is located within the second optical system 32 in the direction of the optical axis N. This shortens the distance between lens L13 and the reflective surface 40. Consequently, the projection optical system 3C of this example can achieve the same effects as those of Example 1.

[0171] In the projection optical system 3C of this example, the first optical system 31 has a lens L13 (second lens) and a lens L12 (third lens) arranged adjacent to the reduction side of the lens L13. Lens L12 and lens L3 have aspherical shapes. The projection optical system 3C of this example focuses as follows: by moving the lens L12 toward the magnification side in the direction of the optical axis N, the projection distance is changed from a short distance to a long distance. Therefore, the projection optical system 3C moves the lens L12 that corrects the various aberrations of each image height in the direction of the optical axis N, so that the generation of various aberrations during focusing can be suppressed. In addition, in the case of a structure in which a lens that does not have an aspherical shape is moved in the direction of the optical axis N to perform focusing, it is necessary to have an aspherical lens that corrects the various aberrations. However, in this example, since the lens L12 that moves during focusing has an aspherical shape, the entire projection optical system can be miniaturized.

[0172] Furthermore, lens L13 is fixed in the direction of the optical axis N. Here, lens L13, serving as the second lens, is disposed between the reflecting surface 40 and the first lens 34. Therefore, when focusing is performed by moving lens L13 in the direction of the optical axis N, the mechanism for moving lens L13 becomes complex, increasing manufacturing costs. Therefore, compared to the projection optical system 3A of Example 1, in which lens L17, serving as the second lens, moves in the direction of the optical axis N, the projection optical system 3C of this example can reduce manufacturing costs.

[0173] Furthermore, the first optical system 31 includes a cemented lens L22 located on the magnification side relative to the aperture 51. Therefore, chromatic aberration can be corrected favorably.

[0174] Here, the projection optical system 3C of this example satisfies conditional expressions (1) and (2), and therefore, the same effects as those of the projection optical system 3A of Example 1 can be obtained. Figure 13 It is a diagram of lateral aberration at the reference distance of the projection optical system 3C. Figure 14 It is a diagram showing spherical aberration, astigmatism, and distortion at a reference distance of the projection optical system 3C. Figure 15 It is a diagram showing spherical aberration, astigmatism, and distortion of the projection optical system 3C at a close distance. Figure 16 This is a diagram showing spherical aberration, astigmatism, and distortion at a long distance of the projection optical system 3C. Figures 13 to 16 As shown, the projection optical system 3C of this example suppresses various aberrations in the magnified image.

[0175] (Example 4)

[0176] Figure 17 This is the ray diagram of the projection optical system 3D of Example 4. Figure 17As shown, the projection optical system 3D of this example is composed of a first optical system 31 and a second optical system 32 in this order from the reduction side toward the magnification side. The second optical system 32 is arranged on the optical axis N of the first optical system 31.

[0177] The first optical system 31 is a refractive optical system. The first optical system 31 is composed of 13 lenses L1 to L13. The lenses L1 to L13 are arranged in order from the reduction side to the magnification side. An aperture 51 is arranged between the lens L6 and the lens L7.

[0178] Lens L5 has aspherical surfaces on both surfaces. Lens L8 has aspherical surfaces on both surfaces. Lens L12 (the third lens) has aspherical surfaces on both surfaces. Lens L13 (the second lens) has aspherical surfaces on both surfaces. Lenses L3 and L4 form a cemented lens L21. Lenses L10 and L11 form a cemented lens L22.

[0179] The second optical system 32 includes an optical element 33 and a first lens 34. The optical element 33 and the first lens 34 are arranged in this order from the reduction side to the magnification side. The optical element 33 has a first surface 36 facing the reduction side and a second surface 37 facing the opposite side of the first surface 36. Furthermore, the optical element 33 has a reflective coating on the second surface 37. The first surface 36 has a concave shape. The second surface 37 has a convex shape. Here, the optical element 33 includes, in this order from the reduction side to the magnification side, a first transmissive surface 41, a reflective surface 42, and a second transmissive surface 43. The first transmissive surface 41 is provided on the first surface 36. The first transmissive surface 41 has a concave shape. The reflective surface 42 is a reflective coating and has a concave shape that is a transfer of the surface shape of the second surface 37. The reflective surface 42 reflects light within the interior of the optical element 33. The second transmissive surface 43 is provided on the first surface 36. The second transmissive surface 43 has a concave shape. The first transmission surface 41, the reflection surface 42 and the second transmission surface 43 have aspherical shapes. Figure 17 As shown, the first transmissive surface 41 , the reflective surface 42 , and the second transmissive surface 43 are located below the optical axis N by Y2 .

[0180] The first lens 34 is located closer to the optical element 33 in the first direction Z1 and is positioned upward Y1 relative to the optical axis N. The first lens 34 has negative refractive power. The first lens 34 has a convex shape on its magnification-side surface and a concave shape on its reduction-side surface. Both surfaces of the first lens 34 have aspherical shapes.

[0181] Here, the liquid crystal panel 18 of the image forming unit 2 is arranged on the reduction-side conjugate surface of the projection optical system 3D. The screen S is arranged on the magnification-side conjugate surface of the projection optical system 3D.

[0182] The liquid crystal panel 18 forms a projected image on an image forming surface perpendicular to the optical axis N of the first optical system 31. The liquid crystal panel 18 is arranged at a position offset upward by Y1 relative to the optical axis N of the first optical system 31. Therefore, the projected image is formed at a position offset upward by Y1 relative to the optical axis N.

[0183] The liquid crystal panel 18 forms a projected image on an image forming surface perpendicular to the optical axis N of the first optical system 31. The liquid crystal panel 18 is arranged at a position offset upward by Y1 relative to the optical axis N of the first optical system 31. Therefore, the projected image is formed at a position offset upward by Y1 relative to the optical axis N.

[0184] Light from the liquid crystal panel 18 passes sequentially through the first optical system 31 and the second optical system 32. Between the first and second optical systems 31 and 32, the light passes below Y2 of the optical axis N. Thereby, the light is incident on the first transmission surface 41 of the optical element 33 constituting the second optical system 32.

[0185] Light rays incident on the optical element 33 via the first transmissive surface 41 travel toward the reflective surface 42. Light rays reaching the reflective surface 42 are then reflected in the first direction Z1 and upward Y1. Light rays reflected by the reflective surface 42 travel toward the second transmissive surface 43. Light rays emitted from the second transmissive surface 43 travel upward Y1, crossing the optical axis N, and travel toward the first lens 34. Light rays transmitted through the first lens 34 are then expanded by the first lens 34 and reach the screen S.

[0186] Here, the lens L13 of the first optical system 31 is arranged between the reflecting surface 42 and the first lens 34 in the direction of the optical axis N. The intermediate image 30 is formed between the lens L13 and the reflecting surface 42 .

[0187] In the projection optical system 3D, the reduction side relative to the first optical system 31 is telecentric.

[0188] Here, the projection optical system 3D can change the projection distance. When the projection distance is changed, the four lenses L9 to L12 of the first optical system 31 are moved along the optical axis N to perform focusing.

[0189] When the numerical aperture of the liquid crystal panel 18 is set to NA, the first distance from the optical axis N to the maximum image height of the liquid crystal panel 18 is set to imy, the second distance from the optical axis N to the maximum image height of the magnified image projected onto the screen S is set to scy, the distance from the first lens 34 to the screen S, i.e. the projection distance, is set to PD, the projection magnification obtained by dividing the second distance by the first distance is set to M, the projection ratio obtained by dividing the projection distance by the second distance is set to TR, the axial surface interval from the liquid crystal panel 18 to the reflecting surface 42 is set to OAL, and the maximum radius of the first lens 34 is set to LL, the data of the projection optical system 3D are as follows.

[0190]

[0191] The lens data for the 3D projection optical system is as follows. Surface numbers are assigned in order from the reduction side to the magnification side. The numbers refer to the LCD panel, dichroic prism, lens, optical element, primary lens, and screen. Surface numbers not corresponding to the LCD panel, dichroic prism, lens, optical element, primary lens, or screen are fictitious data. R is the radius of curvature. D is the axial surface spacing. C is the aperture radius, which is twice the aperture radius and represents the lens surface diameter. The units of R, D, and C are mm.

[0192]

[0193]

[0194] Here, the projection optical system 3D of this example can change the projection distance between a reference distance, a short distance shorter than the reference distance, and a long distance longer than the reference distance. When the projection distance is changed, the four lenses L9 to L12 of the first optical system 31 are moved along the optical axis N to perform focusing. In addition, when focusing in a manner such that the projection distance is changed from a short distance to a long distance, the lens L9 moves toward the reduction side along the optical axis N. When focusing in the same manner, the lens L10 and the lens L11 move toward the magnification side along the optical axis N. When focusing in the same manner, the lens L12 moves toward the magnification side along the optical axis N. In addition, in the projection optical system 3D of this example, the lens L13 is fixed.

[0195] The following shows variable spacing 1, variable spacing 2, variable spacing 3, variable spacing 4, and variable spacing 5 at various projection distances during focusing. Variable spacing 1 is the axial spacing between lenses L8 and L9. Variable spacing 2 is the axial spacing between lenses L9 and L10. Variable spacing 3 is the axial spacing between lenses L11 and L12. Variable spacing 4 is the axial spacing between lenses L12 and L13. Variable spacing 5 represents the projection distance.

[0196]

[0197] The aspheric coefficients are as follows.

[0198]

[0199]

[0200] Here, when the axial interval from the liquid crystal panel 18 to the reflecting surface 42 is set to OAL, the first distance from the optical axis N to the maximum image height of the liquid crystal panel 18 is set to imy, the maximum radius of the first lens 34 is set to LL, the projection ratio obtained by dividing the projection distance by the second distance from the optical axis N to the maximum image height of the magnified image projected onto the screen S is set to TR, and the numerical aperture of the liquid crystal panel 18 is set to NA, the projection optical system 3D of this example satisfies all of the following conditional expressions (1) and (2).

[0201] TR≤0.3(1)

[0202] 35≤(OAL / imy)×(LL / imy)×TR×(1 / NA)≤60(2)

[0203] Furthermore, it is more preferable that all of the following conditional expressions (1) and (2') are satisfied.

[0204] TR≤0.3(1)

[0205] 35≤(OAL / imy)×(LL / imy)×TR×(1 / NA)≤53(2')

[0206] In this example,

[0207]

[0208]

[0209] Therefore, TR = 0.257, which satisfies the conditional expression (1). (OAL / imy) × (LL / imy) × TR × (1 / NA) = 53, which satisfies the conditional expression (2).

[0210] (Effect)

[0211] In the projection optical system 3D of this example, the lens L13 (second lens) located closest to the magnification side of the first optical system 31 is formed separately from the first lens 34. Lens L13 is located between the reflective surface 42 and the first lens 34 in the direction of the optical axis N. That is, the lens L13 located closest to the magnification side of the first optical system 31 is located within the second optical system 32 in the direction of the optical axis N. This shortens the distance between lens L13 and the reflective surface 42. Consequently, the projection optical system 3D of this example can achieve the same effects as those of Example 1.

[0212] In the projection optical system 3D of this example, the first optical system 31 has a lens L13 (second lens) and a lens L12 (third lens) arranged adjacent to the reduction side of the lens L13. Lens L12 and lens L3 have aspherical shapes. The projection optical system 3D of this example focuses as follows: by moving the lens L12 toward the magnification side in the direction of the optical axis N, the projection distance is changed from a short distance to a long distance. Therefore, the projection optical system 3D moves the lens L12 that corrects the various aberrations of each image height in the direction of the optical axis N, so that the generation of various aberrations during focusing can be suppressed. In addition, in the case of a structure in which a lens that does not have an aspherical shape is moved in the direction of the optical axis N to perform focusing, it is necessary to have an aspherical lens that corrects the various aberrations. However, in this example, since the lens L12 that moves during focusing has an aspherical shape, the entire projection optical system can be miniaturized.

[0213] Furthermore, lens L13 is fixed in the direction of the optical axis N. Here, lens L13, serving as the second lens, is disposed between the reflecting surface 42 and the first lens 34. Therefore, when focusing is performed by moving lens L13 in the direction of the optical axis N, the mechanism for moving lens L13 becomes complex, increasing manufacturing costs. Therefore, compared to the projection optical system 3A of Example 1, in which lens L17, serving as the second lens, moves in the direction of the optical axis N, the projection optical system 3D of this example can reduce manufacturing costs.

[0214] Furthermore, the first optical system 31 includes a cemented lens L22 located on the magnification side relative to the aperture 51. Therefore, chromatic aberration can be corrected favorably.

[0215] Here, the projection optical system 3D of this example satisfies conditional expressions (1) and (2), and therefore, the same effects as those of the projection optical system 3A of Example 1 can be obtained. Figure 18 This is a diagram of lateral aberration at the reference distance of the projection optical system 3D. Figure 19 This diagram shows spherical aberration, astigmatism, and distortion at a reference distance of the projection optical system 3D. Figure 20 This diagram shows spherical aberration, astigmatism, and distortion of a 3D projection optical system at close distances. Figure 21 This is a diagram showing the spherical aberration, astigmatism, and distortion of a 3D projection optical system at long distances. Figures 18 to 21 As shown, the projection optical system 3D of this example suppresses various aberrations in the magnified image.

Claims

1. A projection optical system for magnifying a projection image formed by an image forming element arranged on a reduction-side conjugate surface and projecting the magnified image onto the magnification-side conjugate surface, the projection optical system being characterized in that: The first optical system and the second optical system are provided in order from the reduction side to the magnification side. The first optical system has an aperture, The second optical system comprises, in order from the reduction side toward the magnification side: an optical element having a concave reflecting surface; and a first lens having a negative refractive power. An intermediate image conjugated with the reduction-side conjugate surface and the magnification-side conjugate surface is formed between the first optical system and the second optical system. The reduction side of the first optical system is telecentric. When the axial distance from the image forming element to the reflecting surface is set as OAL, the first distance from the optical axis to the maximum image height of the image forming element is set as imy, the maximum radius of the first lens is set as LL, the throw ratio obtained by dividing the projection distance by the second distance from the optical axis to the maximum image height of the magnified image is set as TR, and the numerical aperture of the image forming element is set as NA, all of the following conditional expressions (1) and (2) are satisfied: TR≤0.3(1) 35≤(OAL / imy)×(LL / imy)×TR×(1 / NA)≤60(2).

2. The projection optical system according to claim 1, characterized in that The reflective surface has a reflective layer on its surface.

3. The projection optical system according to claim 1 or 2, characterized in that: The second lens disposed closest to the magnification side in the first optical system is formed separately from the first lens. The second lens is arranged between the reflecting surface and the first lens in the optical axis direction.

4. The projection optical system according to claim 3, characterized in that The first optical system includes the second lens and a third lens disposed adjacent to the second lens on the reduction side. The second lens and the third lens have aspherical shapes, Focusing is performed by moving the third lens toward the magnification side in the optical axis direction so that the projection distance changes from a short distance to a long distance.

5. The projection optical system according to claim 4, characterized in that: The second lens is fixed in the optical axis direction.

6. The projection optical system according to claim 1 or 2, characterized in that: The first optical system includes a cemented lens on the magnification side of the aperture.

7. A projector, characterized in that: The projector features: The projection optical system according to any one of claims 1 to 6; and The image forming element forms a projection image on the reduction-side conjugate surface of the projection optical system.

Images