Projection optics and projectors

Abstract

To provide a projection optical system that can achieve a wider angle and miniaturization.SOLUTION: A projection optical system comprises, in order from an enlargement side toward a reduction side, a first lens group having a positive power, an aperture stop, and a second lens group having a positive power. The projection optical system is telecentric on a reduction side of a reduction-side lens located on the most-reduction side of the second lens group. When the maximum half angle of view of the entire lens system is defined as ω, the distance from an optical axis to the maximum image height of a projected image formed by an image forming element as YIM, and the distance from the optical axis to a principal ray of the maximum image height on a virtual plane orthogonal to the optical axis and passing through an apex of an enlargement-side lens surface of an enlargement-side lens located on the most enlargement side of the first lens group as YL1, the following conditional expressions (1) and (2) are satisfied. (1) ω>40°. (2) YL1 / YIM<6.0.SELECTED DRAWING: Figure 3

Description

Technical Field

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

Background Art

[0002] A projector that enlarges a projection image formed on an image display element and projects it onto a screen is described in Patent Document 1. The projection optical system of this document includes, in order from the enlargement side to the reduction side, a first lens group having a negative power and a second lens group having a positive power. The lens on the most enlargement side of the first lens group is an aspherical lens, and among the plurality of lenses constituting the projection optical system, it has the largest effective diameter. The second lens group includes an aperture stop.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] For a projection optical system mounted on a projector, compatibility between wide-angle and miniaturization is required. The projection optical system of Patent Document 1 has a semi-field angle larger than 40°, achieving wide-angle. However, for the maximum image height of the projection image formed by the image display element, the lens on the most enlargement side of the first lens group is large in the projection optical system of Patent Document 1. Therefore, there is room for improvement in radial miniaturization in the projection optical system of Patent Document 1.

Means for Solving the Problems

[0005] To solve the above problems, the projection optical system of the present invention is a projection optical system for projecting an enlarged image onto an enlarged conjugate surface by enlarging a projection image formed by an image forming element arranged on the reduction side conjugate surface, and comprises, in order from the enlargement side to the reduction side, a first lens group having positive power, an aperture diaphragm, and a second lens group having positive power, wherein the reduction side of the reduction lens located furthest to the reduction side of the second lens group is telecentric, the maximum half-angle of view of the entire lens system is ω, the distance from the optical axis to the maximum image height of the projection image formed by the image forming element is YIM, and the distance from the optical axis to the principal ray of the maximum image height on a virtual plane that passes through the vertex of the enlargement lens surface of the enlargement lens located furthest to the enlargement side of the first lens group and is perpendicular to the optical axis is YL1, and the following conditions (1) and (2) are satisfied. ω>40 (1) YL1 / YIM <6.0 (2) Furthermore, in order to solve the above problems, the projection optical system of the present invention is a projection optical system for projecting an enlarged image onto an enlargement-side conjugate surface by enlarging a projection image formed by an image forming element arranged on the reduction-side conjugate surface, and comprises, in order from the enlargement side to the reduction side, a first lens group having positive power, an aperture diaphragm, and a second lens group having positive power, wherein the reduction side of the reduction-side lens located furthest to the reduction side of the second lens group is telecentric, the maximum half-angle of view of the entire lens system is ω, the distance from the optical axis to the maximum image height of the projection image formed by the image forming element is YIM, and the distance from the optical axis to the principal ray of the maximum image height on a virtual plane that passes through the vertex of the enlargement-side lens surface of the enlargement-side lens located furthest to the enlargement-side of the first lens group and is perpendicular to the optical axis is YL1, and the following conditions (1) and (2) are satisfied. ω>40 (1) YL1 / YIM <6.0 (2)

[0006] Next, the projector of the present invention is characterized by having the above-described projection optical system and the image forming element that forms a projected image on the reduction-side conjugate surface of the projection optical system. [Brief explanation of the drawing]

[0007] [Figure 1] This figure shows a schematic configuration of a projector equipped with the projection optical system of the present invention. [Figure 2] This is a ray diagram of a projection optical system. [Figure 3] This is a ray diagram of the projection optical system of Example 1. [Figure 4] This figure shows the longitudinal aberration, astigmatism, and distortion of Example 1. [Figure 5] This is a ray diagram of the projection optical system of Example 2. [Figure 6] This figure shows the longitudinal aberration, astigmatism, and distortion of Example 2. [Figure 7] It is a ray diagram of the projection optical system of Example 3. [Figure 8] It is a diagram showing the longitudinal aberration, spherical aberration, and distortion of Example 3. [Figure 9] It is a ray diagram of the projection optical system of Example 4. [Figure 10] It is a diagram showing the longitudinal aberration, spherical aberration, and distortion of Example 4. [Figure 11] It is a ray diagram of the projection optical system of Example 5. [Figure 12] It is a diagram showing the longitudinal aberration, spherical aberration, and distortion of Example 5. [Figure 13] It is a ray diagram of the projection optical system of Example 6. [Figure 14] It is a diagram showing the longitudinal aberration, spherical aberration, and distortion of Example 6. [Figure 15] It is a ray diagram of the projection optical system of Example 7. [Figure 16] It is a diagram showing the longitudinal aberration, spherical aberration, and distortion of Example 7.

Embodiments for Carrying Out the Invention

[0008] Hereinafter, an optical system and a projector according to embodiments of the present invention will be described with reference to the drawings.

[0009] (Projector) FIG. 1 is a diagram showing a schematic configuration of a projector including the projection optical system 3 of the present invention. As shown in FIG. 1, the projector 1 includes an image forming unit 2 that generates a projection image to be projected onto the screen S, a projection optical system 3 that enlarges the projection image and projects an enlarged image onto the screen S, and a control unit 4 that controls the operation of the image forming unit 2.

[0010] (Image Forming Unit and Control Unit) 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 light source, or the like. The first integrator lens 11 and the second integrator lens 12 each have a plurality of lens elements arranged in an array. The first integrator lens 11 divides the light beam from the light source 10 into a plurality of beams. Each lens element of the first integrator lens 11 condenses the light beam from the light source 10 near each lens element of the second integrator lens 12.

[0011] The polarization conversion element 13 converts the light from the second integrator lens 12 into a predetermined linearly polarized light. The superimposing lens 14 superimposes the images of the respective lens elements of the first integrator lens 11 on the display regions of a liquid crystal panel 18R, a liquid crystal panel 18G, and a liquid crystal panel 18B, which will be described later, via the second integrator lens 12.

[0012] In addition, the image forming unit 2 includes a first dichroic mirror 15, a reflection mirror 16, a field lens 17R, and a liquid crystal panel 18R. The first dichroic mirror 15 reflects R light, which is a part of the light rays incident from the superimposing lens 14, and transmits G light and B light, which are parts of the light rays incident from the superimposing lens 14. The R light reflected by the first dichroic mirror 15 enters the liquid crystal panel 18R through the reflection mirror 16 and the field lens 17R. The liquid crystal panel 18R is an image forming element. The liquid crystal panel 18R forms a red projection image by modulating the R light according to an image signal.

[0013] Furthermore, the image forming unit 2 includes a second dichroic mirror 21, a field lens 17G, and a liquid crystal panel 18G. The second dichroic mirror 21 reflects G light, which is a portion of the light rays from the first dichroic mirror 15, and transmits B light, which is a portion of the light rays from the first dichroic mirror 15. The G light reflected by the second dichroic mirror 21 passes through the field lens 17G and enters the liquid crystal panel 18G. The liquid crystal panel 18G is an image forming element. The liquid crystal panel 18G modulates the G light according to the image signal to form a green projected image.

[0014] 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 transmitted 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 before entering the liquid crystal panel 18B. The liquid crystal panel 18B is an image forming element. The liquid crystal panel 18B modulates the B light according to the image signal to form a blue projected image.

[0015] Liquid crystal panels 18R, 18G, and 18B surround the cross dichroic prism 19 from three directions. The cross dichroic prism 19 is a photosynthetic prism that generates a projected image by combining the light modulated by each of the liquid crystal panels 18R, 18G, and 18B.

[0016] The projection optical system 3 projects the combined image from the cross dichroic prism 19 onto the screen S, enlarging it as it is.

[0017] The control unit 4 includes an image processing unit 6 that receives external image signals such as video signals, and a display drive unit 7 that drives the liquid crystal panel 18R, liquid crystal panel 18G, and liquid crystal panel 18B based on the image signals output from the image processing unit 6.

[0018] The image processing unit 6 converts an image signal input from an external device into an image signal that includes the gradation of each color. The display drive unit 7 operates the liquid crystal panels 18R, 18G, and 18B based on the projected image signals of each color output from the image processing unit 6. As a result, the image processing unit 6 displays the projected image corresponding to the image signal on the liquid crystal panels 18R, 18G, and 18B.

[0019] (Projection optical system) Next, the projection optical system 3 will be described. Figure 2 is a ray diagram of the projection optical system 3. In Figure 2, liquid crystal panels 18R, 18G, and 18B are represented as liquid crystal panel 18. As shown in Figure 2, the screen S is positioned on the magnifying conjugate plane of the projection optical system 3. The liquid crystal panel 18 is positioned on the reducing conjugate plane of the projection optical system 3.

[0020] For convenience, in the following explanation, the three mutually orthogonal axes will be referred to as the X-axis, Y-axis, and Z-axis. The direction along the optical axis N of the projection optical system 3 will be defined as the Z-axis direction. In the Z-axis direction, the side where the screen S is located will be the first direction Z1, and the side where the liquid crystal panel 18 is located will be 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 upward Y1 and the other side downward Y2. The X-axis extends in the width direction of the screen.

[0021] As shown in Figure 2, the liquid crystal panel 18 positioned on the reduction-side conjugate surface forms a projected image downward Y2 with respect to the optical axis N of the projection optical system 3. The enlarged image projected onto the screen S by the projection optical system 3 is formed upward Y1 with respect to the optical axis N.

[0022] Below, we will describe Examples 1 to 7 as configurations of the projection optical system 3 installed in the projector 1.

[0023] (Example 1) Figure 3 is a ray diagram of the projection optical system 3A of Embodiment 1. As shown in Figure 3, the projection optical system 3A comprises, in order from the magnification side to the reduction side, a first lens group 31 having positive power, an aperture diaphragm 41, and a second lens group 32 having positive power. The aperture diaphragm 41 is set to define the brightness of the projection optical system 3A.

[0024] The first lens group 31 comprises five lenses L1 to L5. Lenses L1 to L5 are arranged in this order from the magnification side to the reduction side.

[0025] Lens L1 (magnifying lens) has negative power. Lens L1 has a concave shape near the optical axis N on the magnifying surface and a convex shape at the periphery. Lens L1 has a convex shape near the optical axis N on the reducing surface and a concave shape at the periphery. Lens L1 has aspherical shapes on both sides. Lens L2 has negative power. Lens L2 is a meniscus lens. Lens L2 has a convex shape on the magnifying surface and a concave shape on the reducing surface.

[0026] Lens L3 (first lens) and lens L4 (second lens) are joined together to form a cemented lens L21. Lens L3 has negative power. Lens L3 has a concave shape on its magnifying and reducing surfaces. Lens L4 has positive power. Lens L4 has a convex shape on its magnifying and reducing surfaces. The cemented lens L21 has negative power. Lens L5 has positive power. Lens L5 has a convex shape on its magnifying and reducing surfaces.

[0027] The second lens group 32 comprises six lenses L6 to L11. Lenses L6 to L11 are arranged in this order from the magnification side to the reduction side.

[0028] Lenses L6 and L7 are joined together to form a cemented lens L22. Lens L6 has negative power. Lens L6 has a concave shape on its magnifying and reducing surfaces. Lens L7 has positive power. Lens L7 has a convex shape on its magnifying and reducing surfaces. The cemented lens L22 has negative power.

[0029] Lens L8 has positive power. Lens L8 has a convex shape on the magnifying and reducing surfaces. Lens L8 has an aspherical shape on both sides.

[0030] Lenses L9 and L10 are joined together to form a cemented lens L23. Lens L9 has negative power. Lens L9 has a concave shape on its magnifying and reducing surfaces. Lens L10 has positive power. Lens L10 has a convex shape on its magnifying and reducing surfaces. Lens L10 has an aspherical shape on its reducing surface. The cemented lens L23 has positive power.

[0031] Lens L11 (the reducing lens) has positive power. Lens L11 has a convex shape on both its magnifying and reducing surfaces.

[0032] Lens L1 is made of resin. Lenses L2 through L11 are made of glass.

[0033] In the projection optical system 3A, the reduction side from lens L11 is telecentric. Telecentricity from the reduction side means that the central ray of each light beam passing between lens L11 and the liquid crystal panel 18 located on the conjugate surface of the reduction side is parallel to or approximately parallel to the optical axis N.

[0034] Assuming that the F-number of the projection optical system 3A is FNo, the total optical length is TTL, the distance on the optical axis N from the magnifying surface of lens L1 to the reducing surface of lens L11 is L, the back focus is BF, the maximum half-angle of view of the entire lens system is ω, the focal length of the entire lens system is F, the focal length of the first lens group 31 is Fg1, the focal length of the second lens group 32 is Fg2, the focal length of lens L1 is Fls, the focal length of lens L11 is Flf, and the focal length of cemented lens L21 is Fc, the data for the projection optical system 3A of Example 1 is as follows.

[0035] Fno 2.000 TTL 99.504mm L 65,000mm BF 34.504mm ω 51.161° F 8.354mm Fg1 88.353mm Fg2 22.232mm Fls -38.968mm Flf 36.884mm Fc -99.855mm

[0036] As shown in Figure 3, when YIM is defined as the distance from the optical axis N to the maximum image height of the projected image formed by the liquid crystal panel 18, and YL1 is defined as the distance from the optical axis N to the principal ray α of the maximum image height on a virtual plane P that passes through the vertex of the magnifying lens surface of lens L1 and is perpendicular to the optical axis N, the data for the projection optical system 3A of Example 1 is as follows. Note that the vertex of the lens surface is the intersection point of the lens surface and the optical axis N.

[0037] YIM 10.350mm YL1 16.536mm

[0038] The lens data for projection optical system 3A is as follows. The surface numbers are assigned sequentially from the magnification side to the reduction side. The symbols are those of the screen, lens, aperture diaphragm, dichroic prism, and liquid crystal panel. Surfaces marked with an asterisk (*) are aspherical. R is the radius of curvature. D is the axial spacing. nd is the refractive index of the d line. νd is the Abbe number of the d line. The units for R and D are mm.

[0039] Code Surface number RD nd vd S 0 inf 10900.000 L01 1* -8.14 2.000 1.5311 55.8 2* -14.53 3.787 L02 3 27.80 1.206 1.9229 20.9 4 12.03 11.013 L03 5 -19.85 1.200 1.7725 49.6 L04 6 12.60 4.818 1.6889 31.1 7 -22.43 0.100 L05 8 25.56 5.807 1.7283 28.5 9 -77.33 0.574 41 10 inf 2.483 L06 11 -36.11 1.000 1.9537 32.3 L07 12 10.64 5.023 1.7847 25.7 13 -42.29 1.815 L08 14* 41.75 6.298 1.4971 81.6 15* -13.75 1.895 L09 16 -23.31 1.000 2.0006 25.5 L10 17 29.95 7.999 1.4971 81.6 18* -15.31 0.100 L11 19 69.43 6.88 1.4970 81.55 -24.17 2.00 19 20 inf 27.43 1.52 64.20 inf 5.03 18 21 inf 0.05

[0040] The aspherical coefficients are as follows:

[0041] Face number 1 2 Conic constant: -3.55898E+00 -3.59351E-02 The coefficients of the third degree are 2.03084E+01 and 9.32258E+00. The coefficients of the fourth order are 1.99441E+01 and 1.12957E+01. The coefficient of the fifth degree is -9.32560E+01 -1.57267E+00 The coefficient of the sixth degree is 1.00422E+02 -1.75079E+01 The coefficient of the 7th degree -2.57668E+01 2.01490E+00 The coefficient of the 8th order is -2.17920E+01, which is equal to 1.55978E+01. The coefficient of the 9th degree is 1.28981E+01 -4.65184E-01 The coefficient of the 10th order is -5.46354E-01 -5.36687E+00

[0042] Page numbers 14, 15, 18 Conic constant 6.77949E+00 -2.54428E-01 -1.63386E+00 The coefficients of the fourth order are -1.21234E-05, 6.23756E-05, and -4.75133E-05. Coefficient of the 6th order: -7.57407E-08 -2.01718E-07 8th order coefficients: -2.10980E-09 -2.37450E-09 The coefficients of the 10th order are 2.16919E-11 and 8.17896E-12. The coefficient of the 12th order is -4.85082E-14

[0043] Here, in this example, the projection optical system 3A satisfies the following conditions (1) and (2), where ω is the maximum half-angle of view of the entire lens system, YIM is the distance from the optical axis N to the maximum image height of the projected image formed by the liquid crystal panel 18, and YL1 is the distance from the optical axis N to the principal ray α of the maximum image height on a virtual plane P that passes through the vertex of the magnifying lens surface of lens L1 and is perpendicular to the optical axis N. ω>40° (1) YL1 / YIM <6.0 (2)

[0044] In this example, ω 51.161° YIM 10.350mm YL1 16.536mm Therefore, ω = 51.161°, satisfying condition (1). YL1 / YIM = 1.598, satisfying condition (2).

[0045] In this example, the projection optical system 3A satisfies all of the following conditions (3), (4), and (5), provided that the total focal length of the lens system is F, the air-equivalent length of the back focus is BF, the focal length of lens L1 is Fls, and the focal length of lens L11 is Flf. BF / F > 2.0 (3) -15.0 < Fls / F < -1.8 (4) 1.6 <Flf / F < 15.0 (5)

[0046] In this example, Bf 34.504mm F 8.354mm Fls -38.968mm Flf 36.884mm Therefore, BF / F = 4.131, satisfying condition (3). Fls / F = -4.665, satisfying condition (4). Flf / F = 4.415, satisfying condition (5).

[0047] In this example, the projection optical system 3A satisfies all of the following conditions (6), (7), and (8), provided that the focal length of the entire lens system is F, the difference between the Abbe number of lens L3 on the d line and the Abbe number of lens L4 on the d line is Δvd, the difference between the refractive index of lens L3 on the d line and the refractive index of lens L4 on the d line is Δnd, and the focal length of the cemented lens L21 is Fc. |Δvd|< 20.0 (6) |Δnd|< 0.35 (7) 2.0 < | Fc / F | < 15.0 (8)

[0048] In this example, F 8.354mm Fc -99.855mm |Δvd| 18.520 |Δnd| 0.084 Therefore, |Δvd|=18.520, satisfying condition (6). |Δnd|=0.084, satisfying condition (7). | Fc / F| = 11.954, which satisfies condition (8).

[0049] (Effects and Benefits) In this example, the projection optical system 3A satisfies condition (1), thus enabling wide-angle projection. Furthermore, in this example, the projection optical system 3A has positive power in the first lens group 31 and satisfies condition (2), so the lens on the most magnifying side of the first lens group can be made smaller relative to the maximum image height of the projected image formed by the liquid crystal panel 18.

[0050] In other words, when the first lens group 31 has positive power, it is easier to make the lens on the most magnifying side of the first lens group smaller relative to the maximum image height of the projected image formed by the liquid crystal panel 18, compared to when the first lens group 31 has negative power. Here, if the value of condition (2) exceeds the upper limit, the first lens group 31 has negative power. Therefore, when the value of condition (2) exceeds the upper limit, the lens on the most magnifying side of the first lens group becomes larger relative to the maximum image height of the projected image formed by the liquid crystal panel 18, and the radial dimension of the projection optical system 3A becomes larger.

[0051] Here, as a comparative example, we will consider Example 2 of the prior art document, Japanese Patent Application Publication No. 2009-104048. The projection optical system of the comparative example comprises a first lens group and a second lens group, arranged in order from the magnification side to the reduction side. The second lens group includes an aperture diaphragm. In the projection optical system of the comparative example, the lens group located on the magnification side of the aperture diaphragm has positive power. Also, the lens group located on the reduction side of the aperture diaphragm has positive power. The data for the comparative example is as follows.

[0052] ω 59.6° YIM 1.756mm YL1 12.394mm

[0053] In the comparative example, ω = 59.6°. Therefore, the projection optical system of the comparative example satisfies condition (1). However, in the comparative example, condition (2) becomes YL1 / YIM = 7.059. Therefore, in the projection optical system of the comparative example, the lens group positioned on the magnifying side of the aperture diaphragm has positive power, but does not satisfy condition (2). Thus, when the maximum half-angle of view is the same and the lens group positioned on the magnifying side of the aperture diaphragm has positive power, YL1 / YIM in the comparative example is larger than YL1 / YIM in the projection optical system 3A of the present example. In other words, compared to the projection optical system 3A of the present example, in the projection optical system of the comparative example, the lens on the magnifying side of the first lens group is larger with respect to the maximum image height of the projected image formed by the pixel display element.

[0054] In this example, lens L1 has negative power. Therefore, it is easy to increase the maximum half-angle of view of the projection optical system 3A. Also, in this example, lens L11 has positive power. Therefore, it is easy to make the reduction side from the second lens group 32 telecentric.

[0055] In this example, the first lens group 31 has multiple negative lenses arranged continuously from the magnification side to the reduction side. In this example, lenses L1 and L2 are negative lenses arranged continuously from the magnification side to the reduction side. Lens L1 is a plastic aspherical lens. With this configuration, it is possible to suppress the field curvature that occurs in the projection optical system 3A.

[0056] In this example, the projection optical system 3A satisfies all of the following conditions (3), (4), and (5), provided that the total focal length of the lens system is F, the air-equivalent length of the back focus is BF, the focal length of lens L1 is Fls, and the focal length of lens L11 is Flf. BF / F > 2.0 (3) -15.0 < Fls / F < -1.8 (4) 1.6 < Flf / F < 15.0 (5)

[0057] Since the projection optical system 3A satisfies condition (3), it becomes easy to secure back focus. That is, if the value of condition (3) exceeds the lower limit, the back focus becomes too short, making it difficult to secure space for the color synthesis prism and the correction plate of the liquid crystal panel, which are placed on the reduction side of the second lens group 32. In addition, it becomes difficult to make the area on the reduction side of the second lens group 32 telecentric.

[0058] Furthermore, the projection optical system 3A in this example satisfies condition (4), so it is possible to ensure sufficient back focus while also ensuring the imaging performance of the projection optical system 3A. That is, if the value of condition (4) exceeds the lower limit, the focal length Fls of lens L1 becomes too short. This ensures the imaging performance of the projection optical system 3A, but the power of lens L1 becomes stronger, making it difficult to ensure a sufficiently long back focus. If the value of condition (4) exceeds the upper limit, the focal length Fls of lens L1 becomes too long. This weakens the power of lens L1, allowing for a sufficiently long back focus, but the imaging performance of the projection optical system 3A deteriorates.

[0059] Furthermore, since the projection optical system 3A in this example satisfies condition (5), it is possible to ensure the imaging performance of the projection optical system 3A while making the reduction side from the second lens group 32 telecentric. That is, if the value of condition (5) exceeds the lower limit, the focal length Flf of lens L11 becomes too short. This ensures the imaging performance of the projection optical system 3A, but the power of lens L11 becomes strong, making it difficult to make the reduction side from the second lens group 32 telecentric. If the value of condition (5) exceeds the upper limit, the focal length Flf of lens L11 becomes too long. This weakens the power of lens L11, making it easy to make the reduction side from the second lens group 32 telecentric, but the imaging performance of the projection optical system 3A deteriorates.

[0060] The first lens group 31 includes a cemented lens L21 formed by joining lens L3 (first lens) and lens L4 (second lens). The projection optical system 3A satisfies all of the following conditions (6), (7), and (8), where F is the focal length of the entire lens system, Δvd is the difference between the Abbe number of lens L3 on the d line and the Abbe number of lens L4 on the d line, Δnd is the difference between the refractive index of lens L3 on the d line and the refractive index of lens L4 on the d line, and Fc is the focal length of the cemented lens L21. |Δvd|< 20.0 (6) |Δnd|< 0.35 (7) 2.0 < Fc / F < 15.0 (8)

[0061] The projection optical system 3A satisfies conditions (6) and (7), so it can effectively correct chromatic aberration. In other words, if the values ​​of conditions (6) and (7) exceed the upper limit, it becomes difficult to effectively correct chromatic aberration.

[0062] Furthermore, since the projection optical system 3A satisfies condition (8), it is possible to make the overall length of the projection optical system 3A compact while effectively correcting chromatic aberration. That is, if the value of condition (8) exceeds the lower limit, the focal length Fc of the cemented lens L21 becomes too short. As a result, the power of the cemented lens L21 becomes stronger, which allows for effective correction of chromatic aberration and makes the overall length of the projection optical system 3A compact, but various aberrations become more likely to occur. If the value of condition (8) exceeds the upper limit, the focal length Fc of the cemented lens L21 becomes too long. As a result, the power of the cemented lens L21 becomes weaker, which suppresses the occurrence of various aberrations, but it becomes impossible to effectively correct chromatic aberration, and the overall length of the projection optical system 3A becomes larger.

[0063] Figure 4 shows the spherical aberration, astigmatism, and distortion of the projection optical system 3A. As shown in Figure 4, the projection optical system 3A in this example suppresses various aberrations in the enlarged image.

[0064] (Example 2) Figure 5 is a ray diagram of the projection optical system 3B of Embodiment 2. As shown in Figure 5, the projection optical system 3B comprises, in order from the magnification side to the reduction side, a first lens group 31 having positive power, an aperture diaphragm 41, and a second lens group 32 having positive power. The aperture diaphragm 41 is set to define the brightness of the projection optical system 3B.

[0065] The first lens group 31 comprises seven lenses L1 to L7. Lenses L1 to L7 are arranged in this order from the magnification side to the reduction side.

[0066] Lens L1 (magnifying lens) has negative power. Lens L1 has a concave shape near the optical axis N on the magnifying surface and a convex shape at the periphery. Lens L1 has a convex shape near the optical axis N on the reducing surface and a concave shape at the periphery. Lens L1 has aspherical shapes on both sides.

[0067] Lens L2 has negative power. Lens L2 is a meniscus lens. Lens L2 has a convex shape on the magnifying side and a concave shape on the reducing side. Lens L3 has negative power. Lens L3 is a meniscus lens. Lens L3 has a convex shape on the magnifying side and a concave shape on the reducing side.

[0068] Lens L4 (first lens) and lens L5 (second lens) are joined together to form a cemented lens L21. Lens L4 has positive power. Lens L4 has a convex shape on its magnifying and reducing surfaces. Lens L5 has negative power. Lens L5 has a concave shape on its magnifying and reducing surfaces. The cemented lens L21 has negative power.

[0069] Lens L6 has positive power. Lens L6 has convex shapes on its magnifying and reducing surfaces. Lens L7 has positive power. Lens L7 is a meniscus lens. Lens L7 has a convex shape on its magnifying surface and a concave shape on its reducing surface.

[0070] The second lens group 32 comprises eight lenses L8 to L15. Lenses L8 to L15 are arranged in this order from the magnification side to the reduction side.

[0071] Lenses L8 and L9 are joined together to form a cemented lens L22. Lens L8 has positive power. Lens L8 has convex shapes on its magnifying and reducing surfaces. Lens L9 has negative power. Lens L9 has concave shapes on its magnifying and reducing surfaces. The cemented lens L22 has negative power.

[0072] Lens L10 has negative power. Lens L10 has a concave shape on its magnifying and reducing surfaces. Lens L11 has positive power. Lens L11 has a convex shape on its magnifying and reducing surfaces. Lens L11 has an aspherical shape on both sides.

[0073] Lenses L12, L13, and L14 are joined together to form a cemented lens L23. Lens L12 has negative power. Lens L12 has concave shapes on its magnifying and reducing surfaces. Lens L13 has positive power. Lens L13 has convex shapes on its magnifying and reducing surfaces. Lens L14 has negative power. Lens L14 is a meniscus lens. Lens L14 has a concave shape on its magnifying surface and a convex shape on its reducing surface. The cemented lens L23 has negative power.

[0074] Lens L15 (the reducing lens) has positive power. Lens L15 has a convex shape on both the magnifying and reducing surfaces.

[0075] Lens L1 is made of resin. Lenses L2 through L15 are made of glass.

[0076] In projection optical system 3B, the reduction side from lens L15 is telecentric.

[0077] Assuming that the F-number of the projection optical system 3B is FNo, the total optical length is TTL, the distance on the optical axis N from the magnifying surface of lens L1 to the reducing surface of lens L15 is L, the back focus is BF, the maximum half-angle of view of the entire lens system is ω, the focal length of the entire lens system is F, the focal length of the first lens group 31 is Fg1, the focal length of the second lens group 32 is Fg2, the focal length of lens L1 is Fls, the focal length of lens L15 is Flf, and the focal length of cemented lens L21 is Fc, the data for the projection optical system 3B of Example 2 is as follows.

[0078] Fno 1.600 TTL 196.072mm L 155.632mm Bf 40.440mm ω 59.527° F 6.346mm Fg1 19.516mm Fg2 40.014mm Fls -82.470mm Flf 40.479mm Fc -70.861mm

[0079] As shown in Figure 5, when YIM is defined as the distance from the optical axis N to the maximum image height of the projected image formed by the liquid crystal panel 18, and YL1 is defined as the distance from the optical axis N to the principal ray α of the maximum image height on a virtual plane P that passes through the vertex of the magnifying lens surface of lens L1 and is perpendicular to the optical axis N, the data for the projection optical system 3B of Example 2 is as follows.

[0080] YIM 10,800mm YL1 48.804mm

[0081] The lens data for projection optical system 3B is as follows. The surface numbers are assigned sequentially from the magnification side to the reduction side. The symbols are those of the screen, lens, aperture diaphragm, dichroic prism, and liquid crystal panel. Surfaces marked with an asterisk (*) are aspherical. R is the radius of curvature. D is the axial spacing. nd is the refractive index of the d line. νd is the Abbe number of the d line. The units for R and D are mm.

[0082] Symbol face number RD nd vd S 0 inf 937.000 L01 1* -21.05 5.000 1.5350 55.7 2* -43.44 11.444 L02 3 59.15 1.500 1.6385 55.4 4 31.36 9.264 L03 5 134.83 1.500 1.6584 50.9 6 22.52 6.868 L04 7 71.57 8.262 1.5814 40.7 L05 8 -39.51 1.500 1.9037 31.3 9 60.49 39.168 L06 10 116.63 4.721 1.7283 28.5 11 -143.94 14.752 L07 12 36.13 2.703 1.8467 23.8 13 72.81 12.287 41 14 inf 0.100 L08 15 57.80 5.329 1.7283 28.5 L09 16 -21.22 1.000 1.8515 40.8 17 106.42 0.911 L10 18 -366.07 1.000 1.8515 40.8 19 26.00 0.20 L11 20* 22.18 7.83 1.5866 59.0 21* -31.15 0.15 L12 22 -315.90 1.00 1.8467 23.8 L13 23 19.79 10.50 1.4970 81.5 L14 24 -15.29 1.00 1.7620 40.1 25 -30.98 0.15 L15 26 84.76 7.50 1.4970 81.5 27 -25.69 0.10 19 28 inf 30.69 1.5168 64.2 18 29 inf 9.62

[0083] The aspherical coefficients are as follows:

[0084] Face number 1 2 Conic constant -4.65698E+00 0.00000E+00 The coefficients of the third order are 6.40812E-04 and 5.97213E-04. The coefficient of the fourth order is -6.67159E-06, which is 3.19711E-05. The coefficients of the fifth order are -1.19688E-07 and -1.04449E-06. The coefficient of the sixth degree is 3.18694E-10 -1.02162E-09 The coefficients of the 7th order are 2.14148E-11 and 1.04227E-10. The coefficients of the 8th order are 1.32953E-12 and 2.50920E-12. The coefficient of the 9th order is -2.74043E-15, which is 5.10421E-14. The coefficient of the 10th order is -1.99411E-16, which is 5.14582E-16. 11th order coefficients: -9.09455E-18 -1.34495E-17 12th degree coefficients: -1.15855E-19 -5.34850E-19 The coefficient of the 13th order is 2.95122E-21 -1.35806E-20 The coefficient of the 14th order is 7.72821E-23 -2.14658E-22 The coefficient of the 15th order is 3.24485E-25 -8.84318E-25 16th degree coefficient -8.46992E-27 8.78914E-26 17th degree coefficient -2.38266E-28 4.39353E-27 18th order coefficient -4.92232E-30 1.02850E-28 19th coefficient -1.60652E-32 6.22593E-31 The coefficient of the 20th order is 1.90227E-33 -6.48263E-32

[0085] Page numbers 20 21 Conic constant: -8.64572E-01 -1.36585E+00 The coefficient of the fourth order is -1.00607E-05 -4.36799E-06 The coefficient of the sixth degree is 1.43627E-08 -2.18442E-08 The coefficient of the 8th order is -4.94939E-11 -5.00791E-11 The coefficient of the 10th order is 2.97500E-14 -5.34787E-14

[0086] Here, in this example, the projection optical system 3B satisfies the following conditions (1) and (2), where ω is the maximum half-angle of view of the entire lens system, YIM is the distance from the optical axis N to the maximum image height of the projected image formed by the liquid crystal panel 18, and YL1 is the distance from the optical axis N to the principal ray α of the maximum image height on a virtual plane P that passes through the vertex of the magnifying lens surface of lens L1 and is perpendicular to the optical axis N. ω>40° (1) YL1 / YIM <6.0 (2)

[0087] In this example, ω 59.527° YIM 10,800mm YL1 48.804mm Therefore, ω = 59.527°, satisfying condition (1). YL1 / YIM = 4.519, satisfying condition (2).

[0088] In this example, the projection optical system 3B satisfies all of the following conditions (3), (4), and (5), provided that the total focal length of the lens system is F, the air-equivalent length of the back focus is BF, the focal length of lens L1 is Fls, and the focal length of lens L15 is Flf. BF / F > 2.0 (3) -15.0 < Fls / F < -1.8 (4) 1.6 <Flf / F < 15.0 (5)

[0089] In this example, Bf 40.440mm F 6.346mm Fls -82.470mm Flf 40.479mm Therefore, BF / F = 6.373, satisfying condition (3). Fls / F = -12.996, satisfying condition (4). Flf / F = 6.379, satisfying condition (5).

[0090] In this example, the projection optical system 3B satisfies all of the following conditions (6), (7), and (8), provided that the focal length of the entire lens system is F, the difference between the Abbe number of lens L4 on the d line and the Abbe number of lens L5 on the d line is Δvd, the difference between the refractive index of lens L4 on the d line and the refractive index of lens L5 on the d line is Δnd, and the focal length of the cemented lens L21 is Fc. |Δvd|< 20.0 (6) |Δnd|< 0.35 (7) 2.0 < | Fc / F | < 15.0 (8)

[0091] In this example, F 6.346mm Fc -70.861mm |Δvd| 9.064 |Δnd| 0.322 Therefore, |Δvd|=9.064, satisfying condition (6). |Δnd|=0.322, satisfying condition (7). | Fc / F | = 11.166, which satisfies condition (8).

[0092] (Effects and Benefits) In this example, the projection optical system 3B satisfies condition (1), thus enabling wide-angle projection. Furthermore, in this example, the projection optical system 3B has positive power in the first lens group 31 and satisfies condition (2), so the lens on the most magnifying side of the first lens group can be made smaller relative to the maximum image height of the projected image formed by the liquid crystal panel 18.

[0093] In the projection optical system 3B of this example, lens L1 has negative power. Therefore, it is easy to increase the maximum half-angle of view of the projection optical system 3B. In this example, lens L15 has positive power. Therefore, it is easy to make the reduction side from the second lens group 32 telecentric.

[0094] In this example, the first lens group 31 has multiple negative lenses arranged continuously from the magnification side to the reduction side. In this example, lenses L1, L2, and L3 are negative lenses with negative power. Lens L1 is also a plastic aspherical lens. With this configuration, it is possible to suppress the field curvature that occurs in the projection optical system 3B.

[0095] Here, the projection optical system 3B in this example satisfies conditions (3) to (8), and therefore the same effects as the projection optical system 3A in Example 1 can be obtained. Figure 6 shows the spherical aberration, astigmatism, and distortion of the projection optical system 3B. As shown in Figure 6, the projection optical system 3B in this example suppresses various aberrations in the magnified image.

[0096] (Example 3) Figure 7 is a ray diagram of the projection optical system 3C of Embodiment 3. As shown in Figure 7, the projection optical system 3C comprises, in order from the magnification side to the reduction side, a first lens group 31 having positive power, an aperture diaphragm 41, and a second lens group 32 having positive power. The aperture diaphragm 41 is set to define the brightness of the projection optical system 3C.

[0097] The first lens group 31 comprises four lenses L1 to L4. Lenses L1 to L4 are arranged in this order from the magnification side to the reduction side.

[0098] Lens L1 (magnifying lens) has negative power. Lens L1 has a concave shape near the optical axis N on the magnifying surface and a convex shape at the periphery. Lens L1 has a convex shape near the optical axis N on the reducing surface and a concave shape at the periphery. Lens L1 has aspherical shapes on both sides.

[0099] Lens L2 has negative power. Lens L2 is a meniscus lens. Lens L2 has a convex shape on the magnifying side and a concave shape on the reducing side.

[0100] Lenses L3 (first lens) and L4 (second lens) are joined together to form a cemented lens L21. Lens L3 has positive power. Lens L3 has convex shapes on its magnifying and reducing surfaces. Lens L4 has negative power. Lens L4 is a meniscus lens. Lens L4 has a concave shape on its magnifying surface and a convex shape on its reducing surface. The cemented lens L21 has negative power.

[0101] The second lens group 32 comprises five lenses L5 to L9. Lenses L5 to L9 are arranged in this order from the magnification side to the reduction side.

[0102] Lenses L5, L6, and L7 are joined together to form a cemented lens L22. Lens L5 has negative power. Lens L5 has concave shapes on its magnifying and reducing surfaces. Lens L6 has positive power. Lens L6 has convex shapes on its magnifying and reducing surfaces. Lens L7 has negative power. Lens L7 is a meniscus lens. Lens L7 has a concave shape on its magnifying surface and a convex shape on its reducing surface. The cemented lens L22 has negative power.

[0103] Lens L8 has positive power. Lens L8 is a meniscus lens. Lens L8 has a concave shape on the magnifying side and a convex shape on the reducing side. Lens L9 (reducing lens) has positive power. Lens L9 has convex shapes on both the magnifying and reducing sides. Lens L9 has aspherical shapes on both sides.

[0104] Lens L1 is made of resin. Lenses L2 through L9 are made of glass.

[0105] In the projection optical system 3C, the reduction side from lens L9 is telecentric.

[0106] Assuming that the F-number of the projection optical system 3C is FNo, the total optical length is TTL, the distance on the optical axis N from the magnifying surface of lens L1 to the reducing surface of lens L9 is L, the back focus is BF, the maximum half-angle of view of the entire lens system is ω, the focal length of the entire lens system is F, the focal length of the first lens group 31 is Fg1, the focal length of the second lens group 32 is Fg2, the focal length of lens L1 is Fls, the focal length of lens L9 is Flf, and the focal length of cemented lens L21 is Fc, the data for the projection optical system 3C of Example 3 is as follows.

[0107] Fno 2.022 TTL 94.125mm L 65,000mm Bf 29.125mm ω 41.836° F 11.713mm Fg1 28.353mm Fg2 29.175mm Fls -22.805mm Flf 26.457mm Fc 26.205mm

[0108] As shown in Figure 7, when YIM is defined as the distance from the optical axis N to the maximum image height of the projected image formed by the liquid crystal panel 18, and YL1 is defined as the distance from the optical axis N to the principal ray α of the maximum image height on a virtual plane P that passes through the vertex of the magnifying lens surface of lens L1 and is perpendicular to the optical axis N, the data for the projection optical system 3C of Example 3 is as follows.

[0109] YIM 10.350mm YL1 13.024mm

[0110] The lens data for projection optical system 3C is as follows. The surface numbers are assigned sequentially from the magnification side to the reduction side. The symbols are those of the screen, lens, aperture diaphragm, dichroic prism, and liquid crystal panel. Surfaces marked with an asterisk (*) are aspherical. R is the radius of curvature. D is the axial spacing. nd is the refractive index of the d line. νd is the Abbe number of the d line. The units for R and D are mm.

[0111] Code Surface number RD nd vd S 0 inf 1129.752 L01 1* -23.48 3.474 1.5365 56.0 2* 27.08 5.041 L02 3 60.03 1.500 1.4970 81.5 4 26.39 18.526 L03 5 38.17 3.631 1.8502 30.0 L04 6 -20.87 1.200 1.7783 23.9 7 -59.09 0.628 41 8 inf 10.467 L05 9 -185.71 1.185 1.5955 39.2 L06 10 14.01 8.000 1.4970 81.5 L07 11 -11.98 1.200 1.7552 27.5 12 -49.12 0.861 L08 13 -29.14 2.577 1.4875 70.2 14 -22.91 0.200 L09 15* 34.03 6.510 1.5365 56.0 16* -22.87 0.200 19 17 inf 23.925 1.5168 64.2 18 inf 4.951 18 19 inf 0.05

[0112] The aspherical coefficients are as follows:

[0113] Face number 1 2 Conic constant 9.79982E-01 -1.00000E+02 The coefficient of the third degree is -5.26163E-04 -3.33856E-04 The coefficients of the fourth order are 9.73141E-04 and 1.74274E-03. The coefficient of the fifth order is -1.06181E-04 -2.57210E-04 Coefficients of the 6th order: 3.09797E-06, 1.64780E-05 Coefficients of the 7th order: 1.56807E-07 2.82510E-07 The coefficients of the 8th order are -3.81796E-09 and -7.66840E-08. The coefficient of the 9th order is -4.94478E-10 -2.18789E-09 The coefficient of the 10th order is -6.57052E-12, which is 2.69128E-10. The coefficients of the 11th order are 5.48905E-13 and 2.52517E-11. The coefficients of the 12th order are 6.83865E-14 and 1.78375E-12. The coefficient of the 13th order is 4.15052E-15 -1.65247E-13 14th order coefficients: -1.51501E-16 -2.80152E-14 15th order coefficients: -1.32438E-17 -1.93588E-16 Coefficient of the 16th order: -5.23600E-19 5.40380E-17 The coefficient of the 17th order is 9.21135E-21, which is 2.46012E-17. 18th order coefficients: -1.67077E-21 -5.92818E-19 The coefficient of the 19th order is 4.59226E-22 -1.47137E-19 20th order coefficient -1.47004E-23 6.79063E-21

[0114] Page numbers 15 16 Conic constant 0.00000E+00 0.00000E+00 The coefficient of the fourth order is -1.86424E-05, which is 2.10628E-05. Coefficient of the 6th order: 6.41789E-08 2.06661E-08 The coefficient of the 8th order is -2.23860E-10 -7.02491E-11 The coefficient of the 10th order is 8.33454E-14 -2.23189E-13

[0115] Here, in this example, the projection optical system 3C satisfies the following conditions (1) and (2), where ω is the maximum half-angle of view of the entire lens system, YIM is the distance from the optical axis N to the maximum image height of the projected image formed by the liquid crystal panel 18, and YL1 is the distance from the optical axis N to the principal ray α of the maximum image height on a virtual plane P that passes through the vertex of the magnifying lens surface of lens L1 and is perpendicular to the optical axis N. ω>40° (1) YL1 / YIM <6.0 (2)

[0116] In this example, ω 41.836° YIM 10.350mm YL1 13.024mm Therefore, ω = 41.836°, satisfying condition (1). YL1 / YIM = 1.258, satisfying condition (2).

[0117] In this example, the projection optical system 3C satisfies all of the following conditions (3), (4), and (5), where F is the total focal length of the lens system, BF is the air-equivalent length of the back focus, Fls is the focal length of lens L1, and Flf is the focal length of lens L9. BF / F > 2.0 (3) -15.0 < Fls / F < -1.8 (4) 1.6 <Flf / F < 15.0 (5)

[0118] In this example, Bf 29.125mm F 11.713mm Fls -22.805mm Flf 26.457mm Therefore, BF / F = 2.487, satisfying condition (3). Fls / F = -1.947, satisfying condition (4). Flf / F = 2.259, satisfying condition (5).

[0119] In this example, the projection optical system 3C satisfies all of the following conditions (6), (7), and (8), provided that the focal length of the entire lens system is F, the difference between the Abbe number of lens L3 on the d line and the Abbe number of lens L4 on the d line is Δvd, the difference between the refractive index of lens L3 on the d line and the refractive index of lens L4 on the d line is Δnd, and the focal length of the cemented lens L21 is Fc. |Δvd|< 20.0 (6) |Δnd|< 0.35 (7) 2.0 < | Fc / F | < 15.0 (8)

[0120] In this example, F 11.713mm Fc 26.205mm |Δvd| 6.135 |Δnd| 0.072 Therefore, |Δvd|=6.135, satisfying condition (6). |Δnd|=0.072, satisfying condition (7). | Fc / F| = 2.237, which satisfies condition (8).

[0121] (Effects and Benefits) In this example, the projection optical system 3C satisfies condition (1), thus enabling wide-angle projection. Furthermore, in this example, the projection optical system 3C has positive power in the first lens group 31 and satisfies condition (2), so the lens on the most magnifying side of the first lens group can be made smaller relative to the maximum image height of the projected image formed by the liquid crystal panel 18.

[0122] In the projection optical system 3C of this example, lens L1 has negative power. Therefore, it is easy to increase the maximum half-angle of view of the projection optical system 3C. In this example, lens L9 has positive power. Therefore, it is easy to make the reduction side from the second lens group 32 telecentric.

[0123] In this example, the first lens group 31 has multiple negative lenses arranged continuously from the magnification side to the reduction side. In this example, lenses L1 and L2 are negative lenses with negative power. Lens L1 is also a plastic aspherical lens. With this configuration, it is possible to suppress the field curvature that occurs in the projection optical system 3C.

[0124] Here, the projection optical system 3C in this example satisfies conditions (3) to (8), and therefore the same effects as the projection optical system 3A in Example 1 can be obtained. Figure 8 shows the spherical aberration, astigmatism, and distortion of the projection optical system 3C. As shown in Figure 8, the projection optical system 3C in this example suppresses various aberrations in the magnified image.

[0125] (Example 4) Figure 9 is a ray diagram of the projection optical system 3D of Embodiment 4. As shown in Figure 9, the projection optical system 3D comprises, in order from the magnification side to the reduction side, a first lens group 31 with positive power, an aperture diaphragm 41, and a second lens group 32 with positive power. The aperture diaphragm 41 is set to define the brightness of the projection optical system 3D.

[0126] The first lens group 31 comprises six lenses L1 to L6. Lenses L1 to L6 are arranged in this order from the magnification side to the reduction side.

[0127] Lens L1 (magnifying lens) has negative power. Lens L1 has a concave shape near the optical axis N on the magnifying surface and a convex shape at the periphery. Lens L1 has a convex shape near the optical axis N on the reducing surface and a concave shape at the periphery. Lens L1 has aspherical shapes on both sides.

[0128] Lens L2 has negative power. Lens L2 is a meniscus lens. Lens L2 has a convex shape on the magnifying side and a concave shape on the reducing side. Lens L3 has negative power. Lens L3 has concave shapes on both the magnifying and reducing sides.

[0129] Lens L4 (first lens) and lens L5 (second lens) are joined together to form a cemented lens L21. Lens L4 has positive power. Lens L4 has convex shapes on its magnifying and reducing surfaces. Lens L5 has negative power. Lens L5 is a meniscus lens. Lens L5 has a concave shape on its magnifying surface and a convex shape on its reducing surface. The cemented lens L21 has positive power.

[0130] Lens L6 has positive power. Lens L6 is a meniscus lens. Lens L6 has a convex shape on the magnifying side and a concave shape on the reducing side.

[0131] The second lens group 32 comprises eight lenses L7 to L14. Lenses L7 to L14 are arranged in this order from the magnification side to the reduction side.

[0132] Lenses L7 and L8 are joined together to form a cemented lens L22. Lens L7 has positive power. Lens L7 is a meniscus lens. Lens L7 has a concave shape on the magnifying side and a convex shape on the reducing side. Lens L8 has negative power. Lens L8 has concave shapes on both the magnifying and reducing sides. The cemented lens L22 has negative power.

[0133] Lens L9 has negative power. Lens L9 is a meniscus lens. Lens L9 has a convex shape on the magnifying side and a concave shape on the reducing side. Lens L9 has aspherical shapes on both sides. Lens L10 has positive power. Lens L10 has convex shapes on both the magnifying and reducing sides.

[0134] Lenses L11, L12, and L13 are joined together to form a cemented lens L23. Lens L11 has negative power. Lens L11 has concave shapes on its magnifying and reducing surfaces. Lens L12 has positive power. Lens L12 has convex shapes on its magnifying and reducing surfaces. Lens L13 has negative power. Lens L13 is a meniscus lens. Lens L13 has a concave shape on its magnifying surface and a convex shape on its reducing surface. The cemented lens L23 has negative power.

[0135] Lens L14 (the reducing lens) has positive power. Lens L14 has a convex shape on both its magnifying and reducing surfaces.

[0136] Lens L1 is made of resin. Lenses L2 through L14 are made of glass.

[0137] In the 3D projection optical system, the reduction side from lens L14 is telecentric.

[0138] Assuming that the F-number of the projection optical system 3D is FNo, the total optical length is TTL, the distance on the optical axis N from the magnifying surface of lens L1 to the reducing surface of lens L14 is L, the back focus is BF, the maximum half-angle of view of the entire lens system is ω, the focal length of the entire lens system is F, the focal length of the first lens group 31 is Fg1, the focal length of the second lens group 32 is Fg2, the focal length of lens L1 is Fls, the focal length of lens L14 is Flf, and the focal length of cemented lens L21 is Fc, the data for the projection optical system 3D of Example 4 is as follows.

[0139] Fno 1.600 TTL 198.183mm L 157.743mm Bf 40.440mm ω 59.589° F 6.346mm Fg1 15.031mm Fg2 36.370mm Fls -69.014mm Flf 39.839mm Fc 60.902mm

[0140] As shown in Figure 9, when YIM is defined as the distance from the optical axis N to the maximum image height of the projected image formed by the liquid crystal panel 18, and YL1 is defined as the distance from the optical axis N to the principal ray α of the maximum image height on a virtual plane P that passes through the vertex of the magnifying lens surface of lens L1 and is perpendicular to the optical axis N, the data for the projection optical system 3D of Example 4 is as follows.

[0141] YIM 10,800mm YL1 61.092mm

[0142] The lens data for the 3D projection optical system is as follows. The surface numbers are assigned sequentially from the magnification side to the reduction side. The symbols are those of the screen, lens, aperture diaphragm, dichroic prism, and liquid crystal panel. Surfaces marked with an asterisk (*) are aspherical. R is the radius of curvature. D is the axial spacing. nd is the refractive index of the d line. νd is the Abbe number of the d line. The units for R and D are mm.

[0143] Symbol face number RD nd vd S 0 inf 937.000 L01 1* -17.94 4.979 1.5350 55.7 2* -38.13 10.666 L02 3 55.43 1.500 1.8061 40.9 4 24.82 12.005 L03 5 -101.52 1.500 1.8061 40.9 6 29.05 39.622 L04 7 61.72 9.861 1.6727 32.1 L05 8 -45.29 1.500 1.8467 23.8 9 -87.20 25.866 L06 10 27.75 2.998 1.7618 26.5 11 45.18 8.405 41 12 inf 0.600 L07 13 -304.47 6.608 1.7283 28.5 L08 14 -13.83 1.000 1.8515 40.8 15 168.56 0.199 L09 16* 80.13 1.000 1.8344 37.3 17 * 27.70 0.201 L10 18 28.11 7.971 1.4875 70.2 19 -18.78 0.15 L11 20 -345.52 1.00 1.9037 31.3 L12 21 21.42 10.50 1.4970 81.5 L13 22 -16.40 1.00 1.9037 31.3 23 -28.09 0.15 L14 24 132.40 8.46 1.4970 81.5 25 -22.86 0.10 19 26 inf 30.69 1.5168 64.2 27 inf 9.66 19 28 inf -0.01

[0144] The aspherical coefficients are as follows:

[0145] Face number 1 2 Conic constant -3.98766E+00 0.00000E+00 The coefficients of the third order are 7.54720E-04 and 7.17021E-04. The coefficient of the fourth order is -7.67436E-06, which is 3.40907E-05. The coefficients of the fifth order are -2.02752E-07 and -8.65413E-07. The coefficient of the sixth degree is 2.75924E-09 -4.51327E-09 The coefficient of the 7th order is 4.79235E-11, which is 1.15162E-11. The coefficient of the 8th order is -4.56502E-14, which is 1.47502E-12. The coefficient of the 9th order is -9.65806E-15, which is 5.93761E-14. The coefficients of the 10th order are 3.96955E-16 and 1.11149E-15. 11th order coefficient -1.25544E-17 6.03964E-18 12th degree coefficients: -1.54368E-19 -2.47768E-19 The coefficient of the 13th order is 3.20580E-21 -1.14956E-20 The coefficient of the 14th order is 8.37917E-23 -2.96220E-22 The coefficient of the 15th order is 2.11755E-25 -4.68797E-24 Coefficients of the 16th order: -8.97852E-27 -2.98671E-26 17th degree coefficient -2.63525E-28 2.46500E-27 18th order coefficient -4.43567E-30 7.71252E-29 19th coefficient -9.92722E-33 1.92916E-30 The coefficients of the 20th order are 2.28460E-33 and 6.41410E-32.

[0146] Page numbers 16 and 17 Conic constant 0.00000E+00 0.00000E+00 The coefficient of the fourth order is -4.50613E-05 -1.91158E-05 Coefficients of the 6th order: 3.46887E-08 6.17285E-08 The coefficients of the 8th order are 1.04484E-09 and 7.87953E-10. The coefficient of the 10th order is -1.13350E-12 -2.0160E-12

[0147] Here, the projection optical system 3D in this example satisfies the following conditions (1) and (2), where ω is the maximum half-angle of view of the entire lens system, YIM is the distance from the optical axis N to the maximum image height of the projected image formed by the liquid crystal panel 18, and YL1 is the distance from the optical axis N to the principal ray α of the maximum image height on a virtual plane P that passes through the vertex of the magnifying lens surface of lens L1 and is perpendicular to the optical axis N. ω>40° (1) YL1 / YIM <6.0 (2)

[0148] In this example, ω 59.589° YIM 10,800mm YL1 61.092mm Therefore, ω = 59.589°, satisfying condition (1). YL1 / YIM = 5.657, satisfying condition (2).

[0149] In this example, the projection optical system 3D satisfies all of the following conditions (3), (4), and (5), where F is the focal length of the entire lens system, BF is the air-equivalent length of the back focus, Fls is the focal length of lens L1, and Flf is the focal length of lens L14. BF / F > 2.0 (3) -15.0 < Fls / F < -1.8 (4) 1.6 <Flf / F < 15.0 (5)

[0150] In this example, Bf 40.440mm F 6.346mm Fls -69.014mm Flf 39.839mm Therefore, BF / F = 6.373, satisfying condition (3). Fls / F = -10.875, satisfying condition (4). Flf / F = 6.278, satisfying condition (5).

[0151] In this example, the projection optical system 3D satisfies all of the following conditions (6), (7), and (8), provided that the focal length of the entire lens system is F, the difference between the Abbe number of lens L4 on the d line and the Abbe number of lens L5 on the d line is Δvd, the difference between the refractive index of lens L4 on the d line and the refractive index of lens L5 on the d line is Δnd, and the focal length of the cemented lens L21 is Fc. |Δvd|< 20.0 (6) |Δnd|< 0.35 (7) 2.0 < | Fc / F | < 15.0 (8)

[0152] In this example, F 6.346mm Fc 60.902mm |Δvd| 8.321 |Δnd| 0.174 Therefore, |Δvd|=8.321, satisfying condition (6). |Δnd|=0.174, satisfying condition (7). | Fc / F | = 9.597, which satisfies condition (8).

[0153] (Effects and Benefits) Since the projection optical system 3D of this example satisfies the conditional expression (1), wide-angleization is achieved. Further, since the first lens group 31 of the projection optical system 3D of this example has a positive power and satisfies the conditional expression (2), the lens on the most magnifying side of the first lens group can be made smaller with respect to the maximum image height of the projection image formed on the liquid crystal panel 18.

[0154] In the projection optical system 3D of this example, the lens L1 has a negative power. Therefore, it is easy to increase the maximum half-angle of the projection optical system 3D. In this example, the lens L14 has a positive power. Therefore, it is easy to make the reduction side from the second lens group 32 telecentric.

[0155] In this example, the first lens group 31 has a plurality of negative lenses continuously arranged from the most magnifying side toward the reducing side. In this example, the lenses L1, L2, and L3 are negative lenses having negative powers. Further, the lens L1 is an aspherical lens made of plastic. According to such a configuration, it is possible to suppress the field curvature generated in the projection optical system 3D.

[0156] Here, since the projection optical system 3D of this example satisfies the conditional expressions (3) to (8), the same operational effects as those of the projection optical system 3A of the first embodiment can be obtained. FIG. 10 is a diagram showing the spherical aberration, the coma aberration, and the distortion of the projection optical system 3D. As shown in FIG. 10, various aberrations in the magnified image of the projection optical system 3D of this example are suppressed.

[0157] (Embodiment 5) FIG. 11 is a ray diagram of the projection optical system 3E of Embodiment 5. As shown in FIG. 11, the projection optical system 3E includes, in order from the magnifying side toward the reducing side, a first lens group 31 having a positive power, an aperture stop 41, and a second lens group 32 having a positive power. The aperture stop 41 is set in defining the brightness of the projection optical system 3E.

[0158] The first lens group 31 includes four lenses L1 to L4. The lenses L1 to L4 are arranged in this order from the magnifying side toward the reducing side.

[0159] The lens L1 (enlarging lens) has a negative power. The lens L1 is a meniscus lens. The lens L1 has a convex shape on the enlarging side surface and a concave shape on the reducing side surface. The lens L2 has a negative power. The lens L2 has a convex shape on the enlarging side surface and a concave shape on the reducing side surface. The lens L2 has an aspherical shape on both surfaces.

[0160] The lens L3 (first lens) and the lens L4 (second lens) are a joined lens L21. The lens L3 has a positive power. The lens L3 is a meniscus lens. The lens L3 has a convex shape on the enlarging side surface and a concave shape on the reducing side surface. The lens L4 has a positive power. The lens L4 has a convex shape on both the enlarging side and reducing side surfaces. The joined lens L21 has a positive power.

[0161] The second lens group 32 includes five lenses L5 to L9. The lenses L5 to L9 are arranged in this order from the enlarging side to the reducing side.

[0162] The lenses L5, L6, and L7 are a joined lens L22. The lens L5 has a negative power. The lens L5 is a meniscus lens. The lens L5 has a convex shape on the enlarging side surface and a concave shape on the reducing side surface. The lens L6 has a positive power. The lens L6 has a convex shape on both the enlarging side and reducing side surfaces. The lens L7 has a negative power. The lens L7 has a concave shape on both the enlarging side and reducing side surfaces. The joined lens L22 has a negative power.

[0163] The lens L8 has a positive power. The lens L8 is a meniscus lens. The lens L8 has a concave shape on the enlarging side surface and a convex shape on the reducing side surface. The lens L9 (reducing lens) has a positive power. The lens L9 has a convex shape on both the enlarging side and reducing side surfaces. The lens L9 has an aspherical shape on both surfaces.

[0164] Lens L2 is made of resin. Lenses L1, L3 through L9 are made of glass.

[0165] In projection optical system 3E, the reduction side from lens L9 is telecentric.

[0166] Assuming that the F-number of the projection optical system 3E is FNo, the total optical length is TTL, the distance on the optical axis N from the magnifying surface of lens L1 to the reducing surface of lens L9 is L, the back focus is BF, the maximum half-angle of view of the entire lens system is ω, the focal length of the entire lens system is F, the focal length of the first lens group 31 is Fg1, the focal length of the second lens group 32 is Fg2, the focal length of lens L1 is Fls, the focal length of lens L9 is Flf, and the focal length of cemented lens L21 is Fc, the data for the projection optical system 3E of Example 5 is as follows.

[0167] Fno 2.022 TTL 99.125mm L 70,000mm Bf 29.125mm ω 40.216° F 12.388mm Fg1 51.815mm Fg2 24.823mm Fls -74.517mm Flf 21.011mm Fc 26.445mm

[0168] As shown in Figure 11, when YIM is defined as the distance from the optical axis N to the maximum image height of the projected image formed by the liquid crystal panel 18, and YL1 is defined as the distance from the optical axis N to the principal ray α of the maximum image height on a virtual plane P that passes through the vertex of the magnifying lens surface of lens L1 and is perpendicular to the optical axis N, the data for the projection optical system 3E of Example 5 is as follows.

[0169] YIM 10.350mm YL1 18.009mm

[0170] The lens data of the projection optical system 3E is as follows. The surface numbers are assigned in order from the magnifying side to the reducing side. The signs are those of the screen, lens, aperture stop, dichroic prism, and liquid crystal panel. The surfaces marked with * are aspherical surfaces. R is the radius of curvature. D is the axial distance between surfaces. nd is the refractive index of the d-line. νd is the Abbe number of the d-line. The units of R and D are mm.

[0171] Sign Surface number R D nd vd S 0 inf 1190.000 L01 1 22.43 2.000 1.6230 58.2 2 14.62 6.415 L02 3* -148.69 1.500 1.5365 56.0 4* 12.78 16.108 L03 5 31.20 1.743 1.9037 31.3 L04 6 36.37 6.000 1.8044 39.6 7 -63.07 10.097 41 8 inf 4.689 L05 9 244.61 1.000 1.5317 48.8 L06 10 10.29 7.506 1.4970 81.5 L07 11 -10.15 1.200 1.6477 33.8 12 60.66 1.403 L08 13 -51.24 2.526 1.7200 50.2 14 -29.86 0.200 L09 15* 24.94 7.614 1.5365 56.0 16* -18.50 0.200 19 17 inf 23.925 1.5168 64.2 18 inf 4.950 18 19 inf 0.05

[0172] The aspherical coefficients are as follows.

[0173] Page number 3 4 Conic constant 0.00000E+00 0.00000E+00 The coefficients of the third degree are 1.93615E-03 and 2.23236E-03. The coefficients of the fourth order are -2.66907E-05 and -1.57621E-04. The coefficient of the fifth order is -1.19541E-05, which is 6.77330E-06. The coefficient of the sixth degree is 1.15454E-07 -8.91725E-07 The coefficient of the 7th order is 5.55324E-08 -8.57616E-08 The coefficients of the 8th order are 1.12225E-09 and 3.32983E-09. The coefficient of the 9th order is -3.92719E-10, which is 1.19811E-09. The coefficient of the 10th order is 1.28061E-11 -8.30314E-11

[0174] Page numbers 15 16 Conic constant 0.00000E+00 0.00000E+00 The coefficient of the fourth order is -3.14658E-05, which is 2.32078E-05. Coefficient of the 6th order: 6.07696E-08 2.35492E-08 The coefficient of the 8th order is -3.38344E-10 -2.15202E-10 The coefficient of the 10th order is 8.97097E-13, which is 1.19144E-12.

[0175] Here, in this example, the projection optical system 3E satisfies the following conditions (1) and (2), where ω is the maximum half-angle of view of the entire lens system, YIM is the distance from the optical axis N to the maximum image height of the projected image formed by the liquid crystal panel 18, and YL1 is the distance from the optical axis N to the principal ray α of the maximum image height on a virtual plane P that passes through the vertex of the magnifying lens surface of lens L1 and is perpendicular to the optical axis N. ω>40° (1) YL1 / YIM <6.0 (2)

[0176] In this example, ω 40.216° YIM 10.350mm YL1 18.009mm Therefore, ω = 40.216°, satisfying condition (1). YL1 / YIM = 1.740, satisfying condition (2).

[0177] In this example, the projection optical system 3E satisfies all of the following conditions (3), (4), and (5), where F is the total focal length of the lens system, BF is the air-equivalent length of the back focus, Fls is the focal length of lens L1, and Flf is the focal length of lens L9. BF / F > 2.0 (3) -15.0 < Fls / F < -1.8 (4) 1.6 <Flf / F < 15.0 (5)

[0178] In this example, Bf 29.125mm F 12.388mm Fls -74.517mm Flf 21.011mm Therefore, BF / F = 2.351, satisfying condition (3). Fls / F = -6.015, satisfying condition (4). Flf / F = 1.696, satisfying condition (5).

[0179] In this example, the projection optical system 3E satisfies all of the following conditions (6), (7), and (8), provided that the focal length of the entire lens system is F, the difference between the Abbe number of lens L3 on the d line and the Abbe number of lens L4 on the d line is Δvd, the difference between the refractive index of lens L3 on the d line and the refractive index of lens L4 on the d line is Δnd, and the focal length of the cemented lens L21 is Fc. |Δvd|< 20.0 (6) |Δnd|< 0.35 (7) 2.0 < | Fc / F | < 15.0 (8)

[0180] In this example, F 12.388mm Fc 26.445mm |Δvd| 8.243 |Δnd| 0.099 Therefore, |Δvd|=8.243, satisfying condition (6). |Δnd|=0.099, satisfying condition (7). | Fc / F | = 2.135, which satisfies condition (8).

[0181] (Effects and Benefits) In this example, the projection optical system 3E satisfies condition (1), thus enabling wide-angle projection. Furthermore, in this example, the projection optical system 3E has positive power in the first lens group 31 and satisfies condition (2), so the lens on the widest side of the first lens group can be made smaller relative to the maximum image height of the projected image formed by the liquid crystal panel 18.

[0182] In the projection optical system 3E of this example, lens L1 has negative power. Therefore, it is easy to increase the maximum half-angle of view of the projection optical system 3E. In this example, lens L9 has positive power. Therefore, it is easy to make the reduction side from the second lens group 32 telecentric.

[0183] In this example, the first lens group 31 has multiple negative lenses arranged continuously from the magnification side to the reduction side. In this example, lenses L1 and L2 are negative lenses with negative power. Lens L2 is also a plastic aspherical lens. With this configuration, it is possible to suppress the field curvature that occurs in the projection optical system 3E.

[0184] Here, the projection optical system 3E in this example satisfies conditions (3) to (8), and therefore the same effects as the projection optical system 3A in Example 1 can be obtained. Figure 12 shows the spherical aberration, astigmatism, and distortion of the projection optical system 3E. As shown in Figure 12, the projection optical system 3E in this example suppresses various aberrations in the magnified image.

[0185] (Example 6) Figure 13 is a ray diagram of the projection optical system 3F of Embodiment 6. As shown in Figure 13, the projection optical system 3F comprises, in order from the magnification side to the reduction side, a first lens group 31 with positive power, an aperture diaphragm 41, and a second lens group 32 with positive power. The aperture diaphragm 41 is set to define the brightness of the projection optical system 3F.

[0186] The first lens group 31 comprises five lenses L1 to L5. Lenses L1 to L5 are arranged in this order from the magnification side to the reduction side.

[0187] Lens L1 (magnifying lens) has negative power. Lens L1 has a concave shape near the optical axis N on the magnifying surface and a convex shape at the periphery. Lens L1 has a convex shape near the optical axis N on the reducing surface and a concave shape at the periphery. Lens L1 has aspherical shapes on both sides. Lens L2 has negative power. Lens L2 is a meniscus lens. Lens L2 has a convex shape on the magnifying surface and a concave shape on the reducing surface.

[0188] Lens L3 (first lens) and lens L4 (second lens) are joined together to form a cemented lens L21. Lens L3 has negative power. Lens L3 has a concave shape on its magnifying and reducing surfaces. Lens L4 has positive power. Lens L4 has a convex shape on its magnifying and reducing surfaces. The cemented lens L21 has negative power.

[0189] Lens L5 has positive power. Lens L5 has a convex shape on both the magnifying and reducing surfaces.

[0190] The second lens group 32 comprises six lenses L6 to L11. Lenses L6 to L11 are arranged in this order from the magnification side to the reduction side.

[0191] Lenses L6 and L7 are joined together to form a cemented lens L22. Lens L6 has negative power. Lens L6 has a concave shape on its magnifying and reducing surfaces. Lens L7 has positive power. Lens L7 has a convex shape on its magnifying and reducing surfaces. The cemented lens L22 has negative power.

[0192] Lens L8 has positive power. Lens L8 has a convex shape on the magnifying and reducing surfaces. Lens L8 has an aspherical shape on both sides.

[0193] Lenses L9 and L10 are joined together to form a cemented lens L23. Lens L9 has negative power. Lens L9 has a concave shape on its magnifying and reducing surfaces. Lens L10 has positive power. Lens L10 has a convex shape on its magnifying and reducing surfaces. Lens L10 has an aspherical shape on its reducing surface. The cemented lens L23 has positive power.

[0194] Lens L11 (the reducing lens) has positive power. Lens L11 is a meniscus lens. Lens L11 has a convex shape on the magnifying side and a concave shape on the reducing side.

[0195] Lens L1 is made of resin. Lenses L2 through L11 are made of glass.

[0196] In projection optical system 3F, the reduction side from lens L11 is telecentric.

[0197] Assuming that the F-number of the projection optical system 3F is FNo, the total optical length is TTL, the distance on the optical axis N from the magnifying surface of lens L1 to the reducing surface of lens L11 is L, the back focus is BF, the maximum half-angle of view of the entire lens system is ω, the focal length of the entire lens system is F, the focal length of the first lens group 31 is Fg1, the focal length of the second lens group 32 is Fg2, the focal length of lens L1 is Fls, the focal length of lens L11 is Flf, and the focal length of cemented lens L21 is Fc, the data for the projection optical system 3F of Example 6 is as follows.

[0198] Fno 2.000 TTL 98.341mm L 63.842mm Bf 34.499mm ω 51.245° F 8.362mm Fg1 80.458mm Fg2 19.941mm Fls -36.522mm Flf 100.001mm Fc -23.752mm

[0199] As shown in Figure 13, when YIM is defined as the distance from the optical axis N to the maximum image height of the projected image formed by the liquid crystal panel 18, and YL1 is defined as the distance from the optical axis N to the principal ray α of the maximum image height on a virtual plane P that passes through the vertex of the magnifying lens surface of lens L1 and is perpendicular to the optical axis N, the data for the projection optical system 3F of Example 6 is as follows.

[0200] YIM 10.350mm YL1 18.189mm

[0201] The lens data for projection optical system 3F is as follows. The surface numbers are assigned sequentially from the magnification side to the reduction side. The symbols are those of the screen, lens, aperture diaphragm, dichroic prism, and liquid crystal panel. Surfaces marked with an asterisk (*) are aspherical. R is the radius of curvature. D is the axial spacing. nd is the refractive index of the d line. νd is the Abbe number of the d line. The units for R and D are mm.

[0202] Code Surface number RD nd vd S 0 inf 730.000 L01 1* -8.71 2.000 1.5311 55.8 2* -17.02 3.172 L02 3 26.37 1.398 1.9229 20.9 4 15.68 10.115 L03 5 -19.67 1.200 1.8919 37.1 L04 6 12.15 3.202 1.6398 34.5 7 -30.25 0.100 L05 8 28.62 8.995 1.9229 20.9 9 -32.73 0.321 41 10 inf 1.192 L06 11 -20.65 1.000 1.9537 32.3 L07 12 10.45 3.797 1.7847 25.7 13 -41.30 5.285 L08 14* 37.90 6.502 1.4971 81.6 15* -13.52 1.281 L09 16 -50.19 1.000 2.0006 25.5 L10 17 34.48 9.279 1.4971 81.6 18* -14.80 0.100 L11 19 21.54 3.90 1.4970 81.55 20 35.66 2.50 19 21 inf 27.43 1.5168 64.20 22 inf 4.55 18 23 inf 0.02

[0203] The aspherical coefficients are as follows:

[0204] Face number 1 2 Conic constant -3.42002E+00 -5.60704E-01 The coefficients of the third order are 4.25232E-03 and 4.31180E-03. The coefficients of the fourth order are 3.01571E-04 and 3.92102E-04. The coefficients of the fifth order are -7.90368E-05 and -3.48447E-06. The coefficient of the sixth degree is 4.97710E-06 -4.42544E-06 Coefficient of the 7th order: -7.29863E-08 2.29437E-08 The coefficient of the 8th order is -3.95536E-09, which is 2.41870E-08. The coefficient of the 9th order is 1.38060E-10 -1.13025E-10 The coefficient of the 10th order is -4.19421E-13 -4.95628E-11

[0205] Page numbers 14, 15, 18 Conic constant 3.45419E+00 -8.53411E-03 -1.69646E+00 The coefficients of the fourth order are -3.32603E-05, 6.87379E-05, and -5.39809E-05. Coefficient of the 6th order: 1.87962E-07 1.32192E-07 0.00000E+00 The coefficient of the 8th order is -3.04817E-09 -1.55278E-09 0.00000E+00 The coefficients of the 10th order are 1.78417E-11, 7.00890E-12, and 0.00000E+00. The coefficient of the 12th order is -4.67443E-14 0.00000E+00 0.00000E+00

[0206] Here, in this example, the projection optical system 3F satisfies the following conditions (1) and (2), where ω is the maximum half-angle of view of the entire lens system, YIM is the distance from the optical axis N to the maximum image height of the projected image formed by the liquid crystal panel 18, and YL1 is the distance from the optical axis N to the principal ray α of the maximum image height on a virtual plane P that passes through the vertex of the magnifying lens surface of lens L1 and is perpendicular to the optical axis N. ω>40° (1) YL1 / YIM <6.0 (2)

[0207] In this example, ω 51.245° YIM 10.350mm YL1 18.189mm Therefore, ω = 51.245°, satisfying condition (1). YL1 / YIM = 1.757, satisfying condition (2).

[0208] In this example, the projection optical system 3F satisfies all of the following conditions (3), (4), and (5), where F is the focal length of the entire lens system, BF is the air-equivalent length of the back focus, Fls is the focal length of lens L1, and Flf is the focal length of lens L11. BF / F > 2.0 (3) -15.0 < Fls / F < -1.8 (4) 1.6 <Flf / F < 15.0 (5)

[0209] In this example, Bf 34.499mm F 8.362mm Fls -36.522mm Flf 100.001mm Therefore, BF / F = 4.126, satisfying condition (3). Fls / F = -4.368, satisfying condition (4). Flf / F = 11.960, satisfying condition (5).

[0210] In this example, the projection optical system 3F satisfies all of the following conditions (6), (7), and (8), provided that F is the focal length of the entire lens system, Δvd is the difference between the Abbe number of lens L3 on the d line and the Abbe number of lens L4 on the d line, Δnd is the difference between the refractive index of lens L3 on the d line and the refractive index of lens L4 on the d line, and Fc is the focal length of the cemented lens L21. |Δvd|< 20.0 (6) |Δnd|< 0.35 (7) 2.0 < | Fc / F | < 15.0 (8)

[0211] In this example, F 8.362mm Fc -23.752mm |Δvd| 2.668 |Δnd| 0.254 Therefore, |Δvd|=2.668, satisfying condition (6). |Δnd|=0.254, satisfying condition (7). | Fc / F | = 2.841, which satisfies condition (8).

[0212] (Effects and Benefits) In this example, the projection optical system 3F satisfies condition (1), thus enabling wide-angle projection. Furthermore, in this example, the projection optical system 3F has positive power in the first lens group 31 and satisfies condition (2), so the lens on the most magnifying side of the first lens group can be made smaller relative to the maximum image height of the projected image formed by the liquid crystal panel 18.

[0213] In the projection optical system 3F of this example, lens L1 has negative power. Therefore, it is easy to increase the maximum half-angle of view of the projection optical system 3F. In this example, lens L11 has positive power. Therefore, it is easy to make the reduction side from the second lens group 32 telecentric.

[0214] In this example, the first lens group 31 has multiple negative lenses arranged continuously from the magnification side to the reduction side. In this example, lenses L1 and L2 are negative lenses with negative power. Lens L1 is also a plastic aspherical lens. With this configuration, it is possible to suppress the field curvature that occurs in the projection optical system 3F.

[0215] Here, the projection optical system 3F in this example satisfies conditions (3) to (8), and therefore the same effects as the projection optical system 3A in Example 1 can be obtained. Figure 14 shows the spherical aberration, astigmatism, and distortion of the projection optical system 3F. As shown in Figure 14, the projection optical system 3F in this example suppresses various aberrations in the magnified image.

[0216] (Example 7) Figure 15 is a ray diagram of the projection optical system 3G of Embodiment 7. As shown in Figure 15, the projection optical system 3G comprises, in order from the magnification side to the reduction side, a first lens group 31 having positive power, an aperture diaphragm 41, and a second lens group 32 having positive power. The aperture diaphragm 41 is set to define the brightness of the projection optical system 3G.

[0217] The first lens group 31 comprises five lenses L1 to L5. Lenses L1 to L5 are arranged in this order from the magnification side to the reduction side.

[0218] Lens L1 (magnifying lens) has negative power. Lens L1 is a meniscus lens. Lens L1 has a convex shape on the magnifying side and a concave shape on the reducing side. Lens L2 has negative power. Lens L2 is a meniscus lens. Lens L2 has a convex shape on the magnifying side and a concave shape on the reducing side.

[0219] Lens L3 is a meniscus lens. Lens L3 has a convex shape on the magnifying side and a concave shape on the reducing side. Lens L3 has aspherical shapes on both sides.

[0220] Lens L4 (first lens) and lens L5 (second lens) are joined together to form a cemented lens L21. Lens L4 has negative power. Lens L4 is a meniscus lens. Lens L4 has a convex shape on the magnifying side and a concave shape on the reducing side. Lens L5 has positive power. Lens L5 has convex shapes on both the magnifying and reducing sides. The cemented lens L21 has positive power.

[0221] The second lens group 32 comprises five lenses L6 to L10. Lenses L5 to L10 are arranged in this order from the magnification side to the reduction side.

[0222] Lenses L6, L7, and L8 are joined together to form a cemented lens L22. Lens L6 has negative power. Lens L6 has concave shapes on its magnifying and reducing surfaces. Lens L7 has positive power. Lens L7 has convex shapes on its magnifying and reducing surfaces. Lens L8 has negative power. Lens L8 is a meniscus lens. Lens L8 has a convex shape on its magnifying surface and a concave shape on its reducing surface. The cemented lens L22 has negative power.

[0223] Lens L9 has positive power. Lens L9 is a meniscus lens. Lens L9 has a concave shape on the magnifying side and a convex shape on the reducing side. Lens L10 (reducing lens) has positive power. Lens L10 has convex shapes on both the magnifying and reducing sides. Lens L10 has aspherical shapes on both sides.

[0224] Lens L3 is made of resin. Lenses L1, L2, L4 through L10 are made of glass.

[0225] In projection optical system 3G, the reduction side from lens L10 is telecentric.

[0226] Assuming that the F-number of the projection optical system 3G is FNo, the total optical length is TTL, the distance on the optical axis N from the magnifying surface of lens L1 to the reducing surface of lens L10 is L, the back focus is BF, the maximum half-angle of view of the entire lens system is ω, the focal length of the entire lens system is F, the focal length of the first lens group 31 is Fg1, the focal length of the second lens group 32 is Fg2, the focal length of lens L1 is Fls, the focal length of lens L10 is Flf, and the focal length of cemented lens L21 is Fc, the data for the projection optical system 3G of Example 7 is as follows.

[0227] Fno 2.022 TTL 104.024mm L 75,000mm Bf 29.024mm ω 40.801° F 12.134mm Fg1 50.531mm Fg2 23.981mm Fls -67.029mm Flf 21.642mm Fc 26.162mm

[0228] As shown in Figure 15, when YIM is defined as the distance from the optical axis N to the maximum image height of the projected image formed by the liquid crystal panel 18, and YL1 is defined as the distance from the optical axis N to the principal ray α of the maximum image height on a virtual plane P that passes through the vertex of the magnifying lens surface of lens L1 and is perpendicular to the optical axis N, the data for the projection optical system 3G of Example 7 is as follows.

[0229] YIM 10.350mm YL1 19.527mm

[0230] The lens data for projection optical system 3G is as follows. The surface numbers are assigned sequentially from the magnification side to the reduction side. The symbols are those of the screen, lens, aperture diaphragm, dichroic prism, and liquid crystal panel. Surfaces marked with an asterisk (*) are aspherical. R is the radius of curvature. D is the axial spacing. nd is the refractive index of the d line. νd is the Abbe number of the d line. The units for R and D are mm.

[0231] Code Surface number RD nd vd S 0 inf 1190.000 L01 1 48.30 2.000 1.4875 70.2 2 19.26 5.054 L02 3 46.84 2.000 1.5378 74.7 4 21.45 1.846 L03 5* 73.21 1.500 1.5365 56.0 6* 14.06 15.132 L04 7 29.24 1.200 1.9037 31.3 L05 8 15.81 6.000 1.8044 39.6 9 -54.29 14.872 41 10 inf 4.993 L06 11 -48.08 1.000 1.5317 48.8 L07 12 10.76 8.000 1.4970 81.5 L08 13 -11.07 1.200 1.6477 33.8 14 -83.40 0.200 L09 15 -85.46 2.282 1.7200 50.2 16 -49.52 0.200 L10 17* 26.21 7.521 1.5365 56.0 18* -18.88 0.200 19 19 inf 23.93 1.5168 64.2 20 inf 4.85 19 21 inf 0.05

[0232] The aspherical coefficients are as follows:

[0233] Page numbers 5 and 6 Conic constant 0.00000E+00 0.00000E+00 The coefficients of the third order are 1.57900E-03 and 1.85263E-03. The coefficient of the fourth order is 6.96953E-05 -4.47240E-05 The coefficient of the fifth order is -1.36372E-05, which is 1.04252E-06. Coefficient of the 6th order: -3.02221E-07 -8.19992E-07 The coefficient of the 7th order is 4.84025E-08 -7.76252E-08 The coefficients of the 8th order are 2.52624E-09 and 1.95332E-09. The coefficient of the 9th order is -2.99137E-10, which is 1.09687E-09. The coefficient of the 10th order is 6.56267E-12 -6.17508E-11

[0234] Page numbers 17 and 18 Conic constant 0.00000E+00 0.00000E+00 The coefficient of the fourth order is -2.94834E-05, which is 3.01111E-05. Coefficient of the 6th order: 7.70708E-08 3.90288E-08 The coefficient of the 8th order is -5.67005E-10 -4.82412E-10 The coefficients of the 10th order are 1.54988E-12 and 1.60978E-12.

[0235] Here, in this example, the projection optical system 3G satisfies the following conditions (1) and (2), where ω is the maximum half-angle of view of the entire lens system, YIM is the distance from the optical axis N to the maximum image height of the projected image formed by the liquid crystal panel 18, and YL1 is the distance from the optical axis N to the principal ray α of the maximum image height on a virtual plane P that passes through the vertex of the magnifying lens surface of lens L1 and is perpendicular to the optical axis N. ω>40° (1) YL1 / YIM <6.0 (2)

[0236] In this example, ω 40.801° YIM 10.350mm YL1 19.527mm Therefore, ω = 40.801°, satisfying condition (1). YL1 / YIM = 1.887, satisfying condition (2).

[0237] In this example, the projection optical system 3G satisfies all of the following conditions (3), (4), and (5), where F is the focal length of the entire lens system, BF is the air-equivalent length of the back focus, Fls is the focal length of lens L1, and Flf is the focal length of lens L10. BF / F > 2.0 (3) -15.0 < Fls / F < -1.8 (4) 1.6 <Flf / F < 15.0 (5)

[0238] In this example, Bf 29.024mm F 12.134mm Fls -67.029mm Flf 21.642mm Therefore, BF / F = 2.392, satisfying condition (3). Fls / F = -5.524, satisfying condition (4). Flf / F = 1.784, satisfying condition (5).

[0239] In this example, the projection optical system 3G satisfies all of the following conditions (6), (7), and (8), provided that the focal length of the entire lens system is F, the difference between the Abbe number of lens L4 on the d line and the Abbe number of lens L5 on the d line is Δvd, the difference between the refractive index of lens L4 on the d line and the refractive index of lens L5 on the d line is Δnd, and the focal length of the cemented lens L21 is Fc. |Δvd|< 20.0 (6) |Δnd|< 0.35 (7) 2.0 < | Fc / F | < 15.0 (8)

[0240] In this example, F 12.134mm Fc 26.162mm |Δvd| 2.668 |Δnd| 0.254 Therefore, |Δvd|=2.668, and condition (6) is satisfied. |Δnd|= The value is 0.254, which satisfies condition (7). | Fc / F | = 2.156, and condition (8) It satisfies the condition.

[0241] (Effects and Benefits) In this example, the projection optical system 3G satisfies condition (1), thus enabling wide-angle projection. Furthermore, in this example, the projection optical system 3G has positive power in the first lens group 31 and satisfies condition (2), so the lens on the most magnifying side of the first lens group can be made smaller relative to the maximum image height of the projected image formed by the liquid crystal panel 18.

[0242] In the projection optical system 3G of this example, lens L1 has negative power. Therefore, it is easy to increase the maximum half-angle of view of the projection optical system 3G. In this example, lens L10 has positive power. Therefore, it is easy to make the reduction side from the second lens group 32 telecentric.

[0243] In this example, the first lens group 31 has multiple negative lenses arranged continuously from the magnification side to the reduction side. In this example, lenses L1, L2, and L3 are negative lenses with negative power. Lens L3 is also a plastic aspherical lens. With this configuration, it is possible to suppress the field curvature that occurs in the projection optical system 3G.

[0244] Here, the projection optical system 3G in this example satisfies conditions (3) to (8), and therefore the same effects as the projection optical system 3A in Example 1 can be obtained. Figure 16 shows the spherical aberration, astigmatism, and distortion of the projection optical system 3G. As shown in Figure 16, the projection optical system 3G in this example suppresses various aberrations in the magnified image.

[0245] (Other examples) In the above embodiment, focusing can be performed by moving one or more lenses in the first lens group 31 along the optical axis N direction. In this case, it is desirable to move the cemented lenses and positive lenses included in the first lens group 31 along the optical axis N direction.

[0246] Although preferred embodiments of the present invention have been described above, the present invention is not limited to the specific embodiments described above, and unless otherwise specifically limited in the above description, various modifications and changes are possible within the scope of the spirit of the invention as described in the claims. For example, in the embodiments of the present invention, a liquid crystal panel 18 is used as the image forming element, but it is not limited to a liquid crystal panel 18, and a reflective liquid crystal panel or a DMD (Digital Micromirror Device) may also be used. [Explanation of symbols]

[0247] 1...Projector, 2...Image forming unit, 3·3A·3B·3C·3D·3E·3F·3G...Projection optical system, 4...Control unit, 6...Image processing unit, 7...Display drive unit, 10...Light source, 11...Integrator lens, 12...Integrator lens, 13...Polarization conversion element, 14...Superimposed lens, 15...Dichroic mirror, 16...Reflective mirror, 17R...Field lens, 17G...Field lens, 17B...Field Drenthes, 18 (18B, 18R, 18G)...LCD panel, 19...Cross dichroic prism, 21...Dichroic mirror, 22...Relay lens, 23...Reflective mirror, 24...Relay lens, 25...Reflective mirror, 31...First lens group, 32...Second lens group, 41...Aperture diaphragm, L1~L15...Lenses, L21~L24...Cemented lenses, N...Optical axis, P...Virtual plane, S...Screen, α...Principal ray at maximum image height.

Claims

1. In a projection optical system for projecting an enlarged image onto an enlarged conjugate surface by enlarging a projected image formed by an image forming element arranged on the reduction side conjugate surface, It comprises, in order from the magnification side to the reduction side, a first lens group with positive power, an aperture diaphragm, and a second lens group with positive power. The second lens group is telecentric from the reducing lens located on the most reducing side. Let ω be the maximum half-angle of view of the entire lens system, and YIM be the distance from the optical axis to the maximum image height of the projected image formed by the image forming element. On a virtual plane that passes through the vertex of the magnifying lens surface of the magnifying lens located on the most magnifying side of the first lens group and is perpendicular to the optical axis, A projection optical system characterized by satisfying the following conditions (1) and (2), where YL1 is the distance from the optical axis to the principal ray of the maximum image height. ω > 40° (1) YL1 / YIM <2.0 (2)

2. The magnifying lens has negative power, The projection optical system according to claim 1, characterized in that the reduction lens has positive power.

3. The first lens group comprises a plurality of negative lenses arranged continuously from the magnification side to the reduction side, The projection optical system according to claim 1 or 2, characterized in that one of the multiple negative lenses is a plastic aspherical lens.

4. The projection optical system according to any one of claims 1 to 3, characterized in that, if the focal length of the entire lens system is F, the air-equivalent length of the back focus is BF, the focal length of the magnifying lens is Fls, and the focal length of the reducing lens is Flf, then all of the following conditions (3), (4), and (5) are satisfied. BF / F > 2.0 (3) -15.0 < Fls / F < -1.8 (4) 1.6 < Flf / F < 15.0 (5)

5. The first lens group includes a cemented lens formed by joining a first lens and a second lens. A projection optical system according to any one of claims 1 to 3, characterized in that, if the focal length of the entire lens system is F, the difference between the Abbe number of the first lens on the d line and the Abbe number of the second lens on the d line is Δvd, the difference between the refractive index of the first lens on the d line and the refractive index of the second lens on the d line is Δnd, and the focal length of the cemented lens is Fc, then all of the following conditions (6), (7), and (8) are satisfied. |Δvd|< 20.0 (6) |Δnd|< 0.35 (7) 2.0 < |Fc / F| < 15.0 (8)

6. The first lens group comprises a cemented lens formed by joining a first lens and a second lens, The projection optical system according to claim 4, characterized in that, if the focal length of the entire lens system is F, the difference between the Abbe number of the first lens on the d line and the Abbe number of the second lens on the d line is Δvd, the difference between the refractive index of the first lens on the d line and the refractive index of the second lens on the d line is Δnd, and the focal length of the cemented lens is Fc, then all of the following conditions (6), (7), and (8) are satisfied. |Δvd|< 20.0 (6) |Δnd|< 0.35 (7) 2.0 < |Fc / F| < 15.0 (8)

7. The projection optical system according to any one of claims 1 to 6 is characterized in that it has a fixed focus.

8. A projection optical system according to any one of claims 1 to 7, The image forming element that forms the projected image on the reduction-side conjugate surface of the projection optical system, A projector characterized by having the following features.

Images