Projection optical system and projector

Abstract

To provide a projection optical system in which the projection distance is short.SOLUTION: A projection optical system includes a first optical system formed of a plurality of lenses, and a second optical system, in order from a reduction side toward an enlargement side. The first optical system has positive power. The second optical system has a first reflective optical system, a second reflective optical system, and a third reflective optical system, in order from the first optical system on an optical path of beams emitted from the first optical system. The first reflective optical system has a first reflection surface having a concave aspherical shape. The second reflective optical system has a second reflection surface having a concave shape or a planar shape. The third reflective optical system has a third reflection surface having a convex aspherical shape. At least two of the first reflection surface, the second reflection surface, and the third reflection surface each have an aspherical shape. When the focal length of the first reflective optical system is f1, the focal length of the second reflective optical system is f2, and the focal length of the third reflective optical system is f3, the projection optical system satisfies a conditional expression (1) below: |f2|>|f1|>|f3|...(1)SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] A projector that enlarges a projection image displayed on an image display element by a projection optical system and projects the enlarged image on a screen is described in Patent Document 1. The projection optical system includes a refractive optical system and a reflective optical system, in this order from the reduction side to the enlargement side. The refractive optical system includes a plurality of refractive lenses. The reflective optical system includes a first reflective optical system, a second reflective optical system, and a third reflective optical system, which are provided in this order from the refractive optical system side on the optical path of the light beam emitted from the refractive optical system. The first reflective optical system includes a first reflective surface having a concave shape. The second reflective optical system includes a second reflective surface having a curved shape. The third reflective optical system includes a third reflective surface having a convex shape. The absolute value of the focal length of the third reflective optical system is greater than the absolute value of the focal length of the first reflective optical system. The projection distance of the projection optical system in the same document is about 372 mm at its shortest. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-40849 A Summary of the Invention [Problem to be solved by the invention]

[0004] There is a demand for projection optical systems with shorter throw distances.

[0005] In order to solve the above problems, the projection optical system of the present invention comprises, in order from the reduction side to the enlargement side, a first optical system consisting of a plurality of lenses and a second optical system, wherein the first optical system has positive power, the second optical system has, in order from the first optical system, a first reflective optical system, a second reflective optical system, and a third reflective optical system on the optical path of a light ray emitted from the first optical system, wherein the first reflective optical system has a first reflective surface having a concave aspheric shape, the second reflective optical system has a second reflective surface having a concave shape or a planar shape, and the third reflective optical system has a third reflective surface having a convex aspheric shape, and is characterized in that when the focal length of the first reflective optical system is f1, the focal length of the second reflective optical system is f2, and the focal length of the third reflective optical system is f3, the following conditional formula (1) is satisfied. |f2|>|f1|>|f3|···(1)

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

[0007] [Figure 1] FIG. 1 is a diagram showing a schematic configuration of a projector including a projection optical system according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a ray diagram of a projection optical system. [Diagram 3] 2 is a ray diagram of the projection optical system of the first embodiment. [Figure 4] 4 is a diagram showing the MTF on the reduction side of the projection optical system of the first embodiment. FIG. [Diagram 5] FIG. 11 is a ray diagram of a projection optical system according to a second embodiment. [Figure 6] 13 is a diagram showing the MTF on the reduction side of the projection optical system of the second embodiment. FIG. [Figure 7] FIG. 11 is a ray diagram of a projection optical system according to a third embodiment. [Figure 8] 13 is a diagram showing the MTF on the reduction side of the projection optical system of Example 3. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] An optical system and a projector according to an embodiment of the invention will be described below with reference to the drawings.

[0009] (projector) Fig. 1 is a diagram showing a schematic configuration of a projector including a 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 a screen S, a projection optical system 3 that enlarges the projection image and projects the 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, for example, an ultra-high pressure mercury lamp, a solid-state light source, or the like. The first integrator lens 11 and the second integrator lens 12 each have a plurality of lens elements arranged in an array. The first integrator lens 11 splits the light beam from the light source 10 into a plurality of beams. Each lens element of the first integrator lens 11 focuses the light beam from the light source 10 near each lens element of the second integrator lens 12.

[0011] Polarization conversion element 13 converts the light from second integrator lens 12 into a predetermined linearly polarized light. Superimposing lens 14 superimposes the images of each lens element of first integrator lens 11 via second integrator lens 12 onto the display regions of liquid crystal panels 18R, 18G, and 18B, which will be described later.

[0012] The image forming unit 2 also includes a first dichroic mirror 15, a reflecting mirror 16, a field lens 17R, and a liquid crystal panel 18R. The first dichroic mirror 15 reflects the R light, which is a part of the light beam incident from the superimposing lens 14, and transmits the G light and B light, which are a part of the light beam incident from the superimposing lens 14. The R light reflected by the first dichroic mirror 15 passes through the reflecting mirror 16 and the field lens 17R and enters the liquid crystal panel 18R. 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 in response to an image signal.

[0013] The image forming unit 2 further 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 part of the light beam from the first dichroic mirror 15, and transmits B light, which is a part of the light beam 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 forms a green projection image by modulating the G light in response to an image signal.

[0014] The image forming unit 2 also includes a relay lens 22, a reflecting mirror 23, a relay lens 24, a reflecting 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 reflecting mirror 23, the relay lens 24, the reflecting mirror 25, and the field lens 17B, and enters the liquid crystal panel 18B. The liquid crystal panel 18B is an image forming element. The liquid crystal panel 18B forms a blue projection image by modulating the B light in response to an image signal.

[0015] Liquid crystal panels 18R, 18G, and 18B surround cross dichroic prism 19 from three directions. Cross dichroic prism 19 is a prism for light synthesis, and generates a projection image by synthesizing the lights modulated by each of liquid crystal panels 18R, 18G, and 18B.

[0016] The projection optical system 3 projects the projection image synthesized by the cross dichroic prism 19 onto a screen S in an enlarged scale.

[0017] The control unit 4 includes an image processing unit 6 to which an external image signal such as a video signal is input, and a display driving unit 7 that drives the liquid crystal panels 18R, 18G, and 18B based on the image signal output from the image processing unit 6.

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

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

[0020] For convenience, in the following description, three mutually orthogonal axes are referred to as the X-axis, Y-axis, and Z-axis. The direction along the first optical axis N of the projection optical system 3 is referred to as the Z-axis direction. In the Z-axis direction, the side opposite to the side where the liquid crystal panel 18 is located is referred to as the first direction Z1, and the side where the liquid crystal panel 18 is located is referred to as the second direction Z2. The Y-axis extends along the screen S. The Y-axis direction is the up-down direction, with one side in the Y-axis direction referred to as the upward direction Y1 and the other side referred to as the downward direction Y2. The X-axis extends in the width direction of the screen.

[0021] In the following, examples 1 to 3 will be described as configuration examples of the projection optical system 3 mounted on the projector 1. [Example 1] Fig. 3 is a ray diagram of the projection optical system 3A of Example 1. As shown in Fig. 3, the projection optical system 3A is composed of, in order from the reduction side to the enlargement side, a first optical system 31 and a second optical system 32. A first optical axis N of the first optical system 31 and a second optical axis M of the second optical system 32 coincide with each other.

[0022] The first optical system 31 is a refractive optical system having a positive power. The first optical system 31 is made up of a plurality of lenses. Specifically, the first optical system 31 is made up of ten lenses L1 to L10. The lenses L1 to L10 are arranged in this order from the reduction side to the enlargement side. An aperture 51 is arranged between the lenses L4 and L5.

[0023] Lens L1 has positive power. Lens L1 is a meniscus lens. Lens L1 has a concave shape on the reduction side surface and a convex shape on the enlargement side surface. Lens L2 has positive power. Lens L2 is a meniscus lens. Lens L2 has a convex shape on the reduction side surface and a concave shape on the enlargement side surface.

[0024] The lens L3 has a negative power. The lens L3 has a convex shape on the reduction side surface and a concave shape on the enlargement side surface. The lens L4 has a negative power. The lens L4 has a convex shape on both the reduction side and the enlargement side surfaces. The lens L3 and the lens L4 are cemented together to form a cemented lens L21.

[0025] Lens L5 has positive power. Lens L5 has convex shapes on the reduction side and magnification side surfaces. Lens L6 has negative power. Lens L6 has concave shapes on the reduction side and magnification side surfaces. Lens L7 has positive power. Lens L7 has convex shapes on the reduction side and magnification side surfaces. Lens L8 has negative power. Lens L8 is a meniscus lens. Lens L8 has a concave shape on the reduction side surface and a convex shape on the magnification side surface.

[0026] The lens L9 (second lens) has positive power. The lens L9 is a meniscus lens. The lens L9 has a convex shape on the reduction side surface and a concave shape on the enlargement side surface. The lens L9 has a first portion 41 on one side with respect to the first optical axis N and a second portion 42 on the other side. The first portion 41 is a light-transmitting portion that functions as a part of the first optical system 31. More specifically, the first portion 41 is a light-transmitting portion that functions as a refractive lens of the first optical system 31. The second portion 42 is a reflective portion that functions as a second reflective surface 340 described later.

[0027] The lens L10 (first lens) has positive power. The lens L10 is a meniscus lens. The lens L10 has a concave shape on the reduction side surface and a convex shape on the enlargement side surface. The multiple lenses L1 to L10 constituting the first optical system 31 all have shapes that are rotationally symmetric with respect to the first optical axis N of the first optical system 31 as the rotation axis.

[0028] The second optical system 32 has, in the optical path of the light beam emitted from the first optical system 31, a first reflecting optical system 33, a second reflecting optical system 34, and a third reflecting optical system 35, in that order from the first optical system 31. Here, the lens L10 is disposed between the first reflecting optical system 33 and the second reflecting optical system 34, and between the second reflecting optical system 34 and the third reflecting optical system 35, in the first direction Z1.

[0029] The first reflecting optical system 33 is disposed on the enlarged side of the first optical system 31. The first reflecting optical system 33 is located on the lower side Y2 with respect to the second optical axis M. The first reflecting optical system 33 has a first reflecting surface 330 having a concave shape. The first reflecting surface 330 has an aspheric shape.

[0030] The second reflecting optical system 34 is disposed on the optical path on the enlargement side of the first reflecting optical system 33. The second reflecting optical system 34 is located above Y1 with respect to the second optical axis M. The second reflecting optical system 34 has a second reflecting surface 340 having a concave shape. The second reflecting surface 340 is provided on the enlargement side lens surface 420 of the second portion 42 of the lens L9. The second reflecting surface 340 is formed by a reflective coating layer provided on the enlargement side lens surface 420 of the second portion 42.

[0031] The third reflecting optical system 35 is disposed on the optical path on the magnification side of the second reflecting optical system 34. The third reflecting optical system 35 is located above Y1 with respect to the second optical axis M. The third reflecting optical system 35 has a third reflecting surface 350 having a convex shape. The third reflecting surface 350 has an aspheric shape.

[0032] The first reflecting surface 330, the second reflecting surface 340, and the third reflecting surface 350 constituting the second optical system 32 have shapes that are rotationally symmetric with respect to the second optical axis M of the second optical system 32 as the rotation axis.

[0033] Here, the liquid crystal panel 18 forms a projected image in an image forming plane perpendicular to the first optical axis N of the first optical system 31. The liquid crystal panel 18 is disposed at a position offset upward Y1 with respect to the first optical axis N of the first optical system 31. A light ray from the liquid crystal panel 18 passes through the first optical system 31 and the second optical system 32 in this order. Between the first optical system 31 and the second optical system 32, the light ray passes below Y2 of the first optical axis N and heads toward the first reflecting surface 330 of the second optical system 32.

[0034] The light ray that reaches the first reflecting surface 330 crosses the first optical axis N upward Y1 and is reflected toward the second direction Z2 and the upward Y1. The light ray reflected by the first reflecting surface 330 passes through the lens L10 and reaches the second reflecting surface 340. The light ray that reaches the second reflecting surface 340 is reflected toward the first direction Z1 and the upward Y1. The light ray reflected by the second reflecting surface 340 passes through the lens L10 and reaches the third reflecting surface 350. The light ray that reaches the third reflecting surface 350 is reflected toward the second direction Z2 and the upward Y1. The light ray reflected by the third reflecting surface 350 is magnified by the third reflecting surface 350 and reaches the screen S.

[0035] When the F-number of the projection optical system 3A is FNo and the maximum half angle of view of the entire lens system is ω, the data of the projection optical system 3A of the first embodiment is as follows.

[0036] Fno 1.431 ω 80.143°

[0037] The lens data of the projection optical system 3A is as follows. Surface numbers are assigned in order from the reduction side to the enlargement side. The symbols refer to the liquid crystal panel, dichroic prism, lens, first reflecting surface, second reflecting surface, third reflecting surface and screen. R is the radius of curvature. D is the axial surface separation. nd is the refractive index. νd is the Abbe number. Y is the effective radius. The units of R, D and Y are mm.

[0038] Sign Surface No. RD nd vd Mode Y 18 0 0.00000 3.000000 Refraction 19 1 0.00000 25.750000 1.516330 64.14 Refraction 11.623 2 0.00000 3.306682 Refraction 17.017 L01 3 -528.38781 6.000000 1.986125 16.48 Refraction 18.000 4 -53.59618 0.100000 Refraction 18.528 L02 5 36.16025 6.593978 1.913041 28.20 Refraction 18.724 6 102.64785 11.898469 Refraction 17.948 L03 7 360.09349 2.303687 1.986125 16.48 Refraction 14.285 L04 8 23.69596 10.970660 1.486555 77.12 Refraction 13.162 9 -43.41655 31.906933 Refraction 13.000 51,L05 10 39.61222 7.000000 1.611109 57.56 Refraction 13.000 11 -110.42307 14.196605 Refraction 13.255 L06 12 -107.62425 3.384629 1.917513 26.94 Refraction 13.659 13 52.74696 4.002725 Refraction 14.130 L07 14 59.79382 6.739074 1.797855 19.51 Refraction 16.172 15 -64.89773 4.086216 Refraction 16.409 L08 16 -29.85440 6.547540 1.938332 22.41 Refraction 16.368 17 -50.82914 72.919770 Refraction 18.646 L09 18 275.26448 8.000000 1.849076 37.72 Refraction 33.805 19 1396.48188 38.982077 Refraction 34.085 L10 20 -448.48764 19.000000 1.637611 55.29 Refraction 42.321 21 -187.55816 25.392163 Refraction 45.024 330 22* -64.43464 -25.392163 Reflection 47.385 L10 23 -187.55816 -19.000000 1.637611 55.29 Refraction 36.208 24 -448.48764 -38.982077 Refraction 28.586 340 25 1396.48188 38.982077 Reflection 26.127 L10 26 -448.48764 19.000000 1.637611 55.29 Refraction 57.938 27 -187.55816 49.210956 Refraction 64.005 350 28* 53.46671 -155.000000 Reflection 142.233 S 29 0.00000 0.000000 Refraction 1330.358

[0039] The aspheric coefficients are as follows:

[0040] Floor number 22 28 Conic constant 1.051849E-01 -4.789571E+00 4th order coefficient 2.049492E-06 -2.943985E-08 6th order coefficient -4.12751E-10 1.922612E-12 8th order coefficient 2.052322E-13 -8.387132E-17 10th order coefficient -5.492764E-17 2.160308E-21 12th order coefficient 8.652296E-21 -2.42962E-26

[0041] When the focal length of the first reflecting surface 330 of the first reflecting optical system 33 is f1, the focal length of the second reflecting surface 340 of the second reflecting optical system 34 is f2, and the focal length of the third reflecting surface 350 of the third reflecting optical system 35 is f3, the data of the projection optical system 3A of Example 1 is as follows:

[0042] f1 32.217mm f2 698.241mm f3 -26.733mm

[0043] The projection distance of the projection optical system 3A of the first embodiment is as follows.

[0044] Projection distance: 155.000mm

[0045] Here, the projection optical system 3A of this example satisfies the following conditional formula (1), when the focal length of the first reflective optical system is f1, the focal length of the second reflective optical system is f2, and the focal length of the third reflective optical system is f3. |f2|>|f1|>|f3|···(1)

[0046] In this example, |f1| 32.217mm |f2| 698.241mm |f3| 26.733mm Therefore, the projection optical system 3A of this example satisfies conditional expression (1).

[0047] (Action and effect) Since the projection optical system 3A of this example satisfies the conditional expression (1), the projection distance can be shortened. That is, by making the absolute value of the focal length f3 of the third reflecting surface 350 smaller than the absolute value of the focal length f1 of the first reflecting surface 330 and the absolute value of the focal length f2 of the second reflecting surface 340, the angle of view of the light reflected by the third reflecting surface 350 can be greatly widened. This allows the projection distance of the projection optical system 3A to be shortened.

[0048] Moreover, by making the absolute value of the focal length f2 of the second reflecting surface 340 larger than the absolute value of the focal length f1 of the first reflecting surface 330, it becomes easy to widen the angle of the light ray reflected by the second reflecting surface 340. As a result, the third reflecting surface 350 becomes easy to widen the reflection angle of the light ray reflected by the third reflecting surface 350 toward the screen S. If the absolute value of the focal length f2 of the second reflecting surface 340 is made smaller than the absolute value of the focal length f1 of the first reflecting surface 330, the angle of the light ray reflected by the second reflecting surface 340 becomes smaller, and it becomes difficult for the third reflecting surface 350 to widen the angle of view of the light ray reflected by the third reflecting surface 350 toward the screen S. As a result, when the absolute value of the focal length f2 of the second reflecting surface 340 is made smaller than the absolute value of the focal length f1 of the first reflecting surface 330, the projection optical system 3A projects a smaller enlarged image onto the screen S at the same projection distance, which is not preferable compared to when the absolute value of the focal length f2 of the second reflecting surface 340 is made larger than the absolute value of the focal length f1 of the first reflecting surface 330.

[0049] Furthermore, by making the absolute value of the focal length f2 of the second reflecting surface 340 larger than the absolute value of the focal length f1 of the first reflecting surface 330 and the absolute value of the focal length f3 of the third reflecting surface 350, that is, by weakening the power, it is possible to set a well-balanced positive power of the first reflecting surface 330 and a negative power of the third reflecting surface 350. This allows various aberrations to be corrected in a well-balanced manner.

[0050] Here, Example 6 of Japanese Patent Laid-Open Publication No. 2017-40849, which is a prior art document, will be considered as a comparative example. The focal length f1 of the first reflective optical system, the focal length f2 of the second reflective optical system, the focal length f3 of the third reflective optical system, the absolute value of the focal length f1 of the first reflective optical system, the absolute value of the focal length f2 of the second reflective optical system, the absolute value of the focal length f3 of the third reflective optical system, the projection distance, and the maximum half angle of view ω of the entire lens system of the comparative example are as follows:

[0051] f1 29.281mm f2 102.500mm f3 -41.225mm |f1| 29.281mm |f2| 102.500mm |f3| 41.225mm Projection distance: 371.837mm ω 70.2°

[0052] Therefore, the projection optical system of the comparative example does not satisfy the conditional expression (1), and therefore the projection distance of the projection optical system of the comparative example is greater than that of the projection optical system 3A of the present example. Also, the projection optical system of the comparative example has a smaller maximum half angle of view than that of the projection optical system 3A of the present example.

[0053] In this example, the maximum effective radius of the third reflecting surface 350 is smaller than 150 mm. If the maximum effective radius of the third reflecting surface 350 is 150 mm or more, distortion or bending of the third reflecting surface 350 is likely to occur during manufacturing of the third reflecting surface 350, making it difficult to improve the processing accuracy of the third reflecting surface 350. Therefore, in this example, since the maximum effective radius of the third reflecting surface 350 is smaller than 150 mm, the processing accuracy of the third reflecting surface 350 can be improved. This makes it possible to make the enlarged image projected onto the screen S by the projection optical system 3A clear.

[0054] In this example, the lenses include a lens L10 having a positive power arranged on the most enlarged side. The lens L10 is arranged between the first reflecting surface 330 and the second reflecting surface 340 in the first direction Z1 along the first optical axis N of the first optical system 31. The light reflected by the first reflecting surface 330 passes through the lens L10 and reaches the second reflecting surface 340. As a result, the spread and angle of the light reflected by the first reflecting surface 330 can be controlled by the lens L10, so that the on-axis surface distance between the first reflecting surface 330 and the second reflecting surface 340 can be reduced. In addition, the lens L10 can satisfactorily correct various aberrations of the light reflected by the first reflecting surface 330.

[0055] In this example, the lens L10 is disposed between the second reflecting surface 340 and the third reflecting surface 350 in the first direction Z1. The light reflected by the second reflecting surface 340 passes through the lens L10 and reaches the third reflecting surface 350. As a result, the spread and angle of the light reflected by the second reflecting surface 340 can be controlled by the lens L10, so that the on-axis surface distance between the second reflecting surface 340 and the third reflecting surface 350 can be reduced. In addition, the lens L10 can satisfactorily correct various aberrations of the light reflected by the second reflecting surface 340.

[0056] The multiple lenses include a lens L9 disposed on the reduction side relative to the lens L10. The lens L9 has a first portion 41 on one side relative to the first optical axis N and a second portion 42 on the other side. The first portion 41 is a light-transmitting portion that functions as a refractive lens of the first optical system. The second portion 42 is a reflecting portion that functions as the second reflecting surface 340. Thus, since the lens L9 functions both as a refractive lens and as the second reflecting surface 340, it is possible to reduce the number of optical components and simplify the configuration of the projection optical system 3A.

[0057] In this example, the first reflecting surface 330 has an aspheric shape that is a concave surface. The third reflecting surface 350 has an aspheric shape that is a convex surface. Here, the first reflecting surface 330 and the third reflecting surface 350 have stronger power than the second reflecting surface 340, so that the light reflected by the first reflecting surface 330 and the third reflecting surface 350 is more likely to cause various aberrations than the light reflected by the second reflecting surface 340. Therefore, since the first reflecting surface 330 and the third reflecting surface 350 have an aspheric shape, various aberrations occurring in the projection optical system 3A can be corrected well.

[0058] In this example, the multiple lenses L1 to L10 have a rotationally symmetric shape with respect to the first optical axis N. This makes it easy to manufacture each lens of the first optical system 31. Also, it makes it easy to arrange each lens of the first optical system 31 with high precision.

[0059] In this example, the first reflecting surface 330, the second reflecting surface 340, and the third reflecting surface 350 have shapes that are rotationally symmetric with respect to the second optical axis M. This makes it easy to manufacture each reflecting surface of the second optical system 32. It also makes it easy to arrange each reflecting surface of the second optical system 32 with high precision.

[0060] In this example, the first optical axis N coincides with the second optical axis M. This makes it easy to arrange the first optical system 31 and the second optical system 32 with high precision.

[0061] Fig. 4 is a diagram showing the MTF on the enlarged side of the projection optical system 3A. The horizontal axis of Fig. 4 is the spatial frequency, and the vertical axis is the contrast reproduction ratio. As shown in Fig. 4, the projection optical system 3A of this example has high resolution.

[0062] [Example 2] Fig. 5 is a ray diagram of the projection optical system 3B of Example 2. As shown in Fig. 5, the projection optical system 3B is composed of, in order from the reduction side to the enlargement side, a first optical system 31 and a second optical system 32. A first optical axis N of the first optical system 31 and a second optical axis M of the second optical system 32 coincide with each other.

[0063] The first optical system 31 is a refractive optical system having a positive power. The first optical system 31 is made up of a plurality of lenses. Specifically, the first optical system 31 is made up of ten lenses L1 to L10. The lenses L1 to L10 are arranged in this order from the reduction side to the enlargement side. An aperture 51 is arranged between the lenses L4 and L5.

[0064] Lens L1 has positive power. Lens L1 is a meniscus lens. Lens L1 has a concave shape on the reduction side surface and a convex shape on the enlargement side surface. Lens L2 has positive power. Lens L2 is a meniscus lens. Lens L2 has a convex shape on the reduction side surface and a concave shape on the enlargement side surface.

[0065] The lens L3 has a negative power. The lens L3 has a convex shape on the reduction side surface and a concave shape on the enlargement side surface. The lens L4 has a negative power. The lens L4 has a convex shape on both the reduction side and the enlargement side surfaces. The lens L3 and the lens L4 are cemented together to form a cemented lens L21.

[0066] Lens L5 has positive power. Lens L5 has convex shapes on the reduction side and the enlargement side surfaces. Lens L6 has negative power. Lens L6 has concave shapes on the reduction side and the enlargement side surfaces. Lens L7 has positive power. Lens L7 has convex shapes on the reduction side and the enlargement side surfaces.

[0067] Lens L8 has negative power. Lens L8 is a meniscus lens. Lens L8 has a concave shape on the reduction side surface and a convex shape on the enlargement side surface. Lens L9 (second lens) has positive power. Lens L9 is a meniscus lens. Lens L9 has a concave shape on the reduction side surface and a convex shape on the enlargement side surface.

[0068] The lens L10 (first lens) has positive power. The lens L10 is a meniscus lens. The lens L10 has a concave shape on the reduction side surface and a convex shape on the enlargement side surface. The multiple lenses L1 to L10 constituting the first optical system 31 all have shapes that are rotationally symmetric with respect to the first optical axis N of the first optical system 31 as the rotation axis.

[0069] The second optical system 32 has, in the optical path of the light beam emitted from the first optical system 31, a first reflecting optical system 33, a second reflecting optical system 34, and a third reflecting optical system 35, in that order from the first optical system 31. Here, the lens L10 is disposed between the first reflecting optical system 33 and the second reflecting optical system 34, and between the second reflecting optical system 34 and the third reflecting optical system 35, in the first direction Z1.

[0070] The first reflecting optical system 33 is disposed on the enlarged side of the first optical system 31. The first reflecting optical system 33 is located on the lower side Y2 with respect to the second optical axis M. The first reflecting optical system 33 has a first reflecting surface 330 having a concave shape. The first reflecting surface 330 has an aspheric shape.

[0071] The second reflecting optical system 34 is disposed on the optical path on the enlarged side of the first reflecting optical system 33. The second reflecting optical system 34 is located above Y1 with respect to the second optical axis M. The second reflecting optical system 34 has a second reflecting surface 340 having a planar shape. The second reflecting surface 340 is disposed between the lens L9 and the lens L10 in the first direction Z1.

[0072] The third reflecting optical system 35 is disposed on the optical path on the magnification side of the second reflecting optical system 34. The third reflecting optical system 35 is located above Y1 with respect to the second optical axis M. The third reflecting optical system 35 has a third reflecting surface 350 having a convex shape. The third reflecting surface 350 has an aspheric shape.

[0073] The first reflecting surface 330, the second reflecting surface 340, and the third reflecting surface 350 constituting the second optical system 32 have shapes that are rotationally symmetric with respect to the second optical axis M of the second optical system 32 as the rotation axis.

[0074] A light ray from the liquid crystal panel 18 passes through the first optical system 31 and the second optical system 32 in this order. Between the first optical system 31 and the second optical system 32, the light ray passes below Y2 of the first optical axis N and heads toward the first reflecting surface 330 of the second optical system 32.

[0075] The light ray that reaches the first reflecting surface 330 crosses the first optical axis N upward Y1 and is reflected toward the second direction Z2 and the upward Y1. The light ray reflected by the first reflecting surface 330 passes through the lens L10 and reaches the second reflecting surface 340. The light ray that reaches the second reflecting surface 340 is reflected toward the first direction Z1 and the upward Y1. The light ray reflected by the second reflecting surface 340 passes through the lens L10 and reaches the third reflecting surface 350. The light ray that reaches the third reflecting surface 350 is reflected toward the second direction Z2 and the upward Y1. The light ray reflected by the third reflecting surface 350 is magnified by the third reflecting surface 350 and reaches the screen S.

[0076] When the F-number of the projection optical system 3B is FNo and the maximum half angle of view of the entire lens system is ω, the data of the projection optical system 3B of the second embodiment is as follows.

[0077] Fno 1.429 ω 80.182°

[0078] The lens data of the projection optical system 3B is as follows. Surface numbers are assigned in order from the reduction side to the enlargement side. The symbols refer to the liquid crystal panel, dichroic prism, lens, first reflecting surface, second reflecting surface, third reflecting surface and screen. R is the radius of curvature. D is the axial surface separation. nd is the refractive index. νd is the Abbe number. Y is the effective radius. The units of R, D and Y are mm.

[0079] Sign Surface No. RD nd vd Mode Y 18 0 0.00000 3.000000 Refraction 19 1 0.00000 25.750000 1.516330 64.14 Refraction 11.623 2 0.00000 3.648092 Refraction 17.017 L01 3 -250.28858 6.000000 1.986125 16.48 Refraction 18.000 4 -49.21333 0.100000 Refraction 18.588 L02 5 33.51972 8.000000 1.927010 24.64 Refraction 18.513 6 86.85688 9.357735 Refraction 17.288 L03 7 434.14453 2.126957 1.986125 16.48 Refraction 14.319 L04 8 22.97156 11.390743 1.459223 85.62 Refraction 13.131 9 -38.15519 27.987780 Refraction 13.000 51,L05 10 39.00070 7.000000 1.673378 52.73 Refraction 13.000 11 -113.64727 15.328936 Refraction 13.202 L06 12 -54.49192 4.372790 1.930507 23.90 Refraction 13.281 13 58.30287 4.000000 Refraction 14.243 L07 14 79.10658 7.000000 1.843691 18.54 Refraction 16.577 15 -52.92728 4.530482 Refraction 16.976 L08 16 -27.26682 7.589622 1.986125 16.48 Refraction 17.000 17 -39.01552 64.695899 Refraction 20.038 L09 18 -118.25109 8.000000 1.903700 31.30 Refraction 32.090 19 -94.77445 37.635425 Refraction 33.538 L10 20 -442.36880 19.000000 1.804198 46.50 Refraction 42.522 21 -188.49008 30.169182 Refraction 45.241 330 22* -65.57949 -30.169182 Reflection 47.982 L10 23 -188.49008 -19.000000 1.804198 46.50 Refraction 33.939 24 -442.36880 -35.635425 Refraction 26.789 340 25 0.00000 35.635425 Reflection 26.903 L10 26 -442.36880 19.000000 1.804198 46.50 Refraction 58.075 27 -188.49008 51.551139 Refraction 63.986 350 28* 52.78429 -155.000000 Reflection 144.673 S 29 0.00000 0.000000 Refraction 1330.167

[0080] The aspheric coefficients are as follows:

[0081] Floor number 22 28 Conic constant 1.061689E-01 -4.787871E+00 4th order coefficient 2.073994E-06 -2.904389E-08 6th order coefficient -4.391544E-10 1.909389E-12 8th order coefficient 1.949004E-13 -8.308591E-17 10th order coefficient -4.812829E-17 2.11295E-21 12th order coefficient 7.116146E-21 -2.328039E-26

[0082] When the focal length of the first reflecting surface 330 of the first reflecting optical system 33 is f1, the focal length of the second reflecting surface 340 of the second reflecting optical system 34 is f2, and the focal length of the third reflecting surface 350 of the third reflecting optical system 35 is f3, the data of the projection optical system 3B of Example 2 is as follows:

[0083] f1 32.790mm f2∞mm f3 -26.392mm

[0084] The projection distance of the projection optical system 3B of the second embodiment is as follows.

[0085] Projection distance: 155.000mm

[0086] Here, the projection optical system 3B of this example satisfies the following conditional formula (1), when the focal length of the first reflective optical system is f1, the focal length of the second reflective optical system is f2, and the focal length of the third reflective optical system is f3. |f2|>|f1|>|f3|···(1)

[0087] In this example, |f1| 32.790mm |f2|∞mm |f3| 26.392mm Therefore, the projection optical system 3B of this example satisfies conditional expression (1).

[0088] (Action and effect) In this example, the multiple lenses L1 to L10 include a lens L9 that is disposed on the reduction side relative to the lens L10. The second reflecting surface 340 is disposed between the lenses L9 and L10 in the first direction Z1. Therefore, compared to a case in which the second reflecting surface 340 is provided on the enlargement side lens surface of the lens L9, it is easier to align the second reflecting surface 340 when incorporating the projection optical system 3B into the projector 1. In addition, the second reflecting surface 340 has a planar shape. Therefore, the second reflecting surface 340 is easier to manufacture.

[0089] Since the projection optical system 3B of this example satisfies the conditional expression (1), it is possible to obtain the same effect as the projection optical system 3A of the embodiment 1. Fig. 6 is a diagram showing the MTF on the enlargement side of the projection optical system 3B. As shown in Fig. 6, the projection optical system 3B of this example has high resolution.

[0090] [Example 3] Fig. 7 is a ray diagram of a projection optical system 3C of Example 3. As shown in Fig. 7, the projection optical system 3C is composed of, in order from the reduction side to the enlargement side, a first optical system 31 and a second optical system 32. A first optical axis N of the first optical system 31 and a second optical axis M of the second optical system 32 coincide with each other.

[0091] The first optical system 31 is a refractive optical system having a positive power. The first optical system 31 is made up of a plurality of lenses. Specifically, the first optical system 31 is made up of ten lenses L1 to L10. The lenses L1 to L10 are arranged in this order from the reduction side to the enlargement side. An aperture 51 is arranged between the lenses L4 and L5.

[0092] Lens L1 has positive power. Lens L1 is a meniscus lens. Lens L1 has a concave shape on the reduction side surface and a convex shape on the enlargement side surface. Lens L2 has positive power. Lens L2 has convex shapes on both the reduction side and the enlargement side surfaces.

[0093] The lens L3 has a negative power. The lens L3 has a concave shape on the reduction side and the enlargement side. The lens L4 has a positive power. The lens L4 has a convex shape on the reduction side and the enlargement side. The lens L3 and the lens L4 are cemented together to form a cemented lens L21.

[0094] Lens L5 has positive power. Lens L5 has convex shapes on the reduction side and magnification side surfaces. Lens L6 has negative power. Lens L6 has a concave shape on the reduction side surface and a convex shape on the magnification side surface. Lens L7 has positive power. Lens L7 has convex shapes on the reduction side and magnification side surfaces. Lens L8 has negative power. Lens L8 is a meniscus lens. Lens L8 has a concave shape on the reduction side surface and a convex shape on the magnification side surface.

[0095] The lens L9 (second lens) has a positive power. The lens L9 is a meniscus lens. The lens L9 has a convex shape on the reduction side surface and a concave shape on the enlargement side surface. The lens L9 has an aspheric shape on the enlargement side surface. The lens L9 has a first portion 41 on one side with respect to the first optical axis N and a second portion 42 on the other side. The first portion 41 is a light-transmitting portion that functions as a part of the first optical system 31. More specifically, the first portion 41 is a light-transmitting portion that functions as a refractive lens of the first optical system 31. The second portion 42 is a reflecting portion that functions as the second reflecting surface 340.

[0096] The lens L10 (first lens) has positive power. The lens L10 is a meniscus lens. The lens L10 has a concave shape on the reduction side surface and a convex shape on the enlargement side surface. The multiple lenses L1 to L10 constituting the first optical system 31 all have shapes that are rotationally symmetric with respect to the first optical axis N of the first optical system 31 as the rotation axis.

[0097] The second optical system 32 has, in the optical path of the light beam emitted from the first optical system 31, a first reflecting optical system 33, a second reflecting optical system 34, and a third reflecting optical system 35, in that order from the first optical system 31. Here, the lens L10 is disposed between the first reflecting optical system 33 and the second reflecting optical system 34, and between the second reflecting optical system 34 and the third reflecting optical system 35, in the first direction Z1.

[0098] The first reflecting optical system 33 is disposed on the enlarged side of the first optical system 31. The first reflecting optical system 33 is located on the lower side Y2 with respect to the second optical axis M. The first reflecting optical system 33 has a first reflecting surface 330 having a concave shape. The first reflecting surface 330 has an aspheric shape.

[0099] The second reflecting optical system 34 is disposed on the optical path on the enlargement side of the first reflecting optical system 33. The second reflecting optical system 34 is located above Y1 with respect to the second optical axis M. The second reflecting optical system 34 has a second reflecting surface 340 having a concave shape. The second reflecting surface 340 is provided on the enlargement side lens surface 420 of the second portion 42 of the lens L9. Therefore, the second reflecting surface 340 has an aspheric shape. The second reflecting surface 340 is formed by a reflective coating layer provided on the enlargement side lens surface 420 of the second portion 42.

[0100] The third reflecting optical system 35 is disposed on the optical path on the magnification side of the second reflecting optical system 34. The third reflecting optical system 35 is located above Y1 with respect to the second optical axis M. The third reflecting optical system 35 has a third reflecting surface 350 having a convex shape. The third reflecting surface 350 has an aspheric shape.

[0101] The first reflecting surface 330, the second reflecting surface 340, and the third reflecting surface 350 constituting the second optical system 32 have shapes that are rotationally symmetric with respect to the second optical axis M of the second optical system 32 as the rotation axis.

[0102] A light ray from the liquid crystal panel 18 passes through the first optical system 31 and the second optical system 32 in this order. Between the first optical system 31 and the second optical system 32, the light ray passes below Y2 of the first optical axis N and heads toward the first reflecting surface 330 of the second optical system 32.

[0103] The light ray that reaches the first reflecting surface 330 crosses the first optical axis N upward Y1 and is reflected toward the second direction Z2 and the upward Y1. The light ray reflected by the first reflecting surface 330 passes through the lens L10 and reaches the second reflecting surface 340. The light ray that reaches the second reflecting surface 340 is reflected toward the first direction Z1 and the upward Y1. The light ray reflected by the second reflecting surface 340 passes through the lens L10 and reaches the third reflecting surface 350. The light ray that reaches the third reflecting surface 350 is reflected toward the second direction Z2 and the upward Y1. The light ray reflected by the third reflecting surface 350 is magnified by the third reflecting surface 350 and reaches the screen S.

[0104] When the F-number of the projection optical system 3C is FNo and the maximum half angle of view of the entire lens system is ω, the data of the projection optical system 3C of the third embodiment is as follows.

[0105] Fno 1.433 ω 80.457°

[0106] The lens data for the projection optical system 3C is as follows. Surface numbers are assigned in order from the reduction side to the enlargement side. The symbols refer to the liquid crystal panel, dichroic prism, lens, first reflecting surface, second reflecting surface, third reflecting surface and screen. R is the radius of curvature. D is the axial surface separation. nd is the refractive index. νd is the Abbe number. Y is the effective radius. The units for R, D and Y are mm.

[0107] Sign Surface No. RD nd vd Mode Y 18 0 0.00000 3.000000 Refraction 19 1 0.00000 25.750000 1.516330 64.14 Refraction 11.623 2 0.00000 5.500921 Refraction 17.017 L01 3 -66.02661 6.000000 1.903658 31.32 Refraction 18.000 4 -35.31143 0.100000 Refraction 18.985 L02 5 42.65748 8.000000 1.969346 18.11 Refraction 19.852 6 -1169.06825 13.341182 Refraction 19.225 L03 7 -63.97830 2.000000 1.986125 16.48 Refraction 13.489 L04 8 33.87145 10.217155 1.472590 81.12 Refraction 12.901 9 -33.17772 18.422090 Refraction 13.000 51,L05 10 39.23909 7.000000 1.438022 94.60 Refraction 13.000 11 -117.65820 32.866322 Refraction 13.532 L06 12 -28.56052 6.702939 1.882780 33.40 Refraction 17.426 13 -47.97692 14.148390 Refraction 20.704 L07 14 129.72400 7.000000 1.982136 16.81 Refraction 28.569 15 -362.02294 9.107801 Refraction 28.703 L08 16 -55.17402 6.921911 1.986125 16.48 Refraction 28.746 17 -71.36157 67.992188 Refraction 31.120 L09 18 289.04180 8.000000 1.986125 16.48 Refraction 41.451 19* 461.29891 20.572641 Refraction 41.403 L10 20 -241.32846 19.000000 1.448364 89.89 Refraction 41.926 21 -135.63243 60.926881 Refraction 43.245 330 22* -64.15676 -60.926881 Reflection 48.611 L10 23 -135.63243 -19.000000 1.448364 89.89 Refraction 19.080 24 -241.32846 -20.572641 Refraction 26.092 340 25* 461.29891 20.572641 Reflection 42.654 L10 26 -241.32846 19.000000 1.448364 89.89 Refraction 53.351 27 -135.63243 48.356460 Refraction 59.878 350 28* 53.00842 -155.000000 Reflection 138.968 S 29 0.00000 0.000000 Refraction 1330.080

[0108] The aspheric coefficients are as follows:

[0109] Floor number 19 22 25 28 Conic constant 6.166722E+01 3.383186E-02 6.166722E+01 -4.559562E+00 4th order coefficient -3.115222E-07 1.809685E-06 -3.115222E-07 -3.095255E-08 6th order coefficient 5.312844E-11 -3.658264E-10 5.312844E-11 1.835285E-12 8th order coefficient -1.756324E-14 2.037076E-13 -1.756324E-14 -7.421759E-17 10th order coefficient -5.418827E-17 1.78666E-21 12th order coefficient 7.93418E-21 -1.910778E-26

[0110] When the focal length of the first reflecting surface 330 of the first reflecting optical system 33 is f1, the focal length of the second reflecting surface 340 of the second reflecting optical system 34 is f2, and the focal length of the third reflecting surface 350 of the third reflecting optical system 35 is f3, the data of the projection optical system 3C of Example 3 is as follows:

[0111] f1 32.078mm f2 230.649mm f3 -26.504mm

[0112] The projection distance of the projection optical system 3C of the third embodiment is as follows.

[0113] Projection distance: 155.000mm

[0114] Here, the projection optical system 3C of this example satisfies the following conditional formula (1), when the focal length of the first reflective optical system is f1, the focal length of the second reflective optical system is f2, and the focal length of the third reflective optical system is f3. |f2|>|f1|>|f3|···(1)

[0115] In this example, |f1| 32.078mm |f2| 230.649mm |f3| 26.504mm Therefore, the projection optical system 3C of this example satisfies conditional expression (1).

[0116] (Action and effect) In this example, the second reflecting surface 340 has an aspheric shape, which makes it possible to more effectively correct various aberrations that occur in the projection optical system 3C.

[0117] The projection optical system 3C of this example satisfies the conditional expression (1), and therefore can obtain the same effects as the projection optical system 3A of the first embodiment. Fig. 8 is a diagram showing the MTF of the enlargement side of the projection optical system 3C. As shown in Fig. 8, the projection optical system 3C of this example has high resolution.

[0118] [Other Examples] In the above embodiment, the first reflecting surface 330 and the third reflecting surface 350 are described as separate members, but the first reflecting surface 330 and the third reflecting surface 350 may be provided on a single member.

[0119] [Summary of this disclosure] The following is a summary of this disclosure.

[0120] (Appendix 1) The optical system includes, in order from the reduction side to the enlargement side, a first optical system and a second optical system each of which is made up of a plurality of lenses; the first optical system has a positive power, the second optical system has, on an optical path of a light beam emitted from the first optical system, a first reflecting optical system, a second reflecting optical system, and a third reflecting optical system, in this order from the first optical system; the first reflecting optical system has a first reflecting surface having a concave aspheric shape; the second reflecting optical system has a second reflecting surface having a concave shape or a planar shape; the third reflecting optical system has a third reflecting surface having an aspheric shape that is a convex surface, A projection optical system characterized in that, when the focal length of the first reflective optical system is f1, the focal length of the second reflective optical system is f2, and the focal length of the third reflective optical system is f3, the projection optical system satisfies the following conditional formula (1): |f2|>|f1|>|f3|···(1)

[0121] As a result, the projection optical system 3 satisfies conditional expression (1), and the projection distance can be shortened. That is, by making the absolute value of the focal length f3 of the third reflecting surface smaller than the absolute value of the focal length f1 of the first reflecting surface and the absolute value of the focal length f2 of the second reflecting surface 340, the reflection angle of the light beam at the third reflecting surface can be increased, and the projection distance of the projection optical system can be shortened.

[0122] (Appendix 2) 2. The projection optical system according to claim 1, wherein the third reflecting surface has a maximum effective radius of less than 150 mm.

[0123] This allows the processing precision of the third reflecting surface to be increased, thereby making it possible to sharpen the enlarged image projected onto the screen by the projection optical system.

[0124] (Appendix 3) the plurality of lenses includes a first lens having a positive power and disposed on the most magnifying side; the first lens is disposed between the first reflecting optical system and the second reflecting optical system in a first direction along a first optical axis of the first optical system, 3. The projection optical system described in claim 1 or 2, wherein the light reflected by the first reflecting optical system passes through the first lens and reaches the second reflecting optical system.

[0125] As a result, the spread and angle of the light reflected by the first reflecting surface can be controlled by the first lens, so that the on-axis surface distance between the first reflecting surface and the second reflecting surface can be reduced. Also, the first lens can satisfactorily correct various aberrations of the light reflected by the first reflecting surface.

[0126] (Appendix 4) the first lens is disposed between the second reflecting optical system and the third reflecting optical system in the first direction, The projection optical system described in Appendix 3, wherein the light reflected by the second reflecting optical system passes through the first lens and reaches the third reflecting optical system.

[0127] As a result, the spread and angle of the light reflected by the second reflecting surface can be controlled by the first lens, so that the on-axis surface distance between the second reflecting surface and the third reflecting surface can be reduced. Also, the first lens can satisfactorily correct various aberrations of the light reflected by the second reflecting surface.

[0128] (Appendix 5) the plurality of lenses includes a second lens disposed on a reduction side relative to the first lens, the second lens has a first portion on one side with respect to the first optical axis and a second portion on the other side with respect to the first optical axis, the first portion is a light-transmitting portion that functions as a part of the first optical system, 5. The projection optical system according to claim 3, wherein the second portion is a reflective portion that functions as the second reflective surface.

[0129] With this, the second lens functions both as a refractive lens and as the second reflecting surface, so that the number of optical components can be reduced and the configuration of the projection optical system 3 can be simplified.

[0130] (Appendix 6) the plurality of lenses includes a second lens disposed on a reduction side relative to the first lens, 5. The projection optical system according to claim 3, wherein the second reflecting surface is disposed between the first lens and the second lens in the first direction.

[0131] Therefore, compared to the case where the second reflecting surface is provided on the second lens, alignment of the second reflecting surface can be facilitated when disposing the second reflecting surface in the projection optical system.

[0132] (Appendix 7) 7. The projection optical system according to claim 3, wherein the plurality of lenses have a rotationally symmetric shape with the first optical axis as a rotation axis.

[0133] This makes it easier to manufacture each lens of the first optical system, and also makes it easier to position each lens of the first optical system with high precision.

[0134] (Appendix 8) The projection optical system described in Appendix 7, characterized in that the first reflecting surface, the second reflecting surface, and the third reflecting surface have rotationally symmetric shapes with the second optical axis of the second optical system as the rotation axis.

[0135] This makes it easier to manufacture each of the reflecting surfaces of the second optical system, and also makes it easier to position each of the reflecting surfaces of the second optical system with high precision.

[0136] (Appendix 9) 9. The projection optical system according to claim 8, wherein the first optical axis and the second optical axis coincide with each other.

[0137] This makes it easy to arrange the first optical system and the second optical system with high precision.

[0138] (Appendix 10) A projection optical system according to any one of claims 1 to 9; an image forming unit that forms a projection image on a reduction-side image forming plane of the projection optical system; A projector comprising: [Explanation of symbols]

[0139] 1...projector, 2...image forming section, 3, 3A, 3B, 3C...projection optical system, 4...control section, 6...image processing section, 7...display driving section, 10...light source, 11...integrator lens, 12...integrator lens, 13...polarization conversion element, 14...superimposing lens, 15...dichroic mirror, 16...reflection mirror, 17R...field lens, 17G...field lens, 17B...field lens, 18 (18B, 18R, 18G)...liquid crystal panel, 19...cross dichroic prism , 21... dichroic mirror, 22... relay lens, 23... reflective mirror, 24... relay lens, 25... reflective mirror, 31... first optical system, 32... second optical system, 33... first reflective optical system, 34... second reflective optical system, 35... third reflective optical system, 41... first part, 42... second part, 51... aperture stop, 330... first reflective surface, 340... second reflective surface, 350... third reflective surface, 420... enlargement side lens surface, L1 to L10... lenses, L21... cemented lens, N... first optical axis, M... second optical axis, S... screen.

Claims

1. The optical system includes, in order from the reduction side to the enlargement side, a first optical system and a second optical system each including a plurality of lenses; the first optical system has a positive power, the second optical system includes, in order from the first optical system, a first reflective optical system, a second reflective optical system, and a third reflective optical system on an optical path of a light beam emitted from the first optical system, the first reflecting optical system has a first reflecting surface having a concave aspheric shape; the second reflecting optical system has a second reflecting surface having a concave shape or a planar shape; the third reflecting optical system has a third reflecting surface having an aspheric shape that is a convex surface, A projection optical system characterized in that, when the focal length of the first reflective optical system is f1, the focal length of the second reflective optical system is f2, and the focal length of the third reflective optical system is f3, the projection optical system satisfies the following conditional formula (1): |f2|>|f1|>|f3|...(1)

2. 2. The projection optical system according to claim 1, wherein the third reflecting surface has a maximum effective radius smaller than 150 mm.

3. the plurality of lenses includes a first lens having a positive power and disposed on the most magnifying side; the first lens is disposed between the first reflecting optical system and the second reflecting optical system in a first direction along a first optical axis of the first optical system, 2. The projection optical system according to claim 1, wherein the light reflected by the first reflecting optical system passes through the first lens and reaches the second reflecting optical system.

4. the first lens is disposed between the second reflecting optical system and the third reflecting optical system in the first direction, 4. The projection optical system according to claim 3, wherein the light reflected by the second reflecting optical system passes through the first lens and reaches the third reflecting optical system.

5. the plurality of lenses includes a second lens disposed on a reduction side relative to the first lens, the second lens has a first portion on one side with respect to the first optical axis and a second portion on the other side with respect to the first optical axis, the first portion is a light-transmitting portion that functions as a part of the first optical system, The projection optical system according to claim 3 , wherein the second portion is a reflective portion that functions as the second reflective surface.

6. the plurality of lenses includes a second lens disposed on a reduction side relative to the first lens, The projection optical system according to claim 3 , wherein the second reflecting surface is disposed between the first lens and the second lens in the first direction.

7. The projection optical system according to claim 3 , wherein the plurality of lenses have a shape that is rotationally symmetric with respect to the first optical axis as a rotation axis.

8. The projection optical system according to claim 7 , wherein the first reflecting surface, the second reflecting surface, and the third reflecting surface have shapes that are rotationally symmetric with respect to a second optical axis of the second optical system.

9. The projection optical system according to claim 8 , wherein the first optical axis and the second optical axis coincide with each other.

10. A projection optical system according to any one of claims 1 to 9; an image forming unit that forms a projection image on a reduction-side image forming plane of the projection optical system; A projector comprising:

Images