Projection optics and projectors

Abstract

To provide a projection optical system that can prevent the occurrence of chromatic aberration of magnification despite a wider angle.SOLUTION: A projection optical system has a first lens group, an aperture stop, and a second lens group. The projection optical system is telecentric on a reduction side of the second lens group. The first lens group includes a first sub lens group having a negative power, and a second sub lens group having a positive power. An air gap larger than the air gap between the other adjacent lenses is provided between a lens located on the most reduction side of the first sub lens group and a lens located on the most enlargement side of the second sub lens group. A lens located on the most reduction side in the first lens group is a positive lens. A cemented lens of the second lens group is composed of, in order from the enlargement side toward the reduction side, a first lens having a negative power, a second lens having a positive power, and a third lens having a negative power. When the maximum half angle of view of the entire lens system is defined as ω, the following conditional formula (1) is satisfied. (1) ω>40.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 including a projection optical system capable of wide-angle projection with a half angle exceeding 40° is described in Patent Document 1. The projection optical system of this document includes, in order from the magnification side to the reduction side, a first lens group having a negative power and a second lens group having a positive power. The first lens group includes, in order from the magnification side to the reduction side, a first lens made of an aspherical lens, a second lens, a third lens made of a negative meniscus lens with a concave surface facing the reduction side, and a first cemented lens. The first cemented lens includes, from the magnification side to the reduction side, a fourth lens made of a negative lens with a concave surface facing the reduction side, a fifth lens made of a biconvex lens, and a sixth lens made of a negative lens with a concave surface facing the magnification side.

[0003] The second lens group includes, from the magnification side to the reduction side, a seventh lens made of a positive lens, an aperture stop, an eighth lens made of a negative lens, a second cemented lens, a twelfth lens made of an aspherical lens, a third cemented lens, and a sixteenth lens made of a biconvex lens. The second cemented lens includes, from the magnification side to the reduction side, a ninth lens made of a positive lens, a tenth lens made of a biconcave lens, and an eleventh lens made of a positive lens. The third cemented lens includes a thirteenth lens made of a positive lens, a fourteenth lens made of a biconcave lens, and a fifteenth lens made of a positive lens.

[0004] In the projection optical system of Patent Document 1, the seventh lens is located next to the magnification side of the aperture stop. Also, the air interval between the seventh lens and the sixth lens is wide compared to the air intervals between other adjacent lenses.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] The projection optical system of Patent Document 1 has the widest air gap between the seventh lens and the sixth lens. The seventh lens is a positive lens and is located next to the magnifying side of the aperture diaphragm. Therefore, in the projection optical system, the positive power of the seventh lens can be made relatively small, and the light beam emitted from the seventh lens and reaching the sixth lens can be spread out. Thus, in the projection optical system, it is easy to project the light ray from the seventh lens by magnifying it at each image height using the first to sixth lenses located on its magnifying side. However, in a projection optical system like that of Patent Document 1, where the widest air gap is located on the magnifying side of the positive lens located next to the magnifying side of the aperture diaphragm, chromatic aberration is likely to occur in the positive lens. [Means for solving the problem]

[0007] To solve the above problems, the projection optical system of the present invention comprises, in order from the magnification side to the reduction side, a first lens group having refractive power, an aperture diaphragm, and a second lens group having refractive power, and the reduction side from the second lens group is telecentric, and the first lens group comprises, in order from the magnification side to the reduction side, a first sub-lens group having negative power and a second sub-lens group having positive power, and there is an air gap between the lens located on the reduction side of the first sub-lens group and the lens located on the magnification side of the second sub-lens group that is wider than the air gap between other adjacent lenses, and the lens located on the reduction side of the first lens group is a positive lens, and the second lens group comprises a cemented lens, and the cemented lens comprises, in order from the magnification side to the reduction side, a first lens having negative power, a second lens having positive power, and a third lens having negative power, and the maximum half-angle of view of the entire lens system is ω, and the following condition (1) is satisfied. ω > 40 (1) Furthermore, the projection optical system of the present invention comprises, in order from the magnification side to the reduction side, a first lens group having refractive power, an aperture diaphragm, and a second lens group having refractive power, and the reduction side from the second lens group is telecentric, and the first lens group comprises, in order from the magnification side to the reduction side, a first sub-lens group having negative power and a second sub-lens group having positive power, and the air gap between the lens located on the reduction side of the first sub-lens group and the lens located on the magnification side of the second sub-lens group is greater than the air gap between other adjacent lenses. A wide air gap is provided, the lens located furthest to the reduction side in the first lens group is a positive lens, the second lens group comprises a cemented lens, the cemented lens consists of a first lens with negative power, a second lens with positive power, and a third lens with negative power, in order from the enlargement side to the reduction side, and if the maximum half-angle of view of the entire lens system is ω, the following condition (1) is satisfied, and the cemented lens comprises a fourth lens cemented to the reduction side of the third lens, the fourth lens having positive power. ω > 40 (1)

[0008] Next, the projector of the present invention is characterized by having the above-mentioned projection optical system and an image forming element that forms a projected image on the reduction-side conjugate surface of the projection optical system. [Brief explanation of the drawing]

[0009] [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] This is a ray diagram of the projection optical system of Example 3. [Figure 8] This figure shows the longitudinal aberration, astigmatism, and distortion of Example 3. [Figure 9] This is a ray diagram of the projection optical system of Example 4. [Figure 10] This figure shows the longitudinal aberration, astigmatism, and distortion of Example 4. [Figure 11] This is a ray diagram of the projection optical system of Example 5. [Figure 12] This figure shows the longitudinal aberration, astigmatism, and distortion of Example 5. [Figure 13] This is a ray diagram of the projection optical system of Example 6. [Figure 14] This figure shows the longitudinal aberration, astigmatism, and distortion of Example 6. [Figure 15] This is a ray diagram of the projection optical system of Example 7. [Figure 16] This figure shows the longitudinal aberration, astigmatism, and distortion of Example 7.

Best Mode for Carrying Out the Invention

[0010] <000008?Hereinafter, an optical system and a projector according to an embodiment of the present invention will be described with reference to the drawings.

[0011] (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 an enlarged image onto the screen S, and a control unit 4 that controls the operation of the image forming unit 2.

[0012] (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 in the vicinity of each lens element of the second integrator lens 12.

[0013] The polarization conversion element 13 converts the light from the second integrator lens 12 into predetermined linearly polarized light. The superimposing lens 14 superimposes the images of the respective lens elements of the first integrator lens 11 on the display regions of a liquid crystal panel 18R, a liquid crystal panel 18 G, and a liquid crystal panel 18B via the second integrator lens 12.

[0014] The image forming unit 2 also includes a first dichroic mirror 15, a reflective mirror 16, a field lens 17R, and a liquid crystal panel 18R. The first dichroic mirror 15 reflects red light, which is part of the light rays incident from the superimposed lens 14, and transmits green light and blue light, which are also parts of the light rays incident from the superimposed lens 14. The red light reflected by the first dichroic mirror 15 passes through the reflective mirror 16 and the field lens 17R and enters the liquid crystal panel 18R. The liquid crystal panel 18R is an image forming element. The liquid crystal panel 18R modulates the red light according to the image signal to form a red projected image.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] The projection optical system 3 projects the combined image from the cross dichroic prism 19 onto the screen S, enlarging it as it is.

[0019] 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.

[0020] 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.

[0021] (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.

[0022] 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.

[0023] 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.

[0024] Below, we will describe Examples 1 to 7 as configurations of the projection optical system 3 installed in the projector 1.

[0025] (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.

[0026] The first lens group 31 comprises, in order from the magnification side to the reduction side, a first sub-lens group 33 having negative power and a second sub-lens group 34 having positive power.

[0027] The first sub-lens group 33 comprises two lenses, L1 and L2. Lenses L1 and L2 are arranged in this order from the magnification side to the reduction side.

[0028] 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.

[0029] The second sub-lens group 34 comprises one lens L3. Lens L3 has positive power. Lens L3 has a convex shape on its magnifying and reducing surfaces.

[0030] The second lens group 32 comprises five lenses L4 to L8. Lenses L4 to L8 are arranged in this order from the magnification side to the reduction side.

[0031] Lenses L4 (first lens), L5 (second lens), and L6 (third lens) are joined together to form a cemented lens L21. Lens L4 has negative power. Lens L4 has concave shapes on its magnifying and reducing surfaces. Lens L5 has positive power. Lens L5 has convex shapes on its magnifying and reducing surfaces. Lens L6 has negative power. Lens L6 is a meniscus lens. Lens L6 has a concave shape on its magnifying surface and a convex shape on its reducing surface. The cemented lens L21 has negative power.

[0032] 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.

[0033] Lens L8 (the reducing lens) has positive power. Lens L8 has a convex shape on both the magnifying and reducing surfaces. Lens L8 has an aspherical shape on both sides.

[0034] Lens L1 is made of resin. Lenses L2 through L8 are made of glass.

[0035] In the projection optical system 3A, the projection from lens L8 towards the reduction side is telecentric. Telecentric projection from the reduction side means that the central ray of each light beam passing between lens L8 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.

[0036] A first air gap G1, wider than the air gap between other adjacent lenses, is provided between the lens L2 located on the most reduced side of the first sub-lens group 33 and the lens L3 located on the most enlarged side of the second sub-lens group 34.

[0037] 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 L8 is L, the back focus is BF, the maximum half-angle of view of the entire lens system is ω, the distance from the optical axis N to the maximum image height of the projected image formed by the liquid crystal panel 18 is YIM, the focal length of the entire lens system is F, the power of the entire lens system is P, the focal length of lens L1 is Fls, the focal length of lens L8 is Flf, the power of lens L4 in air is Pc1, the Abbe number of lens L4 is Vc1, the power of lens L5 in air is Pc2, the Abbe number of lens L5 is Vc2, the power of lens L6 in air is Pc3, the Abbe number of lens L6 is Vc3, and the focal length of lens L3 is Flp, the data for the projection optical system 3A of Example 1 is as follows. Note that the power of the lens in air refers to the power of the lens alone before it is joined to form a cemented lens.

[0038] Fno 2.011 TTL 94.125mm L 65,000mm Bf 29.125mm ω 43.478° YIM 10.350mm F 11.061mm P 0.090 Fls -25.729mm Flf 25.805mm Pc1 -0.042 Vc1 39.242 Pc2 0.067 Vc2 81.546 Pc3 -0.046 Vc3 27.512 Flp 26.855mm

[0039] 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.

[0040] Code Surface number RD nd vd S 0 inf 1063.000 L01 1* -24.60 3.412 1.5365 56.0 2* 33.26 4.940 L02 3 62.59 1.500 1.4875 70.2 4 18.74 19.922 L03 5 42.22 3.090 1.8340 37.2 6 -46.68 0.500 41 7 inf 12.190 L04 8 -307.14 1.000 1.5955 39.2 L05 9 15.05 8.000 1.4970 81.5 L06 10 -12.26 1.200 1.7552 27.5 11 -49.05 0.200 L07 12 -59.52 2.385 1.4875 70.2 13 -39.24 0.200 L08 14* 40.24 6.461 1.5365 56.0 15* -20.04 0.200 19 16 inf 23.925 1.5168 64.2 17 inf 5.003 18 18 inf -0.003

[0041] The aspherical coefficients are as follows:

[0042] Face number 1 2 Conic constant 1.09448E+00 -1.00000E+02 The coefficient of the third order is -8.78634E-04 -1.20376E-03 The coefficients of the fourth order are 1.00159E-03 and 1.70343E-03. The coefficient of the fifth order is -1.05886E-04 -2.43171E-04 Coefficients of the 6th order: 3.06988E-06 1.62609E-05 Coefficients of the 7th order: 1.55509E-07 2.28363E-07 The coefficients of the 8th order are -3.86698E-09 and -7.88741E-08. The coefficient of the 9th order is -4.95579E-10 -2.09364E-09 The coefficient of the 10th order is -6.53534E-12, which is 2.87495E-10. The coefficients of the 11th order are 5.54636E-13 and 2.78596E-11. The coefficient of the 12th degree is 6.91541E-14 and 1.83829E-12. The coefficient of the 13th order is 4.16933E-15 -1.77922E-13 14th degree coefficients: -1.51364E-16 -2.96733E-14 15th order coefficients: -1.32836E-17 -2.32779E-16 Coefficient of the 16th order: -5.29770E-19 6.11188E-17 The coefficients of the 17th order are 8.92389E-21 and 2.46593E-17. 18th order coefficients: -1.68839E-21 -5.88329E-19 The coefficient of the 19th order is 4.58578E-22 -1.39215E-19 20th order coefficient -1.46956E-23 6.13128E-21

[0043] Page numbers 14 15 Conic constant 0.00000E+00 0.00000E+00 The coefficient of the fourth order is -2.18999E-05, which is 2.39426E-05. Coefficient of the 6th order: 7.03290E-08 2.26359E-08 The coefficient of the 8th order is -1.49424E-10, which is 7.38394E-11. The coefficient of the 10th order is -4.06354E-13 and -7.55428E-13.

[0044] Here, the projection optical system 3A in this example satisfies the following condition (1), where ω is the maximum half-angle of view of the entire lens system. ω > 40 (1)

[0045] In this example, ω 43.478° Therefore, ω = 43.478°, which satisfies condition (1).

[0046] In this example, the projection optical system 3A satisfies all of the following conditions (2), (3), (4), and (5), where L is the total length from the magnifying lens surface of lens L1 to the reducing lens surface of lens L8, 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 L8. 5.0 < L / F < 30.0 (2) BF / F > 2.0 (3) -20.0 < Fls / F < -2.0 (4) 1.6 < Flf / F < 30.0 (5)

[0047] In this example, L 65,000mm F 11.061mm Bf 29.125mm Fls -25.729mm Flf 25.805mm Therefore, L / F = 5.876, satisfying condition (2). BF / F = 2.633, satisfying condition (3). Fls / F = -2.326, satisfying condition (4). Flf / F = 2.333, satisfying condition (5).

[0048] In this example, the projection optical system 3A satisfies the following condition (6) when the total power of the lens system is P, the power of lens L4 in air is Pc1, the Abbe number of lens L4 is Vc1, the power of lens L5 in air is Pc2, the Abbe number of lens L5 is Vc2, the power of lens L6 in air is Pc3, and the Abbe number of lens L6 is Vc3. -0.05 < (Pc1 / P) / Vc1+(Pc2 / P) / Vc2+(Pc3 / P) / Vc3 < 0.01 (6)

[0049] In this example, P 0.090 Pc1 -0.042 Vc1 39.242 Pc2 0.067 Vc2 81.546 Pc3 -0.046 Vc3 27.512 Therefore, (Pc1 / P) / Vc1 + (Pc2 / P) / Vc2 + (Pc3 / P) / Vc3 = -0.021, which satisfies condition (6).

[0050] In this example, the projection optical system 3A satisfies the following conditions (7) and (8), where F is the focal length of the entire lens system, Flp is the focal length of lens L3, and vdp is the Abbe number of lens L3 on the d line. vdp < 40 (7) 1.5 < Flp / F < 15.0 (8)

[0051] In this example, vdp 37.161 F 11.061mm Flp 26.855mm Therefore, vdp2 = 37.161, satisfying condition (7). Flp / F = 2.428, satisfying condition (8).

[0052] (Effects and Benefits) In this example, the projection optical system has the widest air gap G1 between the first sub-lens group 33, which has negative power, and the second sub-lens group 34, which has positive power, in the first lens group 31. Therefore, in the projection optical system 3A, the positive power of the second sub-lens group 34, which is located on the magnifying side of the aperture diaphragm 41, can be made relatively small, thereby spreading the light beam emitted from the lens on the most magnifying side of the second sub-lens group 34 and reaching the lens on the most constricting side of the first sub-lens group 33. Thus, in the projection optical system 3A, it becomes easy to magnify the light rays emitted from the second sub-lens group 34 for each image height and project them using the first sub-lens group 33, which is located on its magnifying side. Therefore, the projection optical system 3A in this example can have a half-angle of view exceeding 40° so as to satisfy condition (1).

[0053] Here, if the projection optical system has the widest air gap G1 on the magnifying side of the second sub-lens group 34, which has positive power, there is a problem that chromatic aberration is likely to occur in the second sub-lens group 34. To address this problem, in this example, the cemented lens L21 of the second lens group 32 consists of a lens L4 with negative power, a lens L5 with positive power, and a lens L6 with negative power, in order from the magnifying side to the reducing side. With a cemented lens L21 consisting of such three lenses, it is easier to suppress chromatic aberration occurring in the second sub-lens group 34 compared to a cemented lens in which a positive lens, a negative lens, and a positive lens are cemented together in order from the magnifying side to the reducing side.

[0054] Furthermore, if the cemented lens L21 consists of a negative power lens L4, a positive power lens L5, and a negative power lens L6, arranged in order from the magnification side to the reduction side, it becomes easier to make the overall length more compact compared to a projection optical system that has a positive lens, a negative lens, and a cemented lens formed by joining the positive lenses, arranged in order from the magnification side to the reduction side.

[0055] In this example, the projection optical system 3A has negative power because the lens L1, which is located on the magnification side, has negative power. Therefore, it is easy to increase the maximum half-angle of view of the projection optical system 3A. Also, because the lens L8, which is located on the reduction side, has positive power, it is easy to make the reduction side from the second lens group 32 telecentric.

[0056] 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 easy to suppress the field curvature that occurs in the projection optical system 3A.

[0057] In this example, the projection optical system 3A satisfies all of the following conditions (2), (3), (4), and (5), where L is the total length from the magnifying lens surface of lens L1 to the reducing lens surface of lens L8, 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 L8. 5.0 < L / F < 30.0 (2) BF / F > 2.0 (3) -20.0 < Fls / F < -2.0 (4) 1.6 < Flf / F < 30.0 (5)

[0058] Furthermore, the projection optical system 3A in this example satisfies condition (2), so the overall length of the projection optical system 3A can be reduced while ensuring the imaging performance of the projection optical system 3A. That is, if the value of condition (2) exceeds the lower limit, the distance from the lens on the magnifying side to the lens on the reducing side becomes too short. As a result, the overall length of the projection optical system 3A can be reduced, but the number of lenses necessary to ensure the imaging performance of the projection optical system 3A cannot be obtained. If the value of condition (2) exceeds the upper limit, the distance becomes too long. As a result, the number of lenses necessary to ensure the imaging performance of the projection optical system 3A can be obtained, but the overall length of the projection optical system 3A becomes larger.

[0059] Furthermore, since the projection optical system 3A in this example 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. Also, it becomes difficult to make the area on the reduction side of the second lens group 32 telecentric.

[0060] 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.

[0061] 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. In other words, if the value of condition (5) exceeds the lower limit, the focal length Flf of lens L8 becomes too short. This ensures the imaging performance of the projection optical system 3A, but the power of lens L11 becomes stronger, 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 L8 becomes too long. This weakens the power of lens L8, making it easier to make the reduction side from the second lens group 32 telecentric, but the imaging performance of the projection optical system 3A deteriorates.

[0062] In this example, the projection optical system 3A satisfies the following condition (6) when the total power of the lens system is P, the power of lens L4 in air is Pc1, the Abbe number of lens L4 is Vc1, the power of lens L5 in air is Pc2, the Abbe number of lens L5 is Vc2, the power of lens L6 in air is Pc3, and the Abbe number of lens L6 is Vc3. -0.05 < (Pc1 / P) / Vc1+(Pc2 / P) / Vc2+(Pc3 / P) / Vc3 < 0.01 (6)

[0063] Furthermore, the projection optical system 3A in this example satisfies condition (6), so it can effectively suppress chromatic aberration occurring in the second sub-lens group 34. In other words, if the value of condition (6) exceeds the lower limit, the suppression effect of chromatic aberration by the cemented lens L21 becomes too strong and inappropriate. If the value of condition (6) exceeds the condition value, the suppression effect of chromatic aberration by the cemented lens L21 becomes too weak, and it is not possible to effectively suppress chromatic aberration occurring in the second sub-lens group 34.

[0064] In this example, the projection optical system 3A, where F is the focal length of the entire lens system, Flp is the focal length of lens L3, and vdp is the Abbe number of lens L3 on the d line, satisfies the following condition (7): It satisfies the condition (8). vdp < 40 (7) 1.5 < Flp / F < 15.0 (8)

[0065] Furthermore, since the projection optical system 3A in this example satisfies condition (7), it can effectively correct the chromatic aberration generated by lens L1. That is, lens L3 is a positive lens positioned closest to the aperture diaphragm 41 and is made of a highly dispersive material, so lens L3 can cancel out the chromatic aberration generated by lens L1.

[0066] Furthermore, the projection optical system 3A in this example satisfies condition (8), so it can effectively correct chromatic aberration occurring in lens L1 while suppressing various aberrations occurring in lens L3. That is, if the value of condition (8) exceeds the lower limit, the focal length Flp of lens L3 becomes too short. As a result, the power of lens L3 becomes stronger, so chromatic aberration occurring in lens L1 can be effectively corrected, but various aberrations are more likely to occur in lens L3. If the value of condition (8) exceeds the upper limit, the focal length Flp of lens L3 becomes too long. As a result, the power of lens L3 becomes weaker, so various aberrations occurring in lens L3 can be suppressed, but chromatic aberration occurring in lens L1 cannot be effectively corrected.

[0067] 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.

[0068] (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.

[0069] The first lens group 31 comprises, in order from the magnification side to the reduction side, a first sub-lens group 33 having negative power and a second sub-lens group 34 having positive power.

[0070] The first sub-lens group 33 comprises five lenses L1 to L5. Lenses L1 to L5 are arranged in this order from the magnification side to the reduction side.

[0071] 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.

[0072] 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.

[0073] Lenses L4 and L5 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 has concave shapes on its magnifying and reducing surfaces. The cemented lens L21 has positive power.

[0074] The second sub-lens group 34 comprises two lenses, L6 and L7. Lens L7 is arranged in this order from the magnification side to the reduction side. Lens L6 has positive power. Lens L6 is a meniscus lens. Lens L6 has a convex shape on the magnification side and a concave shape on the reduction side. Lens L7 has positive power. Lens L7 has convex shapes on both the magnification and reduction sides.

[0075] 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.

[0076] 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 positive power.

[0077] Lenses L10 and L11 are joined together to form a cemented lens L23. Lens L10 has negative power. Lens L10 is a meniscus lens. Lens L10 has a convex shape on the magnifying side and a concave shape on the reducing side. Lens L11 has positive power. Lens L11 has convex shapes on both the magnifying and reducing sides. Lens L11 has an aspherical shape on the reducing side. The cemented lens L23 has positive power.

[0078] Lenses L12 (first lens), L13 (second lens), and L14 (third lens) are joined together to form a cemented lens L24. 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 L24 has negative power.

[0079] Lens L15 (the reducing lens) has positive power. Lens L15 has a convex shape on both the magnifying and reducing surfaces.

[0080] Lens L1 is made of resin. Lenses L2 through L15 are made of glass.

[0081] In projection optical system 3B, the reduction side from lens L15 is telecentric.

[0082] A first air gap G1, which is wider than the air gap between other adjacent lenses, is provided between the lens L5 located on the most compact side of the first sub-lens group 33 and the lens L6 located on the most magnified side of the second sub-lens group 34.

[0083] 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 distance from the optical axis N to the maximum image height of the projected image formed by the liquid crystal panel 18 is YIM, the focal length of the entire lens system is F, the power of the entire lens system is P, the focal length of lens L1 is Fls, the focal length of lens L15 is Flf, the power of lens L12 in air is Pc1, the Abbe number of lens L12 is Vc1, the power of lens L13 in air is Pc2, the Abbe number of lens L13 is Vc2, the power of lens L14 in air is Pc3, the Abbe number of lens L14 is Vc3, and the focal length of lens L7 is Flp, the data for the projection optical system 3B of Example 2 is as follows.

[0084] Fno 1.600 TTL 192.808mm L 152.369mm Bf 40.439mm ω 59.317° YIM 10,800mm F 6.346mm P 0.158 Fls -79.244mm Flf 40.732mm Pc1 -0.040 Vc1 23.778 Pc2 0.045 Vc2 81.546 Pc3 -0.015 Vc3 40.100 Flp 75.680mm

[0085] 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.

[0086] Code Surface number RD nd vd S 0 inf 937.000 L01 1* -21.34 5.000 1.5350 55.7 2* -46.30 13.962 L02 3 70.52 1.500 1.6584 50.9 4 28.09 11.279 L03 5 2345.80 1.500 1.7620 40.1 6 24.38 7.946 L04 7 60.28 10.960 1.6976 29.0 L05 8 -33.80 1.500 1.9004 37.4 9 196.49 35.002 L06 10 25.13 2.194 1.5601 47.7 11 25.80 2.262 L07 12 48.30 5.135 1.6314 34.9 13 -9887.97 14.727 41 14 inf 0.100 L08 15 27.53 6.004 1.7450 26.3 L09 16 -29.48 1.000 1.9004 37.4 17 54.58 4.209 L10 18 55.44 1.000 1.9019 35.6 L11 19 17.54 5.50 1.5866 59.0 20* -82.39 1.00 L12 21 -83.49 1.72 1.8467 23.8 L13 22 29.16 10.25 1.4970 81.5 L14 23 -16.02 1.00 1.7620 40.1 24 -24.29 0.15 L15 25 94.19 7.47 1.4970 81.5 26 -25.19 0.10 19 27 inf 30.69 1.5168 64.2 28 inf 9.69 18 29 inf -0.04

[0087] The aspherical coefficients are as follows:

[0088] Face number 1 2 Conic constant -5.75343E+00 0.00000E+00 The coefficients of the third order are 6.65504E-04 and 7.71761E-04. The coefficient of the fourth order is -7.97236E-06, which is 2.74106E-05. The coefficient of the fifth order is -1.00807E-07 -1.06700E-06 The coefficient of the sixth degree is 5.42611E-11 -8.03394E-10 The coefficient of the 7th order is 3.29709E-11, which is equal to 1.10389E-10. The coefficients of the 8th order are 1.15849E-12 and 2.46074E-12. The coefficient of the 9th order is -5.27286E-15, which is 4.82457E-14. The coefficient of the 10th order is -1.50364E-16, which is 4.56095E-16. 11th order coefficients: -7.86924E-18 -1.43519E-17 12th degree coefficients: -1.24414E-19 -5.35072E-19 The coefficient of the 13th order is 2.49472E-21 -1.27071E-20 The coefficient of the 14th order is 7.60941E-23 -1.95871E-22 The coefficient of the 15th order is 3.85155E-25 -7.86560E-25 Coefficient of the 16th order: -8.06777E-27 8.98625E-26 17th degree coefficient -2.19890E-28 4.49957E-27 18th order coefficient -4.42288E-30 9.94600E-29 19th coefficient -2.02762E-32 4.35430E-31 The coefficient of the 20th order is 1.71232E-33 -6.83022E-32

[0089] Page number 20 Conic constant -6.22053E+01 The coefficient of the fourth order is 8.51306E-06. The coefficient of the sixth order is 8.01125E-08. The coefficient of the 8th order is -3.70892E-10 The coefficient of the 10th order is 1.01346E-12

[0090] Here, the projection optical system 3B in this example satisfies the following condition (1), where ω is the maximum half-angle of view of the entire lens system. ω > 40 (1)

[0091] In this example, ω 59.317° Therefore, ω = 59.317°, which satisfies condition (1).

[0092] In this example, the projection optical system 3B satisfies all of the following conditions (2), (3), (4), and (5), where L is the total length from the magnifying lens surface of lens L1 to the reducing lens surface of lens L15, 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 L15. 5.0 < L / F < 30.0 (2) BF / F > 2.0 (3) -20.0 < Fls / F < -2.0 (4) 1.6 < Flf / F < 30.0 (5)

[0093] In this example, L 152.369mm F 6.346mm Bf 40.439mm Fls -79.244mm Flf 40.732mm Therefore, L / F = 24.010, satisfying condition (2). BF / F = 6.372, satisfying condition (3). Fls / F = -12.487, satisfying condition (4). Flf / F = 6.419, satisfying condition (5).

[0094] In this example, the projection optical system 3B satisfies the following condition (6) when the total power of the lens system is P, the power of lens L12 in air is Pc1, the Abbe number of lens L12 is Vc1, the power of lens L13 in air is Pc2, the Abbe number of lens L13 is Vc2, the power of lens L14 in air is Pc3, and the Abbe number of lens L14 is Vc3. -0.05 < (Pc1 / P) / Vc1+(Pc2 / P) / Vc2+(Pc3 / P) / Vc3 < 0.01 (6)

[0095] In this example, P 0.158 Pc1 -0.040 Vc1 23.778 Pc2 0.045 Vc2 81.546 Pc3 -0.015 Vc3 40.100 Therefore, (Pc1 / P) / Vc1 + (Pc2 / P) / Vc2 + (Pc3 / P) / Vc3 = -0.010, which satisfies condition (6).

[0096] In this example, the projection optical system 3B satisfies the following conditions (7) and (8), where F is the focal length of the entire lens system, Flp is the focal length of lens L7, and vdp is the Abbe number of lens L7 on the d line. vdp < 40 (7) 1.5 < Flp / F < 15.0 (8)

[0097] In this example, vdp 34.852 F 6.346mm Flp 75.680mm Therefore, vdp2 = 34.852, satisfying condition (7). Flp / F = 11.926, satisfying condition (8).

[0098] (Effects and Benefits) Since the projection optical system 3B in this example satisfies conditions (1) to (8), it can obtain the same effects as the projection optical system 3A in Example 1.

[0099] 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 possible to make the reduction side from the second lens group 32 telecentric. It is easy.

[0100] 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.

[0101] 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 enlarged image.

[0102] (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.

[0103] The first lens group 31 comprises, in order from the magnification side to the reduction side, a first sub-lens group 33 having negative power and a second sub-lens group 34 having positive power.

[0104] The first sub-lens group 33 comprises two lenses, L1 and L2. Lenses L1 and L2 are arranged in this order from the magnification side to the reduction side.

[0105] 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.

[0106] The second sub-lens group 34 comprises one lens L3. Lens L3 has positive power. Lens L3 has a convex shape on its magnifying and reducing surfaces.

[0107] The second lens group 32 comprises six lenses L4 to L10. Lenses L4 to L10 are arranged in this order from the magnification side to the reduction side.

[0108] Lens L4 has negative power. Lens L4 is a meniscus lens. Lens L4 has a concave shape on the magnifying side and a convex shape on the reducing side. Lens L4 has aspherical shapes on both sides.

[0109] Lenses L5 (first lens), L6 (second lens), and L7 (third lens) are joined together to form a cemented lens L21. Lens L5 has negative power. Lens L5 is a meniscus lens. Lens L5 has a convex shape on the magnifying side and a concave shape on the reducing side. Lens L6 has positive power. Lens L6 has convex shapes on both the magnifying and reducing sides. Lens L7 has negative power. Lens L7 has concave shapes on both the magnifying and reducing sides. The cemented lens L21 has negative power.

[0110] Lens L8 has positive power. Lens L8 has a convex shape on the magnifying side. Lens L8 has a convex shape near the optical axis N and a concave shape at the periphery on the reducing side. Lens L8 has aspherical shapes on both sides.

[0111] Lens L9 has positive power. Lens L9 has a convex shape on both the magnifying and reducing surfaces. It is equipped with the following: Lens L10 (reduction lens) has positive power. Lens L10 has a concave shape on the magnification side and a convex shape on the reduction side. Lens L10 has an aspherical shape on both sides.

[0112] Lens L1 is made of resin. Lenses L2 through L10 are made of glass.

[0113] In the projection optical system 3C, the reduction side from lens L10 is telecentric.

[0114] A first air gap G1, wider than the air gap between other adjacent lenses, is provided between the lens L2 located on the most reduced side of the first sub-lens group 33 and the lens L3 located on the most enlarged side of the second sub-lens group 34.

[0115] 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 L10 is L, the back focus is BF, the maximum half-angle of view of the entire lens system is ω, the distance from the optical axis N to the maximum image height of the projected image formed by the liquid crystal panel 18 is YIM, the focal length of the entire lens system is F, the power of the entire lens system is P, the focal length of lens L1 is Fls, the focal length of lens L10 is Flf, the power of lens L5 in air is Pc1, the Abbe number of lens L5 is Vc1, the power of lens L6 in air is Pc2, the Abbe number of lens L6 is Vc2, the power of lens L7 in air is Pc3, the Abbe number of lens L7 is Vc3, and the focal length of lens L3 is Flp, the data for the projection optical system 3C of Example 3 is as follows.

[0116] Fno 2.007 TTL 94.125mm L 65,000mm Bf 29.125mm ω 51.604° YIM 10.350mm F 8.308mm P 0.120 Fls -40.781mm Flf 239.200mm Pc1 -0.032 Vc1 38.027 Pc2 0.083 Vc2 81.546 Pc3 -0.100 Vc3 31.343 Flp 30.030mm

[0117] 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.

[0118] Code Surface number RD nd vd S 0 inf 797.472 L01 1* -13.02 2.072 1.5365 56.0 2* -33.75 4.102 L02 3 68.89 1.500 1.8348 42.7 4 12.07 19.186 L03 5 47.56 3.786 1.8697 20.0 6 -57.07 0.500 41 7 inf 0.885 L04 8* -916.94 2.000 1.5163 64.1 9* -272.61 5.811 L05 10 24.20 1.242 1.6034 38.0 L06 11 10.47 7.998 1.4970 81.5 L07 12 -10.51 1.200 1.9037 31.3 13 72.70 0.348 L08 14* 328.27 2.929 1.5365 56.0 15* -19.18 0.200 L09 16 53.28 8.705 1.4970 81.5 17 -14.52 0.200 L10 18* -11.86 2.336 1.5365 56.0 19* -11.61 0.20 19 20 inf 23.93 1.5168 64.2 21 inf 5.03 18 22 inf -0.03

[0119] The aspherical coefficients are as follows:

[0120] Face number 1 2 Conic constant -2.15602E+00 -1.00000E+02 The coefficients of the third order are 6.40257E-04 and 7.74472E-04. The coefficients of the fourth order are 1.11405E-03 and 6.53746E-04. The coefficient of the fifth order is -1.28849E-04 -6.97719E-05 Coefficients of the 6th order: 3.26299E-06, 8.27625E-06 The coefficient of the 7th degree is 2.08804E-07 -4.90677E-07 The coefficient of the 8th order is -2.84616E-09 -5.37025E-08 The coefficient of the 9th order is -5.29625E-10, which is 1.92986E-09. The coefficient of the 10th order is -1.35786E-11, which is equal to 5.52705E-10. The coefficients of the 11th order are 3.44014E-13 and 9.63839E-12. The coefficient of the 12th degree is 6.65677E-14 -5.44902E-13 The coefficient of the 13th order is 4.90515E-15 -2.07361E-13 14th degree coefficients: -1.16959E-16 -2.78221E-14 15th order coefficients: -1.16608E-17 -2.17324E-16 The coefficient of the 16th order is -4.93436E-19, which is equal to 1.54783E-16. The coefficient of the 17th order is 6.43046E-21 and 3.06011E-17. 18th order coefficients: -1.98650E-21 -1.06748E-18 The coefficient of the 19th order is 4.34294E-22 -1.85121E-19 20th order coefficient -1.36475E-23 8.10758E-21

[0121] Page numbers 8, 9, 14 Conic constant 0.00000E+00 0.00000E+00 0.00000E+00 The coefficient of the fourth order is -1.90495E-04, -2.43398E-04, and 1.29412E-04. Coefficients of the 6th order: 4.33667E-07, 6.75888E-07, 1.07961E-06 The coefficients of the 8th order are -1.72697E-08, -1.99474E-08, and -8.01000E-09. The coefficients of the 10th order are 1.48432E-11, 8.07157E-11, and -2.79684E-11. The coefficient of the 12th order is 0.00000E+00 0.00000E+00 1.14647E-13 The coefficient of the 14th order is 0.00000E+00 0.00000E+00 -4.11745E-25 The coefficient of the 16th order is 0.00000E+00 0.00000E+00 -1.25432E-26

[0122] Page numbers 15 18 19 Conic constant 0.00000E+00 -1.62095E-01 -4.85731E-01 The coefficients of the fourth order are 2.55028E-04, 3.91706E-04, and 2.85197E-04. Coefficient of the 6th order: 2.08912E-06 -8.81038E-07 -1.59722E-07 Coefficient of the 8th order: -1.01165E-08, 1.06482E-09, -3.51759E-09 The coefficient of the 10th order is -1.11638E-10, -1.08940E-12, and 9.60172E-12. Coefficients of the 12th order: 5.55728E-13, 1.16815E-13, 7.44323E-14 14th order coefficients: -1.99782E-23, -5.51265E-16, -5.92858E-16 Coefficient of the 16th order: -1.31283E-26, 2.70570E-26, -1.69630E-26

[0123] Here, the projection optical system 3C in this example satisfies the following condition (1), where ω is the maximum half-angle of view of the entire lens system. ω > 40 (1)

[0124] In this example, ω 51.604° Therefore, ω = 51.604°, which satisfies condition (1).

[0125] In this example, the projection optical system 3C satisfies all of the following conditions (2), (3), (4), and (5), where L is the total length from the magnifying lens surface of lens L1 to the reducing lens surface of lens L10, 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. 5.0 < L / F < 30.0 (2) BF / F > 2.0 (3) -20.0 < Fls / F < -2.0 (4) 1.6 < Flf / F < 30.0 (5)

[0126] In this example, L 65,000mm F 8.308mm Bf 29.125mm Fls -40.781mm Flf 239.200mm Therefore, L / F = 7.824, satisfying condition (2). BF / F = 3.506, satisfying condition (3). Fls / F = -4.908, satisfying condition (4). Flf / F = 28.791, satisfying condition (5).

[0127] In this example, the projection optical system 3C satisfies the following condition (6) when the total power of the lens system is P, the power of lens L5 in air is Pc1, the Abbe number of lens L5 is Vc1, the power of lens L6 in air is Pc2, the Abbe number of lens L6 is Vc2, the power of lens L7 in air is Pc3, and the Abbe number of lens L7 is Vc3. -0.05 < (Pc1 / P) / Vc1+(Pc2 / P) / Vc2+(Pc3 / P) / Vc3 < 0.01 (6)

[0128] In this example, P 0.120 Pc1 -0.032 Vc1 38.027 Pc2 0.083 Vc2 81.546 Pc3 -0.100 Vc3 31.343 Therefore, (Pc1 / P) / Vc1 + (Pc2 / P) / Vc2 + (Pc3 / P) / Vc3 = -0.025, which satisfies condition (6).

[0129] In this example, the projection optical system 3C satisfies the following conditions (7) and (8), where F is the focal length of the entire lens system, Flp is the focal length of lens L3, and vdp is the Abbe number of lens L3 on the d line. vdp < 40 (7) 1.5 < Flp / F < 15.0 (8)

[0130] In this example, vdp 20.019 F 8.308mm Flp 30.030mm Therefore, vdp = 20.019, satisfying condition (7). Flp / F = 3.615, satisfying condition (8).

[0131] (Effects and Benefits) Since the projection optical system 3C in this example satisfies conditions (1) to (8), it can obtain the same effects as the projection optical system 3A in Example 1.

[0132] 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 L10 has positive power. Therefore, it is easy to make the reduction side from the second lens group 32 telecentric.

[0133] 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.

[0134] 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.

[0135] (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.

[0136] The first lens group 31 comprises, in order from the magnification side to the reduction side, a first sub-lens group 33 having negative power and a second sub-lens group 34 having positive power.

[0137] The first sub-lens group 33 comprises two lenses, L1 and L2. Lenses L1 and L2 are arranged in this order from the magnification side to the reduction side.

[0138] 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.

[0139] The second sub-lens group 34 comprises three lenses L3 to L5. Lenses L3 to L5 are arranged in this order from the magnification side to the reduction side.

[0140] Lenses L3 and L4 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.

[0141] Lens L5 has positive power. Lens L5 has a convex shape on both the magnifying and reducing surfaces.

[0142] The second lens group 32 comprises seven lenses L6 to L12. Lenses L6 to L12 are arranged in this order from the magnification side to the reduction side.

[0143] Lenses L6 (first lens), L7 (second lens), and L8 (third lens) are joined together to form a cemented lens L22. Lens L6 has negative 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. Lens L7 has positive power. Lens L7 has convex shapes on both the magnifying and reducing sides. Lens L8 has negative power. Lens L8 has concave shapes on both the magnifying and reducing sides. The cemented lens L22 has negative power.

[0144] Lens L9 has positive power. Lens L9 has a convex shape on both the magnifying and reducing surfaces. Lens L9 has an aspherical shape on both sides.

[0145] Lenses L10 and L11 are joined together to form a cemented lens L23. 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 its reducing surface. The cemented lens L23 has negative power.

[0146] Lens L12 (the reducing lens) has positive power. Lens L12 has a convex shape on both its magnifying and reducing surfaces.

[0147] Lens L1 is made of resin. Lenses L2 through L12 are made of glass.

[0148] In a 3D projection optical system, the reduction side from lens L12 is telecentric.

[0149] A first air gap G1, wider than the air gap between other adjacent lenses, is provided between the lens L2 located on the most reduced side of the first sub-lens group 33 and the lens L3 located on the most enlarged side of the second sub-lens group 34.

[0150] 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 L12 is L, the back focus is BF, and the lens Assuming that the maximum half-angle of view of the entire lens system is ω, the distance from the optical axis N to the maximum image height of the projected image formed by the liquid crystal panel 18 is YIM, the focal length of the entire lens system is F, the power of the entire lens system is P, the focal length of lens L1 is Fls, the focal length of lens L12 is Flf, the power of lens L6 in air is Pc1, the Abbe number of lens L6 is Vc1, the power of lens L7 in air is Pc2, the Abbe number of lens L7 is Vc2, the power of lens L8 in air is Pc3, the Abbe number of lens L8 is Vc3, and the focal length of lens L5 is Flp, the data for the projection optical system 3D of Example 4 is as follows.

[0151] Fno 2.000 TTL 99.126mm L 65.126mm Bf 34,000mm ω 51.275° YIM 10.350mm F 8.350mm P 0.120 Fls -41.126mm Flf 36.090mm Pc1 -0.082 Vc1 31.343 Pc2 0.114 Vc2 25.683 Pc3 -0.056 Vc3 34.967 Flp 29.292mm

[0152] 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.

[0153] Code Surface number RD nd vd S 0 inf 730.000 L01 1* -8.11 2.000 1.5311 55.8 2* -13.96 3.752 L02 3 26.79 1.260 1.9229 20.9 4 11.79 9.960 L03 5 -15.33 1.200 1.7880 47.4 L04 6 13.55 4.037 1.6477 33.8 7 -19.96 0.100 L05 8 32.51 5.079 1.7400 28.3 9 -62.10 2.508 41 10 inf 0.298 L06 11 57.34 1.000 1.9037 31.3 L07 12 9.25 5.288 1.7847 25.7 L08 13 -20.76 1.660 1.8010 35.0 14 50.00 3.098 L09 15* 30.63 5.775 1.4971 81.6 16* -13.91 1.747 L10 17 -26.01 1.000 2.0006 25.5 L11 18 26.84 8.157 1.4971 81.6 19* -15.77 0.10 L12 20 47.56 7.11 1.4970 81.5 21 -27.48 2.00 19 22 inf 27.43 1.5168 64.2 23 inf 4.53 18 24 inf 0.04

[0154] The aspherical coefficients are as follows:

[0155] Face number 1 2 Conic constant: -3.28760E+00 -3.50091E-01 The coefficients of the third order are 4.56008E-03 and 4.65351E-03. The coefficients of the fourth order are 2.73066E-04 and 4.31668E-04. The coefficients of the fifth order are -7.71202E-05 and -4.48917E-06. The coefficient of the sixth degree is 5.00832E-06 -4.49202E-06 Coefficient of the 7th order: -7.68562E-08 3.25455E-08 The coefficient of the 8th order is -4.02343E-09, which is 2.51396E-08. The coefficient of the 9th order is 1.40595E-10 -1.00330E-10 The coefficient of the 10th order is -1.43594E-13 and -5.54462E-11.

[0156] Page numbers 15 16 19 Conic constant 4.76497E+00 -2.31470E-01 -1.72445E+00 The coefficients of the fourth order are -3.03413E-05, 5.78654E-05, and -4.82060E-05. Coefficients of the 6th order -9.95954E-08 -1.32591E-07 0.00000E+00 Coefficients of the 8th order -2.48938E-09 -2.62097E-09 0.00000E+00 Coefficients of the 10th order 2.33921E-11 1.18427E-11 0.00000E+00 Coefficients of the 12th order -8.97735E-14 0.00000E+00 0.00000E+00

[0157] Here, for the projection optical system 3D in this example, when the maximum half angle of the entire lens system is ω, it satisfies the following conditional expression (1). ω > 40 (1)

[0158] In this example, ω = 51.275° That is. Thus, ω = 51.275°, and it satisfies the conditional expression (1).

[0159] For the projection optical system 3D in this example, when the total length from the magnifying lens surface of lens L1 to the reducing lens surface of lens L12 is L, the focal length of the entire 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 L12 is Flf, it satisfies all of the following conditional expressions (2), (3), (4), and (5). 5.0 < L / F < 30.0 (2) BF / F > 2.0 (3) -20.0 < Fls / F < -2.0 (4) 1.6 < Flf / F < 30.0 (5)

[0160] In this example, L = 65.126mm F = 8.350mm Bf = 34.000mm Fls = -41.126mm Flf = 36.090mm Therefore, L / F = 7.800, satisfying condition (2). BF / F = 4.072, satisfying condition (3). Fls / F = -4.925, satisfying condition (4). Flf / F = 4.322, satisfying condition (5).

[0161] In this example, the projection optical system 3D satisfies the following condition (6) when the total power of the lens system is P, the power of lens L6 in air is Pc1, the Abbe number of lens L6 is Vc1, the power of lens L7 in air is Pc2, the Abbe number of lens L7 is Vc2, the power of lens L8 in air is Pc3, and the Abbe number of lens L8 is Vc3. -0.05 < (Pc1 / P) / Vc1+(Pc2 / P) / Vc2+(Pc3 / P) / Vc3 < 0.01 (6)

[0162] In this example, P 0.120 Pc1 -0.082 Vc1 31.343 Pc2 0.114 Vc2 25.683 Pc3 -0.056 Vc3 34.967 Therefore, (Pc1 / P) / Vc1 + (Pc2 / P) / Vc2 + (Pc3 / P) / Vc3 = 0.002, which satisfies condition (6).

[0163] In this example, the projection optical system 3D satisfies the following conditions (7) and (8), where F is the focal length of the entire lens system, Flp is the focal length of lens L5, and vdp is the Abbe number of lens L5 on the d line. vdp < 40 (7) 1.5 < Flp / F < 15.0 (8)

[0164] In this example, vdp 28.296 F 8.350mm Flp 29.292mm Therefore, vdp = 28.296, satisfying condition (7). Flp / F = 3.508, satisfying condition (8).

[0165] (Effects and Benefits) Since the projection optical system 3D in this example satisfies conditions (1) to (8), it can obtain the same effects as the projection optical system 3A in Example 1.

[0166] In the projection optical system 3D 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 3D. In this example, lens L12 has positive power. Therefore, it is easy to make the reduction side from the second lens group 32 telecentric.

[0167] 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 a plastic aspherical lens. According to the company, it is possible to suppress the image field curvature that occurs in 3D projection optics.

[0168] Figure 10 shows the spherical aberration, astigmatism, and distortion of the projection optical system 3D. As shown in Figure 10, the projection optical system 3D in this example suppresses various aberrations in the magnified image.

[0169] (Example 5) Figure 11 is a ray diagram of the projection optical system 3E of Embodiment 5. As shown in Figure 11, the projection optical system 3E 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 3E.

[0170] The first lens group 31 comprises, in order from the magnification side to the reduction side, a first sub-lens group 33 having negative power and a second sub-lens group 34 having positive power.

[0171] The first sub - lens group 33 includes two lenses L1 and L2. The lenses L1 and L2 are arranged in this order from the magnifying side to the reducing side.

[0172] The lens L1 (magnifying - side lens) has a negative power. The lens L1 has a concave shape near the optical axis N on the magnifying - side surface and a convex shape in the peripheral portion. The lens L1 has a convex shape near the optical axis N on the reducing - side surface and a concave shape in the peripheral portion. The lens L1 has an aspherical shape on both surfaces. The lens L2 has a negative power. The lens L2 is a meniscus lens. The lens L2 has a convex shape on the magnifying - side surface and a concave shape on the reducing - side surface.

[0173] The second sub - lens group 34 includes three lenses L3 to L5. The lenses L3 to L5 are arranged in this order from the magnifying side to the reducing side.

[0174] The lenses L3 and L4 are a combined lens L21 joined together. The lens L3 has a negative power. The lens L3 has a concave shape on both the magnifying - side and reducing - side surfaces. The lens L4 has a positive power. The lens L4 has a convex shape on both the magnifying - side and reducing - side surfaces. The combined lens L21 has a negative power.

[0175] The lens L5 has a positive power. The lens L5 has a convex shape on both the magnifying - side and reducing - side surfaces.

[0176] The second lens group 32 includes seven lenses L6 to L12. The lenses L6 to L12 are arranged in this order from the magnifying side to the reducing side. <00009​​​​ Lens L8 has positive power. Lens L8 has a convex shape on both the magnifying and reducing surfaces. Lens L8 has an aspherical shape on both sides.

[0179] Lenses L9 (first lens), L10 (second lens), and L11 (third lens) are joined together to form a cemented lens L23. 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 L10 has positive power. Lens L10 is a magnifying lens. The lens L11 has a convex shape on its side and the reduction side. The lens L11 has negative power. The lens L11 has a concave shape on its side and the reduction side. The cemented lens L23 has negative power.

[0180] Lens L12 (the reducing lens) has positive power. Lens L12 has a convex shape on both its magnifying and reducing surfaces.

[0181] Lens L1 is made of resin. Lenses L2 through L12 are made of glass.

[0182] In the projection optical system 3E, the reduction side from lens L12 is telecentric.

[0183] A first air gap G1, wider than the air gap between other adjacent lenses, is provided between the lens L2 located on the most reduced side of the first sub-lens group 33 and the lens L3 located on the most enlarged side of the second sub-lens group 34.

[0184] 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 L12 is L, the back focus is BF, the maximum half-angle of view of the entire lens system is ω, the distance from the optical axis N to the maximum image height of the projected image formed by the liquid crystal panel 18 is YIM, the focal length of the entire lens system is F, the power of the entire lens system is P, the focal length of lens L1 is Fls, the focal length of lens L12 is Flf, the power of lens L9 in air is Pc1, the Abbe number of lens L9 is Vc1, the power of lens L10 in air is Pc2, the Abbe number of lens L10 is Vc2, the power of lens L11 in air is Pc3, the Abbe number of lens L11 is Vc3, and the focal length of lens L5 is Flp, the data for the projection optical system 3E of Example 5 is as follows.

[0185] Fno 2.000 TTL 105.407mm L 71.407mm Bf 34,000mm ω 49.009° YIM 10.350mm F 9.024mm P 0.111 Fls -43.324mm Flf 28.008mm Pc1 -0.031 Vc1 37.134 Pc2 0.030 Vc2 70.236 Pc3 -0.032 Vc3 29.845 Flp 24.232mm

[0186] The lens data for projection optical system 3E 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.

[0187] Code Surface number RD nd vd S 0 inf 730.000 L01 1* -7.70 2.000 1.5311 55.8 2* -12.59 4.818 L02 3 32.02 1.200 1.9229 20.9 4 13.57 14.884 L03 5 -15.47 1.739 1.8919 37.1 L04 6 17.70 3.293 1.7174 29.5 7 -21.04 0.100 L05 8 43.84 2.132 1.8929 20.4 9 -42.59 0.339 41 10 inf 9.888 L06 11 -64.54 1.000 1.9037 31.3 L07 12 14.95 5.865 1.6393 44.9 13 -31.43 0.348 L08 14* 54.90 7.333 1.4971 81.6 15* -15.58 0.100 L09 16 125.67 1.000 1.8919 37.1 L10 17 23.25 6.034 1.4875 70.2 L11 18 -50.00 1.200 1.8000 29.8 19 50.00 0.10 L12 20 38.12 8.03 1.4970 81.5 21 -20.47 2.00 19 22 inf 27.43 1.5168 64.2 23 inf 4.53 18 24 inf 0.05

[0188] The aspherical coefficients are as follows:

[0189] Face number 1 2 Conic constant: -2.58463E+00 -3.99724E-01 The coefficients of the third order are 4.82890E-03 and 4.71425E-03. The coefficients of the fourth order are 2.94928E-04 and 3.66704E-04. The coefficient of the fifth order is -7.91955E-05, which is 7.64841E-06. The coefficient of the sixth degree is 4.92926E-06 -4.60362E-06 The coefficient of the 7th order is -7.41337E-08, which is 2.14709E-09. The coefficient of the 8th order is -3.72649E-09, which is 2.37266E-08. The coefficient of the 9th degree is 1.47036E-10 -6.58601E-11 The coefficient of the 10th order is -1.17941E-12 and -4.33752E-11.

[0190] Page numbers 14 15 Conic constant -4.68097E+00 2.17431E-01 The coefficient of the fourth order is -2.96461E-05, which is 4.03934E-05. Coefficient of the 6th order: 7.35538E-08 5.27088E-08 The coefficient of the 8th order is -6.27185E-10 -4.59944E-10 The coefficients of the 10th order are 2.96982E-13 and 2.19885E-12. The coefficient of the 12th degree is 1.19210E-14 = 0.00000E+00

[0191] Here, the projection optical system 3E in this example satisfies the following condition (1), where ω is the maximum half-angle of view of the entire lens system. ω > 40 (1)

[0192] In this example, ω 49.009° Therefore, ω = 49.009°, which satisfies condition (1).

[0193] In this example, the projection optical system 3E satisfies all of the following conditions (2), (3), (4), and (5), where L is the total length from the magnifying lens surface of lens L1 to the reducing lens surface of lens L12, 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 L12. 5.0 < L / F < 30.0 (2) BF / F > 2.0 (3) -20.0 < Fls / F < -2.0 (4) 1.6 < Flf / F < 30.0 (5)

[0194] In this example, L 71.407mm F 9.024mm Bf 34,000mm Fls -43.324mm Flf 28.008mm Therefore, L / F = 7.913, satisfying condition (2). BF / F = 3.768, satisfying condition (3). Fls / F = -4.801, satisfying condition (4). Flf / F = 3.104, satisfying condition (5).

[0195] In this example, the projection optical system 3E satisfies the following condition (6) when the total power of the lens system is P, the power of lens L9 in air is Pc1, the Abbe number of lens L9 is Vc1, the power of lens L10 in air is Pc2, the Abbe number of lens L10 is Vc2, the power of lens L11 in air is Pc3, and the Abbe number of lens L11 is Vc3. -0.05 < (Pc1 / P) / Vc1+(Pc2 / P) / Vc2+(Pc3 / P) / Vc3 < 0.01 (6)

[0196] In this example, P 0.111 Pc1 -0.031 Vc1 37.134 Pc2 0.030 Vc2 70.236 Pc3 -0.032 Vc3 29.845 Therefore, (Pc1 / P) / Vc1 + (Pc2 / P) / Vc2 + (Pc3 / P) / Vc3 = -0.014, which satisfies condition (6).

[0197] In this example, the projection optical system 3E satisfies the following conditions (7) and (8), where F is the focal length of the entire lens system, Flp is the focal length of lens L5, and vdp is the Abbe number of lens L5 on the d line. vdp < 40 (7) 1.5 < Flp / F < 15.0 (8)

[0198] In this example, vdp 20.362 F 9.024mm Flp 24.232mm Therefore, vdp = 20.362, satisfying condition (7). Flp / F = 2.685, satisfying condition (8).

[0199] (Effects and Benefits) Since the projection optical system 3E in this example satisfies conditions (1) to (8), it can obtain the same effects as the projection optical system 3A in Example 1.

[0200] 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 L12 has positive power. Therefore, it is easy to make the reduction side from the second lens group 32 telecentric.

[0201] 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 a plastic aspherical lens. With this configuration, it is possible to suppress the field curvature that occurs in the projection optical system 3E.

[0202] 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.

[0203] (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.

[0204] The first lens group 31 comprises, in order from the magnification side to the reduction side, a first sub-lens group 33 having negative power and a second sub-lens group 34 having positive power.

[0205] The first sub-lens group 33 comprises two lenses, L1 and L2. Lenses L1 and L2 are arranged in this order from the magnification side to the reduction side.

[0206] 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.

[0207] The second sub-lens group 34 comprises three lenses L3 to L5. Lenses L3 to L5 are arranged in this order from the magnification side to the reduction side.

[0208] Lenses L3 and L4 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.

[0209] Lens L5 has positive power. Lens L5 has a convex shape on both the magnifying and reducing surfaces. It is equipped with.

[0210] The second lens group 32 comprises seven lenses L6 to L12. Lenses L6 to L12 are arranged in this order from the magnification side to the reduction side.

[0211] 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.

[0212] Lens L8 has positive power. Lens L8 has a convex shape on both the magnifying and reducing surfaces. Lens L8 has an aspherical shape on both sides.

[0213] Lenses L9 (first lens), L10 (second lens), L11 (third lens), and L12 (fourth lens, reduction side lens) are joined together to form a cemented lens L23. 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 reduction side. Lens L10 has positive power. Lens L10 has convex shapes on both the magnifying and reduction sides. Lens L11 has negative power. Lens L11 has concave shapes on both the magnifying and reduction sides. Lens L12 has positive power. Lens L12 is a meniscus lens. Lens L12 has a concave shape on the magnifying side and a convex shape on the reduction side. The cemented lens L23 has positive power.

[0214] Lens L1 is made of resin. Lenses L2 through L12 are made of glass.

[0215] In projection optical system 3F, the reduction side from lens L12 is telecentric.

[0216] A first air gap G1, wider than the air gap between other adjacent lenses, is provided between the lens L2 located on the most reduced side of the first sub-lens group 33 and the lens L3 located on the most enlarged side of the second sub-lens group 34.

[0217] 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 L12 is L, the back focus is BF, the maximum half-angle of view of the entire lens system is ω, the distance from the optical axis N to the maximum image height of the projected image formed by the liquid crystal panel 18 is YIM, the focal length of the entire lens system is F, the power of the entire lens system is P, the focal length of lens L1 is Fls, the focal length of lens L12 is Flf, the power of lens L9 in air is Pc1, the Abbe number of lens L9 is Vc1, the power of lens L10 in air is Pc2, the Abbe number of lens L10 is Vc2, the power of lens L11 in air is Pc3, the Abbe number of lens L11 is Vc3, and the focal length of lens L5 is Flp, the data for the projection optical system 3F of Example 6 is as follows.

[0218] Fno 2.000 TTL 107.822mm L 73.821mm Bf 34,000mm ω 49.024° YIM 10.350mm F 9.024mm P 0.111 Fls -44.333mm Flf 43.166mm Pc1 -0.036 Vc1 37.134 Pc2 0.050 Vc2 67.736 Pc3 -0.034 Vc3 31.343 Flp 25.819mm

[0219] 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.

[0220] Code Surface number RD nd vd S 0 inf 730.000 L01 1* -7.50 2.000 1.5311 55.8 2* -12.00 4.154 L02 3 36.49 1.200 1.9229 20.9 4 14.69 14.756 L03 5 -17.02 2.500 1.8919 37.1 L04 6 17.87 3.093 1.7174 29.5 7 -22.20 0.456 L05 8 40.44 2.018 1.8929 20.4 9 -53.61 0.328 41 10 inf 11.124 L06 11 -84.03 1.000 1.9037 31.3 L07 12 14.48 6.658 1.6393 44.9 13 -40.40 0.200 L08 14* 44.13 7.962 1.4971 81.6 15* -16.01 0.100 L09 16 339.16 1.000 1.8919 37.1 L10 17 22.96 8.362 1.5952 37.7 L11 18 -21.51 1.739 1.9037 31.3 L12 19 -119.37 5.172 1.6400 60.08 20 -22.88 2.000 19 21 inf 27.425 1.5168 64.2 22 inf 4.525 18 23 inf 0.050

[0221] The aspherical coefficients are as follows:

[0222] Face number 1 2 Conic constant: -2.55589E+00 -5.38855E-01 The coefficients of the third order are 4.81457E-03 and 4.75038E-03. The coefficients of the fourth order are 2.99026E-04 and 3.70291E-04. The coefficient of the fifth order is -7.96300E-05, which is 6.96633E-06. The coefficient of the sixth degree is 4.92336E-06 -4.64326E-06 The coefficient of the 7th order is -7.37902E-08 -9.43588E-10 The coefficient of the 8th order is -3.70464E-09, which is 2.35545E-08. The coefficient of the 9th degree is 1.47866E-10 -6.84558E-11 The coefficient of the 10th order is -1.24656E-12 -4.27212E-11

[0223] Page numbers 14 15 Conic constants: 1.01712E+00 2.16921E-01 The coefficient of the fourth order is -2.56806E-05, which is 3.83240E-05. Coefficients of the 6th order: 7.62347E-08 7.17844E-08 The coefficient of the 8th order is -4.35874E-10 -3.80479E-10 The coefficient of the 10th order is 6.31496E-13 and 1.86295E-12. The coefficient of the 12th degree is 4.41245E-16 = 0.00000E+00

[0224] Here, the projection optical system 3F in this example satisfies the following condition (1), where ω is the maximum half-angle of view of the entire lens system. ω > 40 (1)

[0225] In this example, ω 49.024° Therefore, ω = 49.024°, which satisfies condition (1).

[0226] In this example, the projection optical system 3F satisfies all of the following conditions (2), (3), (4), and (5), where L is the total length from the magnifying lens surface of lens L1 to the reducing lens surface of lens L12, 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 L12. 5.0 < L / F < 30.0 (2) BF / F > 2.0 (3) -20.0 < Fls / F < -2.0 (4) 1.6 < Flf / F < 30.0 (5)

[0227] In this example, L 73.821mm F 9.024mm Bf 34,000mm Fls -44.333mm Flf 43.166mm Therefore, L / F = 8.180, satisfying condition (2). BF / F = 3.768, satisfying condition (3). Fls / F = -4.913, satisfying condition (4). Flf / F = 4.783, satisfying condition (5).

[0228] In this example, the projection optical system 3F satisfies the following condition (6) when the total power of the lens system is P, the power of lens L9 in air is Pc1, the Abbe number of lens L9 is Vc1, the power of lens L10 in air is Pc2, the Abbe number of lens L10 is Vc2, the power of lens L11 in air is Pc3, and the Abbe number of lens L11 is Vc3. -0.05 < (Pc1 / P) / Vc1+(Pc2 / P) / Vc2+(Pc3 / P) / Vc3 < 0.01 (6)

[0229] In this example, P 0.111 Pc1 -0.036 Vc1 37.134 Pc2 0.050 Vc2 67.736 Pc3 -0.034 Vc3 31.343 Therefore, (Pc1 / P) / Vc1 + (Pc2 / P) / Vc2 + (Pc3 / P) / Vc3 = -0.012, which satisfies condition (6).

[0230] In this example, the projection optical system 3F satisfies the following conditions (7) and (8), where F is the focal length of the entire lens system, Flp is the focal length of lens L5, and vdp is the Abbe number of lens L5 on the d line. vdp < 40 (7) 1.5 < Flp / F < 15.0 (8)

[0231] In this example, vdp 20.362 F 9.024mm Flp 25.819mm Therefore, vdp = 20.362, satisfying condition (7). Flp / F = 2.861, satisfying condition (8).

[0232] (Effects and Benefits) Since the projection optical system 3F in this example satisfies conditions (1) to (8), it can obtain the same effects as the projection optical system 3A in Example 1.

[0233] 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 L12 has positive power. Therefore, it is easy to make the reduction side from the second lens group 32 telecentric.

[0234] 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.

[0235] In this example, the cemented lens L23 includes a positive-power lens L12 bonded to the reduction side of lens L11. Therefore, chromatic aberration occurring in the second sub-lens group 34 can be further suppressed.

[0236] 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 enlarged image.

[0237] (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.

[0238] The first lens group 31 comprises, in order from the magnification side to the reduction side, a first sub-lens group 33 having negative power and a second sub-lens group 34 having positive power.

[0239] The first sub-lens group 33 comprises three lenses L1 to L3. Lenses L1 to L3 are arranged in this order from the magnification side to the reduction side.

[0240] 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. 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. Lens L3 has aspherical shapes on both sides.

[0241] The second sub-lens group 34 comprises two lenses, L4 and L5. Lenses L4 and L5 are arranged in this order from the magnification side to the reduction side.

[0242] Lenses L4 and L5 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.

[0243] The second lens group 32 comprises five lenses L6 to L10. Lenses L6 to L10 are arranged in this order from the magnification side to the reduction side.

[0244] Lenses L6 (first lens), L7 (second lens), and L8 (third lens) 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 concave shape on its magnifying surface and a convex shape on its reducing surface. The cemented lens L23 has negative power.

[0245] 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.

[0246] Lens L10 (the reducing lens) has positive power. Lens L10 has a convex shape on both the magnifying and reducing surfaces. Lens L10 has an aspherical shape on both sides.

[0247] Lens L3 is made of resin. Lenses L1, L2, L4 through L10 are made of glass.

[0248] In projection optical system 3G, the reduction side from lens L10 is telecentric.

[0249] A first air gap G1, which is wider than the air gap between other adjacent lenses, is provided between the lens L3 located on the most reduced side of the first sub-lens group 33 and the lens L4 located on the most enlarged side of the second sub-lens group 34.

[0250] 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 side surface of lens L1 to the reducing side 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 distance from the optical axis N to the maximum image height of the projected image formed by the liquid crystal panel 18 is YIM, the focal length of the entire lens system is F, the power of the entire lens system is P, the focal length of lens L1 is Fls, the focal length of lens L10 is Flf, and the power of lens L6 in air is Assuming that Pc1 is the Abbe number of lens L6, Pc2 is the power of lens L7 in air, Vc2 is the Abbe number of lens L7, Pc3 is the power of lens L8 in air, Vc3 is the Abbe number of lens L8, and Flp is the focal length of lens L5, the data for the projection optical system 3G of Example 7 is as follows.

[0251] Fno 2.022 TTL 104.024mm L 75,000mm Bf 29.024mm ω 40.801° YIM 10.350mm F 12.134mm P 0.082 Fls -67.029mm Flf 21.642mm Pc1 -0.011 Vc1 48.841 Pc2 0.046 Vc2 81.546 Pc3 -0.051 Vc3 33.793 Flp 15.746mm

[0252] 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.

[0253] 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 18 21 inf 0.05

[0254] The aspherical coefficients are as follows:

[0255] 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

[0256] 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.

[0257] Here, the projection optical system 3G in this example satisfies the following condition (1), where ω is the maximum half-angle of view of the entire lens system. ω > 40 (1)

[0258] In this example, ω 40.801° Therefore, ω = 40.801°, which satisfies condition (1).

[0259] In this example, the projection optical system 3G satisfies all of the following conditions (2), (3), (4), and (5), where L is the total length from the magnifying lens surface of lens L1 to the reducing lens surface of lens L10, 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. 5.0 < L / F < 30.0 (2) BF / F > 2.0 (3) -20.0 < Fls / F < -2.0 (4) 1.6 < Flf / F < 30.0 (5)

[0260] In this example, L 75,000mm F 12.134mm Bf 29.024mm Fls -67.029mm Flf 21.642mm Therefore, L / F = 6.181, satisfying condition (2). BF / F = 2.392, satisfying condition (3). Fls / F = -5.524, satisfying condition (4). Flf / F = 1.784, satisfying condition (5).

[0261] In this example, the projection optical system 3G satisfies the following condition (6) when the total power of the lens system is P, the power of lens L6 in air is Pc1, the Abbe number of lens L6 is Vc1, the power of lens L7 in air is Pc2, the Abbe number of lens L7 is Vc2, the power of lens L8 in air is Pc3, and the Abbe number of lens L8 is Vc3. -0.05 < (Pc1 / P) / Vc1+(Pc2 / P) / Vc2+(Pc3 / P) / Vc3 < 0.01 (6)

[0262] In this example, P 0.082 Pc1 -0.011 Vc1 48.841 Pc2 0.046 Vc2 81.546 Pc3 -0.051 Vc3 33.793 Therefore, (Pc1 / P) / Vc1 + (Pc2 / P) / Vc2 + (Pc3 / P) / Vc3 = -0.014, which satisfies condition (6).

[0263] In this example, the projection optical system 3G satisfies the following conditions (7) and (8), where F is the focal length of the entire lens system, Flp is the focal length of lens L5, and vdp is the Abbe number of lens L5 on the d line. vdp < 40 (7) 1.5 < Flp / F < 15.0 (8)

[0264] In this example, vdp 39.586 F 12.134mm Flp 15.746mm Therefore, vdp = 39.586, satisfying condition (7). Flp / F = 1.298, satisfying condition (8).

[0265] (Effects and Benefits) Since the projection optical system 3G in this example satisfies conditions (1) to (8), it can obtain the same effects as the projection optical system 3A in Example 1.

[0266] 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.

[0267] 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.

[0268] 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 enlarged image.

[0269] (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 lens or positive lens included in the first lens group 31 along the optical axis N direction.

[0270] 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]

[0271] 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 lens Z, 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, 33...First sub-lens group, 34...Second sub-lens group, 41...Aperture diaphragm, L1~L15...Lenses, L21~L23...Coupled lenses, N...Optical axis, S...Screen.

Claims

1. It consists of, in order from the magnification side to the reduction side, a first lens group with refractive power, an aperture diaphragm, and a second lens group with refractive power. The part of the lens group smaller than the second lens group is telecentric. The first lens group comprises, in order from the magnification side to the reduction side, a first sub-lens group having negative power and a second sub-lens group having positive power. A wider air gap than the air gap between other adjacent lenses is provided between the lens located on the most reduced side of the first sub-lens group and the lens located on the most enlarged side of the second sub-lens group. The lens located furthest to the reduction side in the first lens group is a positive lens. The second lens group comprises a cemented lens, The aforementioned cemented lens consists of, in order from the magnification side to the reduction side, a first lens having negative power, a second lens having positive power, and a third lens having negative power. If ω is the maximum half-angle of view of the entire lens system, then the following condition (1) is satisfied, The bonded lens comprises a fourth lens bonded to the reduced side of the third lens, The projection optical system is characterized in that the fourth lens has positive power. ω > 40 (1)

2. In the first lens group, the magnifying lens located at the most magnified end has negative power. The projection optical system according to claim 1, characterized in that the reduction lens located furthest to the reduction side in the second lens group has positive power.

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

4. The projection optical system according to claim 3, characterized in that, if the total length from the magnifying lens surface of the magnifying lens to the reducing lens surface of the reducing lens is L, 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 (2), (3), (4), and (5) are satisfied. 5.0<L / F<30.0 (2) BF / F > 2.0 (3) -20.0 < Fls / F < -2.0 (4) 1.6 < Flf / F < 30.0 (5)

5. The projection optical system according to any one of claims 1 to 4, characterized in that, if the power of the entire lens system is P, the power of the first lens in air is Pc1, the Abbe number of the first lens is Vc1, the power of the second lens in air is Pc2, the Abbe number of the second lens is Vc2, the power of the third lens in air is Pc3, and the Abbe number of the third lens is Vc3, then the following conditional equation (6) is satisfied. -0.05 < (Pc1 / P) / Vc1+(Pc2 / P) / Vc2+(Pc3 / P) / Vc3 < 0.01 (6)

6. The projection optical system according to any one of claims 1 to 5, characterized in that, if the focal length of the entire lens system is F, the focal length of the positive lens is Flp, and the Abbe number on the d line of the positive lens is vdp, then the following conditions (7) and (8) are satisfied. vdp < 40 (7) 1.5 < Flp / F < 15.0 (8)

7. A projection optical system according to any one of claims 1 to 6, An image forming element that forms a projected image on the reduction-side conjugate surface of the projection optical system, A projector characterized by having the following features.

Images