Optical systems and projectors

Abstract

The optical system and projector consist of 6 lenses with an F-value less than 2. The optical system consists of the following lenses in sequence from the magnification side to the reduction side: a first lens with negative refractive power, an aperture stop, a second lens with positive refractive power, an aperture stop, a third lens with positive refractive power, a fourth lens with negative refractive power, a fifth lens with positive refractive power, and a sixth lens with positive refractive power. The third lens and the fourth lens are joined together as a joint lens. The joint lens has negative refractive power. One of the fifth lens and the sixth lens is made of plastic and has aspherical surfaces on two sides, while the other is made of glass. The reduction side of the sixth lens is telecentric. When the effective radius of the aperture stop is SD12 and the effective radius of the second lens is SD2, the following condition (1) is satisfied: SD12 / SD2 < 0.9…(1).

Description

Technical Field

[0001] This invention relates to optical systems and projectors. Background Technology

[0002] Patent Document 1 describes an optical system with six lenses. The optical system in this document, from the reduced-size side, comprises the following lenses in sequence: a first lens with negative refractive power and concave surface facing the image side; a second lens with positive refractive power and acting as a biconvex lens; a third lens with positive refractive power; an aperture stop; a fourth lens L4 with negative refractive power and acting as a biconcave lens; a fifth lens L5 with positive refractive power and convex surface facing the image side; and a sixth lens L6 with positive refractive power and convex surface facing the object side. The optical system disclosed in this document has an F-number of 2.00.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2010-91697

[0004] As an optical system consisting of 6 lenses, a brighter optical system is required. Summary of the Invention

[0005] To solve the above-mentioned problems, the optical system of the present invention is characterized in that the optical system is arranged sequentially from the magnification side to the reduction side as follows: a first lens with negative refractive power, an aperture stop, a second lens with positive refractive power, an aperture stop, a third lens with positive refractive power, a fourth lens with negative refractive power, a fifth lens with positive refractive power, and a sixth lens with positive refractive power, wherein the third lens and the fourth lens are joined together as a combined lens, the combined lens having negative refractive power, one of the fifth lens and the sixth lens is made of plastic and has aspherical surfaces on two sides, the other of the fifth lens and the sixth lens is made of glass, and the reduction side of the sixth lens is telecentric. When the effective radius of the aperture stop is SD12 and the effective radius of the second lens is SD2, the following condition (1) is satisfied:

[0006] SD12 / SD2<0.9…(1).

[0007] Next, the projector of the present invention is characterized in that it has: the optical system described above; and an image forming unit that forms a projected image on the conjugate surface of the reduced side of the optical system. Attached Figure Description

[0008] Figure 1 This is a diagram showing a schematic structure of a projector having the optical system of the present invention.

[0009] Figure 2 It is a ray diagram of an optical system.

[0010] Figure 3This is a ray diagram of the optical system in Example 1.

[0011] Figure 4 This is a diagram showing the longitudinal aberrations, astigmatism, and distortion of Example 1.

[0012] Figure 5 This is a ray diagram of the optical system in Example 2.

[0013] Figure 6 This is a diagram showing the longitudinal aberrations, astigmatism, and distortion of Example 2.

[0014] Figure 7 This is a ray diagram of the optical system in Example 3.

[0015] Figure 8 This is a diagram showing the longitudinal aberrations, astigmatism, and distortion of Example 3.

[0016] Figure 9 This is a ray diagram of the optical system in Example 4.

[0017] Figure 10 This is a diagram showing the longitudinal aberrations, astigmatism, and distortion of Example 4.

[0018] Figure 11 This is a light diagram of the optical system in Example 5.

[0019] Figure 12 This is a diagram showing the longitudinal aberrations, astigmatism, and distortion of Example 5.

[0020] Figure 13 This is a ray diagram of the optical system in Example 6.

[0021] Figure 14 This is a diagram showing the longitudinal aberrations, astigmatism, and distortion of Example 6.

[0022] Figure 15 This is a light diagram of the optical system in Example 7.

[0023] Figure 16 This is a diagram showing the longitudinal aberrations, astigmatism, and distortion of Example 7.

[0024] Figure 17 This is a light diagram of the optical system in Example 8.

[0025] Figure 18 This is a diagram showing the longitudinal aberrations, astigmatism, and distortion of Example 8.

[0026] Label Explanation

[0027] 1: Projector; 2: Image forming unit; 3, 3A, 3B, 3C, 3D, 3E, 3F, 3G, 3H: Optical system; 4: Control unit; 6: Image processing unit; 7: Display driving unit; 10: Light source; 11: Integrating lens; 12: Integrating lens; 13: Polarization conversion element; 14: Overlapping lens; 15: Dichroic mirror; 16: Reflecting mirror; 17R: Field lens; 17G: Field lens; 17B: Field lens; 18 (18B, 18R, 18G): Liquid crystal panel; 19: Cross dichroic prism; 21: Dichroic mirror; 22: Relay lens; 23: Reflecting mirror; 24: Relay lens; 25: Reflecting mirror; 31: Aperture stop; 32: Aperture stop; L1~L6: First~Sixth lens; L21: Joining lens; N: Optical axis; S: Screen. Detailed Implementation

[0028] Hereinafter, the optical system and projector of embodiments of the present invention will be described with reference to the accompanying drawings.

[0029] (Projector)

[0030] Figure 1 This is a diagram showing a schematic structure of a projector having the optical system 3 of the present invention. (See diagram for reference.) Figure 1 As shown, the projector 1 includes: an image forming unit 2 that generates a projected image that is projected onto a screen S; an optical system 3 that magnifies the projected image and projects a magnified image onto the screen S; and a control unit 4 that controls the operation of the image forming unit 2.

[0031] (Image forming unit and control unit)

[0032] The image forming unit 2 includes a light source 10, a first integrating lens 11, a second integrating lens 12, a polarization conversion element 13, and a superimposed lens 14. The light source 10 is, for example, a high-pressure mercury lamp or a solid-state light source. The first integrating lens 11 and the second integrating lens 12 each have multiple lens elements arranged in an array. The first integrating lens 11 divides the light beam from the light source 10 into multiple segments. Each lens element of the first integrating lens 11 converges the light beam from the light source 10 to the vicinity of each lens element of the second integrating lens 12.

[0033] The polarization conversion element 13 converts the light from the second integrating lens 12 into linearly polarized light. The overlapping lens 14 overlaps the images of each lens element of the first integrating lens 11 on the display areas of the liquid crystal panels 18R, 18G, and 18B, which will be described later, via the second integrating lens 12.

[0034] Additionally, the image forming unit 2 includes a first dichroic mirror 15, a reflector 16, a field lens 17R, and a liquid crystal panel 18R. The first dichroic mirror 15 reflects the red light, which is part of the light incident from the overlapping lens 14, while allowing the G light and B light, which are also part of the light incident from the overlapping lens 14, to pass through. The red light reflected by the first dichroic mirror 15 is incident on the liquid crystal panel 18R via the reflector 16 and the field lens 17R. The liquid crystal panel 18R is a light modulation element. The liquid crystal panel 18R modulates the red light according to the image signal, thereby forming a red projected image.

[0035] 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 the G light, which is part of the light from the first dichroic mirror 15, and allows the B light, which is also part of the light from the first dichroic mirror 15, to pass through. The G light reflected by the second dichroic mirror 21 is incident on the liquid crystal panel 18G via the field lens 17G. The liquid crystal panel 18G is a light modulation element. The liquid crystal panel 18G modulates the G light according to the image signal, thereby forming a green projected image.

[0036] Additionally, the image forming unit 2 includes a relay lens 22, a reflector 23, a relay lens 24, a reflector 25, a field lens 17B, a liquid crystal panel 18B, and a cross-shaped dichroic prism 19. B-light, which has passed through the second dichroic mirror 21, is incident on the liquid crystal panel 18B via the relay lens 22, reflector 23, relay lens 24, reflector 25, and field lens 17B. The liquid crystal panel 18B is a light modulation element. The liquid crystal panel 18B modulates the B-light according to the image signal, thereby forming a blue projected image.

[0037] Liquid crystal panels 18R, 18G, and 18B surround the cross-shaped dichroic prism 19 from three directions. The cross-shaped dichroic prism 19 is a prism used for light synthesis, generating a projected image by synthesizing the light modulated by each of the liquid crystal panels 18R, 18G, and 18B.

[0038] The optical system 3 magnifies and projects the image synthesized by the cross dichroic prism 19 onto the screen S.

[0039] The control unit 4 includes: an image processing unit 6, which receives external image signals such as video signals; and a display driving unit 7, which drives the liquid crystal panel 18R, liquid crystal panel 18G, and liquid crystal panel 18B according to the image signals output from the image processing unit 6.

[0040] The image processing unit 6 converts the image signal input from the external device into image signals of various colors, including grayscale. The display driving unit 7 operates the liquid crystal panels 18R, 18G, and 18B according to the projected image signals of various colors 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.

[0041] (Optical System)

[0042] Next, the optical system 3 will be described. Figure 2 This is the ray diagram of optical system 3. Furthermore, in Figure 2 In this context, LCD panel 18R, LCD panel 18G, and LCD panel 18B are referred to as LCD panel 18. For example... Figure 2 As shown, a screen S is disposed on the conjugate surface of the optical system 3 on the magnification side. A liquid crystal panel 18 is disposed on the conjugate surface of the optical system 3 on the reduction side.

[0043] like Figure 2 As shown, the liquid crystal panel 18, disposed on the conjugate surface of the reduction side, forms a projected image on one side of the optical axis N of the optical system 3. The magnified image projected onto the screen S by the optical system 3 is formed on the other side of the optical axis N.

[0044] Hereinafter, embodiments 1 to 8 will be described as examples of the structure of the optical system 3 mounted on the projector 1.

[0045] (Example 1)

[0046] Figure 3 This is a ray diagram of the optical system 3A in Example 1. (As shown) Figure 3 As shown, the optical system 3A has six lenses, from the first lens L1 to the sixth lens L6. The first lens L1 to the sixth lens L6 are arranged sequentially from the magnifying side to the reducing side.

[0047] Lens L1 has negative refractive power. The magnifying side of lens L1 is convex, and the reducing side is concave. Lens L1 has aspherical surfaces on both sides. Lens L2 has positive refractive power. The magnifying and reducing sides of lens L2 are convex. Lens L2 has spherical surfaces on both sides. Lens L3 has positive refractive power. The magnifying and reducing sides of lens L3 are convex. Lens L3 has spherical surfaces on both sides. Lens L4 has negative refractive power. The magnifying and reducing sides of lens L4 are concave. Lens L4 has spherical surfaces on both sides.

[0048] The fifth lens L5 has positive refractive power. The magnifying and reducing surfaces of the fifth lens L5 are convex. The fifth lens L5 has spherical surfaces on both surfaces. The sixth lens L6 has positive refractive power. The magnifying and reducing surfaces of the sixth lens L6 are convex. The sixth lens L6 has aspherical surfaces on both surfaces. The first lens L1 and the sixth lens L6 are made of plastic. The second lens L2, the third lens L3, the fourth lens L4, and the fifth lens L5 are made of glass. The third lens L3 and the fourth lens L4 are combined into a joint lens L21.

[0049] Optical system 3A has an aperture stop 31 and an aperture stop 32. Aperture stop 31 is disposed between the first lens L1 and the second lens L2. Aperture stop 31 is a light-shielding component provided in the lens barrel or the like that holding each lens. Aperture stop 31 blocks peripheral light beams in the light beam passing between the first lens L1 and the second lens L2. Aperture stop 32 is disposed between the second lens L2 and the third lens L3. Aperture stop 32 defines the brightness of optical system 3A. The opening diameter of aperture stop 32 is the opening diameter of the entrance pupil of optical system 3A.

[0050] In optical system 3A, the reduction side of the sixth lens L6 is telecentric. Telecentricity of the reduction side means that the central rays of each beam passing through the sixth lens L6 and the liquid crystal panel 18 disposed on the conjugate surface of the reduction side are parallel to or approximately parallel to the optical axis. In this example, the angle between the central rays of each beam and the optical axis N is within ±5°.

[0051] With the F-number of optical system 3A set to FNo, the total optical length set to TTL, the distance on the optical axis N from the magnifying side of the first lens L1 to the reducing side of the sixth lens L6 set to L, the back focal length (the total value of the on-axis spacing D from surface number 14 to surface number 18 recorded in the lens data) set to BF, the sum of the wall thicknesses on the optical axis N of the first lens L1, second lens L2, third lens L3, fourth lens L4, fifth lens L5 and sixth lens L6 set to LTH, the on-axis spacing between the first lens L1 and the second lens L2 set to D12, the effective radius of the aperture set to SD12, the effective radius of the second lens L2 set to SD2, the focal length of the entire system set to F, the focal length of the glass fifth lens L5 set to Fg, the focal length of the plastic sixth lens L6 set to Fp, the diameter of the entrance pupil set to φent, and the Abbe number of the d-line of the second lens L2 set to νd2, the data of optical system 3A in Embodiment 1 are as follows.

[0052]

[0053] The lens data for optical system 3A is as follows. Surface numbers are sequentially labeled from the magnifying side to the reducing side. These labels correspond to the screen, lens, aperture stop, dichroic prism, and LCD panel. Surface numbers not corresponding to the screen, lens, aperture stop, dichroic prism, or LCD panel are fictitious. Surfaces marked with an asterisk (*) are aspherical. R is the radius of curvature. D is the on-axis spacing. nd is the refractive index. νd is the Abbe number of the d-line. The units for R and D are mm.

[0054]

[0055] The aspherical coefficients are as follows.

[0056]

[0057] (Effects)

[0058] The optical system 3A in this example comprises the following components arranged sequentially from the magnifying side to the reducing side: a first lens L1 with negative refractive power, an aperture stop 31 for light blocking, a second lens L2 with positive refractive power, an aperture stop 32, a third lens L3 with positive refractive power, a fourth lens L4 with negative refractive power, a fifth lens L5 with positive refractive power, and a sixth lens L6 with positive refractive power. The third lens L3 and the fourth lens L4 are joined together by a bonding lens L21. The bonding lens L21 has negative refractive power. The fifth lens L5 is made of glass and has spherical surfaces on two sides. The sixth lens L6 is made of plastic and has aspherical surfaces on two sides. Furthermore, in the optical system 3A, the reducing side of the sixth lens L6 is telecentric.

[0059] In addition, when the effective radius of the aperture 31 of the optical system 3A in this example is set to SD12 and the effective radius of the second lens L2 is set to SD2, the following condition (1) is satisfied.

[0060] SD12 / SD2 < 0.9…(1)

[0061] The optical system 3A in this example, by setting the refractive power and arrangement of the six lenses as described above, can ensure a brightness of F-number 1.6 or higher and effectively correct various aberrations. Furthermore, a light-blocking stop 31 is disposed between the first lens L1 and the second lens L2, and an aperture stop 32 is disposed between the second lens L2 and the third lens L3. Therefore, even with a relatively small number of lenses constituting the projection lens—such as six—performance degradation in the peripheral region of the magnified image can be suppressed.

[0062] Here, condition (1) is the ratio of the effective radius SD12 of the aperture used for light blocking to the effective radius SD2 of the second lens. The optical system 3A in this example satisfies condition (1), and therefore can properly block the peripheral light of the projected light.

[0063] That is, in this example,

[0064] SD12 10.300mm.

[0065] SD2 14.223mm.

[0066] Therefore, SD12 / SD2 = 0.724.

[0067] Furthermore, in this example, the sixth lens L6 is a plastic aspherical lens, and the fifth lens L5 is a glass spherical lens. Therefore, compared to the case where both the fifth lens L5 and the sixth lens L6 are glass spherical lenses, various aberrations can be corrected much better. Additionally, the coefficient of thermal expansion of a glass lens is smaller than that of a plastic lens. Therefore, compared to the case where both the fifth lens L5 and the sixth lens L6 are plastic aspherical lenses, the effects of heat on the optical system can be suppressed.

[0068] In the optical system 3A of this example, the reduction side is telecentric. Therefore, compared to the case where the reduction side is not telecentric, the setting accuracy relative to the liquid crystal panel 18 is less stringent when assembling the optical system 3A to the projector 1. In addition, the projected light from the liquid crystal panel 18 becomes parallel light, thus making it easier to suppress various aberrations generated in the optical system 3A.

[0069] In this example, the first lens L1 is made of plastic and has aspherical surfaces on two sides. This gives the first lens L1, located on the magnifying side, a degree of freedom in shape. Therefore, it is easy to correct distortions and aberrations generated in the magnified image.

[0070] In this example, the third lens L3 and the fourth lens L4 are made of glass. Therefore, these two lenses can easily be used as a joining lens.

[0071] In this example, when the focal length of the plastic sixth lens L6 is set to Fp and the focal length of the glass fifth lens L5 is set to Fg, the following condition (2) is satisfied.

[0072] 0.3 < Fg / Fp < 0.8…(2)

[0073] That is, in this example,

[0074] Fg 34.595mm

[0075] Fp 60.000mm

[0076] therefore,

[0077] Fg / Fp = 0.577

[0078] The optical system 3A in this example satisfies condition (2), thus suppressing heat-induced resolution degradation and effectively correcting various aberrations. That is, when the value of condition (2) exceeds the upper limit, aberration correction is possible, but the plastic sixth lens L6 is easily affected by heat, leading to resolution degradation. When the value of condition (2) exceeds the lower limit, heat-induced resolution degradation is suppressed, but aberration correction becomes difficult.

[0079] In this example, when the Abbe number of the d-line of the second lens L2 is set to vd2, the following condition (3) is satisfied.

[0080] vd2<45…(3)

[0081] That is, in this example,

[0082] vd2 = 32.270

[0083] The optical system 3A satisfies condition (3), so it is easy to correct the chromatic aberration generated in the first lens.

[0084] In this example, when the sum of the wall thicknesses on the optical axis N of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5 and the sixth lens L6 is set as LTH, and the distance on the optical axis N from the magnifying side of the first lens L1 to the reducing side of the sixth lens L6 is set as L, the following condition (4) is satisfied.

[0085] 0.25 < LTH / L < 0.5…(4)

[0086] That is, in this example,

[0087] LTH 27.053mm

[0088] L 79.520mm

[0089] therefore,

[0090] LTH / L = 0.340

[0091] The optical system 3A in this example satisfies condition (4), thus making the manufacture of each lens easier and suppressing the heat-induced degradation of the magnified image resolution. That is, when the value of condition (4) exceeds the upper limit, the wall thickness of each lens increases, making each lens more susceptible to heat. Therefore, the resolution of the optical system is easily degraded due to heat. When the value of condition (4) exceeds the upper limit, the heat-induced degradation of the optical system resolution can be suppressed, but the wall thickness of each lens needs to be thinned, making it difficult to manufacture lenses with the required refractive power.

[0092] In this example, when the axial spacing between the first lens L1 and the second lens L2 is set to D12, and the distance on the optical axis N from the magnifying side of the first lens L1 to the reducing side of the sixth lens L6 is set to L, the following condition (5) is satisfied.

[0093] 0.2 < D12 / L < 0.5…(5)

[0094] That is, in this example,

[0095] D12 28.389mm

[0096] L 79.520mm

[0097] therefore,

[0098] D12 / L=0.357

[0099] The optical system 3A in this example satisfies condition (5), thus suppressing the reduction in peripheral light intensity of the projected light and preventing the overall length of the optical system 3A from becoming too large. That is, the optical system 3A in this example satisfies condition (5), so the air gap between the first lens L1 and the second lens L2 is appropriate, and the diffusion of the projected light between the first lens L1 and the second lens L2 is appropriate. As a result, it is easy to correct each aberration at each image height. In particular, it is easy to correct astigmatism at each image height, thus ensuring the peripheral light intensity of the projected light. Here, when the value of condition (5) exceeds the upper limit, it is easy to correct astigmatism and ensure the peripheral light intensity of the projected light, but the overall length of the optical system 3A tends to increase. When the value of condition (5) exceeds the lower limit, it is easy to reduce the overall length of the optical system 3A, but insufficient correction of astigmatism leads to a reduction in peripheral light intensity.

[0100] In this example, when the focal length of the entire system is set to F and the diameter of the incident pupil is set to φent, the following condition (6) is satisfied.

[0101] F / φent<1.6…(6)

[0102] That is, in this example,

[0103] F 16.518mm

[0104] φent 11.485mm

[0105] therefore,

[0106] F / φent=1.438

[0107] In this example, the optical system 3A satisfies condition (6), therefore the optical system has sufficient brightness.

[0108] Figure 4This is a diagram showing the longitudinal aberrations, astigmatism, and distortion of the magnified image in optical system 3A. For example... Figure 4 As shown, the optical system 3A in this example suppresses various aberrations in the magnified image.

[0109] (Example 2)

[0110] Figure 5 This is a ray diagram of the optical system 3B in Example 2. (As shown) Figure 5 As shown, the optical system 3B has six lenses, from the first lens L1 to the sixth lens L6. The first lens L1 to the sixth lens L6 are arranged sequentially from the magnifying side to the reducing side.

[0111] Lens L1 has negative refractive power. The magnifying side of lens L1 is convex, and the reducing side is concave. Lens L1 has aspherical surfaces on both sides. Lens L2 has positive refractive power. The magnifying and reducing sides of lens L2 are convex. Lens L2 has spherical surfaces on both sides. Lens L3 has positive refractive power. The magnifying and reducing sides of lens L3 are convex. Lens L3 has spherical surfaces on both sides. Lens L4 has negative refractive power. The magnifying and reducing sides of lens L4 are concave. Lens L4 has spherical surfaces on both sides.

[0112] The fifth lens L5 has positive refractive power. The surface of the fifth lens L5 facing the magnifying side is concave, and the surface facing the reducing side is convex. The fifth lens L5 has aspherical surfaces on both surfaces. The sixth lens L6 has positive refractive power. The surface of the sixth lens L6 facing the magnifying side is concave, and the surface facing the reducing side is convex. The sixth lens L6 has spherical surfaces on both surfaces. The first lens L1 and the fifth lens L5 are made of plastic. The second lens L2, the third lens L3, the fourth lens L4, and the sixth lens L6 are made of glass. The third lens L3 and the fourth lens L4 are combined into a joint lens L21.

[0113] Optical system 3B has an aperture stop 31 and an aperture diaphragm 32. Aperture stop 31 is disposed between the first lens L1 and the second lens L2. Aperture stop 31 is a light-shielding component provided in the lens barrel or the like that holding each lens. Aperture stop 31 blocks peripheral light beams in the light beam passing between the first lens L1 and the second lens L2. Aperture stop 32 is disposed between the second lens L2 and the third lens L3. Aperture stop 32 defines the brightness of optical system 3B. The opening diameter of aperture stop 32 is the opening diameter of the entrance pupil of optical system 3B.

[0114] In optical system 3B, the reduction side of the sixth lens L6 is telecentric. Telecentricity of the reduction side means that the central rays of each beam passing through the sixth lens L6 and the liquid crystal panel 18 disposed on the conjugate surface of the reduction side are parallel to or approximately parallel to the optical axis. In this example, the angle between the central rays of each beam and the optical axis N is within ±5°.

[0115] With the F-number of optical system 3B set to FNo, the total optical length set to TTL, the distance on the optical axis N from the magnifying side of the first lens L1 to the reducing side of the sixth lens L6 set to L, the back focal length (the total value of the on-axis spacing D from surface number 14 to surface number 18 recorded in the lens data) set to BF, the sum of the wall thicknesses on the optical axis N of the first lens L1, second lens L2, third lens L3, fourth lens L4, fifth lens L5 and sixth lens L6 set to LTH, the on-axis spacing between the first lens L1 and the second lens L2 set to D12, the effective radius of the aperture set to SD12, the effective radius of the second lens L2 set to SD2, the focal length of the entire system set to F, the focal length of the glass sixth lens L6 set to Fg, the focal length of the plastic fifth lens L5 set to Fp, the diameter of the entrance pupil set to φent, and the Abbe number of the d-line of the second lens L2 set to νd2, the data of optical system 3B in Embodiment 2 are as follows.

[0116]

[0117] The lens data for optical system 3B is as follows. Surface numbers are sequentially labeled from the magnifying side to the reducing side. These labels correspond to the screen, lens, aperture stop, dichroic prism, and LCD panel. Surface numbers not corresponding to the screen, lens, aperture stop, dichroic prism, or LCD panel are fictitious. Surfaces marked with an asterisk (*) are aspherical. R is the radius of curvature. D is the on-axis spacing. nd is the refractive index. νd is the Abbe number of the d-line. R and D are in mm.

[0118]

[0119] The aspherical coefficients are as follows.

[0120]

[0121] In this example, when the effective radius of the aperture 31 is set to SD12 and the effective radius of the second lens L2 is set to SD2, the following condition (1) is satisfied.

[0122] SD12 / SD2 < 0.9…(1)

[0123] In this example,

[0124] SD12 10.975mm

[0125] SD2 13.315mm

[0126] therefore,

[0127] SD12 / SD2 = 0.824

[0128] In this example, when the focal length of the fifth lens L5 made of plastic is set to Fp and the focal length of the sixth lens L6 made of glass is set to Fg, the following condition (2) is satisfied.

[0129] 0.3 < Fg / Fp < 0.8…(2)

[0130] In this example,

[0131] Fg 35.495mm

[0132] Fp 71.722mm

[0133] therefore,

[0134] Fg / Fp = 0.495

[0135] In this example, when the Abbe number of the d-line of the second lens L2 is set to vd2, the following condition (3) is satisfied.

[0136] vd2<45…(3)

[0137] In this example,

[0138] vd2 = 37.160

[0139] In this example, when the sum of the wall thicknesses on the optical axis N of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5 and the sixth lens L6 is set as LTH, and the distance on the optical axis N from the magnifying side of the first lens L1 to the reducing side of the sixth lens L6 is set as L, the following condition (4) is satisfied.

[0140] 0.25 < LTH / L < 0.5…(4)

[0141] In this example,

[0142] LTH 24.225mm

[0143] L 79.520mm

[0144] therefore,

[0145] LTH / L = 0.305

[0146] In this example, when the axial spacing between the first lens L1 and the second lens L2 is set to D12, and the distance on the optical axis N from the magnifying side of the first lens L1 to the reducing side of the sixth lens L6 is set to L, the following condition (5) is satisfied.

[0147] 0.2 < D12 / L < 0.5…(5)

[0148] In this example,

[0149] D12 26.668mm

[0150] L 79.520mm

[0151] therefore,

[0152] D12 / L=0.335

[0153] In this example, when the focal length of the entire system is set to F and the diameter of the incident pupil is set to φent, the following condition (6) is satisfied.

[0154] F / φent<1.6…(6)

[0155] In this example,

[0156] F 16.451mm

[0157] φent 11.443mm

[0158] therefore,

[0159] F / φent=1.438

[0160] (Effects)

[0161] The optical system 3B in this example can achieve the same effect as the optical system 3A in Example 1. Figure 6 This is a diagram showing the longitudinal aberrations, astigmatism, and distortion of the magnified image in optical system 3B. For example... Figure 6 As shown, the optical system 3B in this example suppresses various aberrations in the magnified image.

[0162] (Example 3)

[0163] Figure 7 This is a ray diagram of the optical system 3C in Example 3. For example... Figure 7 As shown, the optical system 3C has six lenses, from the first lens L1 to the sixth lens L6. The first lens L1 to the sixth lens L6 are arranged sequentially from the magnifying side to the reducing side.

[0164] Lens L1 has negative refractive power. The magnifying side of lens L1 is convex, and the reducing side is concave. Lens L1 has aspherical surfaces on both sides. Lens L2 has positive refractive power. The magnifying and reducing sides of lens L2 are convex. Lens L2 has spherical surfaces on both sides. Lens L3 has positive refractive power. The magnifying and reducing sides of lens L3 are convex. Lens L3 has spherical surfaces on both sides. Lens L4 has negative refractive power. The magnifying and reducing sides of lens L4 are concave. Lens L4 has spherical surfaces on both sides.

[0165] The fifth lens L5 has positive refractive power. The surface of the fifth lens L5 facing the magnifying side is concave, and the surface facing the reducing side is convex. The fifth lens L5 has aspherical surfaces on both surfaces. The sixth lens L6 has positive refractive power. The surface of the sixth lens L6 facing the magnifying side is concave, and the surface facing the reducing side is convex. The sixth lens L6 has spherical surfaces on both surfaces. The first lens L1 and the fifth lens L5 are made of plastic. The second lens L2, the third lens L3, the fourth lens L4, and the sixth lens L6 are made of glass. The third lens L3 and the fourth lens L4 are combined into a joint lens L21.

[0166] Optical system 3C has an aperture stop 31 and an aperture stop 32. Aperture stop 31 is disposed between the first lens L1 and the second lens L2. Aperture stop 31 is a light-shielding component provided in the lens barrel or the like that holding each lens. Aperture stop 31 blocks peripheral light beams in the light beam passing between the first lens L1 and the second lens L2. Aperture stop 32 is disposed between the second lens L2 and the third lens L3. Aperture stop 32 defines the brightness of optical system 3C. The opening diameter of aperture stop 32 is the opening diameter of the entrance pupil of optical system 3C.

[0167] In the optical system 3C, the reduction side of the sixth lens L6 is telecentric. Telecentricity of the reduction side means that the central rays of each beam passing through the sixth lens L6 and the liquid crystal panel 18 disposed on the conjugate surface of the reduction side are parallel to or approximately parallel to the optical axis. In this example, the angle between the central rays of each beam and the optical axis N is within ±5°.

[0168] With the F-number of optical system 3C set to FNo, the total optical length set to TTL, the distance on the optical axis N from the magnifying side of the first lens L1 to the reducing side of the sixth lens L6 set to L, the back focal length (the total value of the on-axis spacing D from surface number 14 to surface number 18 recorded in the lens data) set to BF, the sum of the wall thicknesses on the optical axis N of the first lens L1, second lens L2, third lens L3, fourth lens L4, fifth lens L5 and sixth lens L6 set to LTH, the on-axis spacing between the first lens L1 and the second lens L2 set to D12, the effective radius of the aperture set to SD12, the effective radius of the second lens L2 set to SD2, the focal length of the entire system set to F, the focal length of the glass sixth lens L6 set to Fg, the focal length of the plastic fifth lens L5 set to Fp, the diameter of the entrance pupil set to φent, and the Abbe number of the d-line of the second lens L2 set to νd2, the data of optical system 3C in embodiment 3 are as follows.

[0169]

[0170] The lens data for 3C optical systems is as follows. Surface numbers are sequentially labeled from the magnifying side to the reducing side. These labels correspond to the screen, lens, aperture stop, dichroic prism, and LCD panel. Surface numbers not corresponding to the screen, lens, aperture stop, dichroic prism, or LCD panel are fictitious. Surfaces marked with an asterisk (*) are aspherical. R is the radius of curvature. D is the on-axis spacing. nd is the refractive index. νd is the Abbe number of the d-line. R and D are in mm.

[0171]

[0172] The aspherical coefficients are as follows.

[0173]

[0174] Here, in this example, when the effective radius of the aperture 31 is set to SD12 and the effective radius of the second lens L2 is set to SD2, the following condition (1) is satisfied.

[0175] SD12 / SD2 < 0.9…(1)

[0176] In this example,

[0177] SD12 10.700mm

[0178] SD2 13.586mm

[0179] therefore,

[0180] SD12 / SD2 = 0.788

[0181] In this example, when the focal length of the fifth lens L5 made of plastic is set to Fp and the focal length of the sixth lens L6 made of glass is set to Fg, the following condition (2) is satisfied.

[0182] 0.3 < Fg / Fp < 0.8…(2)

[0183] In this example,

[0184] Fg 35.772mm

[0185] Fp 70.000mm

[0186] therefore,

[0187] Fg / Fp = 0.511

[0188] In this example, when the Abbe number of the d-line of the second lens L2 is set to vd2, the following condition (3) is satisfied.

[0189] vd2<45…(3)

[0190] In this example,

[0191] vd2 = 40.100

[0192] In this example, when the sum of the wall thicknesses on the optical axis N of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5 and the sixth lens L6 is set as LTH, and the distance on the optical axis N from the magnifying side of the first lens L1 to the reducing side of the sixth lens L6 is set as L, the following condition (4) is satisfied.

[0193] 0.25 < LTH / L < 0.5…(4)

[0194] In this example,

[0195] LTH 23.798mm

[0196] L 79.520mm

[0197] therefore,

[0198] LTH / L = 0.299

[0199] In this example, when the axial spacing between the first lens L1 and the second lens L2 is set to D12, and the distance on the optical axis N from the magnifying side of the first lens L1 to the reducing side of the sixth lens L6 is set to L, the following condition (5) is satisfied.

[0200] 0.2 < D12 / L < 0.5…(5)

[0201] In this example,

[0202] D12 27.493mm

[0203] L 79.520mm

[0204] therefore,

[0205] D12 / L=0.346

[0206] In this example, when the focal length of the entire system is set to F and the diameter of the incident pupil is set to φent, the following condition (6) is satisfied.

[0207] F / φent<1.6…(6)

[0208] In this example,

[0209] F 16.451mm

[0210] φent 11.439mm

[0211] therefore,

[0212] F / φent=1.438

[0213] (Effects)

[0214] The optical system 3C in this example can achieve the same effect as the optical system 3A in Example 1. Figure 8 This is a diagram showing the longitudinal aberrations, astigmatism, and distortion of a magnified image in an optical system (3C). For example... Figure 8 As shown, the optical system 3C in this example suppresses various aberrations in the magnified image.

[0215] (Example 4)

[0216] Figure 9 This is a 3D ray diagram of the optical system in Example 4. For example... Figure 9 As shown, the optical system 3D has six lenses, from the first lens L1 to the sixth lens L6. The first lens L1 to the sixth lens L6 are arranged sequentially from the magnifying side to the reducing side.

[0217] Lens L1 has negative refractive power. The magnifying side of lens L1 is convex, and the reducing side is concave. Lens L1 has aspherical surfaces on both sides. Lens L2 has positive refractive power. The magnifying and reducing sides of lens L2 are convex. Lens L2 has spherical surfaces on both sides. Lens L3 has positive refractive power. The magnifying and reducing sides of lens L3 are convex. Lens L3 has spherical surfaces on both sides. Lens L4 has negative refractive power. The magnifying and reducing sides of lens L4 are concave. Lens L4 has spherical surfaces on both sides.

[0218] The fifth lens L5 has positive refractive power. The surface of the fifth lens L5 facing the magnifying side is concave, and the surface facing the reducing side is convex. The fifth lens L5 has aspherical surfaces on both surfaces. The sixth lens L6 has positive refractive power. The surfaces of the sixth lens L6 facing the magnifying and reducing sides are convex. The sixth lens L6 has spherical surfaces on both surfaces. The first lens L1 and the fifth lens L5 are made of plastic. The second lens L2, the third lens L3, the fourth lens L4, and the sixth lens L6 are made of glass. The third lens L3 and the fourth lens L4 are combined into a joint lens L21.

[0219] The 3D optical system has an aperture stop 31 and an aperture diaphragm 32. The aperture stop 31 is positioned between a first lens L1 and a second lens L2. The aperture stop 31 is a light-shielding component disposed in the lens barrel or similar structure that holds the lenses. The aperture stop 31 blocks peripheral light beams in the light beam passing between the first lens L1 and the second lens L2. The aperture diaphragm 32 is positioned between the second lens L2 and a third lens L3. The aperture diaphragm 32 determines the brightness of the 3D optical system. The opening diameter of the aperture diaphragm 32 is the opening diameter of the entrance pupil of the 3D optical system.

[0220] In the 3D optical system, the reduction side of the sixth lens L6 is telecentric. Telecentricity of the reduction side means that the central rays of each beam passing through the sixth lens L6 and the liquid crystal panel 18 disposed on the conjugate surface of the reduction side are parallel to or approximately parallel to the optical axis. In this example, the angle between the central rays of each beam and the optical axis N is within ±5°.

[0221] With the F-number of the optical system 3D set to FNo, the total optical length set to TTL, the distance on the optical axis N from the magnifying side of the first lens L1 to the reducing side of the sixth lens L6 set to L, the back focal length (the total value of the on-axis spacing D from surface number 14 to surface number 18 recorded in the lens data) set to BF, the sum of the wall thicknesses on the optical axis N of the first lens L1, second lens L2, third lens L3, fourth lens L4, fifth lens L5 and sixth lens L6 set to LTH, the on-axis spacing between the first lens L1 and the second lens L2 set to D12, the effective radius of the aperture set to SD12, the effective radius of the second lens L2 set to SD2, the focal length of the entire system set to F, the focal length of the glass sixth lens L6 set to Fg, the focal length of the plastic fifth lens L5 set to Fp, the diameter of the entrance pupil set to φent, and the Abbe number of the d-line of the second lens L2 set to νd2, the data of the optical system 3D in Example 4 are as follows.

[0222]

[0223] The lens data for the 3D optical system is as follows. Surface numbers are sequentially labeled from the magnifying side to the reducing side. These labels correspond to the screen, lens, aperture stop, dichroic prism, and LCD panel. Surface numbers not corresponding to the screen, lens, aperture stop, dichroic prism, or LCD panel are fictitious. Surfaces marked with an asterisk (*) are aspherical. R is the radius of curvature. D is the on-axis spacing. nd is the refractive index. vd is the Abbe number of the d-line. R and D are in mm.

[0224]

[0225] The aspherical coefficients are as follows.

[0226]

[0227] In this example, when the effective radius of the aperture 31 is set to SD12 and the effective radius of the second lens L2 is set to SD2, the following condition (1) is satisfied.

[0228] SD12 / SD2 < 0.9…(1)

[0229] In this example,

[0230] SD12 10.300mm

[0231] SD2 14.500mm

[0232] therefore,

[0233] SD12 / SD2 = 0.710

[0234] In this example, when the focal length of the fifth lens L5 made of plastic is set to Fp and the focal length of the sixth lens L6 made of glass is set to Fg, the following condition (2) is satisfied.

[0235] 0.3 < Fg / Fp < 0.8…(2)

[0236] In this example,

[0237] Fg 36.941mm

[0238] Fp 65.000mm

[0239] therefore,

[0240] Fg / Fp = 0.568

[0241] In this example, when the Abbe number of the d-line of the second lens L2 is set to vd2, the following condition (3) is satisfied.

[0242] vd2<45…(3)

[0243] In this example,

[0244] vd2 = 31.343

[0245] In this example, if the sum of the wall thicknesses on the optical axis N of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5 and the sixth lens L6 is set as LTH, and the distance on the optical axis N from the magnifying side of the first lens L1 to the reducing side of the sixth lens L6 is set as L, then the following condition (4) is satisfied.

[0246] 0.25 < LTH / L < 0.5…(4)

[0247] In this example,

[0248] LTH 23.171mm

[0249] L 80.050mm

[0250] therefore,

[0251] LTH / L = 0.289

[0252] In this example, when the axial spacing between the first lens L1 and the second lens L2 is set to D12, and the distance on the optical axis N from the magnifying side of the first lens L1 to the reducing side of the sixth lens L6 is set to L, the following condition (5) is satisfied.

[0253] 0.2 < D12 / L < 0.5…(5)

[0254] In this example,

[0255] D12 31.803mm

[0256] L 80.050mm

[0257] therefore,

[0258] D12 / L=0.397

[0259] In this example, when the focal length of the entire system is set to F and the diameter of the incident pupil is set to φent, the following condition (6) is satisfied.

[0260] F / φent<1.6…(6)

[0261] In this example,

[0262] F 16.451mm

[0263] φent 11.445mm

[0264] therefore,

[0265] F / φent=1.437

[0266] (Effects)

[0267] The optical system 3D in this example can achieve the same effect as the optical system 3A in Example 1. Figure 10 This is a diagram illustrating the longitudinal aberrations, astigmatism, and distortion of a magnified image in a 3D optical system. For example... Figure 10 As shown, the optical system in this example 3D suppresses various aberrations in the magnified image.

[0268] (Example 5)

[0269] Figure 11 This is a ray diagram of the optical system 3E in Example 5. (As shown...) Figure 11 As shown, the optical system 3E has six lenses, from the first lens L1 to the sixth lens L6. The first lens L1 to the sixth lens L6 are arranged sequentially from the magnifying side to the reducing side.

[0270] Lens L1 has negative refractive power. The magnifying side of lens L1 is convex, and the reducing side is concave. Lens L1 has aspherical surfaces on both sides. Lens L2 has positive refractive power. The magnifying and reducing sides of lens L2 are convex. Lens L2 has spherical surfaces on both sides. Lens L3 has positive refractive power. The magnifying and reducing sides of lens L3 are convex. Lens L3 has spherical surfaces on both sides. Lens L4 has negative refractive power. The magnifying and reducing sides of lens L4 are concave. Lens L4 has spherical surfaces on both sides.

[0271] The fifth lens L5 has positive refractive power. The magnifying and reducing surfaces of the fifth lens L5 are convex. The fifth lens L5 has spherical surfaces on both surfaces. The sixth lens L6 has positive refractive power. The magnifying and reducing surfaces of the sixth lens L6 are convex. The sixth lens L6 has aspherical surfaces on both surfaces. The first lens L1 and the sixth lens L6 are made of plastic. The second lens L2, the third lens L3, the fourth lens L4, and the fifth lens L5 are made of glass. The third lens L3 and the fourth lens L4 are combined into a joint lens L21.

[0272] Optical system 3E has an aperture stop 31 and an aperture stop 32. Aperture stop 31 is disposed between the first lens L1 and the second lens L2. Aperture stop 31 is a light-shielding component provided in the lens barrel or the like that holding each lens. Aperture stop 31 blocks peripheral light beams in the light beam passing between the first lens L1 and the second lens L2. Aperture stop 32 is disposed between the second lens L2 and the third lens L3. Aperture stop 32 defines the brightness of optical system 3E. The opening diameter of aperture stop 32 is the opening diameter of the entrance pupil of optical system 3E.

[0273] In optical system 3E, the reduction side of the sixth lens L6 is telecentric. Telecentricity of the reduction side means that the central rays of each beam passing through the sixth lens L6 and the liquid crystal panel 18 disposed on the conjugate surface of the reduction side are parallel to or approximately parallel to the optical axis. In this example, the angle between the central rays of each beam and the optical axis N is within ±5°.

[0274] With the F-number of optical system 3E set to FNo, the total optical length set to TTL, the distance on the optical axis N from the magnifying side of the first lens L1 to the reducing side of the sixth lens L6 set to L, the back focal length (the total value of the on-axis spacing D from surface number 14 to surface number 18 recorded in the lens data) set to BF, the sum of the wall thicknesses on the optical axis N of the first lens L1, second lens L2, third lens L3, fourth lens L4, fifth lens L5 and sixth lens L6 set to LTH, the on-axis spacing between the first lens L1 and the second lens L2 set to D12, the effective radius of the aperture set to SD12, the effective radius of the second lens L2 set to SD2, the focal length of the entire system set to F, the focal length of the glass fifth lens L5 set to Fg, the focal length of the plastic sixth lens L6 set to Fp, the diameter of the entrance pupil set to φent, and the Abbe number of the d-line of the second lens L2 set to νd2, the data of optical system 3E in Embodiment 5 are as follows.

[0275]

[0276] The lens data for the 3E optical system is as follows. Surface numbers are sequentially labeled from the magnifying side to the reducing side. These labels correspond to the screen, lens, aperture stop, dichroic prism, and LCD panel. Surface numbers not corresponding to the screen, lens, aperture stop, dichroic prism, or LCD panel are fictitious. Surfaces marked with an asterisk (*) are aspherical. R is the radius of curvature. D is the on-axis spacing. nd is the refractive index. νd is the Abbe number of the d-line. R and D are in mm.

[0277]

[0278] The aspherical coefficients are as follows.

[0279]

[0280] In this example, when the effective radius of the aperture 31 is set to SD12 and the effective radius of the second lens L2 is set to SD2, the following condition (1) is satisfied.

[0281] SD12 / SD2 < 0.9…(1)

[0282] In this example,

[0283] SD12 10.500mm

[0284] SD2 13.166mm

[0285] therefore,

[0286] SD12 / SD2 = 0.798

[0287] In this example, when the focal length of the plastic sixth lens L6 is set to Fp and the focal length of the glass fifth lens L5 is set to Fg, the following condition (2) is satisfied.

[0288] 0.3 < Fg / Fp < 0.8…(2)

[0289] In this example,

[0290] Fg 43.080mm

[0291] Fp 44.302mm

[0292] therefore,

[0293] Fg / Fp = 0.972

[0294] In this example, when the Abbe number of the d-line of the second lens L2 is set to vd2, the following condition (3) is satisfied.

[0295] vd2<45…(3)

[0296] In this example,

[0297] vd2 = 34.967

[0298] In this example, when the sum of the wall thicknesses on the optical axis N of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5 and the sixth lens L6 is set as LTH, and the distance on the optical axis N from the magnifying side of the first lens L1 to the reducing side of the sixth lens L6 is set as L, the following condition (4) is satisfied.

[0299] 0.25 < LTH / L < 0.5…(4)

[0300] In this example,

[0301] LTH 24.727mm

[0302] L 80.036mm

[0303] therefore,

[0304] LTH / L = 0.309

[0305] In this example, when the axial spacing between the first lens L1 and the second lens L2 is set to D12, and the distance on the optical axis N from the magnifying side of the first lens L1 to the reducing side of the sixth lens L6 is set to L, the following condition (5) is satisfied.

[0306] 0.2 < D12 / L < 0.5…(5)

[0307] In this example,

[0308] D12 28.846mm

[0309] L 80.036mm,

[0310] therefore,

[0311] D12 / L=0.360

[0312] In this example, when the focal length of the entire system is set to F and the diameter of the incident pupil is set to φent, the following condition (6) is satisfied.

[0313] F / φent<1.6…(6)

[0314] In this example,

[0315] F 16.451mm

[0316] φent 10.567mm

[0317] therefore,

[0318] F / φent=1.557

[0319] (Effects)

[0320] The optical system 3E in this example can achieve the same effect as the optical system 3A in Example 1. Figure 12 This is a diagram showing the longitudinal aberrations, astigmatism, and distortion of the magnified image in optical system 3E. For example... Figure 12 As shown, the optical system 3E in this example suppresses various aberrations in the magnified image.

[0321] (Example 6)

[0322] Figure 13 This is a ray diagram of the optical system 3F in Example 6. (As shown) Figure 13 As shown, the optical system 3F has six lenses, from the first lens L1 to the sixth lens L6. The first lens L1 to the sixth lens L6 are arranged sequentially from the magnifying side to the reducing side.

[0323] Lens L1 has negative refractive power. The magnifying side of lens L1 is convex, and the reducing side is concave. Lens L1 has aspherical surfaces on both sides. Lens L2 has positive refractive power. The magnifying and reducing sides of lens L2 are convex. Lens L2 has spherical surfaces on both sides. Lens L3 has positive refractive power. The magnifying and reducing sides of lens L3 are convex. Lens L3 has spherical surfaces on both sides. Lens L4 has negative refractive power. The magnifying and reducing sides of lens L4 are concave. Lens L4 has spherical surfaces on both sides.

[0324] The fifth lens L5 has positive refractive power. The magnifying and reducing surfaces of the fifth lens L5 are convex. The fifth lens L5 has spherical surfaces on both surfaces. The sixth lens L6 has positive refractive power. The magnifying and reducing surfaces of the sixth lens L6 are convex. The sixth lens L6 has aspherical surfaces on both surfaces. The first lens L1 and the sixth lens L6 are made of plastic. The second lens L2, the third lens L3, the fourth lens L4, and the fifth lens L5 are made of glass. The third lens L3 and the fourth lens L4 are combined into a joint lens L21.

[0325] Optical system 3F has an aperture stop 31 and an aperture stop 32. Aperture stop 31 is positioned between the first lens L1 and the second lens L2. Aperture stop 31 is a light-shielding component provided in the lens barrel or the like that holding each lens. Aperture stop 31 blocks peripheral light beams in the light beam passing between the first lens L1 and the second lens L2. Aperture stop 32 is positioned between the second lens L2 and the third lens L3. Aperture stop 32 defines the brightness of optical system 3F. The opening diameter of aperture stop 32 is the opening diameter of the entrance pupil of optical system 3F.

[0326] In optical system 3F, the reduction side of the sixth lens L6 is telecentric. Telecentricity of the reduction side means that the central rays of each beam passing through the sixth lens L6 and the liquid crystal panel 18 disposed on the conjugate surface of the reduction side are parallel to or approximately parallel to the optical axis. In this example, the angle between the central rays of each beam and the optical axis N is within ±5°.

[0327] With the F-number of optical system 3F set to FNo, the total optical length set to TTL, the distance on the optical axis N from the magnifying side of the first lens L1 to the reducing side of the sixth lens L6 set to L, the back focal length (the total value of the on-axis spacing D from surface number 14 to surface number 18 recorded in the lens data) set to BF, the sum of the wall thicknesses on the optical axis N of the first lens L1, second lens L2, third lens L3, fourth lens L4, fifth lens L5 and sixth lens L6 set to LTH, the on-axis spacing between the first lens L1 and the second lens L2 set to D12, the effective radius of the aperture set to SD12, the effective radius of the second lens L2 set to SD2, the focal length of the entire system set to F, the focal length of the glass fifth lens L5 set to Fg, the focal length of the plastic sixth lens L6 set to Fp, the diameter of the entrance pupil set to φent, and the Abbe number of the d-line of the second lens L2 set to νd2, the data of optical system 3F in Example 6 are as follows.

[0328]

[0329] The lens data for the 3F optical system is as follows. Surface numbers are sequentially labeled from the magnifying side to the reducing side. These labels correspond to the screen, lens, aperture stop, dichroic prism, and LCD panel. Surface numbers not corresponding to the screen, lens, aperture stop, dichroic prism, or LCD panel are fictitious. Surfaces marked with an asterisk (*) are aspherical. R is the radius of curvature. D is the on-axis spacing. nd is the refractive index. νd is the Abbe number of the d-line. R and D are in mm.

[0330]

[0331] The aspherical coefficients are as follows.

[0332]

[0333] In this example, when the effective radius of the aperture 31 is set to SD12 and the effective radius of the second lens L2 is set to SD2, the following condition (1) is satisfied.

[0334] SD12 / SD2 < 0.9…(1)

[0335] In this example,

[0336] SD12 10.300mm

[0337] SD2 14.535mm

[0338] therefore,

[0339] SD12 / SD2 = 0.709

[0340] In this example, when the focal length of the plastic sixth lens L6 is set to Fp and the focal length of the glass fifth lens L5 is set to Fg, the following condition (2) is satisfied.

[0341] 0.3 < Fg / Fp < 0.8…(2)

[0342] In this example,

[0343] Fg 33.896mm

[0344] Fp 55.471mm

[0345] therefore,

[0346] Fg / Fp = 0.611

[0347] In this example, when the Abbe number of the d-line of the second lens L2 is set to vd2, the following condition (3) is satisfied.

[0348] vd2<45…(3)

[0349] In this example,

[0350] vd2 = 32.270

[0351] In this example, when the sum of the wall thicknesses on the optical axis N of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5 and the sixth lens L6 is set as LTH, and the distance on the optical axis N from the magnifying side of the first lens L1 to the reducing side of the sixth lens L6 is set as L, the following condition (4) is satisfied.

[0352] 0.25 < LTH / L < 0.5…(4)

[0353] In this example,

[0354] LTH 35.295mm

[0355] L 80.050mm

[0356] therefore,

[0357] LTH / L = 0.441

[0358] In this example, when the axial spacing between the first lens L1 and the second lens L2 is set to D12, and the distance on the optical axis N from the magnifying side of the first lens L1 to the reducing side of the sixth lens L6 is set to L, the following condition (5) is satisfied.

[0359] 0.2 < D12 / L < 0.5…(5)

[0360] In this example,

[0361] D12 29.453mm

[0362] L 80.050mm

[0363] therefore,

[0364] D12 / L=0.368

[0365] In this example, when the focal length of the entire system is set to F and the diameter of the incident pupil is set to φent, the following condition (6) is satisfied.

[0366] F / φent<1.6…(6)

[0367] In this example,

[0368] F 16.519mm

[0369] φent 11.484mm

[0370] therefore,

[0371] F / φent=1.438

[0372] (Effects)

[0373] The optical system 3F in this example can achieve the same effect as the optical system 3A in Example 1. Figure 14 This is a diagram showing the longitudinal aberrations, astigmatism, and distortion of the magnified image in optical system 3F. For example... Figure 14 As shown, the optical system 3F in this example suppresses various aberrations in the magnified image.

[0374] (Example 7)

[0375] Figure 15 This is a ray diagram of the optical system 3G in Example 7. (As shown) Figure 15 As shown, the optical system 3G has six lenses, from the first lens L1 to the sixth lens L6. The first lens L1 to the sixth lens L6 are arranged sequentially from the magnifying side to the reducing side.

[0376] Lens L1 has negative refractive power. The magnifying and reducing surfaces of lens L1 are concave. Lens L1 has aspherical surfaces on both surfaces. Lens L2 has positive refractive power. The magnifying and reducing surfaces of lens L2 are convex. Lens L2 has spherical surfaces on both surfaces. Lens L3 has positive refractive power. The magnifying and reducing surfaces of lens L3 are convex. Lens L3 has spherical surfaces on both surfaces. Lens L4 has negative refractive power. The magnifying surface of lens L4 is concave, and the reducing surface is convex. Lens L4 has spherical surfaces on both surfaces.

[0377] The fifth lens L5 has positive refractive power. The magnifying and reducing surfaces of the fifth lens L5 are convex. The fifth lens L5 has spherical surfaces on both surfaces. The sixth lens L6 has positive refractive power. The magnifying and reducing surfaces of the sixth lens L6 are convex. The sixth lens L6 has aspherical surfaces on both surfaces. The first lens L1 and the sixth lens L6 are made of plastic. The second lens L2, the third lens L3, the fourth lens L4, and the fifth lens L5 are made of glass. The third lens L3 and the fourth lens L4 are combined into a joint lens L21.

[0378] Optical system 3G has an aperture stop 31 and an aperture stop 32. Aperture stop 31 is positioned between the first lens L1 and the second lens L2. Aperture stop 31 is a light-shielding component provided in the lens barrel or the like that holding each lens. Aperture stop 31 blocks peripheral light beams in the light beam passing between the first lens L1 and the second lens L2. Aperture stop 32 is positioned between the second lens L2 and the third lens L3. Aperture stop 32 defines the brightness of optical system 3G. The opening diameter of aperture stop 32 is the opening diameter of the entrance pupil of optical system 3G.

[0379] In the 3G optical system, the reduction side of the sixth lens L6 is telecentric. Telecentricity of the reduction side means that the central rays of each beam passing through the sixth lens L6 and the liquid crystal panel 18 disposed on the conjugate surface of the reduction side are parallel to or approximately parallel to the optical axis. In this example, the angle between the central rays of each beam and the optical axis N is within ±5°.

[0380] With the F-number of optical system 3G set to FNo, the total optical length set to TTL, the distance on the optical axis N from the magnifying side of the first lens L1 to the reducing side of the sixth lens L6 set to L, the back focal length (the total value of the on-axis spacing D from surface number 14 to surface number 18 recorded in the lens data) set to BF, the sum of the wall thicknesses on the optical axis N of the first lens L1, second lens L2, third lens L3, fourth lens L4, fifth lens L5 and sixth lens L6 set to LTH, the on-axis spacing between the first lens L1 and the second lens L2 set to D12, the effective radius of the aperture set to SD12, the effective radius of the second lens L2 set to SD2, the focal length of the entire system set to F, the focal length of the glass fifth lens L5 set to Fg, the focal length of the plastic sixth lens L6 set to Fp, the diameter of the entrance pupil set to φent, and the Abbe number of the d-line of the second lens L2 set to νd2, the data of optical system 3G in Embodiment 7 are as follows.

[0381]

[0382] The lens data for the 3G optical system is as follows. Surface numbers are sequentially labeled from the magnifying side to the reducing side. These labels correspond to the screen, lens, aperture stop, dichroic prism, and LCD panel. Surface numbers not corresponding to the screen, lens, aperture stop, dichroic prism, or LCD panel are fictitious. Surfaces marked with an asterisk (*) are aspherical. R is the radius of curvature. D is the on-axis spacing. nd is the refractive index. νd is the Abbe number of the d-line. R and D are in mm.

[0383]

[0384] The aspherical coefficients are as follows.

[0385]

[0386] In this example, if the effective radius of the aperture 31 is set to SD12 and the effective radius of the second lens L2 is set to SD2, then the following condition (1) is satisfied.

[0387] SD12 / SD2 < 0.9…(1)

[0388] In this example,

[0389] SD12 10.300mm

[0390] SD2 12.968mm

[0391] therefore,

[0392] SD12 / SD2 = 0.794

[0393] In this example, when the focal length of the plastic sixth lens L6 is set to Fp and the focal length of the glass fifth lens L5 is set to Fg, the following condition (2) is satisfied.

[0394] 0.3 < Fg / Fp < 0.8…(2)

[0395] In this example,

[0396] Fg 40.598mm

[0397] Fp 59.890mm

[0398] therefore,

[0399] Fg / Fp = 0.678

[0400] In this example, when the Abbe number of the d-line of the second lens L2 is set to vd2, the following condition (3) is satisfied.

[0401] vd2<45…(3)

[0402] In this example,

[0403] vd2 = 44.202

[0404] In this example, when the sum of the wall thicknesses on the optical axis N of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5 and the sixth lens L6 is set as LTH, and the distance on the optical axis N from the magnifying side of the first lens L1 to the reducing side of the sixth lens L6 is set as L, the following condition (4) is satisfied.

[0405] 0.25 < LTH / L < 0.5…(4)

[0406] In this example,

[0407] LTH 29.240mm

[0408] L 79.520mm

[0409] therefore,

[0410] LTH / L = 0.368

[0411] In this example, when the axial spacing between the first lens L1 and the second lens L2 is set to D12, and the distance on the optical axis N from the magnifying side of the first lens L1 to the reducing side of the sixth lens L6 is set to L, the following condition (5) is satisfied.

[0412] 0.2 < D12 / L < 0.5…(5)

[0413] In this example,

[0414] D12 18.006mm

[0415] L 79.520mm

[0416] therefore,

[0417] D12 / L=0.226

[0418] In this example, when the focal length of the entire system is set to F and the diameter of the incident pupil is set to φent, the following condition (6) is satisfied.

[0419] F / φent<1.6…(6)

[0420] In this example,

[0421] F 16.557mm

[0422] φent 11.504mm

[0423] therefore,

[0424] F / φent=1.439

[0425] (Effects)

[0426] The optical system 3G in this example can achieve the same effect as the optical system 3A in Example 1. Figure 16 This is a diagram showing the longitudinal aberrations, astigmatism, and distortion of a magnified image in a 3G optical system. For example... Figure 16 As shown, the optical system 3G in this example suppresses various aberrations in the magnified image. Furthermore, in Example 7, the value of conditional expression (5) is close to the lower limit. Therefore, compared to the aberration maps of other embodiments, a slight disturbance occurs in the aberration map of Example 7, but overall, the aberrations are well corrected.

[0427] (Example 8)

[0428] Figure 17 This is a ray diagram of the optical system 3H in Example 8. (As shown...) Figure 17 As shown, the optical system 3H has six lenses, from the first lens L1 to the sixth lens L6. The first lens L1 to the sixth lens L6 are arranged sequentially from the magnifying side to the reducing side.

[0429] Lens L1 has negative refractive power. The magnifying side of lens L1 is convex, and the reducing side is concave. Lens L1 has aspherical surfaces on both sides. Lens L2 has positive refractive power. The magnifying and reducing sides of lens L2 are convex. Lens L2 has spherical surfaces on both sides. Lens L3 has positive refractive power. The magnifying and reducing sides of lens L3 are convex. Lens L3 has spherical surfaces on both sides. Lens L4 has negative refractive power. The magnifying and reducing sides of lens L4 are concave. Lens L4 has spherical surfaces on both sides.

[0430] The fifth lens L5 has positive refractive power. The magnifying and reducing surfaces of the fifth lens L5 are convex. The fifth lens L5 has spherical surfaces on both surfaces. The sixth lens L6 has positive refractive power. The magnifying surface of the sixth lens L6 is convex, and the reducing surface is concave. The sixth lens L6 has aspherical surfaces on both surfaces. The first lens L1 and the sixth lens L6 are made of plastic. The second lens L2, the third lens L3, the fourth lens L4, and the fifth lens L5 are made of glass. The third lens L3 and the fourth lens L4 are combined into a joint lens L21.

[0431] Optical system 3H has an aperture stop 31 and an aperture stop 32. Aperture stop 31 is positioned between the first lens L1 and the second lens L2. Aperture stop 31 is a light-shielding component provided in the lens barrel or the like that holding each lens. Aperture stop 31 blocks peripheral light beams in the light beam passing between the first lens L1 and the second lens L2. Aperture stop 32 is positioned between the second lens L2 and the third lens L3. Aperture stop 32 defines the brightness of optical system 3H. The opening diameter of aperture stop 32 is the opening diameter of the entrance pupil of optical system 3H.

[0432] In optical system 3H, the reduction side of the sixth lens L6 is telecentric. Telecentricity of the reduction side means that the central rays of each beam passing through the sixth lens L6 and the liquid crystal panel 18 disposed on the conjugate surface of the reduction side are parallel to or approximately parallel to the optical axis. In this example, the angle between the central rays of each beam and the optical axis N is within ±5°.

[0433] With the F-number of optical system 3H set to FNo, the total optical length set to TTL, the distance on the optical axis N from the magnifying side of the first lens L1 to the reducing side of the sixth lens L6 set to L, the back focal length (the total value of the on-axis spacing D from surface number 14 to surface number 18 recorded in the lens data) set to BF, the sum of the wall thicknesses on the optical axis N of the first lens L1, second lens L2, third lens L3, fourth lens L4, fifth lens L5 and sixth lens L6 set to LTH, the on-axis spacing between the first lens L1 and the second lens L2 set to D12, the effective radius of the aperture set to SD12, the effective radius of the second lens L2 set to SD2, the focal length of the entire system set to F, the focal length of the glass fifth lens L5 set to Fg, the focal length of the plastic sixth lens L6 set to Fp, the diameter of the entrance pupil set to φent, and the Abbe number of the d-line of the second lens L2 set to νd2, the data of optical system 3H in Example 8 are as follows.

[0434]

[0435] The lens data for optical system 3H is as follows. Surface numbers are sequentially labeled from the magnifying side to the reducing side. These labels correspond to the screen, lens, aperture stop, dichroic prism, and LCD panel. Surface numbers not corresponding to the screen, lens, aperture stop, dichroic prism, or LCD panel are fictitious. Surfaces marked with an asterisk (*) are aspherical. R is the radius of curvature. D is the on-axis spacing. nd is the refractive index. νd is the Abbe number of the d-line. R and D are in mm.

[0436]

[0437] The aspherical coefficients are as follows.

[0438]

[0439] In this example, when the effective radius of the aperture 31 is set to SD12 and the effective radius of the second lens L2 is set to SD2, the following condition (1) is satisfied.

[0440] SD12 / SD2 < 0.9…(1)

[0441] In this example,

[0442] SD12 10.492mm

[0443] SD2 14.573mm

[0444] therefore,

[0445] SD12 / SD2 = 0.720

[0446] In this example, when the focal length of the plastic sixth lens L6 is set to Fp and the focal length of the glass fifth lens L5 is set to Fg, the following condition (2) is satisfied.

[0447] 0.3 < Fg / Fp < 0.8…(2)

[0448] In this example,

[0449] Fg 31.040mm

[0450] Fp 83.461mm

[0451] therefore,

[0452] Fg / Fp = 0.372

[0453] In this example, when the Abbe number of the d-line of the second lens L2 is set to vd2, the following condition (3) is satisfied.

[0454] vd2<45…(3)

[0455] In this example,

[0456] vd2 = 32.270

[0457] In this example, when the sum of the wall thicknesses on the optical axis N of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5 and the sixth lens L6 is set as LTH, and the distance on the optical axis N from the magnifying side of the first lens L1 to the reducing side of the sixth lens L6 is set as L, the following condition (4) is satisfied.

[0458] 0.25 < LTH / L < 0.5…(4)

[0459] In this example,

[0460] LTH 26.417mm

[0461] L 81.391mm

[0462] therefore,

[0463] LTH / L = 0.325

[0464] In this example, when the axial spacing between the first lens L1 and the second lens L2 is set to D12, and the distance on the optical axis N from the magnifying side of the first lens L1 to the reducing side of the sixth lens L6 is set to L, the following condition (5) is satisfied.

[0465] 0.2 < D12 / L < 0.5…(5)

[0466] In this example,

[0467] D12 36.257mm

[0468] L 81.391mm

[0469] therefore,

[0470] D12 / L=0.445

[0471] In this example, when the focal length of the entire system is set to F and the diameter of the incident pupil is set to φent, the following condition (6) is satisfied.

[0472] F / φent<1.6…(6)

[0473] In this example,

[0474] F 16.553mm

[0475] φent 11.505mm

[0476] therefore,

[0477] F / φent=1.498

[0478] (Effects)

[0479] The optical system 3H in this example can achieve the same effect as the optical system 3A in Example 1. Figure 18 This is a diagram showing the longitudinal aberrations, astigmatism, and distortion of the magnified image in optical system 3H. For example... Figure 18 As shown, the optical system 3H in this example suppresses various aberrations in the magnified image.

[0480] (Other implementation methods)

[0481] Furthermore, the optical system in this example can also be used as a camera lens. In this case, the imaging element is arranged on the conjugate surface of the narrowing side of the optical system.

Claims

1. An optical system, characterized in that, The optical system, from the magnification side to the reduction side, consists of the following parts in sequence: a first lens with negative refractive power, an aperture stop, a second lens with positive refractive power, an aperture stop, a third lens with positive refractive power, a fourth lens with negative refractive power, a fifth lens with positive refractive power, and a sixth lens with positive refractive power. The third lens and the fourth lens are joined lenses. The conjugated lens has negative refractive power. One of the fifth and sixth lenses is made of plastic and has aspherical surfaces on two sides; the other of the fifth and sixth lenses is made of glass. The reduced side of the sixth lens is telecentric. The surface of the first lens on the narrowing side is concave. The second lens has convex surfaces on both the magnifying and reducing sides. The magnifying and reducing surfaces of the third lens are convex. The surface of the fourth lens on the magnifying side is concave. The fifth lens has a convex surface on the side facing down. When the effective radius of the aperture is SD12 and the effective radius of the second lens is SD2, the following condition (1) is satisfied: SD12 / SD2 < 0.9 (1), When the focal length of the entire system is F and the diameter of the incident pupil is Φent, the following condition (6) is satisfied: F / Φent < 1.6 (6).

2. The optical system according to claim 1, characterized in that, The first lens is made of plastic and has aspherical surfaces on two sides.

3. The optical system according to claim 1 or 2, characterized in that, The third lens and the fourth lens are made of glass.

4. The optical system according to claim 1 or 2, characterized in that, When the focal length of the plastic lens in the fifth lens and the focal length of the glass lens in the sixth lens are Fp and Fg respectively, the following condition (2) is satisfied: 0.3 < Fg / Fp <0.8 (2)。 5. The optical system according to claim 1 or 2, characterized in that, When the Abbe number of the d-line of the second lens is νd2, the following condition (3) is satisfied: νd2 < 45 (3).

6. The optical system according to claim 1 or 2, characterized in that, When the sum of the wall thicknesses along the optical axis of the first lens, the second lens, the third lens, the fourth lens, the fifth lens, and the sixth lens is LTH, and the distance along the optical axis from the magnifying side of the first lens to the reducing side of the sixth lens is L, the following condition (4) is satisfied: 0.25 < LTH / L < 0.5 (4)。 7. The optical system according to claim 1 or 2, characterized in that, When the axial spacing between the first lens and the second lens is D12, and the optical axis distance from the magnifying side of the first lens to the reducing side of the sixth lens is L, the following condition (5) is satisfied: 0.2 < D12 / L < 0.5 (5).

8. A projector, characterized in that, The projector has: The optical system according to any one of claims 1 to 7; and An image forming unit forms a projected image on the conjugate surface of the reduced side of the optical system.

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