Variable magnification projection optical system and projection device

Abstract

The present disclosure relates to a variable-magnification projection optical system and a projection device. The variable-magnification projection optical system comprises, in order from the magnification side, a first lens group having negative optical power, a second lens group having negative optical power, and a third lens group having positive optical power. During zooming, the first lens group is fixed, and the second and third lens groups move. The second lens group includes a plurality of lenses having positive optical power. All lenses having positive optical power within the first and second lens groups are formed of a glass material having a transmittance greater than 0.98 at a thickness of 10 mm for light having a wavelength of 440 nm.

Description

Technical Field

[0001] The present disclosure relates to a variable magnification projection optical system and a projection device. Background Art

[0002] International Publication No. 2014 / 104083 discloses the following variable magnification projection optical system: it includes, from the magnification side, a first lens group with negative optical focal length, a second lens group with negative optical focal length, a third lens group with positive optical focal length, a fourth lens group with negative optical focal length, a fifth lens group and a sixth lens group with positive optical focal length. Summary of the Invention

[0003] In the zoom projection optical system of International Publication No. 2014 / 104083, the number of lenses included in the second lens group is small. In order to reduce the distortion aberration in the peripheral area of ​​the projected image at the wide-angle end, it is necessary to increase the number of lenses included in the first lens group. However, the first lens group is arranged closer to the magnification side than the second lens group, so the diameter of the lens included in the first lens group tends to be larger than the diameter of the lens included in the second lens group. When the diameter of the lens increases, the thickness of the lens on the optical axis of the zoom projection optical system (the center thickness of the lens) increases, and the light transmittance of the lens decreases. In a bright environment, it is difficult to visually recognize the projected image.

[0004] The present disclosure has been made in view of such problems, and its object is to provide a variable magnification projection optical system and a projection device that can reduce distortion aberration in the peripheral area of ​​a projected image at a wide-angle end and facilitate visual recognition of the projected image in a bright environment.

[0005] The first aspect of the present disclosure is a variable magnification projection optical system that magnifies and projects an image displayed on an image display surface. The variable magnification projection optical system comprises, in order from the magnification side, a first lens group having a negative optical focal length, a second lens group having a negative optical focal length, and a third lens group having a positive optical focal length. When the magnification is changed, the first lens group is fixed and the second lens group and the third lens group move. The second lens group includes a plurality of lenses having a positive optical focal length. All lenses having a positive optical focal length in the first lens group and the second lens group are formed of a glass material having a transmittance greater than 0.98 at a thickness of 10 mm for light having a wavelength of 440 nm.

[0006] The second aspect of the present disclosure relates to a variable magnification projection optical system that magnifies and projects an image displayed on an image display surface. The variable magnification projection optical system comprises, in order from the magnification side, a first lens group having negative optical power, a second lens group having negative optical power, and a third lens group having positive optical power. During zooming, the first lens group is fixed, while the second and third lens groups move. The second lens group includes multiple lenses having positive optical power. The refractive index of all lenses with positive optical power in the first lens group and the second lens group for the d-line is less than 1.6.

[0007] A projection device disclosed herein includes the variable magnification projection optical system according to the first or second aspect of the disclosure and an image display element having an image display surface.

[0008] The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 It is a diagram showing the configuration of a variable magnification projection optical system according to the first embodiment.

[0010] Figure 2 It is a diagram showing the configuration of a variable magnification projection optical system according to the second embodiment.

[0011] Figure 3 It is a diagram showing the configuration of a variable magnification projection optical system according to a third embodiment.

[0012] Figure 4 It is a diagram showing the configuration of a variable magnification projection optical system according to a fourth embodiment.

[0013] Figure 5A These are diagrams showing longitudinal aberrations at the wide-angle end of Example 1, illustrating aberrations (spherical aberration, astigmatism, and distortion) at the wide-angle end.

[0014] Figure 5B These are diagrams showing longitudinal aberrations at the telephoto end of Example 1, illustrating aberrations (spherical aberration, astigmatism, and distortion) at the telephoto end.

[0015] Figure 6A These are diagrams showing longitudinal aberrations at the wide-angle end of Example 2, illustrating aberrations (spherical aberration, astigmatism, and distortion) at the wide-angle end.

[0016] Figure 6B These are diagrams showing longitudinal aberrations at the telephoto end of Example 2, illustrating aberrations (spherical aberration, astigmatism, and distortion) at the telephoto end.

[0017] Figure 7AThese are diagrams showing longitudinal aberrations at the wide-angle end of Example 3, illustrating aberrations (spherical aberration, astigmatism, and distortion) at the wide-angle end.

[0018] Figure 7B These are diagrams showing longitudinal aberrations at the telephoto end of Example 3, illustrating aberrations (spherical aberration, astigmatism, and distortion) at the telephoto end.

[0019] Figure 8A These are diagrams showing longitudinal aberrations at the wide-angle end of Example 4, illustrating aberrations (spherical aberration, astigmatism, and distortion) at the wide-angle end.

[0020] Figure 8B These are diagrams showing longitudinal aberrations at the telephoto end of Example 4, illustrating aberrations (spherical aberration, astigmatism, and distortion) at the telephoto end.

[0021] Figure 9 This is a schematic diagram showing a projection device according to an embodiment. DETAILED DESCRIPTION

[0022] Hereinafter, a variable magnification projection optical system and a projection device according to embodiments of the present disclosure will be described with reference to the accompanying drawings.

[0023] The first aspect of the present embodiment is a variable magnification projection optical system that magnifies and projects an image displayed on an image display surface. The variable magnification projection optical system includes, from the magnification side, a first lens group with negative optical focal length, a second lens group with negative optical focal length, and a third lens group with positive optical focal length. When changing the magnification, the first lens group is fixed and the second lens group and the third lens group move. The second lens group includes a plurality of lenses with positive optical focal length. All lenses with positive optical focal length in the first lens group and the second lens group are formed of a glass material having a transmittance greater than 0.98 at a thickness of 10 mm for light with a wavelength of 440 nm.

[0024] Furthermore, the term "magnification side" refers to the side of the screen (magnification side image plane) onto which the magnified optical image is projected on the optical axis of the variable magnification projection optical system (so-called front side). The term "reduction side" refers to the side of the image display element having an image display surface arranged on the optical axis of the variable magnification projection optical system (so-called rear side).

[0025] The first aspect of the present embodiment has a variable magnification projection optical system comprising, in order from the magnification side, a first lens group having negative optical focal length, a second lens group having negative optical focal length, and a third lens group having positive optical focal length. Therefore, off-axis light rays converge in the third lens group and then advance in the second lens group and the first lens group. The diameter of the lenses included in the first lens group and the second lens group can be reduced. The center thickness of the lenses included in the first lens group and the second lens group can be reduced. The transmittance of the lenses included in the first lens group and the second lens group increases, and the light transmittance of the first lens group and the second lens group increases. The light transmittance of the variable magnification projection optical system increases, and the projected image can be easily visually recognized in a bright environment.

[0026] In the zoom projection optical system of the first aspect of this embodiment, the first lens group is fixed during zooming. Therefore, even if the negative optical power of the first lens group is increased in order to increase the viewing angle of the zoom projection optical system, the variation of aberrations during zooming can be reduced.

[0027] In the first aspect of the present embodiment, the second lens group includes a plurality of lenses having positive optical power. Therefore, even when the negative optical power of the first lens group is increased in order to increase the viewing angle of the variable magnification projection optical system, the distortion aberration caused by the first lens group can be corrected by the plurality of lenses having positive optical power included in the second lens group without increasing the number of lenses having positive optical power included in the first lens group. The distortion aberration in the peripheral area of ​​the projected image at the wide-angle end can be reduced. In addition, the number of lenses in the first lens group, whose lens diameter tends to be large, can be reduced, so that the light transmittance of the first lens group can be increased. The light transmittance of the variable magnification projection optical system is increased, and the projected image can be easily visually recognized in a bright environment.

[0028] In the first aspect of this embodiment, all lenses with positive optical power within the first and second lens groups are formed from a glass material having a transmittance greater than 0.98 at a thickness of 10 mm for light having a wavelength of 440 nm. By using a glass material with high transmittance to form lenses with positive optical power having a larger center thickness than lenses with negative optical power, the light transmittance of the first and second lens groups is increased, thereby increasing the light transmittance of the variable magnification projection optical system. This enables easy visual recognition of projected images in bright environments.

[0029] The second aspect of this embodiment is a variable magnification projection optical system that magnifies and projects an image displayed on an image display surface. The variable magnification projection optical system includes, from the magnification side, a first lens group with negative optical power, a second lens group with negative optical power, and a third lens group with positive optical power. During zooming, the first lens group is fixed, and the second and third lens groups move. The second lens group includes multiple lenses with positive optical power. The refractive index of all lenses with positive optical power in the first lens group and the second lens group for the d-line (wavelength 587.56 nm) is less than 1.6.

[0030] The second aspect of the present embodiment is a variable-magnification projection optical system comprising, in order from the magnification side, a first lens group having negative optical power, a second lens group having negative optical power, and a third lens group having positive optical power. Therefore, off-axis light rays converge in the third lens group and then advance in the second lens group and the first lens group. The diameter of the lenses included in the first lens group and the second lens group can be reduced. The center thickness of the lenses included in the first lens group and the second lens group can be reduced. The transmittance of the lenses included in the first lens group and the second lens group increases, and the light transmittance of the first lens group and the second lens group increases. The light transmittance of the variable-magnification projection optical system increases, and the projected image can be easily visually recognized in a bright environment.

[0031] In the zoom projection optical system of the second aspect of this embodiment, the first lens group is fixed during zooming. Therefore, even if the negative optical power of the first lens group is increased in order to increase the viewing angle of the zoom projection optical system, the variation of aberrations during zooming can be reduced.

[0032] In the second aspect of the present embodiment, the second lens group includes a plurality of lenses having positive optical power. Therefore, even when the negative optical power of the first lens group is increased in order to increase the viewing angle of the variable magnification projection optical system, the distortion aberration caused by the first lens group can be corrected by the plurality of lenses having positive optical power included in the second lens group without increasing the number of lenses having positive optical power included in the first lens group. The distortion aberration in the peripheral area of ​​the projected image at the wide-angle end can be reduced. In addition, the number of lenses in the first lens group, whose lens diameter tends to be large, can be reduced, so that the light transmittance of the first lens group can be increased. The light transmittance of the variable magnification projection optical system is increased, and the projected image can be easily visually recognized in a bright environment.

[0033] Because the first and second lens groups have negative optical powers, the angle of incidence of off-axis light rays incident on lenses with positive optical powers within the first and second lens groups increases. In the second aspect of this embodiment, the refractive index of all lenses with positive optical powers within the first and second lens groups for the d-line is less than 1.6. Therefore, the angle of incidence of off-axis light rays incident on lenses with positive optical powers within the first and second lens groups can be prevented from exceeding the critical angle. This increases the viewing angle of the variable-magnification projection optical system, and allows for easy visual recognition of the projected image in bright environments.

[0034] In this embodiment, it is preferable that all lenses in the first lens group are formed of a glass material having a transmittance greater than 0.97 at a thickness of 10 mm with respect to light having a wavelength of 440 nm.

[0035] Therefore, the light transmittance of the first lens group increases, and the light transmittance of the variable magnification projection optical system increases, making it possible to easily visually recognize the projected image in a bright environment.

[0036] In this embodiment, it is preferable that the refractive index of all lenses in the first lens group for the d-line is less than 1.75.

[0037] In the second aspect of the variable magnification projection optical system of this embodiment, the refractive index of all lenses with positive optical power within the first lens group and the second lens group for the d-line is less than 1.6. Therefore, the Petzval sum of the variable magnification projection optical system of this embodiment tends to be large. By making the refractive index of all lenses within the first lens group for the d-line less than 1.75, the refractive index of the lenses with negative optical power within the first lens group and the second lens group can be reduced. The Petzval sum of the variable magnification projection optical system is reduced, and the deterioration of the field curvature of the variable magnification projection optical system can be suppressed.

[0038] In this embodiment, it is preferable that all lenses in the first lens group and the second lens group are formed of a glass material having a transmittance greater than 0.97 at a thickness of 10 mm with respect to light having a wavelength of 440 nm.

[0039] Therefore, the light transmittance of the first lens group and the second lens group increases, and the light transmittance of the variable magnification projection optical system increases, making it possible to easily visually recognize the projected image in a bright environment.

[0040] In this embodiment, it is preferable that the first lens group is composed of seven or less lenses having optical power.

[0041] The number of lenses in the first lens group, which tends to have a larger lens diameter, can be reduced, thereby increasing the light transmittance of the first lens group. The increased light transmittance of the variable magnification projection optical system allows for easier visual recognition of the projected image in a bright environment.

[0042] In this embodiment, it is preferable that the second lens group is composed of four or more lenses having optical power.

[0043] By increasing the number of lenses in the second lens group, whose lens diameter is more easily reduced than that of the first lens group, the distortion caused by the first lens group can be more effectively corrected by the multiple lenses with positive optical power included in the second lens group, without increasing the number of lenses with positive optical power included in the first lens group. This reduces distortion in the peripheral area of ​​the projected image at the wide-angle end. Furthermore, the number of lenses in the first lens group, which tends to have a larger lens diameter, can be reduced, thereby increasing the light transmittance of the first lens group. This increased light transmittance of the variable magnification projection optical system allows for easier visual recognition of the projected image in bright environments.

[0044] The variable magnification projection optical system of this embodiment preferably further includes at least one lens group that is disposed on the reduction side of the third lens group and that moves along the optical axis of the variable magnification projection optical system during magnification change.

[0045] Therefore, the moving lengths of the second lens group and the third lens group during zooming can be reduced, and the fluctuation of aberrations of the zoom projection optical system during zooming can be reduced.

[0046] In this embodiment, it is preferable that the first lens group does not include an aspherical surface.

[0047] Therefore, equivalent aberration performance can be achieved without using an aspherical surface for aberration correction, and the cost of the first lens group, in which the lens diameter tends to be large, can be reduced.

[0048] The variable magnification projection optical system of this embodiment preferably does not include an aspherical surface.

[0049] Therefore, it is possible to achieve equivalent aberration performance without using an aspherical surface for the purpose of aberration correction, and reduce the cost of the variable magnification projection optical system.

[0050] The projection device of this embodiment includes an image display element having an image display surface and the variable magnification projection optical system of this embodiment.

[0051] The projection device of this embodiment includes the variable magnification projection optical system of this embodiment, thereby reducing distortion in the peripheral area of ​​the projected image at the wide-angle end and making it possible to easily visually recognize the projected image in a bright environment.

[0052] <Specific Optical Structure of the Variable Magnification Projection Optical System of the Embodiment>

[0053] Reference Figures 1 to 4 The specific optical structure of the variable magnification projection optical system ZL of the first to fourth embodiments will be described. Figures 1-4 In each figure, "Wide" is a cross-sectional view of the lens at the wide-angle end, "Tele" is a cross-sectional view of the lens at the telephoto end, and "AX" represents the optical axis of the variable magnification projection optical system ZL. Both "Wide" and "Tele" are cross-sectional views of the lens when focusing on an object at infinity.

[0054] The variable magnification projection optical system ZL projects images displayed on the image display element 7 (see FIG. 1 ) at a viewing angle of, for example, 80° or more. Figure 9 ) is projected on the image display surface IM. On the reduction side of the variable magnification projection optical system ZL, a prism PR (e.g., a TIR (Total Internal Reflection) prism, a color separation and synthesis prism, etc.) and a cover glass CG covering the image display surface IM of the image display element 7 are arranged.

[0055] (First embodiment)

[0056] Reference Figure 1 The variable magnification projection optical system ZL is substantially composed of multiple lens groups having optical power. For example, the variable magnification projection optical system ZL is substantially composed of six lens groups G1-G6 having optical power. In this specification, the variable magnification projection optical system ZL being substantially composed of multiple lens groups having optical power means that the variable magnification projection optical system ZL is composed of multiple lens groups having optical power, or that the variable magnification projection optical system ZL is composed of multiple lens groups having optical power and other lens groups without optical power. The variable magnification projection optical system ZL does not include an aspheric surface.

[0057] The first lens group G1 is the lens group located closest to the magnification side among the multiple lens groups having optical power that constitute the variable magnification projection optical system. The first lens group G1 has negative optical power. The first lens group G1 is composed of no more than seven lenses having optical power. The second lens group G2 is the second lens group from the magnification side among the multiple lens groups having optical power that constitute the variable magnification projection optical system. The second lens group G2 has negative optical power. The second lens group G2 is composed of no more than four lenses having optical power. The second lens group G2 includes multiple lenses having positive optical power. The third lens group G3 is the third lens group from the magnification side among the multiple lens groups having optical power that constitute the variable magnification projection optical system. The third lens group G3 has positive optical power.

[0058] The fourth lens group G4 is the fourth lens group from the magnification side among the multiple lens groups having optical power that constitute the variable magnification projection optical system. The fourth lens group G4 has negative optical power. The fifth lens group G5 is the fifth lens group from the magnification side among the multiple lens groups having optical power that constitute the variable magnification projection optical system. The fifth lens group G5 has positive optical power. The fifth lens group G5 includes an aperture stop ST on the closest magnification side of the fifth lens group G5. The sixth lens group G6 is the sixth lens group from the magnification side among the multiple lens groups having optical power that constitute the variable magnification projection optical system. The sixth lens group G6 has positive optical power.

[0059] During zooming, the distance between two adjacent lens groups among the first lens group G1, the second lens group G2, the third lens group G3, the fourth lens group G4, the fifth lens group G5, and the sixth lens group G6 changes. For example, during zooming, the first lens group G1 and the sixth lens group G6 are fixed, while the second to fifth lens groups G2-G5 move. Specifically, during zooming from the wide-angle end (W) to the telephoto end (T), the second lens group G2 moves along a trajectory that is convex on the reduction side (U-turn movement), the third lens group G3 moves monotonically toward the magnification side, the fourth lens group G4 moves monotonically toward the reduction side, and the fifth lens group G5 moves monotonically toward the magnification side. Since the first lens group G1 and the sixth lens group G6 are fixed during zooming, the total length of the zoom projection optical system based on zooming does not change, and the zoom mechanism of the zoom projection optical system ZL can be simplified.

[0060] The first lens group G1 to the sixth lens group G6 in the first embodiment are configured as follows in order from the object side when each lens is viewed in a paraxial surface shape.

[0061] The first lens group G1 is composed of seven lenses, L11-L17, each having optical power. Specifically, the first lens group G1 includes, in order from the magnification side, a negative meniscus lens L11 with its convex surface facing the magnification side; a negative meniscus lens L12 with its convex surface facing the magnification side; a negative meniscus lens L13 with its convex surface facing the magnification side; a biconvex positive lens L14; a negative meniscus lens L15 with its convex surface facing the magnification side; a biconvex positive lens L16; and a negative meniscus lens L17 with its convex surface facing the magnification side. The first lens group G1 does not include any aspherical surfaces.

[0062] All lenses with positive refractive power within the first lens group G1 (in this embodiment, lenses L14 and L16) are formed from a glass material having a transmittance greater than 0.98 at a thickness of 10 mm for light having a wavelength of 440 nm. Examples of such glass materials include FC5, FCD1, PCD4, BSC7, BACD5, TAC8, E-FD2, FF5, NBFD11, TAF1, TAF3, or TAFD5G (all manufactured by HOYA).

[0063] The refractive index of all lenses (in this embodiment, lenses L14 and L16) with positive power for the d-line (wavelength 587.56 nm) within the first lens group G1 is less than 1.6. By forming all lenses with positive power within the first lens group G1 using, for example, the aforementioned glazing material manufactured by HOYA, the refractive index of all lenses with positive power for the d-line within the first lens group G1 can be reduced to less than 1.6.

[0064] All lenses within the first lens group G1 (in this embodiment, lenses L11-L17) are formed from a glass material having a transmittance greater than 0.97 at a thickness of 10 mm for light having a wavelength of 440 nm. Examples of such a glass material include FC5, FCD1, PCD4, BSC7, BACD5, TAC8, E-FD2, FF5, NBFD11, TAF1, TAF3, TAFD5G, E-FD5, E-FD1, BAFD8, and NBFD13 (all manufactured by HOYA). All lenses with positive optical focal length within the first lens group G1 (lenses L14 and L16 in this embodiment) are formed of a glass material having a transmittance greater than 0.98 at a thickness of 10 mm for light with a wavelength of 440 nm. Therefore, all lenses with positive optical focal length within the first lens group G1 naturally satisfy the condition that the lenses are formed of a glass material having a transmittance greater than 0.97 at a thickness of 10 mm for light with a wavelength of 440 nm.

[0065] The refractive index of all lenses in the first lens group G1 for the d-line (in this embodiment, lenses L11-L17) is less than 1.75. By forming all lenses in the first lens group G1 using the aforementioned glass material, such as that manufactured by HOYA, the refractive index of all lenses in the first lens group G1 with positive optical power for the d-line can be made less than 1.75. Since the refractive index of all lenses in the first lens group G1 with positive optical power for the d-line (in this embodiment, lenses L14 and L16) is less than 1.6, all lenses in the first lens group G1 with positive optical power naturally satisfy the requirement that the refractive index of lenses for the d-line is less than 1.75.

[0066] The second lens group G2 is composed of four lenses, L21-L24, each with optical power. The second lens group G2 includes two lenses with positive optical power. Specifically, from the magnification side, the second lens group G2 comprises, in order: a biconvex positive lens L21, a biconcave negative lens L22, a biconcave negative lens L23, and a biconvex positive lens L24. The second lens group G2 does not include any aspherical surfaces.

[0067] All lenses with positive refractive power within the second lens group G2 (in this embodiment, lenses L21 and L24) are formed from a glass material having a transmittance greater than 0.98 at a thickness of 10 mm for light having a wavelength of 440 nm. Examples of such glass materials include FC5, FCD1, PCD4, BSC7, BACD5, TAC8, E-FD2, FF5, NBFD11, TAF1, TAF3, or TAFD5G (all manufactured by HOYA).

[0068] The refractive index of all lenses with positive refractive power for the d-line within the second lens group G2 (in this embodiment, lenses L21 and L24) is less than 1.6. By forming all lenses with positive refractive power within the second lens group G2 using, for example, the aforementioned nitrile material manufactured by HOYA, the refractive index of all lenses with positive refractive power for the d-line within the second lens group G2 can be reduced to less than 1.6.

[0069] All lenses within the second lens group G2 (in this embodiment, lenses L21-L24) are formed from a glass material having a transmittance greater than 0.97 at a thickness of 10 mm for light having a wavelength of 440 nm. Examples of such glass materials include FC5, FCD1, PCD4, BSC7, BACD5, TAC8, E-FD2, FF5, NBFD11, TAF1, TAF3, TAFD5G, E-FD5, E-FD1, BAFD8, and NBFD13 (all manufactured by HOYA). All lenses with positive optical focal length within the second lens group G2 (lenses L21 and L24 in this embodiment) are formed of a glass material having a transmittance greater than 0.98 at a thickness of 10 mm for light with a wavelength of 440 nm. Therefore, all lenses with positive optical focal length within the second lens group G2 naturally satisfy the condition that the lenses are formed of a glass material having a transmittance greater than 0.97 at a thickness of 10 mm for light with a wavelength of 440 nm.

[0070] The refractive index of all lenses in the second lens group G2 for the d-line (in this embodiment, lenses L21-L24) is less than 1.75. By forming all lenses in the second lens group G2 using the aforementioned glazing material, such as that manufactured by HOYA, the refractive index of all lenses in the second lens group G2 with positive optical power for the d-line can be made less than 1.75. Since the refractive index of all lenses in the second lens group G2 with positive optical power for the d-line (in this embodiment, lenses L21 and L24) is less than 1.6, all lenses in the second lens group G2 with positive optical power naturally satisfy the requirement that the refractive index of lenses for the d-line is less than 1.75.

[0071] The third lens group G3 is composed of two lenses, L31 and L32, each with optical power. Specifically, the third lens group G3 includes, in order from the magnification side, a positive meniscus lens L31 with its convex surface facing the reduction side, and a positive meniscus lens L32 with its convex surface facing the magnification side. The third lens group G3 does not include any aspherical surfaces.

[0072] The fourth lens group G4 is composed of three lenses, L41-L43, each with optical power. Specifically, from the magnification side, the fourth lens group G4 includes, in order: a biconcave negative lens L41, a biconcave negative lens L42, and a biconvex positive lens L43. The fourth lens group G4 does not include any aspherical surfaces.

[0073] The fifth lens group G5 is composed of six lenses, L51-L56, each having optical power. Specifically, from the magnification side, the fifth lens group G5 includes, in order: positive meniscus lens L51 with its convex surface facing the reduction side; negative meniscus lens L52 with its convex surface facing the reduction side; positive meniscus lens L53 with its convex surface facing the reduction side; biconvex positive lens L54; biconcave negative lens L55; and biconvex positive lens L56. The fifth lens group G5 does not include any aspherical surfaces.

[0074] The sixth lens group G6 is composed of a single lens L61 having optical power. Specifically, the sixth lens group G6 is composed of a biconvex positive lens L61. The sixth lens group G6 does not include an aspherical surface.

[0075] (Second embodiment)

[0076] Reference Figure 2 The variable magnification projection optical system ZL of the second embodiment is different from the variable magnification projection optical system ZL of the first embodiment (refer to Figure 1 ) is similarly constructed, but differs from the variable magnification projection optical system ZL of the first embodiment in the following respects. In the second embodiment, the fourth lens group G4 is fixed during magnification change. The variable magnification projection optical system ZL of the second embodiment has a wider viewing angle than the variable magnification projection optical system ZL of the first embodiment.

[0077] (Third embodiment)

[0078] Reference Figure 3 The variable magnification projection optical system ZL of the third embodiment is different from the variable magnification projection optical system ZL of the first embodiment (refer to Figure 1 ) is similarly constructed, but differs from the variable magnification projection optical system ZL of the first embodiment in the following points. In the variable magnification projection optical system ZL of the third embodiment, a negative lens L21 having a flat surface on the magnification side and a concave surface on the reduction side is added to the outermost portion of the second lens group G2. The second lens group G2 is composed of five lenses, L21-L25.

[0079] Specifically, the second lens group G2 in the third embodiment is constructed as follows, starting from the object side, when viewing the lenses in paraxial view. The second lens group G2 is composed of five lenses, L21-L25, each having optical power. The second lens group G2 includes two lenses with positive optical power. Specifically, the second lens group G2 includes, starting from the magnification side, a negative lens L21 with a flat surface on the magnification side and a concave surface on the reduction side; a biconvex positive lens L22; a biconcave negative lens L23; a biconcave negative lens L24; and a biconvex positive lens L25. The second lens group G2 does not include any aspherical surfaces.

[0080] All lenses with positive refractive power within the second lens group G2 (in this embodiment, lenses L22 and L25) are formed from a glass material having a transmittance greater than 0.98 at a thickness of 10 mm for light having a wavelength of 440 nm. Examples of such a glass material include FC5, FCD1, PCD4, BSC7, BACD5, TAC8, E-FD2, FF5, NBFD11, TAF1, TAF3, or TAFD5G (all manufactured by HOYA).

[0081] The refractive index of all lenses with positive refractive power for the d-line within the second lens group G2 (in this embodiment, lenses L22 and L25) is less than 1.6. By forming all lenses with positive refractive power within the second lens group G2 using, for example, the aforementioned nitrile material manufactured by HOYA, the refractive index of all lenses with positive refractive power for the d-line within the second lens group G2 can be reduced to less than 1.6.

[0082] All lenses within the second lens group G2 (in this embodiment, lenses L21-L25) are formed of a glass material having a transmittance greater than 0.97 at a thickness of 10 mm for light having a wavelength of 440 nm. Examples of such glass materials include FC5, FCD1, PCD4, BSC7, BACD5, TAC8, E-FD2, FF5, NBFD11, TAF1, TAF3, TAFD5G, E-FD5, E-FD1, BAFD8, and NBFD13 (all manufactured by HOYA). All lenses with positive optical focal length within the second lens group G2 (lenses L22 and L25 in this embodiment) are formed of a glass material having a transmittance greater than 0.98 at a thickness of 10 mm for light with a wavelength of 440 nm. Therefore, all lenses with positive optical focal length within the second lens group G2 naturally satisfy the condition that the lenses are formed of a glass material having a transmittance greater than 0.97 at a thickness of 10 mm for light with a wavelength of 440 nm.

[0083] The refractive index of all lenses in the second lens group G2 for the d-line (in this embodiment, lenses L21-L25) is less than 1.75. By forming all lenses in the second lens group G2 using the aforementioned glass material, such as that manufactured by HOYA, the refractive index of all lenses in the second lens group G2 with positive optical power for the d-line can be made less than 1.75. Since the refractive index of all lenses in the second lens group G2 with positive optical power for the d-line (in this embodiment, lenses L22 and L25) is less than 1.6, all lenses in the second lens group G2 with positive optical power naturally satisfy the requirement that the refractive index of lenses for the d-line is less than 1.75.

[0084] (Fourth embodiment)

[0085] Reference Figure 4 The variable magnification projection optical system ZL of the fourth embodiment is different from the variable magnification projection optical system ZL of the third embodiment (refer to Figure 3 ) is similarly constructed, but differs from the variable magnification projection optical system ZL of the third embodiment in the following respects. The first lens group G1 is composed of six lenses, L11-L16. The lens L21, located closest to the magnification side in the second lens group G2, is a biconcave negative lens L21.

[0086] Specifically, the first lens group G1 and the second lens group G2 in the fourth embodiment are configured as follows in order from the object side when each lens is viewed in a paraxial surface shape.

[0087] The first lens group G1 is composed of six lenses, L11-L16, each having optical power. Specifically, from the magnification side, the first lens group G1 includes, in order: negative meniscus lens L11 (convex surface facing the magnification side), negative meniscus lens L12 (convex surface facing the magnification side), negative meniscus lens L13 (convex surface facing the magnification side), biconvex positive lens L14, biconvex positive lens L15, and biconcave negative lens L16. The first lens group G1 does not include any aspherical surfaces.

[0088] All lenses with positive refractive power within the first lens group G1 (in this embodiment, lenses L14 and L15) are formed from a glass material having a transmittance greater than 0.98 at a thickness of 10 mm for light having a wavelength of 440 nm. Examples of such a glass material include FC5, FCD1, PCD4, BSC7, BACD5, TAC8, E-FD2, FF5, NBFD11, TAF1, TAF3, or TAFD5G (all manufactured by HOYA).

[0089] The refractive index of all lenses with positive refractive power for the d-line within the first lens group G1 (in this embodiment, lenses L14 and L15) is less than 1.6. By forming all lenses with positive refractive power within the first lens group G1 using, for example, the aforementioned glass material manufactured by HOYA, the refractive index of all lenses with positive refractive power for the d-line within the first lens group G1 can be reduced to less than 1.6.

[0090] All lenses within the first lens group G1 (in this embodiment, lenses L11-L16) are formed from a glass material having a transmittance greater than 0.97 at a thickness of 10 mm for light having a wavelength of 440 nm. Examples of such a glass material include FC5, FCD1, PCD4, BSC7, BACD5, TAC8, E-FD2, FF5, NBFD11, TAF1, TAF3, TAFD5G, E-FD5, E-FD1, BAFD8, and NBFD13 (all manufactured by HOYA). All lenses with positive optical focal length within the first lens group G1 (lenses L14 and L15 in this embodiment) are formed of a glass material having a transmittance greater than 0.98 at a thickness of 10 mm for light with a wavelength of 440 nm. Therefore, all lenses with positive optical focal length within the first lens group G1 naturally satisfy the condition that the lenses are formed of a glass material having a transmittance greater than 0.97 at a thickness of 10 mm for light with a wavelength of 440 nm.

[0091] The refractive index of all lenses in the first lens group G1 for the d-line (in this embodiment, lenses L11-L16) is less than 1.75. By forming all lenses in the first lens group G1 using the aforementioned glazing material, such as that manufactured by HOYA, the refractive index of all lenses in the first lens group G1 with positive optical power for the d-line can be made less than 1.75. Since the refractive index of all lenses in the first lens group G1 with positive optical power for the d-line (in this embodiment, lenses L14 and L15) is less than 1.6, all lenses in the first lens group G1 with positive optical power naturally satisfy the requirement that the refractive index of lenses for the d-line is less than 1.75.

[0092] The second lens group G2 is composed of five lenses, L21-L25, each with optical power. The second lens group G2 includes two lenses with positive optical power. Specifically, from the magnification side, the second lens group G2 includes, in order: biconcave negative lens L21, biconvex positive lens L22, biconcave negative lens L23, biconcave negative lens L24, and biconvex positive lens L25. The second lens group G2 does not include any aspherical surfaces.

[0093] All lenses with positive refractive power within the second lens group G2 (in this embodiment, lenses L22 and L25) are formed from a glass material having a transmittance greater than 0.98 at a thickness of 10 mm for light having a wavelength of 440 nm. Examples of such a glass material include FC5, FCD1, PCD4, BSC7, BACD5, TAC8, E-FD2, FF5, NBFD11, TAF1, TAF3, or TAFD5G (all manufactured by HOYA).

[0094] The refractive index of all lenses with positive refractive power for the d-line within the second lens group G2 (in this embodiment, lenses L22 and L25) is less than 1.6. By forming all lenses with positive refractive power within the second lens group G2 using, for example, the aforementioned nitrile material manufactured by HOYA, the refractive index of all lenses with positive refractive power for the d-line within the second lens group G2 can be reduced to less than 1.6.

[0095] All lenses within the second lens group G2 (in this embodiment, lenses L21-L25) are formed of a glass material having a transmittance greater than 0.97 at a thickness of 10 mm for light having a wavelength of 440 nm. Examples of such glass materials include FC5, FCD1, PCD4, BSC7, BACD5, TAC8, E-FD2, FF5, NBFD11, TAF1, TAF3, TAFD5G, E-FD5, E-FD1, BAFD8, and NBFD13 (all manufactured by HOYA). All lenses with positive optical focal length within the second lens group G2 (lenses L22 and L25 in this embodiment) are formed of a glass material having a transmittance greater than 0.98 at a thickness of 10 mm for light with a wavelength of 440 nm. Therefore, all lenses with positive optical focal length within the second lens group G2 naturally satisfy the condition that the lenses are formed of a glass material having a transmittance greater than 0.97 at a thickness of 10 mm for light with a wavelength of 440 nm.

[0096] The refractive index of all lenses in the second lens group G2 for the d-line (in this embodiment, lenses L21-L25) is less than 1.75. By forming all lenses in the second lens group G2 using the aforementioned glass material, such as that manufactured by HOYA, the refractive index of all lenses in the second lens group G2 with positive optical power for the d-line can be made less than 1.75. Since the refractive index of all lenses in the second lens group G2 with positive optical power for the d-line (in this embodiment, lenses L22 and L25) is less than 1.6, all lenses in the second lens group G2 with positive optical power naturally satisfy the requirement that the refractive index of lenses for the d-line is less than 1.75.

[0097] [Example]

[0098] Hereinafter, the structure data of the examples will be cited to more specifically describe the structure of the variable magnification projection optical system ZL of the first to fourth embodiments. The examples 1 to 4 cited here are numerical examples corresponding to the above-mentioned first to fourth embodiments, respectively. The structural diagram showing the variable magnification projection optical system ZL of the first to fourth embodiments ( Figures 1-4) represent the optical structures (lens configuration, lens shape, etc.) of the corresponding embodiments 1-4 respectively.

[0099] The structural data for each example shows, starting from the left column, the surface data: surface number i, paraxial curvature radius r (mm), on-axis surface separation d (mm), refractive index nd associated with the d-line (wavelength 587.56 nm), and Abbe number vd associated with the d-line. Furthermore, SC denotes screen surface, stop denotes aperture stop, and image denotes image display surface.

[0100] Various data for Examples 1-4 include the focal length (Fl, mm), F-number (Fno.), half angle of view (ω, degrees), image height (y'max, mm), total lens length (TL, mm), back focus (BF, mm), and variable on-axis surface spacing (variable: di (i: surface number), mm) of the entire variable magnification projection optical system ZL at each focal length state, including the zoom ratio, wide-angle end (Wide), intermediate focal length state (Middle), and telephoto end (Tele). Furthermore, the focal length (mm) of each lens group is shown as lens group data. The back focus BF is expressed as the distance from the lens's final surface to the paraxial image plane in terms of air-equivalent length. The total lens length TL is the distance from the lens's frontmost surface (the surface closest to the magnification side of the first lens group G1) to the lens's final surface (the surface closest to the reduction side of the sixth lens group G6) plus the back focus BF. The image height y'max corresponds to half the diagonal length of the image display surface IM.

[0101] about Figures 5A to 8B The spherical aberration diagram uses the offset of the focus position in the optical axis AX direction from the paraxial image plane (unit: mm) to represent the spherical aberration amount for the d line (wavelength 587.56nm) (indicated by a solid line), the spherical aberration amount for the C line (wavelength 656.28nm) (indicated by a single dotted line), and the spherical aberration amount for the g line (wavelength 435.84nm) (indicated by a dotted line). The vertical axis represents the value obtained by normalizing the incident height to the pupil with its maximum height (i.e., the relative pupil height). Figures 5A to 8B In the astigmatism diagram, the dotted line T represents the tangential image plane for the d-line using the amount of focus position offset in the optical axis AX direction from the paraxial image plane (unit: mm), and the solid line S represents the sagittal image plane for the d-line using the amount of focus position offset in the optical axis AX direction from the paraxial image plane (unit: mm). The vertical axis represents the image height (IMG HT, unit: mm). Figures 5A to 8B In the distortion diagram of , the horizontal axis represents the distortion for the d-line (unit: %), and the vertical axis represents the image height (IMGHT, unit: mm).

[0102] Numerical Example 1

[0103] Unit: mm

[0104] Surface data

[0105]

[0106]

[0107]

[0108] Various data

[0109]

[0110] Lens group data

[0111]

[0112] Numerical Example 2

[0113] Unit: mm

[0114] Surface data

[0115]

[0116]

[0117]

[0118] Various data

[0119]

[0120] Lens group data

[0121]

[0122]

[0123] Numerical Example 3

[0124] Unit: mm

[0125] Surface data

[0126]

[0127]

[0128]

[0129] Various data

[0130]

[0131] Lens group data

[0132]

[0133] Numerical Example 4

[0134] Unit: mm

[0135] Surface data

[0136]

[0137]

[0138]

[0139] Various data

[0140]

[0141] Lens group data

[0142]

[0143] Table 1 shows the numerical values ​​of the respective Examples.

[0144]

Table 1

[0145]

[0146] <Projection device>

[0147] Reference Figure 9 The projection device 1 according to the embodiment will be described. Figure 9 As shown, the projection device 1 includes a light source 3, an illumination optical system 5, a reflector 6, a prism PR, a cover glass CG, an image display element 7, a variable magnification projection optical system ZL, an actuator 8, and a control unit 9. The variable magnification projection optical system ZL is any one of the variable magnification projection optical systems ZL of the first to fourth embodiments.

[0148] The light source 3 is, for example, a white light source such as a xenon lamp, or a laser light source. The image display element 7 is, for example, a digital micromirror device (DMD) or a liquid crystal display element (LCD). A cover glass CG is provided on the image display surface IM of the image display element 7. The actuator 8 is capable of moving the movable lens group along the optical axis AX of the variable magnification projection optical system ZL for zooming or focusing. The control unit 9 controls the projection device 1. The control unit 9 controls, for example, the image display element 7 and the actuator 8. The control unit 9 controls the actuator to move the movable lens group for zooming or focusing.

[0149] The illumination light emitted from the light source 3 is incident on the image display element 7 via the illumination optical system 5, the reflector 6, and the prism PR. The image display element 7 modulates the illumination light and reflects the image light. The prism PR is, for example, a TIR prism or a color separation and synthesis prism. The variable magnification projection optical system ZL magnifies and projects the image light formed by the image display element 7 toward the screen SC. On the optical axis AX of the variable magnification projection optical system ZL, the distance between the variable magnification projection optical system ZL and the screen SC is, for example, greater than 1 m and less than 3 m.

[0150] Furthermore, the movable lens group may be moved manually without using the actuator 8. When the image display element 7 is a self-luminous image display element, the light source 3, the illumination optical system 5, and the reflective mirror 6 may be omitted.

[0151] While the embodiments of the present invention have been described, the embodiments disclosed herein are in all respects illustrative only and should not be construed as limiting. The scope of the present invention is indicated by the claims, and is intended to encompass all modifications within the meaning and scope of the claims and equivalents thereof.

Claims

1. A variable magnification projection optical system that magnifies and projects an image displayed on an image display surface. The variable magnification projection optical system comprises, in order from the magnification side: a first lens group having negative optical power; a second lens group having negative optical power; a third lens group having positive optical power; a fourth lens group having negative optical power; A fifth lens group having positive optical power; as well as The sixth lens group has positive optical power. During zooming, the first lens group is fixed, and the second lens group and the third lens group move. The second lens group includes a plurality of lenses having positive optical power. All lenses having positive refractive power in the first lens group and the second lens group are formed of a glass material having a transmittance greater than 0.98 at a thickness of 10 mm for light having a wavelength of 440 nm. All lenses in the first lens group are formed of a glass material having a transmittance greater than 0.97 at a thickness of 10 mm with respect to light having a wavelength of 440 nm.

2. The variable magnification projection optical system according to claim 1, wherein: The refractive index of all lenses having positive refractive power in the first lens group and the second lens group for the d-line is less than 1.

6.

3. The variable magnification projection optical system according to claim 2, wherein: The refractive index of all lenses in the first lens group for the d-line is less than 1.

75.

4. The variable magnification projection optical system according to claim 1, wherein: All lenses in the first lens group and the second lens group are formed of a glass material having a transmittance greater than 0.97 at a thickness of 10 mm with respect to light having a wavelength of 440 nm.

5. The variable magnification projection optical system according to any one of claims 1 to 4, wherein: The first lens group is composed of seven or less lenses having optical power.

6. The variable magnification projection optical system according to any one of claims 1 to 4, wherein: The second lens group is composed of four or more lenses having optical power.

7. The variable magnification projection optical system according to any one of claims 1 to 4, wherein: The variable magnification projection optical system further includes at least one lens group that is arranged on the reduction side of the third lens group and moves along the optical axis of the variable magnification projection optical system during magnification change.

8. The variable magnification projection optical system according to any one of claims 1 to 4, wherein: The first lens group does not include an aspherical surface.

9. The variable magnification projection optical system according to any one of claims 1 to 4, wherein: The variable magnification projection optical system does not include an aspherical surface.

10. A projection device comprising: The variable magnification projection optical system according to any one of claims 1 to 9; and An image display element has the image display surface.

Images