Variable magnification projection optical system and image projection apparatus

A variable magnification projection optical system includes, in order from a magnification conjugate side to a reduction conjugate side, a first lens group, a second lens group, a third lens group, a fourth lens group, a fifth lens group, a sixth lens group, and an optical stop which is arranged at any position from a front of a lens arranged closest to the magnification conjugate side in the fourth lens group to a front of a lens arranged closest to the magnification conjugate side in the fifth lens group, wherein the fourth lens group is configured to include, in order from the magnification conjugate side, two or more negative lenses and a positive lens, and wherein the following condition expressions (1), (2) and (3) are satisfied:|Et/ft|≧10  (1)|EW/fW|≧15  (2)0.87≦23φT/23WT≦1.15  (3).

The entire disclosure of Japanese Patent Application No. 2014-019005 filed on Feb. 4, 2014 including description, claims, drawings, and abstract are incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a variable magnification projection optical system capable of changing a variable magnification ratio to project a magnified image light formed in an image forming element onto a screen and an image projection apparatus using the variable magnification projection optical system.

2. Description of the Related Art

An image projection apparatus which is generally called a projector is an apparatus which projects a magnified image light formed in an image forming element on a screen. In particular, with respect to image projection apparatuses for cinema, with the spread of digital cinema, miniaturization and high definition of image forming elements are required, and accordingly, miniaturization and high resolution of variable magnification projection optical systems installed in the image projection apparatuses for cinema are also required.

As these variable magnification projection optical systems, there are optical systems disclosed in JP 2001-108900 A, JP 2003-015038 A, JP 2002-350727 A, and JP 2008-052174 A. The projection zoom lens disclosed in JP 2001-108900 A is a projection zoom lens which magnifies a plane image and projects and images the magnified plane image. First to sixth groups having respective negative, positive, positive, negative, positive, and positive refracting powers are arranged in order from the magnification side. During changing of a projection distance, in order to conjugate the plane image with a projection surface, the first group is moved in an optical axis direction, and during changing of magnification, the first group, the fourth group, the sixth group are fixed, and the second group, the third group, and the fifth group are moved in the optical axis direction. A focal length fw of the entire system at the wide-angle end, a back focus bf (value in air), a total lens length OAL (length from the surface of the first group closest to the magnification side to the surface of the sixth group closest to the reduction side), a focal length f3 of the third group, an average value ν6P of Abbe numbers of convex lenses constituting the sixth group, an average value ν4M of Abbe numbers of concave lenses constituting the fourth group, and an average value ν5M of Abbe numbers of concave lenses constituting the fifth group satisfy the condition expressions: OAL>90·bf/fw, 1.5<f3/fw<2.5, ν6P>50, and (ν4M+ν5M)/2<40.

The projection zoom lens disclosed in JP 2003-015038 A is a projection zoom lens where, first to sixth groups having the respective refracting powers of negative, positive, positive, negative, positive, and positive are arranged in order from the magnification side, and an aperture stop is arranged between the third and fourth lens groups. During continuously changing of magnification from the wide-angle end to the telephoto end, the first, fourth, and sixth lens groups are fixed, and the second, third, and fifth lens groups are moved on the optical axis. A focal length fw of the entire system at the wide-angle end, a focal length f1 of the first lens group, a back focus Bf when the conjugate point of the magnification side is infinity, and a length L of the entire system satisfy the conditions: 1.4<Bf/fw, 1.0<|f1|/fw<1.7, and 6.5<L/fw<9.0.

In addition, the projection zoom lens disclosed in JP 2002-350727 A is a projection zoom lens where six components of first to sixth groups having respective negative, positive, positive, negative, positive, and positive refracting powers are arranged in order from the magnification side, and the projection zoom lens is substantially telecentric at the reduction side. During change of magnification from the telephoto end to the wide-angle end, the third group and the fifth group are moved from the magnification side to the reduction side, and a stop is arranged in the fourth group.

In addition, the zoom lens disclosed in JP 2008-052174 A, is a zoom lens which magnifies and projects display elements and is configured to include, in order from the magnification side, six groups of first to sixth groups. The zoom lens is configured to include, a first group having a negative refracting power, a second group having a positive refracting power and being moved during changing of magnification, a fifth group having a positive refracting power and being moved during changing of magnification, and a sixth group having a positive refracting power and to include a third group having a positive or negative refracting power and being moved during changing of magnification and a fourth group having a negative refracting power which includes a stop or a third group having a negative refracting power which includes a stop and a fourth group having a positive or negative refracting power and being moved during changing of magnification. The sixth group is configured to include one positive lens, and when a distance on an optical axis from a center of a lens surface at the reduction side of the positive lens of the sixth group to a surface of a display element arranged perpendicular to the optical axis is denoted by Bf, when a radius of curvature of the positive lens of the sixth group at the magnification side is denoted by CR1, and when a minimum F value of the zoom lens is denoted by F, a condition expression 1.35≦Bf/CR1×F≦2.00 is satisfied. In the case where the third group has a negative refracting power and includes a stop and the fourth group has a positive or negative refracting power and is moved during changing of magnification, at least one of the positive lenses constituting the fourth group and the fifth group is configured with a material satisfying nd>1.58νd>59, and herein a refractive index with respect to d-line (wavelength of 587.56 nm) is denoted by nd and an Abbe number with respect to d-line (wavelength of 587.56 nm) is denoted by νd, and in the case where fourth group has a negative refracting power and includes a stop and the third group has a positive or negative refracting power and is moved during changing of magnification, at least one of the positive lenses constituting the fifth group is configured with a material satisfying nd>1.58νd>59. In addition, in the case where the third group has a negative refracting power and includes a stop and the fourth group has a positive or negative refracting power and is moved during changing of magnification, a composite focal length of the fourth group and the fifth group at the time of the zoom lens being at the wide-angle end is denoted by f×w, and in the case where the fourth group has a negative refracting power and includes a stop and the third group has a positive or negative refracting power and is moved during changing of magnification, a focal length of the fifth group is denoted by f×w. In the case where the zoom lens is at the wide-angle end, a focal length is denoted by fw. In this case, a condition expression 1.70≦f×w/fw≦4.80 is satisfied.

However, in order to achieve high resolution, suppression of various types of aberration such as spherical aberration, image surface curvature, axial chromatic aberration, and magnification chromatic aberration is required. However, as the variable magnification ratio is increased, the various types of aberration are greatly changed between the telephoto end and the wide-angle end, so that there is a circumstance that the aforementioned requirement is not compatible with the high variable magnification ratio. Therefore, the high resolution and the high variable magnification ratio are difficult to be compatible with each other.

JP 2001-108900 A, JP 2003-015038 A, JP 2002-350727 A, and JP 2008-052174 A are reviewed from this point of view. In the zoom lenses disclosed in JP 2001-108900 A and JP 2003-015038 A, it is considered that, if the high resolution is achieved, the configuration of the fourth lens group including a stop becomes inappropriate, so that it is not possible to effectively suppress the spherical aberration. In addition, in the zoom lenses disclosed in JP 2002-350727 A and JP 2008-052174 A, it is considered that, if the high resolution is achieved, the chromatic aberration of the fourth lens group is insufficiently suppressed, so the chromatic aberration at the wide-angle end and the telephoto end are increased.

SUMMARY OF THE INVENTION

The present invention has been made in light of the foregoing, and an object thereof is to provide a variable magnification projection optical system capable of sufficiently suppressing various types of aberration such as spherical aberration, image surface curvature, axial chromatic aberration, and magnification chromatic aberration and implementing a higher resolving power and an image projection apparatus using the variable magnification projection optical system.

In order to solve the above-described technical problems, the present invention provides a variable magnification projection optical system and an image projection apparatus having the following configurations. In addition, terms used hereinafter in the description of the specification are defined as follows.

(a) A refractive index ndis a refractive index of d-line (wavelength of 587.56 nm).

(b) An Abbe number is an Abbe number νd defined by νd=(nd−1)/(nF−nC) when refractive indexes of d-line, F-line (wavelength of 486.13 nm), and C-line (wavelength of 656.28 nm) are denoted by nd, nF, and nCrespectively, and the Abbe number is denoted by νd.

(c) θgFis defined as an indicator representing abnormal dispersibility. When a refractive index of g-line (wavelength of 435.84 nm) is denoted by ng, the θgFis defined by the following expression.
θgF=(ng−nF)/(nF−nC)

In addition, ΔθgFis defined as an indicator representing by which degree the abnormal dispersibility is deviated from that of a standard glass material. The ΔθgFis defined by the following expression.
ΔθgF=θgF−(0.6438−0.001682×νd)

(d) With respect to a lens, in the case where terms of “concave”, “convex”, or “meniscus” are used, these terms represent a shape of the lens in the vicinity of an optical axis (in the vicinity of the center of the lens).

(e) A refracting power (optical power, a reciprocal of a focal length) of each single lens constituting a cemented lens represents a power in the case where both sides of the lens surfaces of the single lens are air.

(f) Since a resin material used for a composite aspherical lens has only an auxiliary function for a substrate glass material, the composite aspherical lens is not treated as an independent optical member but it is treated equally as the case where a substrate glass material has an aspherical surface. The number of lenses is also treated to be one. In addition, the refractive index of the lens is also set to be a refractive index of the glass material for the substrate. The composite aspherical lens is a lens having an aspherical shape formed by applying a thin resin material on the glass material for the substrate.

To achieve the abovementioned object, according to an aspect, a variable magnification projection optical system reflecting one aspect of the present invention comprises, in order from a magnification conjugate side to a reduction conjugate side, a first lens group having a totally negative refracting power and being stationary during changing of magnification, a second lens group having a totally positive refracting power and being movable during changing of magnification, a third lens group having a totally positive refracting power and being movable during changing of magnification, a fourth lens group having a totally negative refracting power and being stationary or movable during changing of magnification, a fifth lens group having a totally positive refracting power and being movable during changing of magnification, a sixth lens group having a totally positive refracting power and being stationary during changing of magnification, and an optical stop which is arranged at any position from a front of a lens arranged closest to the magnification conjugate side in the fourth lens group to a front of a lens arranged closest to the magnification conjugate side in the fifth lens group, wherein the fourth lens group is configured to include, in order from the magnification conjugate side, two or more negative lenses and a positive lens, and wherein the following condition expressions (1), (2) and (3) are satisfied.
|ET/fT|≧10  (1)
|EW/fW|≧15  (2)
0.87≦φ23T/≦φ23W≦1.15  (3)

wherein, ETis a paraxial exit pupil position at the telephoto end, EWis a paraxial exit pupil position at the wide-angle end, fTis a focal length at the telephoto end, fWis a focal length at the wide-angle end, φ23Tis a composite refracting power of the second and third lens groups at the telephoto end, and φ23Wis a composite refracting power of the second and third lens groups at the wide-angle end.

In addition, preferably, in the above-described variable magnification projection optical system, during changing of magnification from the telephoto end to the wide-angle end, the third and fifth lens groups are moved from the magnification conjugate side to the reduction conjugate side.

The variable magnification projection optical system is an optical system where six groups are configured to be aligned in order of negative, positive, positive, negative, positive, and positive from the magnification conjugate side to the reduction conjugate side. In the optical system, in the case where the third and fifth lens groups are moved from the magnification conjugate side to the reduction conjugate side during changing of magnification from the telephoto end to the wide-angle end, the third lens group having a positive refracting power approaches the fourth lens group closer to the wide-angle end than to the telephoto end, and on the contrary, the fifth lens group having a positive refracting power approaches the fourth lens group closer to the telephoto end than to the wide-angle end. Therefore, in the variable magnification projection optical system, at both of the telephoto end and the wide-angle end, the lens groups having positive refracting powers are arranged in the vicinity of the optical stop. In general, if the positive refracting power of the lens group arranged in the vicinity of the optical stop is increased, the optical system tends to have spherical aberration in the “under” direction. If the spherical aberration is insufficiently corrected, the resolving power of the on-axis light is decreased. However, in the variable magnification projection optical system, the fourth lens group close to the optical stop consecutively includes negative lenses, so that the spherical aberration is able to be strongly corrected in the “over” direction. Asa result, it is possible to achieve high resolving power.

In addition, the condition expression (1) represents a condition of a paraxial exit pupil position with respect to a focal length at the telephoto end, the condition expression (2) represents a condition of a paraxial exit pupil position with respect to a focal length at the wide-angle end, and the condition expressions (1) and (2) represent that telecentricity is secured. If the values are smaller than the lower limit values of the condition expressions (1) and (2), since an angle of off-axis light is increased, reflection/transmission efficiency at the time of performing color synthesis by a dichroic prism or reflection/transmission efficiency by a TIR (Total Internal Reflection) prism is deteriorated. Therefore, it is not preferred.

In addition, the condition expression (3) represents a condition of the telephoto end to the wide-angle end in the composite refracting power of the second and third lens groups and represents that the composite refracting power of the second and third lens groups is substantially equal at the telephoto end and the wide-angle end. If the value is larger than the upper limit value of the condition expression (3) or smaller than the lower limit value thereof, the variable magnification projection optical system is able to suppress variation of the image plane at the telephoto end and the wide-angle end, and thus it is preferred. However, in the case where the entire first lens group is used as a focusing group, the variable magnification projection optical system has a configuration having a high error sensitivity and is easily affected by manufacturing errors, and focusing performance is not stabilized (not easily focused) during focus manipulation (during focusing), and thus, it is not preferred. Particularly, since a projector is generally configured so that the entire first lens group is used as a focusing group, it is preferable that the variable magnification projection optical system satisfies the condition expression (3).

In addition, in another aspect, in the above-described variable magnification projection optical system, at least one of the negative lenses included in the fourth lens group preferably satisfies the following condition expression (4), and the entire negative lenses included in the fourth lens group preferably satisfy the following condition expression (5).
0.003≦ΔθgF≦0.055  (4)
−0.035≦(Σ(ΔθgF4i×φ4i))/φW≦−0.001  (5)

wherein, ΔθgF4iis ΔθgFof the i-th negative lens from the magnification conjugate side which is included in the fourth lens group. Herein, ΔθgF=θgF−(0.06438−0.01682×νd), θgF=(ng−nF)/(nF−nC), and νd is an Abbe number. In addition, φ4iis a refracting power of the i-th negative lens from the magnification conjugate side which is included in the fourth lens group, and φWis a composite refracting power of the entire optical system at the wide-angle end.

In addition, in another aspect, in the above-described variable magnification projection optical systems, at least one of the negative lenses included in the fourth lens group preferably satisfies the following condition expression (6), and the entire negative lenses included in the fourth lens group preferably satisfy the following condition expression (7).
0.03≦ΔθgF≦0.055  (6)
−0.035≦(Σ(ΔθgF4i×φ4i))/φW≦−0.01  (7)

In a projection optical system, the chromatic aberration needs to be well corrected, and in the variable magnification projection optical system, the axial chromatic aberration and the spherical aberration are able to be corrected. In general, since an imaging optical system has a positive refracting power as the entire system, the refracting power with respect to light having a relatively short wavelength tends to be larger than the refracting power with respect to light having a relatively long wavelength, so that the axial chromatic aberration occurs. In addition, since the refractive index of a lens varies with the wavelength, irregularity according to the wavelength occurs in the spherical aberration occurring due to light beams passing through the peripheries of the lens. On the contrary, if a negative lens having abnormal dispersibility is arranged in the vicinity of an optical stop, a focal position of the light having a short wavelength is moved to the “over” side, so that it is possible to correct the axial chromatic aberration. In addition, as the wavelength of the light passing through the peripheries of the negative lens having the abnormal dispersibility becomes shorter, the effect that the spherical aberration becomes “over” is able to be obtained. Therefore, it is also possible to correct the irregularity of the spherical aberration according to the wavelength.

Herein, the condition expressions (4) and (6) define the magnitude of the abnormal dispersibility. In addition, each of the condition expressions (5) and (7) defines a sum of the values obtained by multiplying the respective refracting powers with the abnormal dispersibilities of the respective negative lenses included in the fourth lens group. As the value is decreased, the abnormal dispersibility of the negative lens becomes strong. Therefore, the variable magnification projection optical system satisfies the condition expressions (4) and (5), and the fourth lens group arranged in the vicinity of the optical stop includes the negative lens having the abnormal dispersibility, so that it is possible to suppress the axial chromatic aberration and the irregularity of the spherical aberration according to the wavelength. Similarly, the variable magnification projection optical system satisfies the condition expressions (6) and (7), and the fourth lens group arranged in the vicinity of the optical stop includes the negative lens having the abnormal dispersibility, so that it is possible to suppress the axial chromatic aberration and the irregularity of the spherical aberration according to the wavelength. Particularly, the condition expressions (6) and (7) are satisfied, so that it is possible to achieve higher resolving power.

In addition, in another aspect, in the above-described variable magnification projection optical systems, lenses included in the fifth lens group preferably satisfy the following condition expressions (8) and (9).
0.025≦(Σ(ΔθgF5i×φ5i))/φW≦0.065  (8)
0.8≦dz5/fW≦1.65  (9)

wherein, ΔθgF5iis ΔθgFof the i-th lens from the magnification conjugate side which is included in the fifth lens group, φ5iis a refracting power of the i-th lens from the magnification conjugate side which is included in the fifth lens group, and dz5is a movement amount of the fifth lens group from the magnification conjugate side to the reduction conjugate side during changing of magnification from the telephoto end to the wide-angle end.

In addition, in another aspect, in the above-described variable magnification projection optical systems, lenses included in the fifth lens group preferably satisfy the following condition expressions (10) and (11).
0.035≦(Σ(ΔθgF5i×φ5i))/φW≦0.045  (10)
1≦dz5/fW≦1.65  (11)

In general, in a variable magnification optical system, the magnification chromatic aberration between the wide-angle end and the telephoto end swings at the plus side and the minus side, in other words, the difference in the magnification chromatic aberration between the wide-angle end and the telephoto end is large, so that the performance at the wide-angle end and the performance at the telephoto end are not compatible to each other, and the balance of the performance is lost between the wide-angle end and the telephoto end.

Herein, each of the condition expressions (8) and (10) defines a sum of the values obtained by multiplying the respective refracting powers with the abnormal dispersibilities of the respective negative lenses included in the fifth lens group. As the value is decreased, the abnormal dispersibility of the negative lens becomes strong. Therefore, as each value of the condition expressions (8) and (10) is increased, the abnormal dispersibility of the positive lens goes to the Krutz side and the abnormal dispersibility of the negative lens goes to the Lange side. Therefore, with respect to the lenses, the magnification chromatic aberration is able to be biased to the minus direction. The light beam passing through the inside of the fifth lens group passes at a high position from the optical axis closer to the wide-angle end than to the telephoto end, and the magnification chromatic aberration at the wide-angle end is larger than the magnification chromatic aberration at the telephoto end and is biased to the minus direction. Therefore, the condition expression (8) or (10) is satisfied, so that it is possible to reduce the difference in the magnification chromatic aberration between the wide-angle end and the telephoto end. In addition, each of the condition expressions (9) and (11) defines a movement amount of the fifth lens group during changing of magnification. As the movement amount of the fifth lens group is increased, the height of the light beam passing through the inside of the lens varies at the telephoto end and the wide-angle end. Therefore, the condition expression (9) or (11) is satisfied, so that it is possible to effectively reduce the difference in the magnification chromatic aberration.

In this manner, in each of the variable magnification projection optical systems satisfies the condition expressions (8) and (10) or satisfies the condition expressions (9) and (11), and the glass material having the abnormal dispersibility is effectively used for the fifth lens group which is moved during changing of magnification. Therefore, the variation of the magnification chromatic aberration according to the changing of magnification is suppressed, so that it is possible to reduce the difference in the magnification chromatic aberration at the telephoto end and the wide-angle end.

In addition, in another aspect, in the above-described variable magnification projection optical systems, the first lens group preferably includes one or more negative lens satisfying the following condition expression (12).
0.03≦ΔθgF≦0.055  (12)

Although the difference in the magnification chromatic aberration at the telephoto end and the wide-angle end is suppressed by moving the fifth lens group using the lens having the abnormal dispersibility during changing of magnification, the difference is not necessarily 0. Therefore, the variable magnification projection optical system according to the embodiment employs the negative lens satisfying the condition expression (12) and having the abnormal dispersibility as the first lens group, so that it is possible to further suppress the difference in the magnification chromatic aberration.

In addition, in another aspect, in the above-described variable magnification projection optical systems, the first to fourth lens groups preferably satisfy the following condition expressions (13) and (14).
|φ14T/φT|≦0.3  (13)
|φ14W/φW|≦0.3  (14)

wherein, φ14Tis a composite refracting power of the first to fourth lens groups at the telephoto end, and φ14Wis a composite refracting power of the first to fourth lens groups at the wide-angle end.

The condition expressions (13) and (14) define afocal properties. A combined system of the first to fourth lens groups arranged from the optical stop in the magnification conjugate side is substantially afocal, so that the width of light flux between the fourth lens group and the fifth lens group are substantially parallel along the optical axis direction. Therefore, since the change in the F number according to the movement of the fifth lens group does not easily occur, in the variable magnification projection optical system, it is possible to suppress the variation of the F number at the telephoto end and the wide-angle end during changing of magnification.

In addition, in another aspect, in the above-described variable magnification projection optical systems, the first lens group is preferably divided into a plurality of sub lens groups during focusing, and at least one lens group of the plurality of sub lens groups is preferably moved in the optical axis direction during focusing, so that focusing is performed. In addition, in another aspect, in the above-described variable magnification projection optical system, the plurality of sub lens groups preferably include a 1A-th sub lens group having a totally negative refracting power and a 1B-th sub lens group, and the 1A-th and 1B-th sub lens groups are preferably moved during focusing so as to have different loci. In addition, in another aspect, in the above-described variable magnification projection optical system, the plurality of sub lens groups preferably include a 1A-th lens group having a totally negative refracting power which is movable during focusing and a 1B-th lens group which is stationary during the focusing.

Each of the variable magnification projection optical systems has a configuration having a low error sensitivity and is not easily affected by manufacturing errors, and focusing performance is stabilized (easily focused) during focus manipulation (during focusing). Particularly, the 1A-th sub lens group and the 1B-th sub lens group are moved so as to have different loci, so that it is possible to widen a focus range (distance range where the focusing is able to be performed). In addition, the 1B-th sub lens group is stationary, so that the configuration becomes simple and the focusing performance is particularly stabilized.

In addition, in another aspect, in the above-described variable magnification projection optical systems, the second lens group is preferably configured to include, in order from the magnification conjugate side to the reduction conjugate side, one or more negative lenses and one or more positive lenses, and the following condition expression (15) is preferably satisfied.
1.8≦dZ2/fW≦2.5  (15)

wherein, dZ2is a movement amount of the second lens group from the magnification conjugate side to the reduction conjugate side during changing of magnification from the telephoto end to the wide-angle end.

In the above-described variable magnification projection optical system, the variation of the light beam passing position of the on-axis light is smaller at the reduction conjugate side than at the optical stop during changing of magnification. Therefore, the range of the axial chromatic aberration during changing of magnification occurring at the rear group may be allowed to be smaller than that at the optical stop. However, in the entire system of the variable magnification projection optical system, the difference in the axial chromatic aberration during changing of magnification is not necessarily small. Therefore, in the variable magnification projection optical system, the movement amount of the second lens group is set so that the condition expression (15) is satisfied, so that it is possible to suppress the variation of the light beam passing position of the on-axis light in the so-called variator group which greatly contributes to the change of magnification, and it is possible to allow the difference in the axial chromatic aberration during changing of magnification to be small.

In addition, in another aspect, in the above-described variable magnification projection optical systems, the following condition expressions (16) and (17) are preferably satisfied.
fT/fW≧1.45  (16)
ωW≧26.5  (17)

wherein, ωWis a half angle of view at the wide-angle end.

In the configuration of the related art, in the case where the condition expression (16) is satisfied, if various types of aberration such as spherical aberration, image surface curvature, axial chromatic aberration, and magnification chromatic aberration are suppressed, the half angle of view ωWat the wide-angle end is not allowed to be set to be large. On the other hand, in the configuration of the related art, in the case where the condition expression (17) is satisfied, if various types of aberration such as spherical aberration, image surface curvature, axial chromatic aberration, and magnification chromatic aberration are suppressed, the variable magnification ratio is not allowed to be set to be large. However, in the above-described variable magnification projection optical system, since the condition expressions (1) to (15) are appropriately satisfied, various types of aberration can be suppressed as described above. Even in the case where the condition expressions (16) and (17) are satisfied, in the above-described variable magnification projection optical system, it is possible to implement high magnification and a wide angle of view (wide angle) while suppressing the various types of aberration such as spherical aberration, image surface curvature, axial chromatic aberration, and magnification chromatic aberration.

In addition, according to another aspect of the present invention, an image projection apparatus preferably includes an image forming element which forms image light and a projection optical system which magnifies and projects the image light formed in the image forming element, and the projection optical system is preferably one of the above-described variable magnification projection optical systems.

In the image projection apparatus, it is possible to sufficiently suppress various types of aberration such as spherical aberration, image surface curvature, axial chromatic aberration, and magnification chromatic aberration and implement a higher resolving power.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the illustrated examples. In addition, in each figure, components designated with the same reference numerals denote the same components, and the description thereof will be appropriately omitted. In addition, the number of lens constituents of a cemented lens is not 1 as the entire cemented lens, but it denotes the number of single lenses constituting the cemented lens.

<Description of Variable Magnification Projection Optical System According to Embodiment and Image Projection Apparatus Using the Same>

FIGS. 1A and 1Bare schematic lens cross-sectional diagrams illustrating a configuration for describing the variable magnification projection optical system according to the embodiment.FIGS. 2A and 2Bare diagrams for describing operations of a first lens group of a first aspect during focusing of the variable magnification projection optical system according to the embodiment.FIG. 2Arepresents the case where, during focusing, the front and rear groups of the first lens group are moved along the optical axis in the same direction, andFIG. 2Brepresents the case where, during focusing, the front and rear groups of the first lens group are moved along the optical axis in the different directions (reverse directions).FIGS. 3A and 3Bare diagrams for describing operations of a first lens group of a second aspect during focusing of the variable magnification projection optical system according to the embodiment.FIG. 3Arepresents the case where, during focusing, the front group of the first lens group is moved along the optical axis and the rear group is stationary, andFIG. 3Brepresents the case where, during focusing, the front group of the first lens group is stationary and the rear group is moved along the optical axis.

The variable magnification projection optical system according to the embodiment is an optical system which magnifies and projects image light formed in an image forming element onto a screen arranged at a position separated by a predetermined distance.

An image projection apparatus using the variable magnification projection optical system is configured to include an image forming element which forms image light and a projection optical system which magnifies and projects the image light formed in the image forming element, and the variable magnification projection optical system according to the embodiment is used as the projection optical system. More specifically, the image projection apparatus is configured with the variable magnification projection optical system according to the embodiment, an image forming element which forms image light, a light source which emits illumination light, and an illumination optical system which guides the illumination light irradiated from the light source to the image forming element. The image forming element is a spatial light modulation element which forms the image light by modulating the illumination light based on video signals input from a video circuit. The image forming element is, for example, a digital micromirror device (DMD), a reflection type liquid crystal panel, a transmission type liquid crystal panel, or the like.

The DMD includes a mirror plane formed by two-dimensionally arranging a large number of micro-mirror elements in linearly independent two directions and is configured so that a reflection angle of each mirror element is able to be switched between the independent two directions. Each mirror element corresponds to each pixel of the image projected onto the screen. If the reflection angle is set to the one of the two directions, the mirror element is in “ON” state, so that the image light reflected on the mirror element in the ON state is projected onto the screen through the variable magnification projection optical system. On the other hand, if the reflection angle is set to the other of the two directions, the mirror element is in “OFF” state, so that the pixel on the screen corresponding to the mirror element in the OFF state is displayed as a black pixel.

For example, as illustrated inFIGS. 1A and 1B, the variable magnification projection optical system1used in the image projection apparatus is configured to include in order from a magnification conjugate side to a reduction conjugate side, first to sixth lens groups11to16having one or plural optical lenses and an optical stop17which is arranged at any position from a front of a lens arranged closest to the magnification conjugate side in the fourth lens group14to a front of a lens arranged closest to the magnification conjugate side in the fifth lens group15, and the fourth lens group14is configured to include, in order from the magnification conjugate side, two or more negative lenses and a positive lens. In addition, the variable magnification projection optical system1exemplified inFIGS. 1A and 1Bhas the same configuration as that of the variable magnification projection optical system1A (FIGS. 4A and 4B) according to Example 1 described later.

The first lens group11has a totally negative refracting power and is stationary during changing of magnification. More specifically, in the example illustrated inFIGS. 1A and 1B, the first lens group11is configured to include six lenses of 1st to 6th lenses111to116. The 1st lens111is a positive meniscus lens which is convex to the magnification conjugate side, the 2nd lens112is a negative meniscus lens which is convex to the magnification conjugate side, the 3rd lens113is a negative meniscus lens which is convex to the magnification conjugate side, the 4th lens114is a plano-concave negative lens of which magnification conjugate side is planar, the 5th lens115is a plano-concave negative lens of which reduction conjugate side is planar, and the 6th lens116is a positive meniscus lens which is convex to the reduction conjugate side.

The second lens group12has a totally positive refracting power and is movable during changing of magnification. More specifically, in the example illustrated inFIGS. 1A and 1B, the second lens group12is configured to include two lenses of 7th and 8th lenses121and122. The 7th lens121is a negative meniscus lens which is convex to the magnification conjugate side, and the 8th lens122is a biconvex positive lens.

The third lens group13has a totally positive refracting power and is movable during changing of magnification. More specifically, in the example of illustrated inFIGS. 1A and 1B, the third lens group13is configured to include one lens of a 9th lens131. The 9th lens131is a biconvex positive lens.

The fourth lens group14has a totally negative refracting power and is stationary or movable during changing of magnification. In the example illustrated inFIGS. 1A and 1B, the fourth lens group14is stationary during changing of magnification, but in Example 2 illustrated inFIGS. 6A and 6Bdescribed later, the fourth lens group Gr4is movable during changing of magnification. More specifically, in the example illustrated inFIGS. 1A and 1B, the fourth lens group14is configured to include three lenses of 10th to 12th lenses141to143. The 10th lens141is a biconcave negative lens, the 11th lens142is a negative meniscus lens which is convex to the reduction conjugate side, and the 12th lens143is a biconvex positive lens. In this manner, the fourth lens group14is configured to include, in order from the magnification conjugate side, two or more negative lenses (in the example illustrated inFIGS. 1A and 1B, the two lenses of the 10th and 11th lenses141and142) and a positive lens (in the example illustrated inFIGS. 1A and 1B, the 12th lens143). In addition, in the example illustrated inFIGS. 1A and 1B, as an example of the optical stop17, the aperture stop17is included in the fourth lens group14so as to be arranged closest to the reduction conjugate side of the fourth lens group14. Therefore, during changing of magnification from the telephoto end to the wide-angle end, the aperture stop17is stationary. Therefore, it is considered that the aperture stop17is arranged to be independent of the fourth and fifth lens groups14and15, or it is considered that the aperture stop17is included in the fifth lens group15so as to be arranged closest to the magnification conjugate side in the fifth lens group15.

The fifth lens group15has a totally positive refracting power and is movable during changing of magnification. More specifically, in the example illustrated inFIGS. 1A and 1B, the fifth lens group15is configured to include six lenses of 13th to 18th lenses151to156. The 13th lens151is a plano-convex positive lens which is convex to the reduction conjugate side, the 14th lens152is a plano-concave negative lens of which reduction conjugate side is planar, the 15th lens153is a biconvex positive lens, the 16th lens154is a biconvex positive lens, the 17th lens155is a plano-concave negative lens of which magnification conjugate side is planar, and the 18th lens156is a biconvex positive lens.

The sixth lens group16has a totally positive refracting power and is stationary during changing of magnification. More specifically, in the example illustrated inFIGS. 1A and 1B, the sixth lens group16is configured to include one lens of a 19th lens161. The 19th lens161is a biconvex positive lens.

Each of the lenses111to161of the first to sixth lens groups11to16may be, for example, a glass lens or may be, for example, a lens configured with a resin material such as a plastic.

In addition, during changing of magnification from the telephoto end to the wide-angle end, the second, third and fifth lens groups12,13, and15of the variable magnification projection optical system1are substantially monotonously moved in the direction from the magnification conjugate side to the reduction conjugate side. More specifically, in the variable magnification projection optical system1illustrated inFIGS. 1A and 1B, the second lens group Gr2is monotonously moved with a proportional relationship in the direction from the magnification conjugate side to the reduction conjugate side so that the locus becomes a straight line, and the third and fifth lens groups Gr3and Gr5are monotonously moved with the movement ratio being gradually decreased in the direction from the magnification conjugate side to the reduction conjugate side so that the locus becomes a curved line.

In addition, in the variable magnification projection optical system1, the first lens group11may be divided into a plurality of sub lens groups during focusing, and at least one lens group among the sub lens groups is moved in the optical axis direction during focusing, so that the focusing is performed. The variable magnification projection optical system1has a configuration having a low error sensitivity and is not easily affected by manufacturing errors, and focusing performance is stabilized (easily focused) during focus manipulation (during focusing).

More specifically, for example, as illustrated inFIGS. 2A and 2BandFIGS. 3A and 3B, the first lens group11may be divided into two sub lens groups (front group11A and rear group11B) during focusing. In addition, for example, as illustrated inFIG. 2A, each of the front group11A and the rear group11B is moved in the same direction along the optical axis during focusing, so that the focusing is performed. In addition, for example, as illustrated inFIG. 2B, for example, the front group11A and the rear group11B are moved in the different directions along the optical axis or moved along the optical axis so as to have different loci during focusing, so that the focusing is performed. In this manner, during focusing, both of the front group11A and the rear group11B are able to be moved, so that it is possible to perform the focusing while correcting the aberration. Particularly, the front group11A and the rear group11B are moved so as to have different loci, so that it is possible to widen a focus range (distance range where the focusing is able to be performed).

In addition, for example, as illustrated inFIG. 3A, the rear group11B is stationary and the front group11A is moved along the optical axis during focusing, so that the focusing is performed. In addition, for example, as illustrated inFIG. 3B, the front group11A is stationary and the rear group11B is moved along the optical axis during focusing, so that the focusing is performed. In this manner, the one of the sub lens groups is stationary during focusing, so that the configuration becomes simple and the focusing performance is particularly stabilized.

In the variable magnification projection optical system1illustrated inFIGS. 1A and 1B, during focusing (focusing manipulation, focus alignment manipulation), the first lens group11is divided into the front group11A having a totally negative refracting power configured to include the 1st to 5th lenses111to115and the rear group11B configured to include the 6th lens116, and as illustrated inFIG. 3A, during focusing, the rear group11B is stationary and the front group11A is moved along the optical axis, so that the focusing is performed.

In addition, in the case where a paraxial exit pupil position at the telephoto end is denoted by ET, a paraxial exit pupil position at the wide-angle end is denoted by EW, a focal length at the telephoto end is denoted by fT, a focal length at the wide-angle end is denoted by fW, a composite refracting power of the second and third lens groups12and13at the telephoto end is denoted by φ23T, and a composite refracting power of the second and third lens groups12and13at the wide-angle end is denoted by φ23W, the variable magnification projection optical system1satisfies the following condition expressions (1), (2), and (3).
|ET/fT|≧10  (1)
|EW/fW|≧15  (2)
0.87≦φ23T/≦φ23W≦1.15  (3)

In addition, in the example illustrated inFIGS. 1A and 1B, a prism18, a plate-shaped optical member19, and an image forming element20are arranged at the reduction conjugate side of the variable magnification projection optical system1. The plate-shaped optical member19is an optical member having a shape of parallel plate and schematically represents various optical filters and a cover glass for the image forming element20, and the like. The image forming element20is the above-described DMD, liquid crystal panel, or the like. By these components, the image light of the image forming element20is guided to the screen along the optical axis AX by the variable magnification projection optical system1with an appropriate variable magnification ratio, and the image light of the image forming element20is magnified and projected on the screen.

The variable magnification projection optical system1having this configuration is an optical system where six groups are configured to be aligned in order of negative, positive, positive, negative, positive, and positive from the magnification conjugate side to the reduction conjugate side. In the optical system, in the case where the third and fifth lens groups13and15are moved from the magnification conjugate side to the reduction conjugate side during changing of magnification from the telephoto end to the wide-angle end, the third lens group13having a positive refracting power approaches the fourth lens group14closer to the wide-angle end than to the telephoto end, and on the contrary, the fifth lens group15having a positive refracting power approaches the fourth lens group14closer to the telephoto end than to the wide-angle end. Therefore, in the variable magnification projection optical system1according to the embodiment, at both of the telephoto end and the wide-angle end, the lens groups having positive refracting powers are arranged in the vicinity of the optical stop17. In general, if the positive refracting power of the lens group arranged in the vicinity of the optical stop is increased, the optical system tends to have spherical aberration in the “under” direction. If the spherical aberration is insufficiently corrected, the resolving power of the on-axis light is decreased. However, in the variable magnification projection optical system1according to the embodiment, the fourth lens group14close to the optical stop17consecutively includes negative lenses (10th and 11th lenses141and142), so that the spherical aberration is able to be strongly corrected in the “over” direction. As a result, it is possible to achieve high resolving power.

In addition, the condition expression (1) represents a condition of a paraxial exit pupil position with respect to a focal length at the telephoto end, the condition expression (2) represents a condition of a paraxial exit pupil position with respect to a focal length at the wide-angle end, and the condition expressions (1) and (2) represent that telecentricity is secured. If the values are smaller than the lower limit values of the condition expressions (1) and (2), since an angle of off-axis light is increased, reflection/transmission efficiency at the time of performing color synthesis by a dichroic prism or reflection/transmission efficiency by a total internal reflection (TIR) prism is deteriorated. Therefore, it is not preferred.

From this point of view, more preferably, the condition expression (1A) is expressed as follows.
|ET/fT|≦25  (1A)

In addition, from this point of view, more preferably, the condition expression (2A) is expressed as follows.
|EW/fW|≧40  (2A)

In addition, the condition expression (3) represents a condition of the telephoto end to the wide-angle end in the composite refracting power of the second and third lens groups12and13and represents that the composite refracting power of the second and third lens groups12and13is substantially equal at the telephoto end and the wide-angle end. If the value is larger than the upper limit value of the condition expression (3) or smaller than the lower limit value thereof, the variable magnification projection optical system1is able to suppress variation of the image plane at the telephoto end and the wide-angle end, and thus it is preferred. However, in the case where the entire first lens group11is used as a focusing group, the variable magnification projection optical system has a configuration having a high error sensitivity and is easily affected by manufacturing errors, and focusing performance is not stabilized (not easily focused) during focus manipulation (during focusing), and thus, it is not preferred. Particularly, since a projector is generally configured so that the entire first lens group11is used as a focusing group, it is preferable that the variable magnification projection optical system1satisfies the condition expression (3).

From this point of view, more preferably, the condition expression (3A) is expressed as follows.
0.89≦φ23T/≦φ23W≦1.11  (3A)

In addition, in the above-described variable magnification projection optical system1according to the embodiment, at least one of the negative lenses included in the fourth lens group14satisfies the following condition expression (4), and the entire negative lenses included in the fourth lens group satisfy the following condition expression (5).
0.003≦ΔθgF≦0.055  (4)
−0.035≦(Σ(ΔθgF4i×φ4i))/φW≦−0.001  (5)

wherein, ΔθgF4iis ΔθgFof the i-th negative lens from the magnification conjugate side which is included in the fourth lens group14. Herein, ΔθgF=θgF−(0.06438−0.01682×νd), θgF=(ng−nF)/(nF−nC), and νd is an Abbe number. In addition, φ4iis a refracting power of the i-th negative lens from the magnification conjugate side which is included in the fourth lens group14, and φWis a composite refracting power of the entire optical system at the wide-angle end.

As the glass material satisfying the condition expressions (4) and (5), for example, there are FC5, FCD1, FCD100, and the like manufactured by HOYA.

In addition, in the above-described variable magnification projection optical system1according to the embodiment, at least one of the negative lenses included in the fourth lens group14satisfies the following condition expression (6), and the entire negative lenses included in the fourth lens group14satisfy the following condition expression (7).
0.03≦ΔθgF≦0.055  (6)
−0.035≦(Σ(ΔθgF4i×φ4i))/φW≦−0.01  (7)

As the glass material satisfying the condition expressions (6) and (7), for example, there are FCD1 and the like manufactured by HOYA.

In general, in a projection optical system, the chromatic aberration needs to be well corrected, and in the variable magnification projection optical system1according to the embodiment, the axial chromatic aberration and the spherical aberration are able to be corrected.

In general, since an imaging optical system has a positive refracting power as the entire system, the refracting power with respect to light having a relatively short wavelength tends to be larger than the refracting power with respect to light having a relatively long wavelength, so that the axial chromatic aberration occurs. In addition, since the refractive index of a lens varies with the wavelength, irregularity according to the wavelength occurs in the spherical aberration occurring due to light beams passing through the peripheries of the lens. On the contrary, if a negative lens having abnormal dispersibility is arranged in the vicinity of an optical stop, a focal position of the light having a short wavelength is moved to the “over” side, so that it is possible to correct the axial chromatic aberration. In addition, as the wavelength of the light passing through the peripheries of the negative lens having the abnormal dispersibility becomes shorter, the effect that the spherical aberration becomes “over” is able to be obtained. Therefore, it is also possible to correct the irregularity of the spherical aberration according to the wavelength.

Herein, the condition expressions (4) and (6) define the magnitude of the abnormal dispersibility. In addition, each of the condition expressions (5) and (7) defines a sum of the values obtained by multiplying the respective refracting powers with the abnormal dispersibilities of the respective negative lenses included in the fourth lens group14. As the value is decreased, the abnormal dispersibility of the negative lens becomes strong. Therefore, the variable magnification projection optical system1according to the embodiment satisfies the condition expressions (4) and (5), and the fourth lens group14arranged in the vicinity of the optical stop17includes the negative lens having the abnormal dispersibility, so that it is possible to suppress the axial chromatic aberration and the irregularity of the spherical aberration according to the wavelength. Similarly, the variable magnification projection optical system1according to the embodiment satisfies the condition expressions (6) and (7), and the fourth lens group14arranged in the vicinity of the optical stop includes the negative lens having the abnormal dispersibility, so that it is possible to suppress the axial chromatic aberration and the irregularity of the spherical aberration according to the wavelength. Particularly, the condition expressions (6) and (7) are satisfied, so that it is possible to achieve higher resolving power.

In addition, in the above-described variable magnification projection optical system1according to the embodiment, the lenses included in the fifth lens group15satisfy the following condition expressions (8) and (9).
0.025≦(Σ(ΔθgF5i×φ5i))/φW≦0.065  (8)
0.8≦dz5/fw≦1.65  (9)

wherein, ΔθgF5iis ΔθgFof the i-th lens from the magnification conjugate side which is included in the fifth lens group15, φ5iis a refracting power of the i-th lens from the magnification conjugate side which is included in the fifth lens group15, and dz5is a movement amount of the fifth lens group15from the magnification conjugate side to the reduction conjugate side during changing of magnification from the telephoto end to the wide-angle end.

In addition, in the above-described variable magnification projection optical system according to the embodiment, the lenses included in the fifth lens group15satisfy the following condition expressions (10) and (11).
0.035≦(Σ(ΔθgF5i×φ5i))/φW≦0.045  (10)
1≦dz5/fW≦1.65  (11)

In general, in a variable magnification optical system, the magnification chromatic aberration between the wide-angle end and the telephoto end swings at the plus side and the minus side, in other words, the difference in the magnification chromatic aberration between the wide-angle end and the telephoto end is large, so that the performance at the wide-angle end and the performance at the telephoto end are not compatible to each other, and the balance of the performance is lost between the wide-angle end and the telephoto end.

Herein, each of the condition expressions (8) and (10) defines a sum of the values obtained by multiplying the respective refracting powers with the abnormal dispersibilities of the respective negative lenses included in the fifth lens group15. As the value is decreased, the abnormal dispersibility of the negative lens becomes strong. Therefore, as each value of the condition expressions (8) and (10) is increased, the abnormal dispersibility of the positive lens goes to the Krutz side and the abnormal dispersibility of the negative lens goes to the Lange side. Therefore, with respect to the lens, the magnification chromatic aberration is able to be biased to the minus direction. The light beam passing through the inside of the fifth lens group15passes at a high position from the optical axis closer to the wide-angle end than to the telephoto end, and the magnification chromatic aberration at the wide-angle end is larger than the magnification chromatic aberration at the telephoto end and is biased to the minus direction. Therefore, the condition expression (8) or (10) is satisfied, so that it is possible to reduce the difference in the magnification chromatic aberration between the wide-angle end and the telephoto end. In addition, each of the condition expressions (9) and (11) defines a movement amount of the fifth lens group during changing of magnification. As the movement amount of the fifth lens group is increased, the height of the light beam passing through the inside of the lens varies at the telephoto end and the wide-angle end. Therefore, the condition expression (9) or (11) is satisfied, so that it is possible to effectively reduce the difference in the magnification chromatic aberration.

In this manner, the variable magnification projection optical system1according to the embodiment satisfies the condition expressions (8) and (10) or satisfies the condition expressions (9) and (11), and the glass material having the abnormal dispersibility is effectively used for the fifth lens group15which is moved during changing of magnification. Therefore, the variation of the magnification chromatic aberration according to the changing of magnification is suppressed, so that it is possible to reduce the difference in the magnification chromatic aberration at the telephoto end and the wide-angle end.

In addition, in the above-described variable magnification projection optical system1according to the embodiment, the first lens group11includes one or more negative lens satisfying the following condition expression (12).
0.03≦ΔθgF≦0.055  (12)

Although the difference in the magnification chromatic aberration at the telephoto end and the wide-angle end is suppressed by moving the fifth lens group15using the lens having the abnormal dispersibility during changing of magnification, the difference is not necessarily 0. Therefore, the variable magnification projection optical system1according to the embodiment employs the negative lens satisfying the condition expression (12) and having the abnormal dispersibility as the first lens group11, so that it is possible to further suppress the difference in the magnification chromatic aberration.

In addition, in the above-described variable magnification projection optical system according to the embodiment, the first to fourth lens groups11to14satisfy the following condition expressions (13) and (14).
|φ14T/φT|≦0.3  (13)
|φ14W/φW|0.3  (14)

wherein, φ14Tis a composite refracting power of the first to fourth lens groups11to14at the telephoto end, and φ14Wis a composite refracting power of the first to fourth lens groups11to14at the wide-angle end.

The condition expressions (13) and (14) define afocal properties. A combined system of the first to fourth lens groups11to14arranged from the optical stop17in the magnification conjugate side is substantially afocal, so that the width of light flux between the fourth lens group14and the fifth lens group15are substantially parallel along the optical axis direction. Therefore, since the change in the F number according to the movement of the fifth lens group15does not easily occur, in the variable magnification projection optical system1according to the embodiment, it is possible to suppress the variation of the F number at the telephoto end and the wide-angle end during changing of magnification.

From this point of view, more preferably, the condition expression (13A) is expressed as follows.
|φ14T/φT|≦0.28  (13A)

From this point of view, more preferably, the condition expression (14A) is expressed as follows.
|φ14W/φW|≦0.28  (14A)

In addition, in the above-described variable magnification projection optical system1according to the embodiment, the second lens group12is configured to include, in order from the magnification conjugate side to the reduction conjugate side, one or more negative lenses (in the example ofFIGS. 1A and 1B, the 7th lens121) and one or more positive lenses (in the example illustrated inFIGS. 1A and 1B, the 8th lens122) and satisfies the following condition expression (15).
1.8≦dz2/fW≦2.5  (15)

wherein, dZ2is a movement amount of the second lens group12from the magnification conjugate side to the reduction conjugate side during changing of magnification from the telephoto end to the wide-angle end.

In the above-described variable magnification projection optical system1, the variation of the light beam passing position of the on-axis light is smaller at the reduction conjugate side than at the optical stop17during changing of magnification. Therefore, the range of the axial chromatic aberration during changing of magnification occurring at the rear group may be allowed to be smaller than that at the optical stop17. However, in the entire system of the variable magnification projection optical system1, the difference in the axial chromatic aberration during changing of magnification is not necessarily small. Therefore, in the variable magnification projection optical system1according to the embodiment, the movement amount of the second lens group12is set so that the condition expression (15) is satisfied, so that it is possible to suppress the variation of the light beam passing position of the on-axis light in the so-called variator group which greatly contributes to the change of magnification, and it is possible to allow the difference in the axial chromatic aberration during changing of magnification to be small.

From this point of view, more preferably, the condition expression (15A) is expressed as follows.
1.9≦dZ2/fW≦2.3  (15A)

In addition, in the above-described variable magnification projection optical system1according to the embodiment, the condition expressions (16) and (17) are satisfied.
fT/fW≧1.45  (16)
ωW≧26.5  (17)

wherein, ωWis a half angle of view at the wide-angle end.

In the configuration of the related art, in the cased where the condition expression (16) is satisfied, if various types of aberration such as spherical aberration, image surface curvature, axial chromatic aberration, and magnification chromatic aberration are suppressed, the half angle of view ωWat the wide-angle end is not allowed to be large. On the other hand, in the configuration of the related art, in the cased where the condition expression (17) is satisfied, if various types of aberration such as spherical aberration, image surface curvature, axial chromatic aberration, and magnification chromatic aberration are suppressed, the variable magnification ratio is not allowed to be large. However, in the variable magnification projection optical system according to the embodiment, since the condition expressions (1) to (15) are appropriately satisfied, as described above, the various types of aberration are able to be suppressed. In addition, in the case where the condition expressions (16) and (17) are satisfied, in the variable magnification projection optical system1according to the embodiment, it is possible to implement high magnification and a high angle of view (wide angle) while suppressing the various types of aberration such as spherical aberration, image surface curvature, axial chromatic aberration, and magnification chromatic aberration.

In addition, since the above-described image projection apparatus according to the embodiment includes the variable magnification projection optical system, it is possible to sufficiently suppress the various types of aberration such as spherical aberration, image surface curvature, axial chromatic aberration, and magnification chromatic aberration and to implement a higher resolving power.

<Description of More Detailed Embodiments (Examples) of Variable Magnification Projection Optical System>

Hereinafter, detailed configurations of the variable magnification projection optical system1illustrated inFIGS. 1A and 1Bwill be described with reference to the drawings.

FIGS. 4A and 4B,FIGS. 6A and 6B,FIGS. 8A and 8B,FIGS. 10A and 10B,FIGS. 12A and 12B, andFIGS. 14A and 14Bare cross-sectional diagrams illustrating arrangement of lenses in each of the variable magnification projection optical systems of Examples 1 to 6.FIG. 4A,FIG. 6A,FIG. 8A,FIG. 10A,FIG. 12A, andFIG. 14Aillustrate the cases of the telephoto end, andFIG. 4B,FIG. 6B,FIG. 8B,FIG. 10B,FIG. 12B, andFIG. 14Billustrate the cases of the wide-angle end. InFIGS. 4A and 4B,FIGS. 6A and 6B,FIGS. 8A and 8B,FIGS. 10A and 10B,FIGS. 12A and 12B, andFIGS. 14A and 14B, a number ri (i=1, 2, 3, . . . ) assigned to each lens surface indicates an i-th lens surface when it is counted from the magnification conjugate side (herein, a lens cementing surface is counted as one surface). In addition, a one-side surface (surface of the magnification conjugate side) of the optical stop ST, both surfaces of the prism P1, both surfaces of the plate-shaped optical member P2, and an image forming surface of the image forming element IG are also treated as one surface, respectively. The above-described treatments and symbol notations are the same in each of Examples 1 to 6. However, it does not denote that the treatment and symbol notations are completely the same. For example, inFIGS. 4A and 4B,FIGS. 6A and 6B,FIGS. 8A and 8B,FIGS. 10A and 10B,FIGS. 12A and 12B, andFIGS. 14A and 14Bof Examples 1 to 6, although the lens surfaces arranged closest to the magnification conjugate side are assigned with the same symbol (r1), it does not denote that the curvature or the like are the same in Examples 1 to 6. In addition,FIG. 5,FIG. 7,FIG. 9,FIG. 11,FIG. 13, andFIG. 15are diagrams for describing the movement amount of each lens group during changing of magnification in each of the variable magnification projection optical systems of Examples 1 to 6. In each ofFIG. 5,FIG. 7,FIG. 9,FIG. 11,FIG. 13, andFIG. 15, the horizontal axis denotes each state from the telephoto end (=0) to the wide-angle end (=90), and the vertical axis denotes the movement amount in units of mm.

As illustrated inFIGS. 4A and 4B,FIGS. 6A and 6B,FIGS. 8A and 8B,FIGS. 10A and 10A,FIGS. 12A and 12B,FIGS. 14A and 14B, each of the variable magnification projection optical systems1A to1F according to Examples 1 to 6 is configured to include, in order from the magnification conjugate side to the reduction conjugate side, a first lens group Gr1having a totally negative refracting power and being stationary during changing of magnification, a second lens group Gr2having a totally positive refracting power and being movable during changing of magnification, a third lens group Gr3having a totally positive refracting power and being movable during changing of magnification, a fourth lens group Gr4having a totally negative refracting power and being stationary or movable during changing of magnification, a fifth lens group Gr5having a totally positive refracting power and being movable during changing of magnification, a sixth lens group Gr6having a totally positive refracting power and being stationary during changing of magnification, and an optical stop ST which is arranged between a lens arranged closest to the reduction conjugate side in the fourth lens group Gr4and a lens arranged closest to the magnification conjugate side in the fifth lens group Gr5, and the fourth lens group Gr4is configured to include, in order from the magnification conjugate side to the reduction conjugate side, two or more negative lenses and a positive lens.

In addition, a prism P1, a plate-shaped optical member P2such as various optical filters or a cover glass, and an image forming element IG are arranged in order from the magnification conjugate side to the reduction conjugate side at the reduction conjugate side of the sixth lens group Gr6.

Under this configuration, the image light formed in the image forming element IG passes, in order along the optical axis AX, through the plate-shaped optical member P2, the prism P1, the sixth lens group Gr6, the fifth lens group Gr5, the fourth lens group Gr4(passing through the optical stop ST in advance), the third lens group Gr3, the second lens group Gr2, and the first lens group Gr1to be guided to the screen with an appropriate variable magnification ratio, so that the image light in the image forming element IG is magnified and projected onto the screen.

More specifically, in each of the variable magnification projection optical systems1A,1B, and1E according to Examples 1, 2, and 5, the first lens group Gr1is configured to include six lenses of the 1st to 6th lenses L1to L6, the second lens group Gr2is configured to include two lenses of the 7th and 8th lenses L7and L8, the third lens group Gr3is configured to include one lens of the 9th lens L9, the fourth lens group Gr4is configured to include three lenses of the 10th to 12th lenses L10to L12, the fifth lens group Gr5is configured to include six lenses of the 13th to 18th lenses L13to L18, and the sixth lens group Gr6is configured to include one lens of the 19th lens L19. In other words, each of the variable magnification projection optical systems1A,1B, and1E according to Examples 1, 2, and 5 is configured to include 19 lenses of the 1st to 19th lenses L1to L19. The optical stop ST is an aperture stop ST, and in Examples 1 and 5, the aperture stop ST may be included in the fourth lens group Gr4so as to be arranged closest to the reduction conjugate side in the fourth lens group, may be arranged between a lens arranged closest to the reduction conjugate side in the fourth lens group Gr4and a lens arranged closest to the magnification conjugate side in the fifth lens group Gr5so as to be independent, or may be included in the fifth lens group Gr5so as to be arranged closest to the magnification conjugate side in the fifth lens group Gr5. In Example 2, since the aperture stop ST is moved together with the lens included in the fourth lens group Gr4, the aperture stop is included in the fourth lens group Gr4so as to be arranged closest to the reduction conjugate side in the fourth lens group Gr4. In addition, in each of the variable magnification projection optical systems1A,1B, and1E according to Examples 1, 2, and 5, as illustrated inFIG. 5,FIG. 7, andFIG. 13, during changing of magnification from the telephoto end to the wide-angle end the second, third, and fifth lens groups Gr2, Gr3, and Gr5are substantially monotonously moved in the direction from the magnification conjugate side to the reduction conjugate side. More specifically, as illustrated inFIG. 5,FIG. 7, andFIG. 13, the second lens group Gr2is monotonously moved with a proportional relationship in the direction from the magnification conjugate side to the reduction conjugate side so that the locus becomes a straight line, and the third and fifth lens groups Gr3and Gr5are monotonously moved with a movement ratio being gradually decreased in the direction from the magnification conjugate side to the reduction conjugate side so that the locus becomes a curved line. In addition, in each of the variable magnification projection optical systems1A and1E of Examples 1 and 5, during changing of magnification from the telephoto end to the wide-angle end, the fourth lens group Gr4is stationary, and in the variable magnification projection optical system1B of Example 2, during changing of magnification from the telephoto end to the wide-angle end, the fourth lens group Gr4is monotonously moved with a movement ratio being gradually decreased in the direction from the magnification conjugate side to the reduction conjugate side.

In addition, during focusing (focusing manipulation, focus alignment manipulation), the first lens group Gr1is divided into a front group Gr1A having a totally negative refracting power which is configured to include the 1st to 5th lenses L1to L5and a rear group Gr1B which is configured to include the 6th lens L6. In addition, during focusing, Examples 1, 2, and 5 operate according to the aspect illustrated inFIG. 3Adescribed above. In addition, Examples 1 and 2 may operate according to the aspect illustrated in FIG.2B described above. In addition, Example 5 may operate according to the aspect illustrated inFIG. 2Bdescribed above or may operate according to the aspect illustrated inFIG. 3Bdescribed above.

Herein, the variable magnification projection optical system1A according to Example 1 is different from the variable magnification projection optical system1B according to Example 2 in terms of 4th, 5th, 13th, and 17th lenses L4, L5, L13, and L17. The variable magnification projection optical system1A according to Example 1 is different from the variable magnification projection optical system1E according to Example 5 in terms of 4th, 5th, 13th, 14th, and 17th lenses L4, L5, L13, L14, and L17. On the other hand, the variable magnification projection optical system1B according to Example 2 is different from the variable magnification projection optical system1E according to Example 5 in terms of 13th and 14th lenses L13and L14.

More specifically, in each of the first lens group Gr1of the variable magnification projection optical systems1A,1B, and1E according to Examples 1, 2, and 5, the 1st lens L1is a positive meniscus lens which is convex to the magnification conjugate side, the 2nd lens L2is a negative meniscus lens which is convex to the magnification conjugate side, and the 3rd lens L3is a negative meniscus lens which is convex to the magnification conjugate side. In addition, in Example 1, the 4th lens L4is a plano-concave negative lens of which magnification conjugate side is planar, and in Examples 2 and 5, the 4th lens L4is a biconcave negative lens. In Example 1, the 5th lens L5is a plano-concave negative lens of which reduction conjugate side is planar, and in Examples 2 and 5, the 5th lens L5is a biconcave negative lens. In all Examples 1, 2, and 5, the 6th lens L6is a positive meniscus lens which is convex to the reduction conjugate side.

In each of the second lens group Gr2of the variable magnification projection optical systems1A,1B, and1E according to Examples 1, 2, and 5, the 7th lens L7is a negative meniscus lens which is convex to the magnification conjugate side, and the 8th lens L8is a biconvex positive lens.

In each of the third lens group Gr3of the variable magnification projection optical systems1A,1B, and1E according to Examples 1, 2, and 5, the 9th lens L9is a biconvex positive lens.

In each of the fourth lens group Gr4of the variable magnification projection optical systems1A,1B, and1E according to Examples 1, 2, and 5, the 10th lens L10is a biconcave negative lens, the 11th lens L11is a negative meniscus lens which is convex to the reduction conjugate side, and the 12th lens L12is a biconvex positive lens. In addition, the aperture stop ST is included in the fourth lens group Gr4. Therefore, during changing of magnification from the telephoto end to the wide-angle end, in Examples 1 and 5, the aperture stop ST is stationary, and in Example 2, the aperture stop ST is moved.

In each of the fifth lens group Gr5of the variable magnification projection optical systems1A,1B, and1E according to Examples 1, 2, and 5, in Example 1, the 13th lens L13is a plano-convex positive lens which is convex to the reduction conjugate side, in Example 2, the 13th lens L13is a positive meniscus lens which is convex to the reduction conjugate side, and in Example 5, the 13th lens L13is a biconvex positive lens. In Examples 1 and 2, the 14th lens L14is a plano-concave negative lens of which reduction conjugate side is planar, and in Example 5, the 14th lens L14is a biconcave negative lens. In all Examples 1, 2, and 5, the 15th lens L15is a biconvex positive lens, and the 16th lens L16is also a biconvex positive lens. In Example 1, the 17th lens L17is a plano-concave negative lens of which magnification conjugate side is planar, and in Examples 2 and 5, the 17th lens L17is a negative meniscus lens which is convex to the magnification conjugate side. In all Examples 1, 2, and 5, the 18th lens L18is a biconvex positive lens.

In each of the sixth lens group Gr6of the variable magnification projection optical systems1A,1B, and1E according to Examples 1, 2, and 5, the 19th lens L19is a biconvex positive lens.

In addition, in each of the variable magnification projection optical systems1C and1D of Examples 3 and 4, the first lens group Gr1is configured to include five lenses of the 1st to 5th lenses L1to L5, the second lens group Gr2is configured to include one lens of the 6th lens L6, the third lens group Gr3is configured to include one lens of the 7th lens L7, the fourth lens group Gr4is configured to include three lenses of the 8th to 10th lenses L8to L10, the fifth lens group Gr5is configured to include six lenses of the 11th to 16th lenses L11to L16, and the sixth lens group Gr6is configured to include two lenses of the 17th and 18th lenses L17and L18. In other words, each of the variable magnification projection optical systems1C and1D according to Examples 3 and 4 is configured to include 18 lenses of the 1st to 18th lenses L1to L18. The optical stop ST is an aperture stop ST, and in Examples 3 and 4, the aperture stop ST may be included in the fourth lens group Gr4so as to be arranged closest to the reduction conjugate side in the fourth lens group, may be arranged between a lens arranged closest to the reduction conjugate side in the fourth lens group Gr4and a lens arranged closest to the magnification conjugate side in the fifth lens group Gr5so as to be independent, or may be included in the fifth lens group Gr5so as to be arranged closest to the magnification conjugate side in the fifth lens group Gr5. In addition, in each of the variable magnification projection optical systems1C and1D of Examples 3 and 4, as illustrated inFIG. 9andFIG. 11, during changing of magnification from the telephoto end to the wide-angle end, the second, third, and fifth lens groups Gr2, Gr3, and Gr5are substantially monotonously moved in the direction from the magnification conjugate side to the reduction conjugate side. More specifically, as illustrated inFIG. 9andFIG. 11, the second lens group Gr2is monotonously moved with the movement ratio being gradually decreased in the direction from the magnification conjugate side to the reduction conjugate side so that the locus becomes a curved line, and the third and fifth lens groups Gr3and Gr5are monotonously moved with a proportional relationship in the direction from the magnification conjugate side to the reduction conjugate side so that the locus becomes a straight line. In addition, in each of the variable magnification projection optical systems1C and1D of Examples 3 and 4, during changing of magnification from the telephoto end to the wide-angle end, the fourth lens group Gr4is stationary.

In addition, during focusing (focusing manipulation, focus alignment manipulation), the first lens group Gr1is divided into a front group Gr1A having a totally negative refracting power which is configured to include the 1st to 4th lenses L1to L4and a rear group Gr1B which is configured to include the 5th lens L5. In addition, during focusing, Examples 3 and 4 operate according to the aspect illustrated inFIG. 3Adescribed above. In addition, Examples 3 and 4 may operate according to the aspect illustrated inFIG. 2Bdescribed above or may operate according to the aspect illustrated inFIG. 3Bdescribed above.

Herein, the variable magnification projection optical system1C according to Example 3 is different from the variable magnification projection optical system1D according to Example 4 in terms of 3rd, 4th, 6th, 14th, and 15th lenses L3, L4, L6, L14, and L15.

More specifically, in each of the first lens groups Gr1of the variable magnification projection optical systems1C and1D according to Examples 3 and 4, the 1st lens L1is a plano-convex positive lens which is convex to the magnification conjugate side, and the 2nd lens L2is a negative meniscus lens which is convex to the magnification conjugate side. In addition, in Example 3, the 3rd lens L3is a negative meniscus lens which is convex to the magnification conjugate side, and in Example 4, the 3rd lens L3is a plano-concave negative lens of which magnification conjugate side is planar. In Example 1, the 4th lens L4is a negative meniscus lens which is convex to the reduction conjugate side, and in Example 4, the 4th lens L4is a biconcave negative lens. In both of Examples 3 and 4, the 5th lens L5is a positive meniscus lens which is convex to the reduction conjugate side.

In each of the second lens groups Gr2of the variable magnification projection optical systems1C and1D according to Examples 3 and 4, in Example 3, the 6th lens L6is a plano-convex positive lens which is convex to the reduction conjugate side, and in Example 4, the 6th lens L6is a plano-convex positive lens which is convex to the magnification conjugate side.

In each of the third lens groups Gr3of the variable magnification projection optical systems1C and1D according to Examples 3 and 4, the 7th lens L7is a plano-convex positive lens which is convex to the magnification conjugate side.

In each of the fourth lens groups Gr4of the variable magnification projection optical systems1C and1D according to Examples 3 and 4, the 8th lens L8is a negative meniscus lens which is convex to the magnification conjugate side, the 9th lens L9is a biconcave negative lens, and the 10th lens L10is a biconvex positive lens. In addition, the aperture stop ST is included in the fourth lens group Gr4. Therefore, in both of Examples 3 and 4, during changing of magnification from the telephoto end to the wide-angle end, the aperture stop ST is stationary.

In each of the fifth lens groups Gr5of the variable magnification projection optical systems1C and1D according to Examples 3 and 4, the 11th lens L11is a positive meniscus lens which is convex to the reduction conjugate side, the 12th lens L12is a negative meniscus lens which is convex to the reduction conjugate side, and the 13th lens L13is a biconvex positive lens. In addition, in Example 3, the 14th lens L14is a biconvex positive lens, and in Example 4, the 14th lens L14is a plano-convex positive lens which is convex to the reduction conjugate side. In Example 3, the 15th lens L15is a biconcave negative lens, and in Example 4, the 15th lens L15is a plano-concave negative lens of which magnification conjugate side is planar. In both of Examples 3 and 4, the 16th lens L16is a biconvex positive lens.

In each of the sixth lens groups Gr6of the variable magnification projection optical systems1C and1D according to Examples 3 and 4, the 17th lens L17is a biconvex positive lens, and the 18th lens L18is a plano-convex positive lens which is convex to the magnification conjugate side.

In addition, in the variable magnification projection optical system.1F of Example 6, the first lens group Gr1is configured to include five lenses of the 1st to 5th lenses L1to L5, the second lens group Gr2is configured to include two lenses of the 6th and 7th lenses L6and L7, the third lens group Gr3is configured to include one lens of the 8th lens L8, the fourth lens group Gr4is configured to include three lenses of the 9th to 11th lenses L9to L11and the aperture stop ST as the optical stop ST, the fifth lens group Gr5is configured to include six lenses of the 12th to 17th lenses L12to L17, and the sixth lens group Gr6is configured to include two lenses of the 18th and 19th lenses L18and L19. In other words, the variable magnification projection optical system1F according to Example 6 is configured to include 19 lenses of the 1st to 19th lenses L1to L19. The optical stop ST is an aperture stop ST, and in Example 6, the aperture stop ST may be included in the fourth lens group Gr4so as to be arranged closest to the reduction conjugate side in the fourth lens group, may be arranged between a lens arranged closest to the reduction conjugate side in the fourth lens group Gr4and a lens arranged closest to the magnification conjugate side in the fifth lens group Gr5so as to be independent, or may be included in the fifth lens group Gr5so as to be arranged closest to the magnification conjugate side in the fifth lens group Gr5. In addition, by comparing the variable magnification projection optical system1F according to Example 6 and each of the variable magnification projection optical systems according to Examples 3 and 4, the second lens group Gr2is configured to include one lens in Examples 3 and 4, but the second lens group Gr2is configured to include two lenses in Example 6. In addition, in the variable magnification projection optical system1F of Example 6, as illustrated inFIG. 15, during changing of magnification from the telephoto end to the wide-angle end, the second, third, and fifth lens groups Gr2, Gr3, and Gr5are substantially monotonously moved in the direction from the magnification conjugate side to the reduction conjugate side. More specifically, as illustrated inFIG. 15, the second lens group Gr2is monotonously moved with a proportional relationship in the direction from the magnification conjugate side to the reduction conjugate side so that the locus becomes a straight line, and the third and fifth lens groups Gr3and Gr5are monotonously moved with a movement ratio being gradually decreased in the direction from the magnification conjugate side to the reduction conjugate side so that the locus becomes a curved line. In addition, in the variable magnification projection optical system1F of Example 6, during changing of magnification from the telephoto end to the wide-angle end, the fourth lens group Gr4is stationary.

In addition, during focusing (focusing manipulation, focus alignment manipulation), the first lens group Gr1is divided into a front group Gr1A having a totally negative refracting power which is configured to include the 1st to 4th lenses L1to L4and a rear group Gr1B which is configured to include the 5th lens L5. In addition, during focusing, Example 6 operates according to the aspect illustrated inFIG. 3Adescribed above. In addition, Example 6 may operate according to the aspect illustrated inFIG. 2Bdescribed above or may operate according to the aspect illustrated inFIG. 3Bdescribed above.

More specifically, in the first lens group Gr1of the variable magnification projection optical system1F of Example 6, the 1st lens L1is a biconvex positive lens, the 2nd lens L2is a negative meniscus lens which is convex to the magnification conjugate side, the 3rd lens L3is a negative meniscus lens which is convex to the magnification conjugate side, the 4th lens L4is a biconcave negative lens, and the 5th lens L5is a positive meniscus lens which is convex to the reduction conjugate side.

In the second lens group Gr2of the variable magnification projection optical system1F of Example 6, the 6th lens L6is a negative meniscus lens which is convex to the magnification conjugate side, and the 7th lens L7is a biconvex positive lens.

In the third lens group Gr3of the variable magnification projection optical system1F of Example 6, the 8th lens L8is a biconvex positive lens.

In the fourth lens group Gr4of the variable magnification projection optical system1F of Example 6, the 9th lens L9is a biconcave negative lens, the 10th lens L10is a negative meniscus lens which is convex to the reduction conjugate side, and the 11th lens L11is a biconvex positive lens. In addition, the aperture stop ST is included in the fourth lens group Gr4. Therefore, during changing of magnification from the telephoto end to the wide-angle end the aperture stop ST is stationary.

In the fifth lens group Gr5of the variable magnification projection optical system1F of Example 6, the 12th lens L12is a positive meniscus lens which is convex to the reduction conjugate side, the 13th lens L13is a negative meniscus lens which is convex to the reduction conjugate side, the 14th lens L14is a biconvex positive lens, the 15th lens L15is a biconvex positive lens, the 16th lens L16is a negative meniscus lens which is convex to the magnification conjugate side, and the 17th lens L17is a positive meniscus lens which is convex to the magnification conjugate side.

In the sixth lens group Gr6of the variable magnification projection optical system1F of Example 6, the 18th lens L18is a plano-convex positive lens which is convex to the magnification conjugate side, and the 19th lens L19is a plano-convex positive lens which is convex to the magnification conjugate side.

In the above-described variable magnification projection optical systems1A to1F according to Examples 1 to 6, construction data of each lens are as follows. In addition, “CR” denotes a radius of curvature (unit: mm) of each surface, “d” denotes an interval (interval of surfaces on the optical axis) of each lens surface of on-axis light at an infinity focused state (focused state in infinite distance), “nd” denotes a refractive index of each lens with respect to d-line (wavelength of 587.56 nm), “νd” denotes an Abbe number, and “R” denotes an effective optical path radius. In addition, since the surfaces of the aperture stop ST and the image forming surfaces of the image forming element IG are planar, the radius of curvature thereof is ∞ (infinity). In addition, with respect to the both surfaces of the prism P1and both surfaces of the plate-shaped optical member P2arranged if necessary, the radius of curvature is ∞ (infinity).

First, construction data of the lenses in the variable magnification projection optical system1A of Example 1 are represented as follows.

Numerical Example 1

Next, construction data of the lenses in the variable magnification projection optical system1B of Example 2 are represented as follows.

Numerical Example 2

Next, construction data of the lenses in the variable magnification projection optical system1C of Example 3 are represented as follows.

Numerical Example 3

Next, construction data of the lenses in the variable magnification projection optical system1D of Example 4 are represented as follows.

Numerical Example 4

Next, construction data of the lenses in the variable magnification projection optical system1E of Example 5 are represented as follows.

Numerical Example 5

Next, construction data of the lenses in the variable magnification projection optical system1F of Example 6 are represented as follows.

Numerical Example 6

Under the lens arrangement and configurations described above, the aberrations in the variable magnification projection optical systems1A to1F according to Examples 1 to 6 are illustrated inFIGS. 16A to 16DtoFIGS. 33A to 33D.FIGS. 16A to 16D,FIGS. 19A to 19D,FIGS. 22A to 22D,FIGS. 25A to 25D,FIGS. 28A to 28D, andFIGS. 31A to 31Dare aberration graphs at the telephoto end,FIGS. 17A to 17D,FIGS. 20A to 20D,FIGS. 23A to 23D,FIGS. 26A to 26D,FIGS. 29A to 29D, andFIGS. 32A to 32Dare aberration graphs at the intermediate point, andFIGS. 18A to 18D,FIGS. 21A to 21D,FIGS. 24A to 24D,FIGS. 27A to 27D,FIGS. 30A to 30D, andFIGS. 33A to 33Dare aberration graphs at the wide-angle end.

FIGS. 16A to 33Aillustrate spherical aberration (sinusoidal condition). The horizontal axis denotes deviation of focal positions in units of mm, and the vertical axis denotes coordinates of light beams on the entrance pupil in units of mm. The solid line indicates spherical aberration with respect to e-line, the one-dot dashed line indicates spherical aberration with respect to wavelength 460 nm, and the two-dot dashed line indicates spherical aberration with respect to wavelength 620 nm.FIGS. 16B to 33Billustrate astigmatism. The horizontal axis denotes deviation of focal positions in units of mm, and the vertical axis denotes image heights in units of mm. The solid line indicates astigmatism with respect to e-line on the tangential (meridional) surface, the one-dot dashed line indicates astigmatism with respect to wavelength 460 nm on the tangential surface, and the two-dot dashed line indicates astigmatism with respect to wavelength 620 nm on the tangential surface. In addition, the broken line by the line having the shortest length indicates astigmatism on the sagittal (radial) surface with respect to e-line, the broken line by the line having the next shortest length (intermediate length) indicates astigmatism on the sagittal surface with respect to wavelength 460 nm, and the broken line by the line having the longest length indicates astigmatism on the sagittal surface with respect to wavelength 620 nm.FIGS. 16C to 33Cillustrate distortion. The vertical axis denotes actual image heights as a ratio (%) to an ideal image height, and the horizontal axis denotes image heights in units of mm.FIGS. 16D to 33Dillustrate magnification chromatic aberration. The vertical axis denotes deviation of coordinates of light beams on an image plane with respect to d-line in units of mm, and the horizontal axis denotes image heights in units of mm. The solid line indicates magnification chromatic aberration with respect to e-line, the one-dot dashed line indicates magnification chromatic aberration with respect to wavelength 460 nm, and the two-dot dashed line indicates magnification chromatic aberration with respect to wavelength 620 nm.

Table 1 lists examples of the glass material having abnormal dispersibility which can be very appropriately used for each lens of the variable magnification projection optical systems1A to1F according to Examples 1 to 6 described above.

In addition, Table 2 lists the numerical values in the case where the above-described condition expressions (1) to (17) are applied to the variable magnification projection optical systems1A to1F according to Examples 1 to 6.

Heretofore, as described above, the variable magnification projection optical systems1A to1F according to Examples 1 to 6 satisfy the above-described requirements, so that it is possible to sufficiently suppress various types of aberration such as spherical aberration, image surface curvature, axial chromatic aberration, and magnification chromatic aberration and implement a higher resolving power.

Although the present invention are appropriately and sufficiently described by employing the embodiments with reference to the drawings so as to represent the present invention, it should be noted that changes and/or modifications of the above-described embodiments can be easily made by the ordinarily skilled in the art. Therefore, it should be noted that the changes or modifications made by the ordinarily skilled are also included in the scope of the claims without departing from the scope disclosed in the claims.