JP2010044263A - Projection variable focus lens and projection display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide projection variable focus lenses and a projection display for making miniaturization, lightweight, and inexpesiveness while being telecentric in a contraction side and in configuration capable of high variable power, and correcting various aberrations with sufficient balance in variable power. <P>SOLUTION: The projection variable focus lenses moving only one group in variable power includes a negative first lens group G<SB>1</SB>, a positive second lens group G<SB>2</SB>, and a positive third lens group G<SB>3</SB>in order from a widening side. When a focal distance is variable, only the second lens group G<SB>2</SB>is moved in an optical axis X direction. In focusing, it is composed to move the third lens group G<SB>3</SB>in the optical axis X direction, and further the contraction side is composed to be substantially telecentric. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a three-group variable focus lens mounted on a projection display device and the like, and a projection display device including the variable focus lens, and more particularly to a transmissive or reflective liquid crystal display device or DMD (digital The present invention relates to a projection type variable focus lens and a projection type display device for enlarging and projecting a light beam carrying image information from a light valve such as a micromirror device on a screen.

  In recent years, projection display devices using light valves such as liquid crystal display devices and DMD display devices have become widespread, and in particular, three light valves are used so as to correspond to RGB three primary color illumination lights. Therefore, it is widely used that each of these illumination lights is modulated, light modulated by individual light valves is combined by a prism or the like, and an image is displayed on a screen via a projection lens.

  In such light valves, miniaturization and high definition are rapidly progressing, and along with the spread of personal computers, the demand for making presentations using such projection display devices is also increasing. Since there is a demand for an aspect that is convenient and easy to install, there is an increasing demand for a projection display device that is higher in performance and capable of high magnification, and that is smaller and lighter. . Along with this, a projection lens is also strongly demanded to have a higher performance, a higher zoom ratio, a smaller size, and a lighter weight. On the other hand, there is a strong demand for cost reduction of the projection lens.

  Furthermore, when a color synthesis prism for synthesizing modulated light from multiple light valves and a TIR prism used for separating illumination light and projection light are provided in the optical system, the former prevents color unevenness. For this reason, the latter requires that the reduction side of the projection lens be substantially telecentric in order to prevent a reduction in separation efficiency.

  Various projection zoom lenses are known as projection lenses aimed at meeting the various requirements as described above. In such zoom lenses, two or more groups that move in association with each other during zooming. In addition to the variable magnification group, in general, it has a focus group consisting of one other group, which complicates the lens driving unit by a cam mechanism and the like, and promotes miniaturization, weight reduction, and cost reduction. It was an obstacle.

  Therefore, there is known a projection zoom lens described in Patent Document 1 described below, in which zooming can be performed by one group and focusing can be performed by another group.

Japanese Patent Laid-Open No. 2005-300619

  However, since the projection zoom lens described in Patent Document 1 also has a zoom function, there are restrictions on the movement of the lens group during zooming, and aberration fluctuations during zooming inevitably become large. .

  In the projection zoom lens described in Patent Document 1, in a system in which the number of lenses arranged on the reduction side of the lens group for performing the zooming is small and the reduction side is substantially telecentric, the zooming ratio is large. There is a problem that it is difficult.

  The present invention has been made in view of the above circumstances, and has a reduction-side telecentric configuration capable of high zooming. An object of the present invention is to provide a projection variable focus lens and a projection display device in which the cost can be reduced and various aberrations, particularly aberrations, are well corrected in a balanced manner.

The projection variable focus lens of the present invention is
In order from the magnification side, the first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power,
When the focal length is variable, the second lens group is moved in the optical axis direction, and during focusing, the third lens group is moved in the optical axis direction, and the reduction side is substantially telecentric. It is characterized by this.

Moreover, it is preferable that the second lens group satisfies the following conditional expression (1).
_{1.0 <f 2 / f w <} 4.0 ···· (1)
here,
f _w : focal length of the entire system at the wide end f ₂ : focal length of the second lens unit

In addition, it is preferable that the second lens group satisfies the following conditional expression (2).
_{0.15 <D 2 / L <0.55} ···· (2)
here,
D ₂ : The longest lens surface interval in the second lens group L: Total lens length

  The second lens group is preferably composed of only two positive lenses.

  The third lens group includes, in order from the magnification side, a negative thirty-first lens, a positive thirty-second lens with a convex surface facing the reduction side, a positive thirty-third lens with a convex surface facing the reduction side, and a magnification side It is preferable to use a positive 34th lens having a convex surface.

  The first lens group is preferably composed of two lenses including a negative lens having a concave surface facing the reduction side, or only one negative lens having a concave surface facing the reduction side.

  The first lens group preferably includes at least one aspheric surface.

  The first lens group includes two lenses including one negative lens having a concave surface facing the reduction side, the second lens group includes two positive lenses, and the third lens group includes In order from the enlargement side, the negative 31st lens, the positive 32nd lens with the convex surface facing the reduction side, the positive 33rd lens with the convex surface facing the reduction side, and the positive 34th lens with the convex surface facing the enlargement side It is preferable that the lens system is composed of eight lenses.

  The first lens group includes one negative lens having a concave surface facing the reduction side, the second lens group includes two positive lenses, and the third lens group is negative in order from the magnification side. Of the first lens, a positive 32nd lens having a convex surface on the reduction side, a positive 33rd lens having a convex surface on the reduction side, and a positive 34th lens having a convex surface on the enlargement side. It is preferable to use seven lenses.

  The projection display device of the present invention includes a light source, a light valve, an illumination optical unit that guides a light beam from the light source to the light valve, and any one of the projection variable focus lenses described above. The light beam is modulated by the light valve and projected onto the screen by the projection variable focus lens.

  According to the projection variable focus lens of the present invention, a three-group lens configuration in which a negative first lens group, a positive second lens group, and a positive third lens group are arranged in order from the magnification side is used. When the distance is variable, the second lens group is moved in the optical axis direction, and during focusing, the first lens group is moved in the optical axis direction, and the reduction side is substantially telecentric.

  As a result of this configuration, the zoom lens has a reduction-side telecentric configuration capable of high zooming, but as described later, it is not affected by the problems inherent in the zoom lens, and is reduced in size, weight, and cost. Can be achieved. In addition, particularly at the time of zooming, the aberration can be corrected well in a balanced manner.

  By the way, in the above-described prior art, since a zoom lens is used to give the projection lens a zooming function, it is necessary to move two or more lens groups in cooperation during zooming, and more generally, The other lens groups had to be moved during focusing. For this reason, there are many moving lens groups, and it has been impossible to reduce the size, weight, and cost of the projection lens.

  However, in the present invention, a variable focus lens is used for zooming of the projection lens, and the zoom lens can be zoomed by moving only one lens group. Since a drive mechanism is not required, it is possible to reduce the size, weight, and cost of each stage compared to the conventional one. Also, in the case of a zoom lens, there is a restriction on the movement of the lens groups at the time of zooming, so aberration fluctuations at the time of zooming inevitably become large. Since it is possible to eliminate the restriction on the movement of the lens group at the time of magnification, the aberration fluctuation at the time of magnification can be greatly improved.

  In addition, such a variable focus lens has been conventionally used for a photographing lens and the like, and the conjugate length changes at the time of zooming. Therefore, it is necessary to adjust the focus for focusing. It was pointed out that was annoying.

  However, in the projection lens, in general, once the projection display device and the screen are set, the magnification is not changed for each projection operation. Therefore, the focus adjustment only needs to be performed once. The above-mentioned points pointed out in photographing lenses and the like hardly cause problems.

  Further, in the projection variable focus lens of the present invention, unlike the projection zoom lens described in the above-mentioned publication, a lens group for zooming is the second lens from the magnification side of the three-group configuration. As a group, a large zoom ratio can be obtained even in a system in which the reduction side is substantially telecentric.

  In addition, it is preferable that the third lens group arranged on the most reduction side is composed of two or more lenses while satisfying the above-described configuration, because telecentricity on the reduction side can be easily secured. .

  Further, the projection display device of the present invention can be reduced in size, weight, and cost while having a configuration capable of high magnification by using the projection variable focus lens of the present invention. Moreover, high optical performance can be maintained.

Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. The projection variable focus lens of the embodiment shown in FIG. 1 (representing the lens of Example 1 as a representative) has, in order from the magnification side, a first lens group G ₁ having a negative refractive power, a positive refractive power. comprising a second lens group G _2, and the third lens group G ₃ having a positive refractive power having a reduction side is configured into a substantially telecentric, glass blocks in the subsequent stage, the color synthesizing prism as the main ( 2) (including a filter portion) and an image display surface 1 of a light valve such as a liquid crystal display panel. In the figure, X represents the optical axis.

Further, at the time of zooming (when the focal length is variable), the second lens group G ₂ (including a mask (which may be an aperture stop) 3 in the lens group) is moved along the optical axis X. It is configured, at the time of focusing, and is configured to move along a first lens group G ₁ to the optical axis X.

Here, the first lens group G ₁ has a first lens L ₁ made of an aspherical lens (preferably made of plastic) with a concave surface facing the reduction side and at least one surface made of an aspherical surface, and a concave surface facing the reduction side. and the negative lens and a second lens L ₂ formed of (example 2, the first lens L ₁ of a negative lens having a concave surface facing the reduction _side, and a concave surface facing the reduction side, at least one surface non made from the second lens L ₂ formed of an aspheric lens made spherical, in example 3, a concave surface facing the reduction side, comprises a first lens L ₁ of a non-spherical lens in which at least one surface is aspherical In Example 4, a negative meniscus lens (preferably made of glass) having a concave surface directed toward the reduction side is provided with a composite aspheric lens in which a resin molded into an aspheric shape is attached to the reduction side surface. Consisting of lens _{L 1.).}

The first lens group G _1, by forming only the two lenses or one negative lens having a concave surface facing the reduction side, including a negative lens having a concave surface directed toward the reduction side, compact lens system In addition, the cost can be reduced. In particular, the first lens group G _1, since the aspherical surface is formed, if small outer diameter, it is possible to significantly reduce costs.

The second lens group G ₂ is composed of 2 positive lenses, thereby achieving a compact and cost of the lens system. More preferably, a mask (which may be an aperture stop; the same shall apply hereinafter) 3 is disposed between _two positive lenses L ₃ and L ₄ (in the second embodiment, two positive lenses L ₂ and L ₃ ). To be configured. By disposing the mask 3 at a position between the two positive lenses, the telecentricity on the reduction side can be made better.

The third lens group G ₃ is directed in order from the magnification side, a negative lens, the reduction side positive (or negative) lens a convex surface directed toward the positive lens with a convex surface on the reduction side, and a convex surface on the enlargement side Further, it is configured by a positive meniscus lens, and this can reduce aberration fluctuations during focusing. More preferably, a fifth lens L _{5 made of} a biconcave lens, a sixth lens L _{6 made of} a positive meniscus lens having a convex surface facing the reduction side, a seventh lens L _{7 made of a} biconvex lens, and a positive lens having a convex surface directed to the enlargement side (example constituting the eighth lens L ₈ made of a meniscus lens 3, in example 4, the fourth lens L ₄ made of a biconcave _lens, the fifth lens L of a positive meniscus lens having a convex surface directed toward the reduction side _5, constituted by a seventh lens L _7, which is a positive meniscus lens having a convex surface directed toward the sixth lens L ₆ and enlarged side is a biconvex lens.). Thus, in the present embodiment, since the third lens group G ₃ is a lens configuration of two or more, it is easy to ensure telecentricity of the lens system reduction side.

In the projection variable focus lens of this embodiment is configured to zoom by simply moving only the second lens group G ₂ becomes possible, complex lens driving mechanism such as a cam mechanism unnecessary Therefore, each stage can be reduced in size, weight, and cost as compared with the conventional one. When the number of lenses of each lens group configured as described above is summed, in the above-described preferred embodiment, the number of lenses is 7 or 8. Such a small number of lenses has been achieved by using a variable focus lens instead of a zoom lens.

  In addition, since it is possible to eliminate restrictions on the coordinated movement of the lens group at the time of zooming, aberration variations at the time of zooming can be greatly improved.

  Here, the “variable focus lens” means that the conjugate length changes at the time of zooming, and the focus is shifted. Therefore, focusing at that time is necessary, but it is possible to set one moving group at the time of zooming. Therefore, even if the focus group consisting of the other one group is taken into consideration, it is sufficient to have at least two moving groups.

  Compared to the “variable focus lens”, the “zoom lens” is adjusted so that the conjugate length is constant at the time of zooming, and a slight deviation of the conjugate length is adjusted by the focusing lens. However, at the time of zooming, two or more moving groups move with each other according to a predetermined rule using a zoom cam mechanism or the like, and when considering a focus group consisting of another group, the moving group Is more than three groups, which is disadvantageous in terms of size reduction, weight reduction, and cost reduction.

  In addition, as described above, the projection variable focus lens according to the present embodiment is a negative lead type zoom lens, so that it is easy to widen the angle and secure a back focus with an appropriate length. Is possible.

  In the projection variable focus lens according to the present embodiment, it is preferable not to use a thermally weak cemented lens, but to use a single lens. As a result, it is possible to prevent the occurrence of a thermal problem even in a projection lens where the temperature in the system (particularly the position where the luminous flux becomes narrow) becomes extremely high.

In the projection variable focus lens according to the present embodiment, the second lens group G ₂ is represented by the following conditional expressions (1), it is preferable to satisfy at least one of (2).
_{1.0 <f 2 / f w <} 4.0 ···· (1)
_{0.15 <D 2 / L <0.55} ···· (2)
here,
f _w : Total system focal length at the wide end f ₂ : Focal length of the second lens group G ₂ D ₂ : Longest lens surface distance in the second lens group G ₂ L: Total lens length

Here, the technical significance of the conditional expressions (1) and (2) will be described.
First, the conditional expression (1) is provided with a focal length f ₂ of the second lens group G ₂ is a movable group for zooming, and defines the range of values of the ratio of the focal length f _w of the wide end it is those, which defines the range of the second lens group G ₂ of the power is obtained by defining a while improving the respective aberration correction to achieve a compact lens system range. That is, aberration correction becomes difficult when the lower limit of conditional expression (1) is reached. On the other hand, if the upper limit is exceeded, the amount of movement of the lens increases and the overall length of the lens increases. In order to obtain the effect of conditional expression (1) more effectively, it is preferable to satisfy the following conditional expression (1 ′), and it is more preferable to satisfy the following conditional expression (1 ″).
_{1.3 <f 2 / f w <} 3.0 ···· (1')
_{1.5 <f 2 / f w <} 2.5 ···· (1'')

The conditional expression (2) is to the lens overall length L, is obtained by defining the longest lens surface range of the ratio of the distance D ₂ in the second lens group G _2, the aberration correction, particularly the image surface correction and distortion It defines the range in which the lens system can be made compact while improving the correction. That is, when the value is less than or equal to the lower limit value of the conditional expression (2), it is difficult to correct aberrations, particularly image plane correction and distortion correction. On the other hand, if the upper limit is exceeded, the amount of movement of the lens increases and the overall length of the lens increases. In order to obtain the effect of the conditional expression (2) more effectively, it is preferable to satisfy the following conditional expression (2 ′), and it is more preferable to satisfy the following conditional expression (2 ″).
0.2 <D2 / L <0.5 ( _{2 '} )
0.25 <D ₂ /L<0.4 (2 ″)

Further, to satisfy the following conditional expression (3), to ensure a long back focus Bf than 1.2 times the focal length f _W of the wide-angle end, by ensuring a good telecentricity, color synthesis and the light beam Even when an optical system such as a prism is arranged on the reduction side for separation, it is possible to solve problems such as color unevenness due to deterioration of dichroic film characteristics and reduction in separation efficiency of illumination light and projection light. it can.
Bf / f _w > 1.2 (3)

In order to obtain the effect of conditional expression (3) more effectively, it is preferable to satisfy the following conditional expression (3 ′).
Bf / f _w > 1.45 (3 ′)

Here, the following projection variable focus lens of each embodiment, both, during the first lens group G _1, is intended to include at least one aspherical surface, thereby, the distortion correction be advantageous be able to. The aspheric shape is represented by the following aspheric expression.

  Next, an example of a projection display device equipped with the above-described projection variable focus lens will be described with reference to FIG. The projection display device shown in FIG. 5 includes transmissive liquid crystal panels 11 a to 11 c as light valves, and uses the projection variable focus lens according to the above-described embodiment as the projection variable focus lens 10. Further, an integrator (not shown) such as a fly eye is disposed between the light source (not shown) and the dichroic mirror 12, and the white light from the light source passes through the illumination optical unit to emit three color light beams. The liquid crystal panels 11a to 11c corresponding to (G light, B light, and R light) are incident on each other, light-modulated, color-combined by the cross dichroic prism 14, and projected onto a screen (not shown) by the projection variable focus lens 10. The This apparatus includes dichroic mirrors 12 and 13 for color separation, a cross dichroic prism 14 for color composition, condenser lenses 16a to 16c, and total reflection mirrors 18a to 18c. Since the projection display device of the present embodiment uses the projection variable focus lens according to the present embodiment, it is possible to achieve a reduction in size, weight, and cost, while having a configuration capable of high magnification. Moreover, high optical performance can be maintained.

  Note that the projection variable focus lens of the present invention is not limited to a use mode as a projection variable focus lens of a projection display device using a transmission type liquid crystal display panel, but a reflection type liquid crystal display panel, DMD, or the like. It can also be used as a projection variable focus lens of an apparatus using other light modulation means.

  Hereinafter, the projection variable focus lens of the present invention will be further described with reference to specific examples.

<Example 1>
The projection variable focus lens according to Example 1 is configured as shown in FIG. 1 as described above. That this projection variable focus lens includes, in order from the magnification side, a first lens group G ₁ is a first lens L ₁ of a biconcave lens having aspherical surfaces (on the axis), the reduction side, towards a stronger concave surface It was composed of the second lens L ₂ Metropolitan comprising a biconcave lens. The second lens group G _2, the third lens L ₃ which is a biconvex _lens, and a fourth lens L ₄ is a positive meniscus lens having a convex surface directed toward the mask 3, and the reduction side. The third lens group G ₃ includes a fifth lens L _{5 made of} a biconcave lens, a sixth lens L _{6 made of} a positive meniscus lens having a convex surface facing the reduction side, a seventh lens L _{7 made of} a biconvex lens, and consisting eighth lens L _8, which is a positive meniscus lens having a convex surface facing the magnification side.

Further, during zooming is due to the transition from the wide angle end to the telephoto end, only the second lens group G ₂ is moved to the magnification side along the optical axis X.
Focusing is performed by moving the third lens group G ₃ in the optical axis X direction.

  The radius of curvature R of each lens surface in the first embodiment (standardized by setting the focal length of the entire lens system to 1.0; the same applies to the following tables), the center thickness of each lens, and the air gap D between each lens ( Table 1 shows the refractive index Nd and Abbe number νd at the d-line of each lens in the upper table. In Table 1 and Table 2 described later, the numbers corresponding to the symbols R, D, Nd, and νd are sequentially increased from the enlargement side.

The middle part of Table 1 shows the values of the constants K and A _{3 to} A ₁₂ corresponding to each aspheric surface, and the lower part of Table 1 shows the wide-angle end (wide) and the telephoto end (tele). in each, in each case the projection distance 125.29 and 542.38, variable interval 1 (the distance between the first lens group G ₁ and the second lens group G ₂₎ and the variable spacing 2 (the second lens group G ₂ and the third lens group distance between G ₃₎ are shown.

  Table 5 shows numerical values corresponding to the conditional expressions (1) to (3), (1 ′) to (3 ′), (1 ″), and (2 ″) in Example 1.

  FIG. 5 shows various aberrations (spherical aberration, astigmatism, distortion, and lateral chromatic aberration) at the wide-angle end (wide: projection distance 125.29) and the telephoto end (tele: projection distance 125.29) of the projection variable focus lens of Example 1. It is an aberration diagram. 3 and the following FIG. 4, each spherical aberration diagram shows aberrations with respect to light of d-line, F-line, and C-line, and each astigmatism diagram shows sagittal image surface and tangential image surface. In each chromatic aberration diagram, aberrations for the F-line and C-line light with respect to the d-line light are shown.

  As is apparent from FIG. 3, according to the projection variable focus lens of Example 1, the field angle 2ω at the wide angle end is as wide as 53.4 degrees, the F value is as bright as 2.04, and each aberration is Corrected well.

Also, as shown in Table 3, according to the projection variable focus lens of Example 1, conditional expressions (1) to (3),
Conditional expressions (1 ′) to (3 ′) and (1 ″) and (2 ″) are all satisfied.

<Example 2>
A schematic configuration of the projection variable focus lens according to Example 2 is shown in FIG. Projection variable focus lens according to Example 2 has been substantially the same configuration as that of Example 1, primarily, the first lens group G _1, aspherical biconcave (on the axis) It is different in that consisting of only the first lens L ₁ composed more. Incidentally, since the first lens group G ₁ is constituted by one lens, other lenses, as compared with the corresponding lens in those of Example 1, lens number is assigned up repeatedly by one ing.

  The upper part of Table 2 shows the curvature radius R of each lens surface, the center thickness of each lens and the air gap D between each lens, the refractive index Nd of each lens at the d-line and the Abbe number νd in Example 2.

The middle part of Table 2 shows the values of constants K and A _{3 to} A ₁₂ corresponding to each aspheric surface, and the lower part of Table 2 shows the wide-angle end (wide) and the telephoto end (tele). in each, in each case the projection distance 125.56 and 543.54, variable interval 1 (the distance between the first lens group G ₁ and the second lens group G ₂₎ and the variable spacing 2 (the second lens group G ₂ and the third lens group distance between G ₃₎ are shown.

  Table 3 shows numerical values corresponding to the above conditional expressions in Example 2.

  FIG. 4 shows various aberrations (spherical aberration, astigmatism, distortion, and lateral chromatic aberration) at the wide-angle end (wide: projection distance 125.56) and the telephoto end (tele: projection distance 125.56) of the projection variable focus lens of Example 2. It is an aberration diagram.

  As is apparent from FIG. 4, according to the projection variable focus lens of Example 2, the angle of view 2ω at the wide angle end is as wide as 54.0 degrees, the F value is as bright as 2.01, and each aberration is Corrected well.

  Further, as shown in Table 3, according to the projection variable focus lens of Example 2, the conditional expressions (1) to (3), the conditional expressions (1 ′) to (3 ′), and further (1 ″) , (2 ″) are all satisfied.

1 is a schematic diagram showing a configuration of a projection variable focus lens according to Embodiment 1 of the present invention at a wide angle end (wide) and a telephoto end (tele). FIG. FIG. 6 is a schematic diagram illustrating a configuration at a wide-angle end (wide) and a telephoto end (tele) of a projection variable focus lens according to Example 2 of the present invention. Aberration diagram showing various aberrations (spherical aberration, astigmatism, distortion and lateral chromatic aberration) of the projection variable focus lens of Example 1 Aberration diagrams showing various aberrations (spherical aberration, astigmatism, distortion and lateral chromatic aberration) of the projection variable focus lens of Example 2 1 is a schematic configuration diagram of a projection display device according to an embodiment of the present invention.

Explanation of symbols

G ₁ ~G ₃ lens group L ₁ ~L ₈ lens R ₁ to R of curvature such as ₁₉ lens surface radius D ₁ to D ₁₈ lens spacing (lens thickness)
X Optical axis 1 Image display surface 2 Glass block (including filter part)
3 Mask (aperture stop)
DESCRIPTION OF SYMBOLS 10 Projection type variable focus lens 11a-c Transmission type liquid crystal panel 12, 13 Dichroic mirror 14 Cross dichroic prism 16a-c Condenser lens 18a-c Total reflection mirror

Claims (11)

In order from the magnification side, the first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power,
When the focal length is variable, the second lens group is moved in the optical axis direction, and during focusing, the third lens group is moved in the optical axis direction, and the reduction side is substantially telecentric. A projection variable focus lens characterized by that. The projection variable focus lens according to claim 1, wherein the second lens group satisfies the following conditional expression (1).
_{1.0 <f 2 / f w <} 4.0 ···· (1)
here,
f _w : focal length of the entire system at the wide end f ₂ : focal length of the second lens unit 3. The projection variable focus lens according to claim 1, wherein the second lens group satisfies the following conditional expression (2).
_{0.15 <D 2 / L <0.55} ···· (2)
here,
D ₂ : The longest lens surface interval in the second lens group L: Total lens length   The projection variable focus lens according to any one of claims 1 to 3, wherein the second lens group includes only two positive lenses.   The third lens group includes, in order from the magnification side, a negative 31st lens, a positive 32nd lens having a convex surface facing the reduction side, a positive 33th lens having a convex surface facing the reduction side, and a convex surface facing the magnification side The projection variable focus lens according to any one of claims 1 to 4, wherein the projection type variable focus lens is formed of a positive 34th lens directed toward the surface.   6. The projection variable focus lens according to claim 1, wherein the first lens group includes two lenses including a negative lens having a concave surface facing the reduction side.   The projection variable focus lens according to any one of claims 1 to 5, wherein the first lens group includes only one negative lens having a concave surface directed toward the reduction side.   The projection variable focus lens according to claim 6 or 7, wherein the first lens group includes at least one aspherical surface.   The first lens group includes two lenses including one negative lens with a concave surface facing the reduction side, the second lens group includes two positive lenses, and the third lens group includes an enlargement Starting from the negative side, the negative thirty-first lens, the positive thirty-second lens with the convex surface facing the reduction side, the positive thirty-third lens with the convex surface facing the reduction side, and the positive thirty-fourth lens with the convex surface facing the magnification side The projection variable focus lens according to claim 1, wherein the entire system is composed of eight lenses.   The first lens group is composed of one negative lens having a concave surface facing the reduction side, the second lens group is composed of two positive lenses, and the third lens group is negative in order from the magnification side. A 31st lens, a positive 32nd lens having a convex surface on the reduction side, a positive 33rd lens having a convex surface on the reduction side, and a positive 34th lens having a convex surface on the enlargement side. 2. The projection variable focus lens according to claim 1, comprising a single lens. A light source, a light valve, an illumination optical unit that guides a light beam from the light source to the light valve, and the projection variable focus lens according to claim 1, and the light beam from the light source The light is modulated by the light valve and projected onto the screen by the projection variable focus lens.

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