JP2010085934A - Projection variable focus lens and projection display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a projection variable focus lens and a protection display device achieving miniaturization, weight reduction and cost reduction of the lens system and the device by having the total number of the moving lens groups at the time of variable magnification and focusing being 2, with a preferable balance of aberrations, in particular, at the time of variable magnification. <P>SOLUTION: The projection variable focus lens includes in this order from the widening side a negative first group G<SB>1</SB>, a positive second group G<SB>2</SB>, a third group G<SB>3</SB>, and a positive fourth group G<SB>4</SB>with the shrinking side provided in a telecentric way. At the time of variable magnification, the second group G<SB>2</SB>and the third group G<SB>3</SB>are moved along the optical axis X with the interval varied with each other. At the time of focusing, the second group G<SB>2</SB>and the third group G<SB>3</SB>are integrally moved along the optical axis X. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a variable focus lens having a four-group structure 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. On the other hand, in general, focusing is performed by moving a lens group different from the zooming group. After all, three or more lens groups must be driven as the moving group. As a result, the lens driving unit becomes complicated, and it has been an obstacle to further miniaturization, weight reduction, and cost reduction.

  In view of this, there is known a projection zoom lens described in the following Patent Document 1 that enables zooming to be performed with one lens group and focusing to be performed with another lens group.

Japanese Patent Laid-Open No. 2005-300619

  However, in the projection zoom lens described in Patent Document 1, since the zoom function is provided by one lens group, the aberration fluctuation at the time of zooming is inevitably 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, while the total number of moving lens groups at zooming and focusing is set to two, thereby providing a lens system. And a projection variable focus lens and a projection display device in which the apparatus can be reduced in size, weight, and cost, and various aberrations, in particular, aberrations are well corrected in a balanced manner. It is intended.

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, a third lens group, and a fourth lens group having a positive refractive power,
When the focal length is variable, the second lens group and the third lens group are moved in the optical axis direction so that the distance between them changes, and at the time of focusing, the second lens group and the third lens group are moved. It is configured to move integrally in the optical axis direction, and further, the reduction side is configured to be substantially telecentric.

  In general, the term “variable focus lens” refers to a varifocal lens, and the conjugate length changes at the time of zooming and is out of focus, so focusing at that time is necessary. In the present specification, when the term “variable focus lens” is used, adjustment is made so that the conjugate length is constant at the time of zooming, and a slight deviation of the conjugate length is adjusted by a focusing lens. “Zoom lens” is not included.

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 : Longest lens surface distance in the second lens group L : Overall lens length (actual length from the most magnified lens magnification side vertex to the most reduced lens magnification side vertex (no air conversion))

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

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

  In addition, it is preferable that the fourth lens group includes only one positive lens having a convex surface on the enlargement side.

Further, it is preferable that the third lens group satisfies the following conditional expression (3).
f ₃ / f _w <−3.0 (3)
here,
f ₃ : Focal length of the third lens group f _w : Whole system focal length at the wide end

  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 magnifying side, a negative 31st lens, a positive 32nd lens having a convex surface on the reduction side, and a positive 33th lens having a convex surface on the reduction side, and the fourth lens group includes an enlargement side It is preferable that the entire system is composed of eight lenses with a convex surface facing the convex surface.

  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 thirty-second lens having a convex surface facing the reduction side, and a positive thirty-third lens having the convex surface facing the reduction side. The fourth lens group is a single lens having the convex surface facing the magnification side. It is preferably composed of a positive lens and composed of seven lenses in the entire system.

  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 four-group lens configuration in which two negative and positive lens groups are arranged in order from the enlargement side, and a positive lens group is arranged on the most reduction side. When the focal length is variable, the second lens group and the third lens group are configured to move in the optical axis direction while changing the distance from each other. At the time of focusing, the second lens group And the third lens group are integrally moved in the optical axis direction, and the reduction side is substantially telecentric.

  In this way, the moving lens group for zooming and the moving lens group for focusing are composed of the same lens group, so that the zoom lens is for reducing magnification and focusing, while being a telecentric reduction side and capable of high zooming. The total number of movable lens groups can be two, and the lens system and apparatus can be reduced in size, weight, and cost. In addition, since two lens groups can be assigned as moving lens groups for zooming, aberrations are balanced and better compared to the prior art in which one lens group is assigned as a moving lens group for zooming. It can be corrected.

  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, the lens group for zooming is the second lens group among the four lens groups from the magnification side. Lens group (main zoom lens group) and third lens group (sub zoom lens group), a large zoom ratio can be obtained even in a system in which the reduction side is substantially telecentric. .

  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. Projection variable focus lens embodiment (shown as a representative of that of Example 1) shown in Figure 1, in order from the magnification side, a first lens group G ₁ having a negative refractive power, positive refractive A second lens group G ₂ having a power, a third lens group G _3, and a fourth lens group G ₄ having a positive refractive power, and the reduction side is configured to be substantially telecentric. A glass block (including a filter unit) 2 mainly including a color synthesis prism and an image display surface 1 of a light valve such as a liquid crystal display panel are disposed. 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 (having an integral mask (which may be an aperture stop) 3) and the third lens group G ₃ are: It is configured to move along the optical axis X while changing a distance from each other, at the time of focusing, integrally with the second lens group G ₂ and the third lens group G _3, so as to move along the optical axis X It is configured.

Here, at the time of zooming, the second lens group G ₂ and the third lens group G ₃ may be configured to move without interlocking, but preferably, during zooming, the second lens group G ₂ and in conjunction with the third lens group G _3, it is possible to configure to move so as to change the distance therebetween. However, in this case at the time of focusing even it is configured so that the second lens group G ₂ and the third lens group G ₃ are moved integrally.

Figure 5 is a representation of an example of what has been described above as conceptual view, during zooming, the second lens group G ₂ and the third lens group G ₃ is moved while both regulated, whereas, focusing while at the time, by moving the entire mechanical mechanism 20 that imparts the regulating in the direction of the optical axis X, the second lens group G ₂ and the third lens group G ₃ is kept constant distance therebetween, to move between the first lens group G ₁ and the fourth lens group G _4, the mechanism is shown as.

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 plano-concave lens or composed of the second lens L ₂ formed of a biconcave lens (example 2, a concave surface facing the reduction side, composed of the first lens L ₁ of a non-spherical lens in which at least one surface is aspherical ).

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, it is constituted by a third lens L _{3 made of} a biconvex lens, a mask (which may be an aperture stop; the same applies hereinafter) 3 and a fourth lens L ₄ made of a biconvex lens. By disposing the mask 3 at a position between the two positive lenses, the telecentricity on the reduction side can be made better.

In the above second lens group G _2, the two positive lenses are both refractive index it is preferable from the viewpoint of aberration correction to be 1.65 or more.

The third lens group G ₃ includes, in order from the magnification side is constituted by a negative lens, a positive a convex surface facing the reduction side (or negative) lens, and a convex surface facing the reduction side positive lens, thereby Aberration variation during focusing can be reduced. More preferably, it is constituted by 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, and a seventh lens L ₇ made of a biconvex lens.

The fourth lens group G ₄ is composed of only the eighth lens L _8, which is a positive meniscus lens having a convex surface facing the magnification side.

In the projection variable focus lens of this embodiment, in any of during zooming and focusing, it is configured to move the second lens group G ₂ and the third lens group G _3, zooming Since there are only two moving lens groups at the time and at the time of focusing, it is possible to achieve a reduction in size, weight and cost as compared with the conventional one.

  In addition, as described above, the projection variable focus lens of the present embodiment is a negative lead type variable focus lens, so that it is easy to widen the angle and ensure 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 : Overall system focal length at the wide end f ₂ : Focal length of the second lens group G ₂ D ₂ : Longest lens surface distance L in the second lens group G ₂ : Lens total length

The fourth lens group G ₄ is preferably composed of only one positive lens having a convex surface facing the magnification side.

Further, it is preferable that the third lens group G ₃ satisfies the following conditional expression (3).
f ₃ / f _w <−3.0 (3)
here,
f ₃ : focal length of the third lens group G ₃

  Next, the technical significance of the conditional expressions (1) to (3) will be described.

First, the conditional expression (1) is provided with a focal length f ₂ during zooming and the second lens group G ₂ is a movable group upon focusing, a range of values of the ratio of the focal length f _w of the wide end are those defined, 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 ″)

The conditional expression (3), the focal length f ₃ of the third lens group G _3, is obtained by defining a range of values of the ratio of the focal length f _w of the wide end, and good aberration correction It defines the range to obtain. That is, when the value exceeds the upper limit value of the conditional expression (3), it is difficult to correct aberrations. In order to obtain the effect of conditional expression (3) more effectively, it is preferable to satisfy the following conditional expression (3 ′).
f ₃ / f _w <−5.0 (3 ′)

Moreover, satisfying the following conditional expression (4), 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 (4)

In order to obtain the effect of conditional expression (4) more effectively, it is preferable to satisfy the following conditional expression (4 ′).
Bf / f _w > 1.45 (4 ′)

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. 6 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 and the dichroic mirror 12, and white light from the light source passes through three illumination light beams (G light, B) via the illumination optical unit. Are incident on the liquid crystal panels 11a to 11c corresponding to the light and the R light, respectively, are light-modulated, color-combined by the cross dichroic prism 14, and projected onto a screen (not shown) by the projection variable focus lens 10. 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 made of a double-sided aspherical lens, a concave surface directed toward the reduction side, the formed of a negative meniscus lens consisting of two lens _{L 2} Metropolitan. The second lens group _{G 2,} the third lens _{L 3} which is a biconvex lens, and a fourth lens _{L 4} made of a mask 3 and a biconvex lens. The third lens group G _3, from the fifth lens L _5, the sixth lens L _6, and the seventh lens L ₇ formed of a biconvex lens is a positive meniscus lens having a convex surface directed toward the reduction side of a biconcave lens Become. The fourth lens group G ₄ is composed of only the 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, while the second lens group G ₂ and the third lens group G ₃ in cooperation with each other, the magnification side along the optical axis X while changing the distance therebetween Move to.
Focusing is performed by moving integrally with the optical axis X direction between the second lens group G ₂ and the third lens group G _3.

  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 109.74 and 470.31, (distance between the first lens group G ₁ and second lens group G ₂₎ variable spacing 1, variable spacing 2 (the second lens group G ₂ and the third lens group G ₃ distance between) and variable spacing 3 (distance between the third lens group G ₃ and the fourth lens group G ₄₎ are shown.

  Table 3 shows numerical values corresponding to the above conditional expressions in the first embodiment.

  FIG. 3 shows various aberrations (spherical aberration, astigmatism, distortion, and lateral chromatic aberration) at the wide-angle end (wide: projection distance 109.74) and the telephoto end (tele: projection distance 109.74) of the projection variable focus lens of Example 1. It is an aberration diagram. In FIG. 3 and FIG. 4 below, each spherical aberration diagram shows aberrations for the d-line, F-line, and C-line, and each astigmatism diagram shows the sagittal image surface and the tangential image surface. Aberrations are shown, and each magnification chromatic aberration diagram shows aberrations for the F-line and the C-line with respect to the d-line.

  As is apparent from FIG. 3, according to the projection variable focus lens of Example 1, the angle of view 2ω at the wide angle end is as wide as 57.6 degrees, the F value is as bright as 2.11, and each aberration is Corrected well.

  Further, as shown in Table 3, according to the projection variable focus lens of Example 1, conditional expressions (1) to (4), conditional expressions (1 ′) to (4 ′), and further (1 ″) , (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, double-sided aspheric lens having a concave surface facing the reduction side It is different in that consisting of only the first lens L ₁ composed of.

  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 125.64 and 543.88, (distance between the first lens group G ₁ and second lens group G ₂₎ variable spacing 1, variable spacing 2 (the second lens group G ₂ and the third lens group G ₃ distance between) and variable spacing 3 (distance between the third lens group G ₃ and the fourth lens group G ₄₎ 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 125.64) and the telephoto end (tele: projection distance 125.64) 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 54.0 degrees and the wide angle is as bright as F5 is 2.05, and each aberration is Corrected well.

  As shown in Table 3, according to the projection variable focus lens of Example 2, the conditional expressions (1) to (4), the conditional expressions (1 ′) to (4 ′), 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 The schematic diagram which shows the concept of the lens group movement at the time of zooming and focusing based on embodiment of this invention 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 ₄ 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 20 Mechanical mechanism

Claims (13)

In order from the magnification side, the first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group, and a fourth lens group having a positive refractive power,
When the focal length is variable, the second lens group and the third lens group are moved in the optical axis direction so that the distance between them changes, and at the time of focusing, the second lens group and the third lens group are moved. A projection variable focus lens, wherein the projection variable focus lens is configured to move integrally in the optical axis direction, and further, the reduction side is configured to be substantially telecentric. 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 : Longest lens surface distance in the second lens group L : Lens total 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 is composed of, in order from the magnification side, only a negative 31st lens, a positive 32nd lens having a convex surface on the reduction side, and a positive 33th lens having a convex surface on the reduction side. The projection variable focus lens according to any one of claims 1 to 4, wherein   6. The projection variable focus lens according to claim 5, wherein the fourth lens group is composed of only one positive lens having a convex surface facing the enlargement side. The projection variable focus lens according to claim 5 or 6, wherein the third lens group satisfies the following conditional expression (3).
f ₃ / f _w <−3.0 (3)
here,
f ₃ : Focal length of the third lens group f _w : Whole system focal length at the wide end   The projection variable focus lens according to any one of claims 1 to 7, wherein the first lens group includes two lenses including a negative lens having a concave surface directed toward the reduction side.   The projection variable focus lens according to any one of claims 1 to 7, 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 8 or 9, 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 The negative lens is composed of a negative 31st lens, a positive 32nd lens having a convex surface facing the reduction side, and a positive 33rd lens having a convex surface facing the reduction side, and the fourth lens group has a convex surface facing the magnification side 2. The projection variable focus lens according to claim 1, wherein said projection type variable focus lens is composed of a single positive lens facing the lens and 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. The fourth lens group includes a thirty-first lens, a positive thirty-second lens having a convex surface facing the reduction side, and a positive thirty-third lens having the convex surface facing the reduction side. 2. The projection variable focus lens according to claim 1, comprising a lens, and the entire system is composed of seven lenses. A light source, a light valve, an illumination optical unit that guides a light beam from the light source to the light valve, and a projection variable focus lens according to any one of claims 1 to 12, wherein the light beam from the light source Is projected on a screen by the projection variable focus lens.

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