JP5244498B2 - Projection variable focus lens and projection display device - Google Patents

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. Therefore, it is necessary to mount a cam mechanism and the like, which complicates the lens driving unit, and has been an obstacle to further miniaturization, weight reduction, and cost reduction.

  In view of this, a projection zoom lens disclosed in Patent Document 1 that enables zooming with one group is known.

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, while relaxing restrictions on lens group movement during zooming, downsizing, weight reduction, and 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, a third lens group, and a fourth lens group having a positive refractive power,
When the focal length is variable, the first lens group and the fourth lens group are fixed, and the second lens group and the third lens group are moved independently from each other in the optical axis direction, and at the time of focusing, The second lens group is configured to move in the optical axis direction, and the reduction side is configured to be substantially telecentric ,
The second lens group satisfies the following conditional expression (2).
0.15 <D2 / L <0.55 (2)
here,
D2: The longest lens surface distance in the second lens group
L: Total lens length

  Here, the “variable focus lens” is also referred to as a varifocal lens. Unlike a zoom lens, the conjugate length changes due to zooming, and the resulting focus shift is adjusted by focusing.

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

  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 _w : Focal length of entire system at wide end f ₃ : Focal length of third lens group

  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. The second lens group and the third lens group are moved independently in the optical axis direction when the focal length is variable, and the second lens group is moved in the optical axis direction during focusing. Further, the reduction side is configured to be substantially telecentric.

  With this configuration, the zoom lens is essentially a reduction-side telecentric and capable of high zooming, but the zoom lens is inherently limited, that is, movement of a plurality of moving lens groups during zooming is restricted by each other. Therefore, it is possible to reduce the size, weight and cost. In addition, particularly at the time of zooming, the aberration can be corrected well in a balanced manner.

  In the prior art described above, 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. For this reason, at the time of zooming, a cam mechanism or the like for moving two or more lens groups in cooperation with each other is required, and the projection lens cannot be reduced in size, weight, and cost.

  However, in the present invention, a variable focus lens is used for zooming of the projection lens, and at the time of zooming, the two lens groups are configured to move independently from each other, and a complicated lens such as a cam mechanism is used. 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 performing zooming is the second lens from the magnification side of the four-group configuration. Since the lens group is the group (main zoom lens group) and the 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. Further, 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 (integrated mask (can be an aperture stop) 3) and the third lens group G ₃ are independent of each other along the optical axis. It is configured to move along the X, at the time of focusing, and is configured to move the second lens group G ₂ along the optical axis X. That is, as the second lens group G ₂ and the third lens group G ₃ is moved in cooperation not configured.

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. was in the plano-concave lens or a biconcave lens and a second lens L ₂ (example 2, biconcave (first lens L ₁ composed of the _axis), 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 composite aspheric lens in which a resin molded into an aspheric shape is attached to the reduction side surface of a negative meniscus lens (preferably made of glass) with a concave surface facing the reduction side. Composed of the first lens _{L 1} that.).

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 (in Example 3). , most sixth lens L ₆ arranged on the reduction side, there is a positive meniscus lens having a convex surface directed toward the reduction side.).

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, (without being bound to each other) to each other independently of the second lens group G ₂ and the third lens group G ₃ to zooming by simply moving it is possible Since a complicated lens driving mechanism such as a cam mechanism is not necessary, it is possible to reduce the size, weight, and cost of each stage compared to 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, so that focusing at that time is necessary. Even when there are two moving groups at the time of zooming, the two moving groups move independently of each other, so that a complicated lens driving mechanism such as a cam mechanism for linking the moving lens groups is unnecessary. It is.

  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 amount 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, which is disadvantageous in terms of miniaturization, 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

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

Here, the technical significance of the conditional expressions (1) to (3) described above 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 ″)

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 projection variable focus lens described above will be described with reference to FIG. The projection display device shown in FIG. 9 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 of a biconcave lens having aspherical surfaces (on the axis), a concave surface directed to the reduction side, negative and a second lens L ₂ Metropolitan consisting of a meniscus lens. 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 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, and a seventh lens L _{7 made of a} biconvex 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, the second lens group G ₂ and the third lens group G ₃ is moved to the magnification side along the optical axis X.
Focusing is performed by moving the second lens group G ₂ 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 of the d-line of each lens in the upper part of the table. In Table 1 and Tables 2 to 4 to be 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 470.30, (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 5 shows numerical values corresponding to the above conditional expressions in Example 1.
FIG. 5 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. 5 and the following FIGS. 6 to 8, 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 plane and tangential. Aberrations for the image plane are shown. 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. 5, 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 5, 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 the one and substantially the same configuration in Example 1, mainly, the first lens group G _1, the first lens L ₁ of a biconcave lens, is different in that consists of the second lens L ₂ Metropolitan consisting aspherical having a concave surface facing the reduction side.

  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 125.74 and 544.31, (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 5 shows numerical values corresponding to the above conditional expressions in Example 2.
FIG. 6 shows various aberrations (spherical aberration, astigmatism, distortion, and lateral chromatic aberration) at the wide-angle end (wide: projection distance 125.74) and the telephoto end (tele: projection distance 125.74) of the projection variable focus lens of Example 2. It is an aberration diagram.

As apparent from FIG. 6, according to the projection variable focus lens of Example 2, the angle of view 2ω at the wide angle end is as wide as 53.8 degrees, the F value is as bright as 2.04, and each aberration is Corrected well.
As shown in Table 5, 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.

<Example 3>
FIG. 3 shows a schematic configuration of the projection variable focus lens according to Example 3. Projection variable focus lens according to Example 3 has been substantially the same configuration as that of Example 1, primarily, first the first lens group G ₁ is composed of a biconcave lens having aspherical surfaces in that consists of only a lens L _1, also, in that the third lens group G ₃ on the most reduction side of the lens (the sixth lens L ₆₎ is a positive meniscus lens having a convex surface facing the reduction side, further The fourth lens group G ₄ is different in that the positive lens (seventh lens L ₇ ) constituting the fourth lens group G ₄ is a biconvex lens. 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 3 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 3.

The middle part of Table 3 shows the values of the constants K and A _{3 to} A ₁₂ corresponding to the respective aspheric surfaces. The lower part of Table 3 shows the wide-angle end (wide) and the telephoto end (tele). in each, in each case the projection distance 125.63 and 543.84, (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 5 shows numerical values corresponding to the conditional expressions in Example 3.

  FIG. 7 shows various aberrations (spherical aberration, astigmatism, distortion, and chromatic aberration of magnification) at the wide-angle end (wide: projection distance 125.63) and the telephoto end (tele: projection distance 125.63) of the projection variable focus lens of Example 3. It is an aberration diagram.

  As is apparent from FIG. 7, according to the projection variable focus lens of Example 3, the angle of view 2ω at the wide angle end is as wide as 54.0 degrees, the F value is as bright as 2.05, and each aberration is Corrected well.

  As shown in Table 5, according to the projection variable focus lens of Example 3, conditional expressions (1) to (4), conditional expressions (1 ′) to (4 ′), and further (1 ″) , (2 ″) are all satisfied.

<Example 4>
FIG. 4 shows a schematic configuration of the projection variable focus lens according to Example 4. Projection variable focus lens according to Example 4 has been substantially the same configuration as that of Example 1, primarily, the lenses constituting the first lens group G ₁ is a composite aspherical lens L ₁ It is different in that it is composed of only. The composite aspherical lens L ₁ is the surface on the reduction side of the spherical glass lens l _1a of negative meniscus shape with a concave surface facing the reduction side, and attaching a resin film l _1b, the reduction side of the resin film l _1b The surface is formed in an aspherical shape. Incidentally, since the first lens group G ₁ is constituted by one lens, other lenses, as compared with that of Example 1, lenses are numbered up repeatedly one by one.

  The upper part of Table 4 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 4.

The middle part of Table 4 shows the values of constants K and A _{3 to} A ₁₂ corresponding to each aspheric surface, and the lower part of Table 4 shows the wide-angle end (wide) and the telephoto end (tele). in each, in each case the projection distance 125.59 and 543.67, (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 5 shows numerical values corresponding to the above conditional expressions in Example 4.

FIG. 8 shows various aberrations (spherical aberration, astigmatism, distortion, and lateral chromatic aberration) at the wide-angle end (wide: projection distance 125.59) and the telephoto end (tele: projection distance 125.59) of the projection variable focus lens of Example 4. It is an aberration diagram.
As is clear from FIG. 8, according to the projection variable focus lens of Example 4, the angle of view 2ω at the wide angle end is as wide as 54.0 degrees, the F value is as bright as 2.06, and each aberration is Corrected well.

  Further, as shown in Table 5, according to the projection variable focus lens of Example 4, conditional expressions (1) to (4), 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. FIG. 7 is a schematic diagram illustrating a configuration of a projection variable focus lens according to Example 3 of the present invention at a wide-angle end (wide) and a telephoto end (tele). FIG. 6 is a schematic diagram illustrating a configuration of a projection variable focus lens according to Example 4 of the present invention at a wide-angle end (wide) and a telephoto end (tele). 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 Aberration diagrams showing various aberrations (spherical aberration, astigmatism, distortion and lateral chromatic aberration) of the projection variable focus lens of Example 3 Aberration diagram showing various aberrations (spherical aberration, astigmatism, distortion and lateral chromatic aberration) of the projection variable focus lens of Example 4 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

Claims (14)

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 first lens group and the fourth lens group are fixed, and the second lens group and the third lens group are moved independently from each other in the optical axis direction, and at the time of focusing, The second lens group is configured to move in the optical axis direction, and the reduction side is configured to be substantially telecentric ,
The projection variable focus lens, wherein the second lens group satisfies the following conditional expression (2).
0.15 <D2 / L <0.55 (2)
here,
D2: The longest lens surface distance in the second lens group
L: Total lens length The projection variable focus lens according to claim 1, wherein the second lens group satisfies the following conditional expression (1).
1.0 <f2 / fw <4.0 (1)
here,
fw: focal length of entire system at wide end f2: focal length of second lens group 3. The projection variable focus lens according to claim 1, 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 3 . 5. The projection variable focus lens according to claim 4, wherein the fourth lens group is composed of only one positive lens having a convex surface facing the enlargement side. 6. The projection variable focus lens according to claim 4, wherein the third lens group satisfies the following conditional expression (3).
f3 / fw <−3.0 (3)
here,
fw: focal length of entire system at wide end f3: focal length of third lens unit 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 6, wherein the first lens group includes only one negative lens having a concave surface directed toward the reduction side. 9. The projection variable focus lens according to claim 7 , wherein the first lens group includes at least one aspheric 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. The projection variable focus lens according to any one of claims 1 to 11, wherein the second lens group satisfies the following conditional expression (2 ').
0.2 <D2 / L <0.5 (2 ') 13. The projection variable focus lens according to claim 1, wherein the second lens group satisfies the following conditional expression (2 ″).
      0.25 <D2 / L <0.4 (2 ″) A light source, a light valve, an illumination optical unit that guides the 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 Is projected on a screen by the projection variable focus lens.

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