JP2011053507A - Projection type variable focus lens and projection type display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact, light-weight, and bright projection type variable focus lens that has a three-group lens configuration, and in particular, satisfactorily corrects various aberrations when varying magnification, and to provide a projection type display device. <P>SOLUTION: The projection type variable focus lens comprising six or seven lenses, includes: a first group G1 having negative refractive power; a second group G2 having positive refractive power; and a third group G3 having positive refractive power. When magnification is varied, the first group G1 is fixed, while the second and third groups G2 and G3 are moved. Toward a telephoto end from a wide angle end, the second group G2 is moved from a magnifying side to a reducing side, and further, a telecentric configuration is achieved on the reducing side. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a variable focus lens having six or seven lenses mounted on a projection display device or 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 / Micromirror Device) The present invention relates to a small projection variable focus lens and a projection display device for enlarging and projecting a light beam carrying image information from a light valve such as a display 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, but the projection lenses mounted on them are also more powerful, brighter, smaller and lighter. Is strongly demanded.

  As zoom lenses having a three-group configuration for projection that satisfy these requirements to some extent, for example, those described in Patent Documents 1 and 2 are known.

Japanese Patent Laid-Open No. 10-133110 JP 2007-256711 A

  However, the one described in Patent Document 1 has a problem that the F value at the wide-angle end is not always as bright as 3.0, and the variation in spherical aberration at the time of zooming is too large. Furthermore, the number of lenses is as large as about 12, and from the viewpoint of miniaturization and weight reduction, the requirement is not satisfactorily satisfied.

  On the other hand, in Patent Document 2, although the F-number is improved to 2.4, there is a demand from the viewpoint of a small size and light weight because the diameter of the constituent lenses of the moving group is large and the number of lenses in the moving group is large. Is not necessarily satisfied.

  The present invention provides a projection variable focus lens and a projection display device that have a three-group lens configuration, can be reduced in size and weight, are bright, and can favorably correct various aberrations particularly during zooming. It is intended.

The projection variable focus lens of the present invention is
In order from the magnification side, a first lens group having negative refractive power, a second lens group having positive refractive power, and a third lens group having positive refractive power are arranged,
During zooming, the first lens group is fixed, while the second lens group and the third lens group move from the reduction side to the enlargement side as they go from the wide-angle end to the telephoto end,
Further, the reduction side has a telecentric configuration.

Moreover, it is preferable that at least one of the following conditional expressions (1) to (4) is satisfied.
| M3 / M2 | ≦ 0.6 (1)
-2.0 ≤ f1 / fw ≤ -0.7 (2)
1.0 ≦ f3 / fw ≦ 8.0 (3)
1.0 ≤ Bf / fw (4)
here,
M2: Amount of movement of the second lens group from the wide-angle end to the telephoto end M3: Amount of movement of the third lens group from the wide-angle end to the telephoto end fw: Whole system focus at the wide-angle end Distance f1: Focal length of the first lens group f3: Focal length of the third lens group Bf: Back focus at the wide angle end

  Further, it is preferable that the first lens group has an aspheric lens having at least one aspheric surface.

    Further, it is preferable that the first lens group is composed of one or two lenses.

  In addition, it is preferable that the second lens group includes two positive lenses.

  Further, it is preferable that the third lens group is composed of three lenses in order from the enlargement side: a negative lens having a concave surface on the reduction side, a positive lens having a convex surface on the reduction side, and a positive lens. .

  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.

  Here, the “variable focus lens” includes a varifocal lens and a zoom lens. Here, unlike a zoom lens, a varifocal lens is a lens that adjusts the focus shift caused by focusing when the conjugate length changes due to zooming.

  The “enlarged side” means the projected side (screen side), and the screen side is also referred to as the enlarged side for the sake of convenience when performing reduced projection. On the other hand, the “reduction side” means the original image display area side (light valve side), and the light valve side is also referred to as the reduction side for the sake of convenience in the case of reduced projection.

  According to the projection variable focus lens of the present invention, the first lens unit on the most enlargement side is set to be negative so that the lens unit having a negative refractive power is preceded. Corners and long back focus can be secured.

  On the other hand, during zooming, the positive second lens group and the positive third lens group are moved, and the second lens group moves from the reduction side along the optical axis in accordance with the movement from the wide-angle end to the telephoto end. Accordingly, the second lens group can be provided with not only a function as a correction group but also a function as a variable power group. Astigmatism and curvature of field can be suppressed, and a high-performance variable projection lens for projection can be configured with a small number of lenses.

  That is, since the first lens group is negative, both on-axis and off-axis light rays enter the second lens group at a high position. By making the second lens group positive, it is possible to have an effect of largely correcting aberrations such as astigmatism with respect to off-axis rays, but in the case of a variable focus lens, this large aberration correction effect is obtained. On the contrary, it becomes a defect, and the fluctuation of aberration (particularly astigmatism) accompanying the lens movement at the time of zooming becomes large. Therefore, in the projection variable focus lens of the present invention, the second lens unit moves from the reduction side to the enlargement side as it goes from the wide-angle end to the telephoto end in order to suppress fluctuations in aberrations during zooming. Thus, at the time of zooming, the height of the off-axis light beam incident on the second lens group can be kept at a height that does not change much. Thereby, it is possible to always exhibit an aberration correction effect for off-axis aberrations such as astigmatism. At the same time, the magnitude of astigmatism itself can be reduced. Moreover, it is set as a 3 group structure, and it can be set as a simple and compact lens system.

  Thus, according to the projection variable focus lens of the present invention, it is possible to reduce the size and weight, and to brighten, and particularly to properly correct various aberrations during zooming.

  In addition, the projection display device of the present invention uses the projection variable focus lens of the present invention, so that various aberrations including astigmatism are well maintained, and cost reduction and weight reduction are promoted. can do.

It is a figure showing the structure of the projection variable focus lens which concerns on Example 1 of this invention. It is a figure showing the structure of the projection variable focus lens which concerns on Example 2 of this invention. It is a figure showing the structure of the projection type variable focus lens which concerns on Example 3 of this invention. It is a figure showing the structure of the projection variable focus lens which concerns on Example 4 of this invention. FIG. 5 is a diagram illustrating all aberrations of the projection variable focus lens according to Example 1; FIG. 6 is a diagram illustrating all aberrations of the projection variable focus lens according to Example 2. FIG. 10 is a diagram illustrating all aberrations of the projection variable focus lens according to Example 3; FIG. 10 is a diagram illustrating all aberrations of the projection variable focus lens according to Example 4; It is a figure showing the schematic structure of the principal part of the projection type display apparatus of this invention.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. As shown in FIG. 1, the projection variable focus lens according to the embodiment of the present invention (representing the lens of Example 1 as a representative) has six lenses (Examples 1 and 2) or seven lenses (Examples). 3, 4), a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, and a third lens group G3 having a positive refractive power are arranged, and at the time of zooming The second lens group G2 and the third lens group G3 are movable while the first lens group is fixed, and in particular, the second lens group G2 moves from the reduction side toward the telephoto end from the wide-angle end. The lens system moves to the enlargement side, and the reduction side of the lens system has a substantially telecentric configuration.

  On the reduction side of the lens system, as shown in FIG. 1 and the like, a glass block 2 mainly including a color synthesis prism and an image display surface 1 of a light valve such as three or more liquid crystal display panels are disposed. . However, in the so-called single plate type using one light valve, the color synthesis prism is not required.

  Further, for example, as shown in FIG. 1, the mask 3 (3a, 3b) can be arranged in the second lens group G2 or at other positions.

  In addition, the “mask” in the present specification has a function of blocking a part of the upper side light or the lower side light of the off-axis light. Such a light shielding effect can maintain the balance between the upper and lower rays of off-axis rays, and can prevent the occurrence of color unevenness.

  The mask can also be an aperture stop that limits the upper and lower rays of off-axis rays and defines the brightness.

  During focusing, one lens group, for example, the third lens group G3 (the third lens group G3 in the following embodiments) is moved along the optical axis Z.

  As described above, according to the projection variable focus lens of the present embodiment, the widest angle of view and the long back focus can be easily secured by setting the first lens group G1 (first lens L1) closest to the enlargement side to be negative. To be able to.

  On the other hand, when zooming from the wide-angle end toward the telephoto end, the positive second lens group G2 is moved from the reduction side to the enlargement side along the optical axis, and thereby the second lens group G2 is moved. In addition to the function as a correction group, the lens can have a function as a zooming group, and can suppress fluctuations in aberrations such as astigmatism and curvature of field in the entire zooming range. It is possible to construct a variable focus lens for projection with high performance.

  That is, the second lens group G2 is moved from the reduction side to the enlargement side from the wide-angle end to the telephoto end, and the height of off-axis rays incident on the second lens group G2 does not change much during zooming. Since the height is maintained, the effect of suppressing aberration fluctuations against off-axis aberrations such as astigmatism can always be exhibited. At the same time, astigmatism itself can be reduced.

  The total number of lenses configured as described above is six or seven, and such a small number of lenses can be configured as a zoom lens, but by using a so-called varifocal lens, Can be easily configured. In this case, it is possible to eliminate the restriction on the coordinated movement of the lens group at the time of zooming, so that the aberration fluctuation at the time of zooming can be greatly improved.

  Here, the “variable focus lens” is a concept that includes both a so-called varifocal lens and a zoom lens. Among them, the “varifocal lens” is a focus lens that is generated when the conjugate length changes during zooming. A focusing operation corresponding to the deviation is required. 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 “vari-focal 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, which is generally disadvantageous in terms of size reduction, weight reduction, and cost reduction. .

In the projection variable focus lens according to this embodiment, it is preferable that the following conditional expressions (1) to (4) are satisfied.
| M3 / M2 | ≦ 0.6 (1)
-2.0 ≤ f1 / fw ≤ -0.7 (2)
1.0 ≦ f3 / fw ≦ 8.0 (3)
1.0 ≤ Bf / fw (4)
here,
M2: Amount of movement of the second lens group G2 from the wide-angle end to the telephoto end M3: Amount of movement of the third lens group G3 from the wide-angle end to the telephoto end fw: Whole system focus at the wide-angle end Distance f1: Focal length of the first lens group G1 f3: Focal length of the third lens group G3 Bf: Back focus at the wide angle end

  Here, the technical significance of the conditional expressions (1), (2), (3), and (4) described above will be described.

  Conditional expression (1) described above is a conditional expression for prescribing the amount of aberration fluctuation that occurs due to the zooming operation. If the upper limit of conditional expression (1) is exceeded, the amount of movement of the third lens group G3 becomes too large, the amount of aberration variation becomes too large, and it becomes difficult to ensure good telecentricity.

From such a viewpoint, it is more preferable that the following conditional expression (1 ′) is satisfied instead of the conditional expression (1).
| M3 / M2 | ≦ 0.5 (1 ′)

  Further, the conditional expression (2) described above is an expression for defining a range for making the aberration correction favorable and setting the distance of the lens back to an appropriate length. If the lower limit of conditional expression (2) is not reached, the negative refractive power of the first lens group G1 becomes too weak and the lens back becomes too short. As a result, the outer diameter of the first lens group G1 must be increased. It becomes difficult to make it compact. On the other hand, if the upper limit is exceeded, the negative refractive power of the first lens group G1 becomes too strong, and it becomes difficult not only to maintain good off-axis aberrations such as coma and field curvature, but also to the lens back. Becomes too long, leading to an increase in the size of the system.

From such a viewpoint, it is more preferable to satisfy the following conditional expression (2 ′) instead of the conditional expression (2).
-1.8 ≤ f1 / fw ≤ -0.9 (2 ')

  Conditional expression (3) described above is a conditional expression for making the lateral chromatic aberration good and realizing telecentricity. That is, below the lower limit, the refractive power of the third lens group G3 becomes too strong, the amount of chromatic aberration of magnification becomes too large, and it becomes difficult to satisfactorily correct the chromatic aberration of magnification with other lens groups. On the other hand, if the upper limit is exceeded, the refractive power of the third lens group G3 becomes too weak, and it becomes difficult to make the reduction side telecentric.

From such a viewpoint, it is more preferable to satisfy the following conditional expression (3 ′) instead of the conditional expression (3).
2.0 ≦ f3 / fw ≦ 6.0 (3 ′)

  Further, the conditional expression (4) described above is an expression that defines the size of the back focus.

  If the lower limit of conditional expression (4) is not reached, it will be difficult to insert a color synthesis unit such as a color synthesis prism between the lens system and the light valve.

From such a viewpoint, it is more preferable to satisfy the following conditional expression (4 ′) instead of the conditional expression (4).
1.1 ≦ Bf / fw ≦ 2.0 (4 ′)

  The first lens group G1 is preferably composed of one or two lenses.

  The second lens group G2 is preferably composed of two positive lenses.

  The third lens group G3 is preferably composed of three lenses in order from the enlargement side: a negative lens having a concave surface on the reduction side, a positive lens having a convex surface on the reduction side, and a positive lens. .

  Here, all of the projection variable focus lenses of the following examples are lenses of the first lens group G1 (the first lens L1 and the second lens L2 in the second example, and the first lens L1 in the other examples). Includes at least one aspherical surface, which makes distortion correction advantageous. In addition, by making at least one surface of the first lens L1 an aspherical surface, it is possible to appropriately correct the aberration for each angle of view. 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 11a to 11c as light valves, and uses the projection variable focus lens 10 according to the above-described embodiment as a projection variable focus lens. 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 11 a to 11 c 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.
<First Example Group>
The first example group includes projection variable focus lenses according to Examples 1 and 2 below, and includes a first lens group G1 including the first lens L1, a second lens L2, and a third lens L3. The second lens group G2 and the third lens group G3 including the fourth lens L4 to the sixth lens L6, and the second lens group G2 and the third lens group G3 are independent from each other during zooming. Configured to move.

  The projection variable focus lens according to Example 1 is configured as shown in FIG.

  In other words, in this projection variable focus lens, in order from the magnification side, the first lens group G1 is composed of a first lens L1 composed of a double-sided aspheric negative meniscus lens (on the axis) with the concave surface facing the reduction side. The second lens group G2 includes a second lens L2 made of a biconvex lens, masks 3a and 3b, and a third lens L3 made of a double-sided aspherical biconvex lens (on the axis). The third lens group G3 includes a fourth lens L4 made of a biconcave lens, a fifth lens L5 made of a biconvex lens, and a sixth lens L6 made of a positive meniscus lens having a concave surface directed toward the reduction side.

  At the time of zooming, the second lens group G2 moves to the enlargement side along the optical axis Z along with the transition from the wide angle end to the telephoto end, and the third lens group G3 moves to the reduction side along the optical axis Z. Move to.

  In addition, focusing is performed by moving the third lens group G3 in the optical axis Z direction (the varifocal lens type).

  The radius of curvature R of each lens surface in Example 1 (standardized with the focal length at the wide-angle end of the entire lens system as 1.00; the same in the following tables), the center thickness of each lens, and the distance between the lenses The upper part of Table 1 shows the air interval D (axis upper surface interval) (standardized in the same manner as the curvature radius R described above: the same in the following tables), the refractive index Nd and the Abbe number νd of each lens at the d-line. . 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, and an asterisk (*) is added to the right side of the surface number. The finished surface is an aspherical surface.

  In the middle of Table 1, the variable interval 1 (the interval between the first lens group G1 and the second lens group G2 (hereinafter referred to as the following) at the wide-angle end (wide), the intermediate position (middle), and the telephoto end (tele) is shown. Same in each table)), variable interval 2 (interval between second lens group G2 and third lens group G3 (same in the following respective tables)) and variable interval 3 (third lens group G3 and glass block 2) The interval: movement 3 (same in Tables 2 to 4 below) is shown, and the lower part of Table 1 shows the values of the constants K and A3 to A16 corresponding to the respective aspheric surfaces.

  Table 5 below shows numerical values corresponding to the above conditional expressions in Example 1.

  FIG. 5 is an aberration diagram showing various aberrations (spherical aberration, astigmatism, distortion, and lateral chromatic aberration) at the wide-angle end (wide), the intermediate position (middle), and the telephoto end (tele) of the projection variable focus lens of Example 1. It is. 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, and each magnification chromatic aberration diagram shows aberrations for the F-line and C-line light with respect to the d-line light.

  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 55.2 degrees, the F value is 2.20, and each aberration is bright. Corrected well.

  Further, as shown in Table 5, according to the projection variable focus lens of Example 1, all the conditional expressions (1) to (4) and (1 ′) to (4 ′) are satisfied.

  The projection variable focus lens according to Example 2 is configured as shown in FIG.

  That is, the projection variable focus lens has substantially the same configuration as that of the first embodiment, but the second lens L2 is a double-sided aspherical positive meniscus lens (on the axis) with the convex surface facing the reduction side. The point that the third lens L3 is composed of a biconvex lens composed of a spherical lens, the point that the fifth lens L5 is composed of a positive meniscus lens having a convex surface facing the reduction side, and the point that the sixth lens L6 is composed of a biconvex lens Is different. A mask is not arranged in the optical path.

  Further, at the time of zooming, the second lens group G2 moves to the enlargement side along the optical axis Z along with the transition from the wide angle end to the telephoto end, and the third lens group G3 temporarily contracts along the optical axis Z. After moving to the side, move to the enlargement side.

  In addition, focusing is performed by moving the third lens group G3 in the optical axis Z direction (the varifocal lens type).

  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 variable interval 1, variable interval 2 and variable interval 3 at the wide-angle end (wide), the intermediate position (middle) and the telephoto end (tele), respectively. The values of the constants K and A3 to A16 corresponding to the respective aspheric surfaces are shown.

  Table 5 below shows numerical values corresponding to the above conditional expressions in Example 2.

  FIG. 6 is an aberration diagram showing various aberrations (spherical aberration, astigmatism, distortion, and lateral chromatic aberration) at the wide-angle end (wide), intermediate position (middle), and telephoto end (tele) of the projection variable focus lens of Example 2. It is.

  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 44.2 degrees, the F value is 2.20, and each aberration is bright. Corrected well.

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

<Second Example Group>
The second example group includes a projection variable focus lens according to Examples 3 and 4 below, and includes a first lens group G1 including a first lens L1 and a second lens L2, and a third lens L3. And a second lens group G2 composed of a fourth lens L4 and a third lens group G3 composed of a fifth lens L5 to a seventh lens L7. During zooming, the second lens group G2 and the third lens group G3 Are configured to move independently of each other.

  The projection variable focus lens according to Example 3 is configured as shown in FIG.

  That is, this projection variable focus lens will be described in order from the magnification side. First, the first lens group G1 is composed of a first lens L1 made of a double-sided aspherical lens having a low power and a second lens L2 made of a biconcave lens. The second lens group G2 includes a third lens L3 made of a biconvex lens, a mask 3, and a fourth lens L4 made of a biconvex lens. The third lens group G3 includes a fifth lens L5 made of a biconcave lens, a sixth lens L6 made of a biconvex lens, and a seventh lens L7 made of a biconvex lens.

  At the time of zooming, the second lens group G2 moves to the enlargement side along the optical axis Z and the third lens group G3 moves to the enlargement side along the optical axis Z along with the transition from the wide angle end to the telephoto end. Move to.

  In addition, focusing is performed by moving the third lens group G3 in the optical axis Z direction (the varifocal lens type).

  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 variable interval 1, variable interval 2 and variable interval 3 at the wide-angle end (wide), the intermediate position (middle) and the telephoto end (tele), respectively. The values of the constants K and A3 to A16 corresponding to the respective aspheric surfaces are shown.

  Table 5 below shows numerical values corresponding to the above conditional expressions in Example 3.

  FIG. 7 is an aberration diagram showing various aberrations (spherical aberration, astigmatism, distortion, and lateral chromatic aberration) at the wide-angle end (wide), the intermediate position (middle), and the telephoto end (tele) of the projection variable focus lens of Example 3. It is.

  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 56.6 degrees, the F value is 2.20, and each aberration is bright. Corrected well.

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

  The projection variable focus lens according to Example 4 is configured as shown in FIG.

  That is, the projection variable focus lens has substantially the same configuration as that of the third embodiment, but the fourth lens L4 includes a double-sided aspheric positive meniscus lens (on the axis) with a convex surface facing the reduction side. This is different in that the sixth lens L6 is a positive meniscus lens having a convex surface on the reduction side.

  At the time of zooming, the second lens group G2 moves to the enlargement side along the optical axis Z and the third lens group G3 moves to the enlargement side along the optical axis Z along with the transition from the wide angle end to the telephoto end. Move to.

  In addition, focusing is performed by moving the third lens group G3 in the optical axis Z direction (the varifocal lens type).

  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 variable interval 1, variable interval 2 and variable interval 3 at the wide-angle end (wide), intermediate position (middle) and telephoto end (tele), respectively. The values of the constants K and A3 to A16 corresponding to the respective aspheric surfaces are shown.

  Table 5 below shows numerical values corresponding to the above conditional expressions in Example 4.

  FIG. 8 is an aberration diagram showing various aberrations (spherical aberration, astigmatism, distortion, and lateral chromatic aberration) at the wide-angle end (wide), intermediate position (middle), and telephoto end (tele) of the projection variable focus lens of Example 4. It is.

  As is apparent 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 56.6 degrees, the F value is 2.20, and each aberration is bright. Corrected well.

  Further, as shown in Table 5, according to the projection variable focus lens of Example 4, all the conditional expressions (1) to (4) and (1 ′) to (4 ′) are satisfied.

G1 to G3 Lens group L1 to L7 Lens R1 to R17 Radius of curvature of lens surface, etc. D1 to D16 Lens surface interval (lens thickness)
Z Optical axis 1 Image display surface 2 Glass block (including filter part)
3, 3a, 3b 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 (10)

In order from the magnification side, a first lens group having negative refractive power, a second lens group having positive refractive power, and a third lens group having positive refractive power are arranged,
During zooming, the first lens group is fixed, while the second lens group and the third lens group move from the reduction side to the enlargement side as they go from the wide-angle end to the telephoto end,
Further, a projection variable focus lens characterized in that the reduction side has a telecentric configuration. The projection variable focus lens according to claim 1, wherein the following conditional expression (1) is satisfied.
| M3 / M2 | ≦ 0.6 (1)
here,
M2: Amount of movement of the second lens group from the wide-angle end to the telephoto end M3: Amount of movement of the third lens group from the wide-angle end to the telephoto end The projection variable focus lens according to claim 1 or 2, wherein the following conditional expression (2) is satisfied.
-2.0 ≤ f1 / fw ≤ -0.7 (2)
here,
fw: focal length of the entire system at the wide angle end f1: focal length of the first lens unit The projection variable focus lens according to claim 1, wherein the following conditional expression (3) is satisfied.
1.0 ≦ f3 / fw ≦ 8.0 (3)
here,
fw: focal length of entire system at wide angle end f3: focal length of the third lens unit The projection variable focus lens according to claim 1, wherein the following conditional expression (4) is satisfied.
1.0 ≤ Bf / fw (4)
here,
fw: Total focal length at wide angle end Bf: Back focus at wide angle end   The projection variable focus lens according to claim 1, wherein the first lens group includes an aspheric lens having at least one aspheric surface.   The projection variable focus lens according to any one of claims 1 to 6, wherein the first lens group includes one or two lenses.   The projection variable focus lens according to any one of claims 1 to 7, wherein the second lens group includes two positive lenses.   The third lens group includes, in order from the magnification side, a negative lens having a concave surface facing the reduction side, a positive lens having a convex surface facing the reduction side, and a positive lens. The projection variable focus lens according to any one of claims 1 to 8.   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 The light is modulated by the light valve and projected onto the screen by the projection variable focus lens.

Images