JP2003215453A - Wide angle zoom lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wide angle zoom lens used in a projection device enlarging and projecting an image to a screen, constituted so that its pupil is long and has little fluctuation with respect to a liquid crystal surface being a display body and back focus is very long, and realizing high-definition image projection. <P>SOLUTION: The wide angle zoom lens is constituted of a 1st lens group, a 2nd lens group and a 3rd lens group in order from an enlargement side, and satisfies conditional expressions 0.5<|f1/f2|<1.0, 0.5<|fw/f1|<0.8, 1.5<bf/fw<2.0 and 2.0<|M2/M1|<6.0 when it is assumed that f1 and f2 are the focal distances of the 1st and the 2nd lens groups respectively, (fw) is the focal distance of an entire system at a wide angle end, (bf) is air-converted length from the 3rd lens group to the display body except a glass block or the like, M1 and M2 are the maximum values of the respective moving amounts of the 1st and the 2nd lens groups in the midst of zooming, and a moving direction to the enlargement side is negative. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens used in a projection device for magnifying and projecting an image on a screen at a fixed finite distance, and more particularly to a zoom lens using a plurality of liquid crystals for each color light on a display body. The present invention relates to a small-sized telecentric zoom lens having a simple structure for performing high-definition image projection through a single projection lens by combining, and particularly to a wide-angle zoom lens for wide-angle projection.

[0002]

2. Description of the Related Art A negative lead type zoom lens preceded by a lens unit having a negative refracting power is characterized in that a wide angle of view is relatively easy, but on the other hand, a moving amount for zooming is small. However, there are drawbacks such as increase in size, difficulty in achieving high zoom ratio, easy occurrence of distortion on the wide angle side, and difficulty in securing a large amount of peripheral light.

Among these, as a zoom lens composed of three groups, a negative lens group that is movable during zooming, a positive lens group that is movable, and a positive lens group that is fixed during zooming, for example, Japanese Patent Publication No. 6-40170. Publication, Japanese Patent Publication 6-10
698, JP-A-6-94996, JP-A-64-52112, JP-A-63-135913.
JP-A-4-114116, JP-A-60-181717, JP-A-62-87925, JP-A-62-200316 and the like.

In each of these publications, the zoom lens is composed of three lens groups as a whole, in order from the object side, having negative, positive, and positive refracting powers, of which the first lens group and the second lens group are formed. It is moved to change the magnification.

Except for some of these applications, lenses for photography are assumed, distortion on the wide-angle side is large, the amount of peripheral light is small, and the pupil on the reduction side is short, which is not a so-called telecentric configuration. In a projector using a liquid crystal or the like for projecting on a screen, since a luminous flux is emitted from the display surface in a substantially telecentric form, unless the pupil of the lens is long, that is, the telecentric configuration, it is substantially The aperture efficiency and peripheral light intensity were insufficient, which was not appropriate.

Further, Japanese Patent Application Laid-Open No. 6-94996 proposes a zoom lens having a negative, positive, and positive three-group configuration in which the length of the pupil is taken into consideration. The present invention is intended for an image pickup system using a solid-state image pickup device, and the zoom ratio is large at about 2 times, but Fno is dark and the length of the pupil is about 3 to 4 times the focal length on the wide angle side. The maximum image height was 4 to 7 times, which was not long enough. Further, as a projection lens using a liquid crystal or the like, there is also a drawback that the back focus is too short to introduce a color synthesizing member such as a cross dichroic prism.

[0007]

When enlarging and projecting a display image on a screen as in the present invention, a liquid crystal display is used separately for each of a plurality of colored lights, and the colored lights are combined into one projection lens. In the case of projecting with the projection, it is necessary to satisfy the following conditions.

(1) In order to eliminate the influence of the light distribution characteristic of the liquid crystal or the angle dependence of the color combining dichroic film when combining a plurality of color lights, and to eliminate the peripheral light drop when irradiating the liquid crystal, A so-called telecentric optical system in which the pupil on the panel side (exit pupil) is at a distance.

This requires a telecentric system rather than an image pickup system using a solid-state image pickup device such as a CCD.

(2) A long back focus is required in order to secure a space for the color synthesizing element interposed between the display body and the projection lens.

(3) Normally, in order to project the display image upward on the screen, the display body is used with its center position shifted with respect to the optical axis of the projection lens, and as a result, it is effective to use the vicinity of the front lens. Since the area is not symmetrical about the optical axis but is biased upward and the diameter of the front lens becomes large, improvement means are necessary.

With respect to the above-mentioned requirements, in the above-mentioned conventional example,
It is hard to say that the exit pupil position is still short and the back focus is long enough.

The present invention has been made in light of the improvement of Japanese Patent Laid-Open No. 6-94996 for irradiating liquid crystal or the like, and has a particularly simple structure, a bright movement and a small distortion with a simple movement, and a chromatic aberration of magnification is small. A telecentric zoom lens with a simple structure that has a long pupil with little variation with respect to the liquid crystal surface that is the display and is used in a magnified projection projection device, has a sufficiently long back focus, and projects wide-angle, high-definition images It is to be.

[0014]

[Means for Solving the Problems] In order to solve the above problems,
The present invention is characterized by the following configurations.

In the substantially telecentric zoom lens for magnifying and projecting the image of the display object on the screen, the first lens group having a negative refracting power which is movable during zooming in order from the magnifying side.
It is composed of a second lens unit having a positive refracting power that is movable during zooming and a third lens unit having a positive refracting power that is fixed during zooming, and the third lens unit is a positive single lens having a strong convex surface on the magnifying side. It is composed of a lens and further satisfies the following conditional expression. (1) 0.5 <| f1 / f2 | <1.0 (2) 0.5 <| fw / f1 | <0.8 (3) 1.5 <bf / fw <2.0 (4) 2 .0 <| M2 / M1 | <6.0 where fi is the focal length of the i-th lens group, fw is the focal length of the entire system at the wide-angle end, and bf is the air-equivalent length from the third lens group to the display body. (Excluding glass block, etc.), M1, M2
Is the maximum value of the amount of movement of each of the first lens group and the second lens group during zooming. However, the moving direction to the enlargement side is minus (-).

The above expressions (1) and (2) are necessary conditions for sufficiently retroreflecting the lens to widen the angle and to secure a sufficient back focus.
If it deviates from this range, it is difficult to secure a desired wide angle and back focus. In particular, if the upper limit of the formula (1) is exceeded, the back focus cannot be secured, and if the lower limit is exceeded, the desired zoom ratio cannot be obtained, and the Petzval sum increases in the negative direction, which is not appropriate.

If the upper limit of the expression (2) is exceeded, the desired wide angle cannot be achieved and the back focus cannot be secured.

If the lower limit of this equation is not satisfied, the distortion at the wide-angle end cannot be properly corrected, and if the upper limit is exceeded, the distortion at the telephoto end cannot be properly adjusted.

The expression (3) defines the relationship between the angle of view and the back focus properly, and if either the upper limit or the lower limit is deviated, it is not suitable together with (1) and (2).

Equation (4) is a necessary equation for ensuring a desired zoom ratio. Especially, if the lower limit is exceeded, the total length becomes large, and the power of the second lens group, which is the main zoom group, is strong. Aberration fluctuation due to zooming becomes large.

When the focal length at the wide-angle end is changed to the focal length at the telephoto end, the following conditions should be satisfied when the image forming magnifications of the second lens unit and the third lens unit are β2 and β3. Is preferred. (5) | β2 |> 0.70 (6) β3 <0.83 This equation (5) relates to the movement of the first and second lens groups during zooming. When shifting from the wide-angle end to the telephoto end, the second lens group moves toward the reduction side (display body side) in the range of 0.7 <β2 <1.0, and the second lens group expands in the range of β2> 1.0. Move to (screen side).

In order to make the whole system compact, it is preferable that the whole system is in the above range.

The expression (6) represents the image forming relationship of the third lens group. This range is preferable in order to optimize the back focus and ensure the optimum pupil. When β3 approaches 1, the power of the third lens group becomes weak and the pupil becomes short, which is not appropriate.

In particular, it is preferable that the third lens group has a convex meniscus shape having a convex surface on the magnifying side. In this way, by directing the concave surface toward the reduction side (liquid crystal panel side),
The principal point position of the lens group moves to the second lens group side, the pupil can be lengthened, and the back focus can be secured long.

More preferably, when the lens constituting the third lens group is a convex meniscus single lens, its refractive index is preferably 1.6 or more.

In particular, the first lens group includes, in order from the magnification side, a positive lens L11 having a convex surface on the magnification side, a negative meniscus lens L12 having a convex surface on the magnification side, a cemented negative lens having a concave surface on the reduction side, or a negative lens. It is preferable that the single lens L13 and the L14 lens are arranged with the largest air gap d7 in the first lens group.

With such a structure, it becomes possible to control lateral chromatic aberration and axial chromatic aberration before and after the interval d7 in the first lens group. Especially when L13 is cemented, the negative lens is made of a low-dispersion glass material, and the negative lens L12 is also made of a low-dispersion glass material to suppress the occurrence of lateral chromatic aberration, and the L14 lens is cemented to control the axial chromatic aberration. .

The glass material of the negative lens used for L12 and L13 preferably has an Abbe number of 70 or more. In addition, when laminating L14, coma is removed by using a glass material having a high refractive index on the positive lens side.

Further, the positive lens L11 uses a glass material having a refractive index of 1.6 or more to remove distortion on the wide angle side.

Further, both L12 and L13 are formed into a negative meniscus shape having a concave surface on the reduction side (display body side), so that the shape becomes more retrofocus and the back focus becomes longer.

The maximum image height on the surface corresponding to the display panel is Y
And the pupil of the lens on the display panel side (reduction side) (exit pupil)
It is preferable that the following conditions are satisfied when the minimum absolute value during zooming of the distance to is tk. (7) | tk | / Y> 18 This condition defines the length of the pupil in the image cycle. If it deviates from this range, it will lead to a substantial reduction in the amount of peripheral light.

In particular, in order to materialize the equation (7), it is preferable that the following conditions are satisfied. (8) | tk | / fw> 10 As a result, it is possible to minimize the decrease in the peripheral light amount at the wide-angle end where the decrease in the peripheral light amount is largest due to the influence of the pupil position variation.

As described above, the pupil (aperture) of the lens system
Is preferably in the second lens group. Specifically, it is preferable that it is aligned with the most screen side surface or panel side surface of the second lens group, and it may be inside the lens group.

In order to properly set the panel-side pupil of the entire system and the distortion, it is particularly preferable that the following expressions are satisfied. (9) 0.1 <bf / f3 <0.3 (10) 0.8 <bf / | f1 | <1.3 bf is the distance from the third lens group to the display body, excluding the dichroic prism and the like. It is the air equivalent length. Expression (9) is an expression necessary for making the whole system properly telecentric. Necessary conditions for the light flux emitted vertically from the display panel to enter the third lens group, be refracted and efficiently reach the pupil (stop), and to make the effective diameter near the front lens (first lens group) appropriate. Is.

If it exceeds the upper limit, the size becomes large, and if it exceeds the lower limit, distortion occurs. Expression (10) is also a condition for making the exit pupil long and telecentric while appropriately taking distortion. If the value goes below the lower limit, the diameter of the first lens unit becomes large, and if it goes beyond the upper limit, distortion particularly at the wide-angle end becomes large, which is not suitable. In particular, it is preferable to satisfy the following conditions in order to optimize the distance from the lens to the panel while optimally making the telecentric system. (11) 5 <f3 / fw <15 If the lower limit is exceeded, the optimum telecentricity cannot be satisfied, and if the upper limit is exceeded, the size is increased, which is not suitable.

Further, it is preferable to satisfy the following formulas in order to make the moving amount of each group appropriate while making the power arrangement of each group appropriate and to make the size small.

As described above, it is preferable to have an aperture stop in the second lens group, but it is particularly preferable that the second lens group has an aperture stop on the most magnification side (screen side).

Further, it is preferable that a biconvex positive lens L21 is disposed in the vicinity of the most magnifying side of the second lens group and any one of the surfaces is made aspheric. The aspherical surface may be made of plastic or glass, and is preferably a lens in the vicinity of the diaphragm in the entire lens system and has a relatively small outer diameter. In particular, it is preferable that this aspherical surface has a convex refracting power that becomes stronger toward the periphery.

Also, the enlarged side of L21 (screen side)
Surface is R211 and the reduction side (display body / panel side) is R2
When it is 212, it is preferable to satisfy (12) R211> R212 (paraxial radius of curvature in case of aspherical surface). With this configuration, the second
The position of the principal point of the lens group can be appropriately set and the distance to the third lens group can be set. If it deviates from this range, the second lens group and the third lens group
It is not suitable because not only the distances at the wide-angle end of the lens groups cannot be properly set, but also an introverted coma is generated.

This L21 may be bonded to correct the axial chromatic aberration.

The second lens group has the largest air space d13 in the second lens group on the reduction side of L21.
It is preferable to arrange the remaining lenses of the second lens group. This is effective because the aberration correction in the second lens group can be shared with the axial aberration on the L21 side and the off-axis aberration correction on the reduction side lens group.

[0042]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.

(First Embodiment) In the first embodiment of the present invention, both the first lens group and the second lens group move to the enlargement side during zooming from the wide-angle end to the telephoto end. This is an example in which the magnification β2 of is always less than or equal to −1 (β2 <−1).

FIG. 1 shows a sectional view of each lens unit of the present embodiment at the wide-angle end. In the figure, GB is a glass block such as a color synthesizing prism, a polarizing filter, and a color filter.

FIG. 2 shows an aberration diagram at the wide-angle end, and FIG. 3 shows an aberration diagram at the telephoto end. In the figure, the solid line is the d line (58
7.6 nm), the two-dot chain line is the aberration at the g-line (435.8 nm), ΔM and ΔS are the meridional image plane, the sagittal image plane,
Chromatic aberration of magnification refers to 470 nm. Further, Table 1 shows numerical examples of the configuration of each lens group in this example. In the table, ri is the curvature radius of the i-th lens surface in order from the object side, di is the i-th lens thickness and air gap in order from the object side, and ni and vi are the glass of the i-th lens in order from the object side, respectively. Is the refractive index and the Abbe number. The flat lens GB closest to the image plane is a glass block such as a color synthesizing prism, a polarizing filter, and a color filter. The aspherical shape has an X axis along the optical axis, an H axis perpendicular to the optical axis, a positive light traveling direction, R is a paraxial radius of curvature, and each aspherical coefficient is K, B, C, D, E. , F, A ', B', C
When expressed as 'and D', they are expressed by the following formula 1.

[0046]

[Equation 1]

In the following, the same contents in the drawings and tables are designated by the same reference numerals and the description thereof will be omitted.

In this embodiment, the Abbe number is 8 in the first lens unit.
Chromatic aberration is removed by using two negative lenses made of glass material of 0 or more. The refractive index of L11 is set to 1.7 or more, and a relatively small diameter glass aspherical lens having an aspherical surface on the magnifying side is adopted for the second lens group L21.

[0049]

[Table 1]

(Second Embodiment) In the second embodiment of the present invention, when zooming from the wide-angle end to the telephoto end, both the second lens group move to the enlargement side and the first lens group moves largely to the reduction side. This is an example of a convex movement toward the reduction side so that it moves toward the enlargement side near the telephoto end. The magnification β2 of the second lens group is -1
This is an example of fluctuations across.

FIG. 4 shows a sectional view of each lens unit of this embodiment at the wide-angle end. Further, FIG. 5 shows an aberration diagram at the wide-angle end, and FIG. 6 shows an aberration diagram at the telephoto end. Further, Table 2 shows numerical examples of the configuration of each lens group in this example.

Chromatic aberration is removed by using two negative lenses made of a glass material having an Abbe number of 80 or more in the first lens group. L1
The refractive index of 1 is 1.7 or less, and a relatively small diameter glass aspherical lens having an aspherical surface on the magnifying side is adopted for the second lens unit L21.

[0053]

[Table 2]

(Third Embodiment) Also in the third embodiment of the present invention, both the second lens group move to the enlargement side during zooming from the wide-angle end to the telephoto end, and the first lens group moves largely to the reduction side. This is an example of a convex movement toward the reduction side so that it moves toward the enlargement side near the telephoto end.

FIG. 7 shows a sectional view of each lens unit of the present embodiment at the wide-angle end. 8 shows an aberration diagram at the wide-angle end, and FIG. 9 shows an aberration diagram at the telephoto end. Further, Table 3 shows numerical examples of the configuration of each lens group in the present example.

In this example, the magnification β2 of the second lens group fluctuates with a value of -1. Abbe number 70 in the first lens group
Chromatic aberration is removed by using two negative lenses made of a glass material, and L12 and L13 are both negative meniscus single lenses. The refractive index of L11 is 1.7 or more, and a relatively small diameter glass aspherical lens having an aspherical surface on the magnifying side is adopted for the second lens group L21.

[0057]

[Table 3]

(Fourth Embodiment) In the fourth embodiment of the present invention, both the second lens group move to the enlargement side during zooming from the wide-angle end to the telephoto end, and the first lens group monotonously moves to the reduction side. This is a moving example.

FIG. 10 shows a sectional view of each lens unit of the present embodiment at the wide-angle end. FIG. 11 is an aberration diagram at the wide-angle end, and FIG.
2 shows aberration diagrams at the telephoto end. Further, Table 4 shows numerical examples of the configuration of each lens group in this example.

The magnification β2 of the second lens group is -1 or more (-1
This is an example in which <β2 <−0.7). Chromatic aberration is removed by using two negative lenses made of a glass material having an Abbe number of 80 or more in the first lens group. The refractive index of L11 is set to 1.7 or less, and a relatively small diameter glass aspherical lens having an aspherical surface on the magnifying side is adopted for the second lens group L21.

[0061]

[Table 4]

(Fifth Embodiment) In the fifth embodiment of the present invention, when zooming from the wide-angle end to the telephoto end, both the second lens group move to the enlargement side, and the first lens group monotonically moves to the reduction side. This is a moving example.

FIG. 13 shows a sectional view of each lens unit of this embodiment at the wide-angle end. FIG. 14 is an aberration diagram at the wide-angle end, and FIG.
5 shows an aberration diagram at the telephoto end. Further, Table 5 shows numerical examples of the configuration of each lens group in the present example.

The magnification β2 of the second lens group is -1 or more (-1
This is an example in which <β2 <−0.7). Chromatic aberration is removed by using two negative lenses made of a glass material having an Abbe number of 80 or more in the first lens group. The refractive index of L11 is set to 1.7 or less, and a relatively small diameter glass aspherical lens having an aspherical surface on the reduction side is used for the second lens group L21.

[0065]

[Table 5]

The values of the conditional expressions of the respective examples are collectively shown in Table 6.
Shown in.

[0067]

[Table 6]

[0068]

According to the present invention, by virtue of the constitution as described above, the liquid crystal which is a display body has a particularly simple constitution and is bright and compact with a simple movement and has a small distortion and a small chromatic aberration of magnification. With respect to the surface, there is little fluctuation of the pupil,
We were able to achieve a wide-angle telecentric zoom lens for high-definition image projection, which is used in a magnified projection device.

Focusing to a finite distance is particularly preferably performed by the first lens group, but the distance may be adjusted by the second lens group, the third lens group, or a part of the lens in the second lens group. The whole process may be performed or the display panel may be moved.

[Brief description of drawings]

FIG. 1 is a sectional view of a lens configuration according to a first example at a wide-angle end.

2A, 2B, 2C, and 2D are aberration diagrams at the wide-angle end in the first embodiment.

3 (a), (b), (c), and (d) are aberration diagrams at the telephoto end in the first embodiment.

FIG. 4 is a sectional view of a lens structure according to a second example at a wide-angle end.

5 (a), (b), (c), and (d) are aberration diagrams at the wide-angle end in the second embodiment.

6 (a), (b), (c), and (d) are aberration diagrams at the telephoto end in the second embodiment.

FIG. 7 is a sectional view of a lens structure according to a third example at a wide-angle end.

8A, 8B, 8C, 8D, and 8D are aberration diagrams at the wide-angle end in the third embodiment.

9 (a), (b), (c), and (d) are aberration diagrams at the telephoto end in the third embodiment.

FIG. 10 is a sectional view of a lens structure according to a fourth example at the wide-angle end.

FIG. 11A, FIG. 11B, FIG. 11C, and FIG. 11D are aberration diagrams at the wide-angle end in the fourth embodiment.

12 (a), (b), (c), and (d) are aberration diagrams at the telephoto end in the fourth embodiment.

FIG. 13 is a sectional view of a lens structure according to a fifth example at a wide-angle end.

14A, 14B, 14C, and 14D are aberration diagrams at the wide-angle end in the fifth embodiment.

15A, 15B, 15C, and 15D are aberration diagrams at the telephoto end in the fifth embodiment.

[Explanation of symbols]

L11 A positive lens having a convex surface on the first expansion side from the expansion side of the first lens group L12 A negative meniscus lens having a convex surface on the second expansion side from the expansion side of the first lens group L13 From the expansion side of the first lens group The third cemented negative lens or the negative single lens L14 having a concave surface on the reduction side is located at the fourth position from the expansion side of the first lens unit, and L
13 and a lens L21 having the largest air gap d7 in the first lens group, a biconvex positive lens GB on the most magnification side of the second lens group GB, which is a flat plate lens on the most image side, and is a color synthesis prism, a polarization filter, and a color filter. , Etc. glass blocks

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Claims (6)

[Claims] 1. A substantially telecentric zoom lens for magnifying and projecting an image of a display member on a screen, in order from the magnification side, a first lens unit having a negative refractive power that is movable during zooming, and a positive lens that is movable during zooming having an aperture. Is composed of a second lens group having a refractive power of 3 and a third lens group having a positive refractive power which is fixed during zooming, and the third lens group is composed of a positive single lens having a strong convex surface on the magnifying side, and further f1, f2 is the focal length of the first lens group and the focal length of the second lens group, fw
Is the focal length of the entire system at the wide-angle end, bf is the air-equivalent length excluding the glass block from the third lens group to the display body, M
1 and M2 are the maximum values of the moving amounts of the first lens group and the second lens group during zooming, and when the moving direction to the enlargement side is negative, the conditional expression 0.5 <| f1 / f2 | <
1.0, 0.5 <| fw / f1 | <0.8, 1.5 <b
A wide-angle zoom lens characterized by satisfying f / fw <2.0 and 2.0 <| M2 / M1 | <6.0. 2. When the imaging magnifications of the second lens group and the third lens group are β2 and β3 when the focal length at the wide-angle end is changed to the focal length at the telephoto end, conditional expression | β2 |> 0.
The wide-angle zoom lens according to claim 1, wherein 70 and β3 <0.85 are satisfied. 3. The wide-angle zoom lens according to claim 1, wherein the third lens group has a convex meniscus shape having a convex surface on the enlargement side. 4. The first lens group includes, in order from the magnification side, a positive lens L11 having a convex surface on the magnification side, a negative meniscus lens L12 having a convex surface on the magnification side, and a cemented negative lens having a concave surface on the reduction side, or a negative lens. Single lens L13 and L14 with the largest air gap in the first lens group
4. The wide-angle zoom lens according to claim 1, wherein the wide-angle zoom lens comprises a lens. 5. The maximum image height on a surface corresponding to the display panel is Y, and the minimum absolute value during zooming of the distance to the pupil (exit pupil) of the lens on the display panel side (reduction side) is tk.
5. The wide-angle zoom lens according to claim 1, wherein the conditional expression | tk | / Y> 18 is satisfied. 6. A conditional expression | tk | / f where tk is a minimum absolute value during zooming of a distance from a display panel to a pupil (exit pupil) of a lens on the display panel side (reduction side).
The wide-angle zoom lens according to any one of claims 1 to 5, wherein w> 10 is satisfied.