JP3337257B2 - Projection zoom lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection zoom lens used for a projection display device such as a liquid crystal projection device.

[0002]

2. Description of the Related Art Conventionally, as one of the image display devices, there is a projection type display device such as a liquid crystal projection device capable of obtaining a large screen relatively easily in a general household or the like.

In this liquid crystal projection device, as described in, for example, Japanese Patent Publication No. 4-35048, light of an illumination light source is converted into three primary colors of red (R), green (G) and blue (B) by a dichroic mirror. Separated into 3
Using a single liquid crystal display panel, light intensity modulation is performed based on a predetermined image signal for each of R, G, and B colors,
The image for each color of R, G, and B obtained by the light intensity modulation is added and synthesized by a dichroic mirror to form a color image, and the color image is projected on a screen by a projection lens. As a projection lens used in such a liquid crystal projection device, a zoom lens is used to obtain a screen of an arbitrary magnification.

In a liquid crystal projection device, since at least two mirrors such as a dichroic mirror or a reflection mirror are located between the projection lens and the liquid crystal display panel, a distance between the projection lens and the liquid crystal display panel, that is, a so-called back focus. Must be secured. A projection zoom lens in such a liquid crystal projection device is disclosed in, for example,
There is a configuration described in Japanese Patent No. 3215.

The projection zoom lens described in Japanese Patent Laid-Open No. 4-83215 has four lens groups, and a back focus is secured by specifying a focal length and a principal point interval of each lens group. are doing.

However, in the configuration described in Japanese Patent Application Laid-Open No. 4-83215, a projection angle of view of about 44 ° can be secured, but a back focus of only about 1.8 times the diagonal length of the screen can be secured. There are restrictions on the arrangement of the liquid crystal display panel and the like.

[0007]

As described above, in the conventional projection zoom lens, the value of the back focus is not sufficient, and further improvement is desired.

SUMMARY OF THE INVENTION An object of the present invention is to provide a projection zoom lens having good imaging performance and capable of obtaining a sufficiently large back focus as compared with the conventional one while maintaining the same projection angle of view as the conventional one. .

[0009]

A projection zoom lens according to the present invention is a projection zoom lens for projecting light emitted from an illumination light source and modulated by a light intensity modulating means onto a screen. A first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, having a positive refractive power The first lens unit and the fourth lens unit do not move, and the second lens unit moves toward the third lens unit during zooming from the wide-angle end to the telephoto end. , The third
The lens group is configured to first move toward the fourth lens group and then move along an arc-shaped trajectory toward the second lens group, and the fourth lens group has a negative curvature with a concave curvature toward the screen side. One lens group composed of a lens and a positive lens and having a negative refractive power, and the other lens group composed of a negative lens having a concave surface and having a large curvature and two positive lenses and having a positive refractive power, A projection zoom lens, which is sequentially arranged from the screen side with an interval, and satisfies the following conditional expression.

(1) 0.4 <| f ₂ | / fw <0.7 (2) 0.5 <e ₃ w / fw <0.8 (3) 2.0 <｛(n−1) / | R |｝ × | f _4a | <
2.8 where fw: focal length at the wide-angle end (the virtual lens position where the distance from the lens tip to the screen (hereinafter, referred to as projection distance) is ∞) f ₂ : focal length of the second lens group e ₃ w: distance between principal points of the third lens group and the fourth lens group at the wide-angle end n: refractive index of the negative lens of the other lens group in the fourth lens group R: negative of the other lens group in the fourth lens group The radius of curvature of the surface of the lens on the screen side, f _4a : the focal length of one lens group in the fourth lens group

[0011]

According to the present invention, the above-mentioned configuration secures a sufficiently long back focus as compared with the conventional one while maintaining the same projection angle of view as the conventional one, and maintains good imaging performance. For the sake of convenience, the reverse tracking, that is, the aberration on the light intensity modulation means will be described.

First, the conditional expression (1), 0.4 <| f ₂ | /
For fw <0.7, | f ₂ | / fw is the upper limit of 0.7
Above, that is, when the negative power of the second lens unit is weakened, the movement amount of the second lens unit in zooming is increased, which undesirably increases the size of the entire lens system. On the other hand, if the lower limit of the second lens group becomes 0.4 or less, that is, if the negative power of the second lens unit becomes strong, it is difficult to correct distortion, curvature of field at the wide-angle end, and higher-order spherical aberration particularly at the telephoto end. Is not preferred.

Also, 0.5 <e ₃ w / f in conditional expression (2)
When e < ₃ > w / fw exceeds the upper limit of 0.8 with respect to w <0.8, the negative power of one of the fourth lens units is increased, and higher-order aberrations are generated. It is not preferable because it is difficult to make a good correction over the entire magnification range. Conversely, if the lower limit is 0.5 or less, the negative power of this one lens unit will be weakened, and a sufficient back focus cannot be secured.

Furthermore, 2.0 <｛(n−) in conditional expression (3) is satisfied.
1) / | R |｝ × | f _4a | <2.8 is a conditional expression regarding aberration correction in the fourth lens group, and within the range of conditional expression (2), ｛(n−1) / | R | When｝ × | f _4a | exceeds the upper limit of 2.8, the negative power of one lens group and the other lens group in the fourth lens group is weakened, which is advantageous for aberration correction. It is not preferable because it leads to chemical conversion.
On the other hand, when the lower limit is 2.0 or less, the negative power of one lens group and the other lens group increases, the load on the positive lens in the other lens group increases, and coma aberration particularly in the entire zoom range. Correction becomes difficult, which is not preferable.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a projection zoom lens according to the present invention will be described below with reference to the drawings.

First, a projection apparatus to which a projection zoom lens is applied will be described with reference to FIG.

In FIG. 2, reference numeral 11 denotes a projection white light source which emits white light as an illumination light source. The white light source 11 has a parabolic reflector 11a and converges the light generated from the white light source 11 into parallel light. . In the optical path of the parallel light, two light separating dichroic mirrors 12 and 13 as light separating means are sequentially arranged. Of these, the light separating dichroic mirror 12 reflects, for example, blue light and transmits green and red light, and the light separating dichroic mirror 13 reflects, for example, green light and emits red light. Let through.

Then, the dichroic mirror for light separation 12
The blue light reflected by the liquid crystal panel is totally reflected by the reflection mirror 14, passes through a liquid crystal display panel 15 which is light intensity modulating means provided in an optical path, and receives an image signal applied to the liquid crystal display panel 15. , And further passes through two light combining dichroic mirrors 16 and 17 as light combining means. Of these, one dichroic mirror 16 for photosynthesis reflects, for example, green light and transmits blue light, and the other dichroic mirror 17 for photosynthesis reflects, for example, red light and emits blue and green light. Light is transmitted.

The green light reflected by the light separating dichroic mirror 13 passes through a liquid crystal display panel 18 which is a light intensity modulating means provided in an optical path, and an image added to the liquid crystal display panel 18 is provided. The light intensity is modulated based on the signal, reflected by one of the dichroic mirrors 16 for light synthesis, and further passed through the dichroic mirror 17 for the other light synthesis.

Furthermore, a dichroic mirror 13 for light separation
Is transmitted through a liquid crystal display panel 19, which is a light intensity modulating means provided in the optical path, is light intensity modulated based on an image signal applied to the liquid crystal display panel 19, and is reflected by a reflection mirror 20. After being totally reflected, the light is reflected by the dichroic mirror 17 for photosynthesis, and is combined with the green and blue lights from the dichroic mirror 16 for photosynthesis.

The light thus synthesized is
The image is projected as a color image on a screen (not shown) by the projection zoom lens 22.

In the above configuration, the light emitted from the white light source 11 is converged into parallel light by the parabolic reflector 11a, and the dichroic mirror for light separation provided on the optical path.
It is separated into three primary colors of blue, green and red by 12,13. Then, after the light intensity is modulated into a predetermined image for each color by the corresponding liquid crystal display panels 15, 18, and 19, the images are synthesized by the dichroic mirrors 16 and 17 for photosynthesis to form a color image. The image is projected on a screen (not shown) by the lens 22.

In a projection apparatus using such an additive three primary color configuration, at least two dichroic mirrors or reflections are provided between the rear end of the projection zoom lens 22 and the liquid crystal display panels 15, 18, and 19 for each color. Since the mirror is disposed, the projection zoom lens 22 is required to have a long back focus.

The construction of such a projection zoom lens 22 will be described with reference to FIGS. 1, 6 and 10 of the first to third embodiments.

As described with reference to FIG. 2, the projection zoom lens 22 irradiates light emitted from the white light source 11 for illumination and light intensity modulated by the liquid crystal display panels 15, 18, and 19 in FIG.
, A first lens group 31 having a positive refractive power and a second lens group having a negative refractive power, which are sequentially arranged along the optical axis 26 from the screen 25 side.
It comprises a lens group 32, a third lens group 33 having a positive refractive power, and a fourth lens group 34 having a positive refractive power.

The fourth lens group 34 includes one lens group 34a having a negative refractive power and a negative lens having a concave surface and a large curvature and having a negative refractive power on the screen 25 side.
The other lens group 34b, which is composed of a negative lens having a concave curvature on the side and two positive lenses and having a positive refractive power, is sequentially arranged from the screen 25 side with an interval therebetween.

The negative lens and the positive lens in one lens group 34a and the negative lens and the positive lens in the other lens group 34b are more preferably separated from each other for aberration correction. In consideration of the above, the air lens portion caused by the separation becomes very sensitive, and the air gap error and the eccentricity of the lens cause deterioration of the imaging performance. Therefore, it is preferable to use a cemented lens as shown in the figure.

FIG. 1 shows the state of the projection zoom lens 22 at the wide-angle end. When the magnification is changed from the wide-angle end to the telephoto end, as shown by arrows in FIG. The 31 and fourth lens groups 34 do not move, the second lens group 32 moves to the third lens group 33 side, and the third lens group 33 first moves to the fourth lens group 34 side, and then moves to the fourth lens group 34 side. 2
It is configured to move on an arc-shaped trajectory toward the lens group 32 side.

Hereinafter, with respect to these projection zoom lenses 22, 0.4 <| f ₂ | / fw <0.7 of conditional expression (1),
0.5 <e ₃ w / fw <0.8 in conditional expression (2) and 2.0 <{(n−1) / | R |} × in conditional expression (3)
A description will be given corresponding to the first to third embodiments in which the numerical values of the respective parts are determined so as to satisfy | f _4a | <2.8. In each embodiment, the projection distance is adjusted by moving the first lens group 31 along the optical axis 26. Each numerical value is a value when the projection distance is 3600. Here, f is the focal length, No. Is a number given to each lens surface from the left side in the figure, r is the radius of curvature of each lens surface, d is the lens thickness or lens surface interval, and nd and νd are the refractive index and Abbe number of each lens.

First, a first embodiment will be described.

This embodiment corresponds to the lens configuration shown in FIG.

Note that f = 11.3 to 155.5 to 21
3.4, FNo. : 5, 2w = 44.4 ° -31.6 °-
22.5 °.

[0033]

[Table 1] Virtual lens spacing db at the projection distance に お け る at the wide-angle end = db
1.409 And according to the numerical relationship, conditional expression (1),
The values in (2) and (3) are as follows, and all satisfy the conditional expressions (1), (2) and (3).

| F ₂ | /fw=0.498 e ₃ w / fw = 0.649 ｛(n−1) / | R |｝ × | f _4a | = 2.376 The projection distance 3600 in the first embodiment. The various aberrations (spherical aberration, astigmatism, distortion) on the liquid crystal display panel at the time of (1) are shown in FIG. 3 to FIG.
3, f = 155.5 and f = 213.4.

Next, a second embodiment will be described.

The second embodiment corresponds to the lens configuration shown in FIG.

Note that f = 11.3 to 155.5 to 21
3.4, FNo. : 5, 2w = 44.4 ° -31.6 °-
22.5 °.

[0038]

[Table 2] Virtual lens spacing db at the projection distance に お け る at the wide-angle end = db
1.421.

According to the numerical relationship, the conditional expression (1)
The values in (2) and (3) are as follows, and all satisfy the conditional expressions (1), (2) and (3).

| F ₂ | /fw=0.494 e ₃ w / fw = 0.636 ｛(n−1) / | R |｝ × | f _4a | = 2.342 The projection distance 3600 in the second embodiment. The various aberrations (spherical aberration, astigmatism, distortion) on the liquid crystal display panel at the time of (1) are shown in FIG. 7 through FIG.
3, f = 155.5 and f = 213.4.

Next, a third embodiment will be described.

This embodiment corresponds to the lens configuration shown in FIG.

Note that f = 11.3 to 155.5 to 21
3.4, FNo. : 5, 2w = 44.4 ° -31.6 °-
22.5 °.

[0044]

[Table 3] Virtual lens spacing db at the projection distance に お け る at the wide-angle end = db
1.382.

According to the numerical relationship, the conditional expression (1)
The values in (2) and (3) are as follows, and all satisfy the conditional expressions (1), (2) and (3).

| F ₂ | / fw = 0.491 e ₃ w / fw = 0.658 ｛(n−1) / | R |｝ × | f _4a | = 2.490 The projection distance 3600 in the third embodiment. The various aberrations (spherical aberration, astigmatism, distortion) on the liquid crystal display panel at the time of (1) are shown by the focal length f = 11 according to FIGS.
3.3, f = 155.5, and f = 213.4 are shown.

Here, in each embodiment, the conditional expression (1)
Since each of (2) and (3) is satisfied, various aberrations are corrected in a well-balanced manner.

Further, according to each of the above embodiments, the angle of view at the wide-angle end is about 44 °, which is the same as the conventional angle of view, and the back focus is 2.2, which is the diagonal length of the screen.
Times, and a sufficient back focus can be obtained as compared with the conventional 1.8 times.

[0049]

According to the projection zoom lens of the present invention,
It is possible to obtain a projection zoom lens with good imaging performance having a back focus of 2.2 times or more the screen diagonal length while securing the same angle of view as the conventional one.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a first embodiment of a projection zoom lens according to the present invention at the wide-angle end.

FIG. 2 is a configuration diagram of a projection device using the same projection zoom lens.

FIG. 3 shows a projection distance 3600, f = in the first embodiment.
It is an aberration curve figure on the liquid crystal display panel at the time of 113.3.

FIG. 4 shows a projection distance 3600, f = in the first embodiment.
It is an aberration curve figure on the liquid crystal display panel at the time of 155.5.

FIG. 5 is a projection distance 3600, f = in the first embodiment.
It is an aberration curve figure on the liquid crystal display panel at the time of 213.4.

FIG. 6 is an explanatory diagram of a lens at a wide-angle end according to the second embodiment.

FIG. 7 shows a projection distance 3600, f = in the second embodiment.
It is an aberration curve figure on the liquid crystal display panel at the time of 113.3.

FIG. 8 shows a projection distance 3600, f = in the second embodiment.
It is an aberration curve figure on the liquid crystal display panel at the time of 155.5.

FIG. 9 shows a projection distance 3600, f = in the second embodiment.
It is an aberration curve figure on the liquid crystal display panel at the time of 213.4.

FIG. 10 is an explanatory diagram of a lens at a wide-angle end according to the third embodiment.

FIG. 11 is a projection distance 3600, f according to the third embodiment.
FIG. 11 is an aberration curve diagram on the liquid crystal display panel when = 113.3.

FIG. 12 is a projection distance 3600, f according to the third embodiment.
FIG. 10 is an aberration curve diagram on the liquid crystal display panel when = 155.5.

FIG. 13 is a projection distance 3600, f according to the third embodiment.
FIG. 14 is an aberration curve diagram on the liquid crystal display panel when = 213.4.

[Explanation of symbols]

 11 White light source as illumination light source 15, 18, 19 Liquid crystal display panel as light intensity modulation means 22 Projection zoom lens 25 Screen 31 First lens group 32 Second lens group 33 Third lens group 34 Fourth lens group 34a One side Lens group 34b the other lens group

Continuation of front page (56) References JP-A-4-191811 (JP, A) JP-A-1-309017 (JP, A) JP-A-62-196614 (JP, A) JP-A-63-8620 (JP, A) JP-A-63-285511 (JP, A) JP-A-63-8819 (JP, A) JP-A-61-249016 (JP, A) JP-A-61-172110 (JP, A) 61-138913 (JP, A) JP-A-61-126515 (JP, A) JP-A-60-6914 (JP, A) JP-A-56-42208 (JP, A) JP-A-55-161207 (JP, A) A) JP-A-52-56947 (JP, A) JP-A-51-2439 (JP, A) JP-A-48-82840 (JP, A) JP-A-48-81545 (JP, A) JP-A-79653 (JP, A) JP-A-48-76554 (JP, A) JP-A-47-45641 (JP, A) JP-A-62-173423 (JP, A) JP-A-61-296321 (JP, A) JP-A-61-296319 (JP, A) JP-A-61-296320 (JP, A) JP-A-61-296318 (JP, A) JP-A-62-296319 266510 (JP, A) Japanese Utility Model Sho 62-68113 (JP, U) Japanese Patent Publication 48-32388 (JP, B1) Japanese Patent Publication 43-9276 (JP, B1) Japanese Patent Publication 42-14982 (JP, B1) (58) Field surveyed (Int. Cl. ⁷ , DB name) G02B 15/16

Claims (1)

(57) [Claims] 1. A projection zoom lens for projecting light, which is emitted from an illumination light source and modulated by a light intensity modulating means, onto a screen, wherein the positive zoom lens is sequentially arranged along the optical axis from the screen side. A first lens group having a refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power. From the wide-angle end to the telephoto end, In zooming, the first lens group and the fourth lens group do not move, the second lens group moves toward the third lens group, and the third lens group starts with the fourth lens group. After moving toward the second lens group side, the fourth lens group is constituted by a negative lens and a positive lens having a concave curvature with a large concave to the screen side. One with power Lens group, and the other lens group having a negative refractive power and two positive lenses concave on the screen side and having a positive refractive power are sequentially arranged from the screen side with an interval therebetween, A projection zoom lens characterized by satisfying the following conditional expression. (1) 0.4 <| f ₂ | / fw <0.7 (2) 0.5 <e ₃ w / fw <0.8 (3) 2.0 <｛(n−1) / | R | ｝ × | f _4a | <
2.8 where fw: focal length at the wide-angle end (the virtual lens position where the distance from the lens tip to the screen (hereinafter, referred to as projection distance) is ∞) f ₂ : focal length of the second lens group e ₃ w: distance between principal points of the third lens group and the fourth lens group at the wide-angle end n: refractive index of the negative lens of the other lens group in the fourth lens group R: negative of the other lens group in the fourth lens group The radius of curvature f _4a of the surface of the lens on the screen side is the focal length of one lens group in the fourth lens group.