JP2000258687A - Projection lens, and video enlarging and projecting system, video projector, rear projector and multivision system using projection lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a projection lens whose entire length is short, which secures long back focus though it is compact, by which even the periphery of an image plane is made bright and whose distortion aberration and transverse chromatic aberration are completely compensated by providing four lens groups, constituting the 2nd to 4th lens groups of two lenses, respectively, and making the lens satisfy a specified expression. SOLUTION: This projection lens is provided with the 1st lens group 1 having negative power, the 2nd lens group 2 having positive power, a 3rd lens group 3 having negative power and the 4th lens group 4 having positive power in order from a screen side. The 2nd to the 4th lens groups 2 to 4 are constituted at least two lenses, respectively. When it is assumed that the focal distance of the entire system of the projection lens is f0, the focal distances of the 1st to the 4th lens groups 1 to 4 are f1g to f4g, respectively, and a distance at the time of setting space from the rear end of the final lens to an image surface to all air is (bf), the projection lens satisfies relation expressed by expressions (1) -0.8<f1g/f0<-0.6, (2) 0.5<f2g/f0<0.7, (3) -0.7<f3g/f0<-0.4, (4) 0.7<f4g/bf<0.9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection lens, and more particularly to a projection lens for a projector for enlarging and projecting an image of a spatial light modulator on a screen and a projector using the same.

[0002]

2. Description of the Related Art As a method of obtaining a large-screen image, there is a method of forming an optical image according to a video signal on a spatial light modulator, irradiating the optical image with light, and enlarging and projecting the image on a screen by a projection lens. Are known. Recently, a projector using a liquid crystal panel as a spatial light modulator has been receiving attention. If a reflective liquid crystal panel is used as the spatial light modulator, the illumination light from the light source can be more effectively guided to the projection lens. There is a demand for small and lightweight projectors, mainly for meetings and presentations, which have high image quality and are easy to carry. Therefore, there is a demand for a projection lens for a projector that has good optical performance and can be made compact.

[0003] As a method of obtaining a color image, R, G,
A method of using three liquid crystal panels corresponding to the video signals of each color of B and synthesizing the images of the three liquid crystal panels using a dichroic prism, and a method of temporally converting the light from the light source to R, G, and B. There is known a method of dividing the data into two.

[0004]

In a projector using a prism, a large space is required between the lens and the spatial modulation element, so that a projection lens having a long back focus is required. Also, in a projector using a prism, since the incident angle with respect to the prism is highly dependent, the light incident at an angle other than the designed incident angle changes the transmittance, causing color unevenness and brightness unevenness on the screen. Will occur. Therefore, the projection lens needs to be telecentric.

[0005] In a projector for data display or graphic display in which performance around the screen is strictly required, it is important that there is no graphic distortion or color bleeding. Therefore, the distortion of the projection lens and the chromatic aberration of magnification are reduced. It must be well corrected. In these projectors, brightness around the screen is also required,
A peripheral light ratio of 70% or more is required.

[0006] These problems generally impede the realization of the miniaturization of the projection lens required for downsizing the set size of the projector.

Japanese Patent Application Laid-Open No. 228620/1990 discloses a projection lens in which back focus, telecentricity and distortion are corrected, but the problem is that the total length of the projection lens is too long for a small set. have.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems in the prior art. By appropriately setting the lens structure, the overall length is short and compact, while the back focus is long and the image is bright to the periphery of the screen. It is an object of the present invention to provide a projection lens capable of sufficiently correcting distortion, chromatic aberration of magnification and chromatic aberration of magnification and obtaining a high-quality image over the entire screen, and a projector using the same.

[0009]

In order to achieve the above object, a projection lens according to the present invention comprises a first lens unit having a negative power and a first lens unit having a positive power, which are arranged in this order from the screen side. A second lens group, a third lens group having a negative power, and a fourth lens group having a positive power, wherein each of the second, third, and fourth lens groups includes at least two lenses; The focal length of the entire projection lens system is f0,
The focal length of the first lens group is f1g, the focal length of the second lens group is f2g, the focal length of the third lens group is f3g, and the fourth lens group is f4g.
When the focal length of the lens group is f4g, and the air interval when all air from the rear end of the final lens to the image plane is bf, the following equation (2) is satisfied.

[0010]

(1) -0.8 <f1g / f0 <-0.6 (2) 0.5 <f2g / f0 <0.7 (3) -0.7 <f3g / f0 <-0.4 (4) 0.7 <f4g / bf <0.9 According to the configuration of the projection lens, the overall length is short and compact, the back focus is long, the telecentricity is satisfied, and the Petzval sum and the magnification are reduced. A projection lens with chromatic aberration corrected can be realized.

In the construction of the projection lens of the present invention, the first lens group is composed of one lens having concave surfaces on both sides, the second lens group is composed of two lenses, and the third lens group is composed of two lenses. It is preferable that the fourth lens group includes three lenses, and that the fourth lens group includes three lenses. According to this preferred example, astigmatism and chromatic aberration of magnification can be corrected.

In the above-described configuration of the projection lens according to the present invention, the second lens group includes a spherical lens having convex surfaces on both sides and a spherical lens having convex surfaces on both sides arranged in order from the screen side.
It is preferable that the fourth lens group includes one aspherical lens and two spherical lenses having low power, which are arranged in order from the screen side. According to this preferred example, spherical aberration can be better corrected by the aspherical surface of the second lens group, and distortion can be better corrected by the aspherical surface of the fourth lens group.

Further, in the configuration of the projection lens of the present invention, the half angle of view is 25 ° or more, and the F-number is 3.0.
It is preferably 0 or less. When the F-number is 3.0 or less, when a liquid crystal panel or a reflection-type mirror device is used as the spatial modulation element, the system can be made as bright as possible without a decrease in contrast, and the half angle of view is 25. If it is higher than the degree, the distance projected onto the screen can be further shortened, and a compact system can be obtained.

[0014] Further, an image enlargement projection system according to the present invention comprises a light source, a spatial light modulator illuminated by light emitted from the light source and forming an optical image,
And a projection unit for projecting an optical image on the spatial light modulator, wherein the projection lens of the present invention is used as the projection unit. According to the configuration of the image enlargement projection system, the optical image formed on the spatial light modulator illuminated by the light source can be enlarged and projected on the focus surface by the projection unit. In this case, since the projection lens of the present invention is used as the projection unit, the total length of the projection unit is short, and a compact image enlarged projection system can be realized.

The video projector according to the present invention comprises a light source, means for temporally limiting light from the light source to three colors of blue, green and red, and illumination by light emitted from the light source. Blue, green, and red that change with time
A spatial light modulator that forms an optical image corresponding to a color; and a projection unit that projects an optical image on the spatial light modulator, wherein the projection lens of the present invention is used as the projection unit. . According to the configuration of the video project, the light from the light source is temporally separated into three colors of blue, green and red by means for temporally restricting the light to three colors of blue, green and red. Illuminates the element. Three kinds of optical images of blue, green, and red are formed on the spatial light modulator in a time-divided manner, and are enlarged and projected by a projection unit. In this case, since the projection lens of the present invention is used as the projection means, an image which is bright and has little color blur or distortion can be obtained. In addition, since the entire length of the projection lens is short, a small and portable video can be obtained. A projector can be realized.

Further, the rear projector according to the present invention comprises a video projector, a mirror for bending light projected from the projection means in the video projector, and a transmission screen for projecting the projected light as an image. Wherein the video projector of the present invention is used as the video projector. According to the configuration of the rear projector, the image projected from the video projector is reflected by the mirror and is imaged on the transmission screen. In this case, since the video projector of the present invention is used as the video projector, the height of the set can be kept low, and a compact set can be realized.

Further, the configuration of the multi-vision system according to the present invention comprises a plurality of systems each comprising a video projector and a transmission screen for projecting light projected from the projection means in the video projector as a video, And a video dividing circuit for dividing the video project, wherein the video project of the present invention is used as the video project.
According to the configuration of the multi-vision system, the video signal is processed and divided by the video dividing circuit and sent to a plurality of video projectors. The image projected from the video projector is formed on a transmission screen. In this case, since the video projector of the present invention is used as a video projector, a set having a short depth can be realized.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described more specifically with reference to embodiments.

<First Embodiment> In the present invention,
By setting the aperture position relatively in front of the lens and adopting a configuration close to the front aperture, a lens configuration that can suppress the inclination angle of the principal ray while giving the principal ray at each angle of view telecentricity. Is to be realized.
In addition, the total length of the lens is shortened while suppressing the occurrence of distortion and chromatic aberration of magnification. Also,
In the first to third groups, a lens having a negative power is disposed at a position where the on-axis light beam is low, so that the Petzval sum is corrected. Although the total length of the projection lens can be shortened by shortening the distance between the first to third groups, the power of each group increases to maintain the Petzval sum, and it is difficult to correct aberrations. Becomes For this reason,
In the present invention, the second group includes two positive-power lenses including an aspheric surface. The fourth group has a large positive power, which is a source of distortion.
For this reason, in the present invention, the fourth group is composed of two lenses: an aspheric correction lens and a positive power spherical lens. The fourth group has a large positive power, and therefore becomes a source of distortion. For this reason, the fourth unit includes an aspheric correction lens and two spherical lenses having positive power.

Hereinafter, the projection lens according to the present embodiment will be described in more detail with reference to the drawings. FIG. 1 is an arrangement diagram showing a configuration of a projection lens according to the present embodiment.

As shown in FIG. 1, the projection lens according to the present embodiment has a first lens group 1, a second lens group 2, a third lens group 3, which are arranged in this order from the screen side. The fourth lens group 4 is provided.

The first lens group 1 has a strong negative power, and can greatly bounce an axial ray to secure a back focus. The first lens group 1 is
Since it has a strong negative power, the entrance pupil can be advanced to realize a large aperture efficiency. Furthermore, since the first lens group 1 has a strong negative power,
Petzval sum can be corrected. The first lens group 1 is composed of a single lens having concave surfaces on both sides.

The third lens group 3 has a strong negative power so that chromatic aberration of magnification can be corrected.
The third lens group 3 is composed of two cemented lenses (laminated lenses): a high-refractive-index, high-dispersion, negative-power lens and a low-dispersion, positive-power lens.

The strong negative power for correcting the chromatic aberration of magnification of the third lens group 3 causes the upper ray of the principal ray to be in an overcorrected state, so that the axial ray incident on the third lens group 3 is converted into convergent light. There is a need to. For this reason, the second lens group 2 in the present embodiment has a strong positive power so that axial rays incident on the third lens group 3 can be converged. Since the second lens group 2 has a strong positive power, it becomes difficult to correct aberrations as it is. For this reason, the second lens group 2 in the present embodiment includes one spherical lens having convex surfaces on both sides and one aspherical lens having convex surfaces on both sides, which are arranged in this order from the screen side. ing.

The fourth lens group 4 has a positive power in order to realize telecentricity. Since the fourth lens group 4 is arranged at a position where the principal ray is high, a large distortion occurs. For this reason, the fourth lens group 4 includes
It is composed of one aspherical lens with weak power for correcting distortion and two spherical lenses.

In the projection lens of this embodiment, the focal length of the entire projection lens system is f0, and the focal length of the first lens group 1 is f.
1g, the focal length of the second lens group is f2g, the focal length of the third lens group 3 is f3g, and the focal length of the fourth lens group 4 is f
4g, when the air gap from the rear end of the final lens to the image plane is all air, bf is satisfied, and the following expression (3) is satisfied.

[0027]

(1) -0.8 <f1g / f0 <-0.6 (2) 0.5 <f2g / f0 <0.7 (3) -0.7 <f3g / f0 <-0.4 (4) 0.7 <f4g / bf <0.9 The above equation (1) is an equation relating to the power of the first lens group 1. When f1g / f0 is -0.8 or less, the Petzval sum cannot be corrected. If f1g / f0 is -0.6 or more, distortion cannot be corrected.

The above equation (2) is an equation relating to the power of the second lens group 2. When f2g / f0 is 0.5 or less, it becomes impossible to correct spherical aberration. f2g /
When f0 is 0.7 or more, the upper ray of the principal ray jumps, and the overall length of the lens further increases.

The above equation (3) is an equation relating to the power of the third lens group 3. When f3g / f0 is equal to or less than -0.7, chromatic aberration of magnification cannot be corrected, and the back focus becomes short. When f3g / f0 is -0.4 or more, the upper ray of the principal ray jumps.

The above equation (4) is an equation relating to the ratio between the power of the fourth lens unit 4 and the back focus. f4g /
When bf is 0.7 or less, it becomes impossible to correct distortion and chromatic aberration of magnification. When f4g / bf is 0.9 or more, the overall length of the projection lens increases.

Since the projection lens of the present embodiment satisfies the relations of the above equations (1) to (4), it has a short overall length, a long back focus, and satisfies telecentricity. In addition, the Petzval sum and the chromatic aberration of magnification are corrected.

Hereinafter, the projection lens of the present embodiment will be described in more detail with reference to specific examples.

(Embodiment 1) In this embodiment, an F-number F _NO
= 3.0, focal length f = 31.6, magnification = 70, half angle of view ω = 26.4 °, the projection lens having the configuration shown in FIG. 1 satisfies the relations of the above expressions (1) to (4). By doing so, the overall length is short and compact, the back focus is long, the telecentricity is satisfied, and distortion and chromatic aberration of magnification are corrected.

In the configuration of the projection lens of FIG. 1, ri is the radius of curvature of each lens surface, and di is the lens thickness or the distance between lenses. These indications are the same in Example 2 below.

The following (Table 1) shows specific numerical values. In the following (Table 1), ni is the refractive index of each lens at d-line, νi
Is the Abbe number of each lens at the d-line. The aspherical shape is a rotationally symmetric aspherical surface expressed by the following (Equation 4), where X is the displacement amount from the lens vertex at the position of the radius distance h of the aperture from the optical axis of the lens.

[0036]

(Equation 4)

[0037]

[Table 1]

The aspherical coefficients of each surface are shown below. Aspherical surface coefficient of five surfaces A4 = 1.01583 × 10 ^-5 A6 = -3.21 300 × 10 ^-9 Aspherical surface coefficient of eleven surfaces A4 = 2.26401 × 10 ^-5 A6 = 3.88497 × 10 ^-8 A8 = 1.14345 × 10 ^-11 A10 = -1.40951 × 10 ^-13 FIGS. 2A, 2B, and 2C show the spherical aberration, astigmatism, and distortion of the projection lens of this embodiment.

(Embodiment 2) In this embodiment, the F number F _NO
= 3.0, focal length f = 31.58, magnification = 70, half angle of view ω = 26.9 °.
By satisfying the relationships (4) to (4), the overall length is short and compact, the back focus is long, the telecentricity is satisfied, and the distortion and the chromatic aberration of magnification are corrected. It was designed as In this case, as shown in FIG. 3, the fourth lens group 4 is different from the first embodiment in that the aspherical lens is disposed at the center, and the power balance of the bispherical lenses is reduced. It is better than 1.

The following Table 2 shows specific numerical values.

[0041]

[Table 2]

The aspherical coefficients of the respective surfaces are shown below. Aspherical surface coefficient of 5 surfaces A4 = 8.19577 × 10 ^-6 A6 = -1.05878 × 10 ^-8 Aspherical surface coefficient of 12 surfaces A4 = -6.50543 × 10 ^-6 A6 = 7.60597 × 10 ^-10 Aspherical surface coefficient of 13 surfaces A4 = 5.08987 × 10 ^-6 A6 = 9.37507 × 10 ^-9 A8 = -2.88443 × 10 ^-12 A10 = 1.9990 × 10 ^-14 FIGS. 4 (a), (b) and (c) show the spherical surface of the projection lens in this embodiment. It shows aberration, astigmatism, and distortion.

In the present embodiment, the half angle of view ω is 26.4 ° or 26.9 °, and the F-number F _NO is 3.0.
Although the projection lens of 0 has been described as an example, it is not necessarily limited to the projection lens having this configuration. If the F-number F _NO is 3.0 or less, the system can be made as bright as possible without a decrease in contrast when a liquid crystal panel or a reflective mirror device is used as the spatial modulation element, and the half angle of view is obtained. If ω is 25 ° or more, the projection distance on the screen can be further reduced, and a compact system can be obtained.

<Second Embodiment> FIG. 5 shows a second embodiment of the present invention.
FIG. 2 is a layout diagram showing a configuration of a video enlarged projection system according to the embodiment. As shown in FIG. 5, the image enlarging and projecting system according to the present embodiment includes a light source C, a spatial light modulator B illuminated with light emitted from the light source C and forming an optical image, and a spatial light modulator. It comprises a projection lens A for projecting an optical image on the element B. Here, as the projection lens A, the projection lens described in the first embodiment is used. In FIG. 3, P is a focus plane of an image projected by the image enlargement projection system.

According to the image enlargement projection system of the present embodiment, the optical image formed on the spatial light modulator B illuminated by the light source C can be enlarged and projected on the focus plane P by the projection lens A. In this case, since the projection lens described in the first embodiment is used as the projection lens A, the total length of the projection lens is short, and a compact image enlarged projection system can be realized.

<Third Embodiment> FIG. 6 shows a third embodiment of the present invention.
FIG. 2 is a layout diagram showing a configuration of a video projector according to the embodiment. As shown in FIG. 6, the video projector according to the present embodiment rotates the light source C and the R, G, and B filters to temporally convert the light from the light source C into three colors of blue, green, and red. D and a light source C
A spatial light modulator B that forms an optical image corresponding to three colors of blue, green, and red that change with time while being illuminated by light emitted from the light source, and projects an optical image on the spatial light modulator B And a projection lens A. here,
As the projection lens A, the projection lens described in the first embodiment is used.

According to the video projector of the present embodiment, the light from the light source C is temporally limited to three colors of blue, green and red by the means D for temporally restricting the light to three colors of blue, green and red. It is decomposed and illuminates the spatial light modulator B. Three kinds of optical images of blue, green and red are formed on the spatial light modulator B in a time-divided manner, and are enlarged and projected by the projection lens A. In this case, since the projection lens described in the first embodiment is used as the projection lens A, an image which is bright and has little color blur or distortion can be obtained, and the entire length of the projection lens is short. Therefore, a small and portable video projector can be realized.

<Fourth Embodiment> FIG. 7 shows a fourth embodiment of the present invention.
FIG. 15 is a layout diagram showing a configuration of a rear projector according to a fourth embodiment. As shown in FIG. 7, the rear projector in the present embodiment is a video projector G
And a mirror H for bending light projected from a projection lens in the video projector G, and a transmission screen I for projecting the projected light as an image. Here, as the video projector G,
The video projector described in the third embodiment is used. Note that, in FIG. 7, J is a housing that houses the rear projector.

According to the rear projector of the present embodiment, the image projected from the video projector G is reflected by the mirror H and is imaged on the transmission screen I. In this case, the third video projector G is used.
Since the video projector described in the embodiment is used, the height of the set can be kept low,
A compact set can be realized.

<Fifth Embodiment> FIG. 8 shows a fifth embodiment of the present invention.
1 is a configuration diagram of a multi-vision system according to an embodiment. As shown in FIG. 8, the multi-vision system according to the present embodiment includes a plurality of systems including a video projector G and a transmission screen I that projects light projected from a projection lens in the video projector G as an image, An image dividing circuit L for dividing an image. Here, as the video projector G, the video projector described in the third embodiment is used. In FIG. 6, K denotes a housing in which each system is accommodated.

According to the multi-vision system of this embodiment, the video signal is processed and divided by the video division circuit L and sent to a plurality of video projectors G. The image projected from the video projector G is formed on the transmission screen I. In this case, since the video projector described in the third embodiment is used as the video projector G, a set having a short depth can be realized.

[0052]

As described above, according to the present invention,
By setting the lens configuration appropriately, the overall length is short and compact, but the back focus is long, the image is bright to the periphery of the screen, distortion and chromatic aberration of magnification are sufficiently corrected, and a high-quality image is obtained over the entire screen. And a projection lens that can be used. Further, according to the present invention, by using such a projection lens, it is possible to compactly realize an image enlargement projection system, a video projector, a rear projector, and a multi-vision system capable of obtaining a bright and high-quality large-screen image. it can.

[Brief description of the drawings]

FIG. 1 is a layout diagram showing a configuration of a projection lens according to a first embodiment of the present invention.

FIG. 2A is Example 1 of the first embodiment of the present invention.
, A spherical aberration diagram of the projection lens, (b) an astigmatism diagram of the projection lens, and (c) a distortion aberration diagram of the projection lens

FIG. 3 is a layout diagram showing another configuration of the projection lens according to the first embodiment of the present invention.

FIG. 4A shows Example 2 of the first embodiment of the present invention.
, A spherical aberration diagram of the projection lens, (b) an astigmatism diagram of the projection lens, and (c) a distortion aberration diagram of the projection lens

FIG. 5 is a layout diagram showing a configuration of an image enlargement projection system according to a second embodiment of the present invention.

FIG. 6 is a layout diagram showing a configuration of a video projector according to a third embodiment of the present invention.

FIG. 7 is a layout diagram showing a configuration of a rear projector according to a fourth embodiment of the present invention.

FIG. 8 is a configuration diagram of a multi-vision system according to a fifth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st lens group 2 2nd lens group 3 3rd lens group 4 4th lens group A Projection lens B Spatial modulation element C Light source D Means which temporally limits to three colors of blue, green, and red G Video projector H Mirror I Transmissive screen J Case K Case L Image dividing circuit P Focus plane of projected image

Continued on the front page F term (reference) 2H087 KA06 LA01 NA02 PA07 PA18 PB08 QA03 QA07 QA19 QA21 QA25 QA34 QA41 QA45 RA05 RA12 RA13 RA41 5C058 EA01 EA12 EA13 EA32 EA54 9A001 JJ72 KK16

Claims (8)

[Claims] 1. A first lens group having a negative power, a second lens group having a positive power, a third lens group having a negative power, and a fourth lens having a positive power arranged in this order from the screen side. Wherein the second, third and fourth lens groups each comprise at least two lenses, the focal length of the entire projection lens system is f0, the focal length of the first lens group is f1g, and the second lens is The focal length of the group is f2g, the focal length of the third lens group is f3g, and the focal length of the fourth lens group is f
A projection lens satisfying the following expression (1), where bf is an air gap when all air from the rear end of the final lens to the image plane is bf. (1) -0.8 <f1g / f0 <-0.6 (2) 0.5 <f2g / f0 <0.7 (3) -0.7 <f3g / f0 <-0.4 (4) 0.7 <f4g / bf <0.9 2. The first lens group is composed of one lens having concave surfaces on both sides, the second lens group is composed of two lenses, the third lens group is composed of two cemented lenses, and the fourth lens is 2. The projection lens according to claim 1, wherein the group includes three lenses. 3. The second lens group includes a spherical lens having convex surfaces on both sides and an aspheric lens having convex surfaces on both sides, which are arranged in order from the screen side. ,
The projection lens according to claim 1, comprising one aspherical lens and two spherical lenses having low power, arranged in order from the screen side. 4. The projection lens according to claim 1, wherein a half angle of view is 25 ° or more, and an F number is 3.0 or less. 5. A light source, a spatial light modulator illuminated by light emitted from the light source and forming an optical image, and projection means for projecting an optical image on the spatial light modulator, An image enlargement projection system using the projection lens according to claim 1 as projection means. 6. A light source, and light from the light source is divided into blue, green, and red light.
Means for temporally limiting to color, and blue, green, and
5. A spatial light modulator for forming optical images corresponding to three colors of red, and a projection unit for projecting an optical image on the spatial light modulator, wherein the projection unit is used as the projection unit. Video project using a projection lens. 7. A rear projector comprising: a video projector, a mirror for bending light projected from projection means in the video projector, and a transmission screen for projecting the projected light as an image.
A rear projector, wherein the video projector according to claim 6 is used as the video projector. 8. A plurality of systems comprising a video project coup and a transmissive screen for projecting light projected from projection means in the video project coup as an image,
A multi-vision system comprising a video division circuit for dividing a video, wherein the video projection system according to claim 6 is used as the video projection system.