JP3450281B2 - Projection zoom lens for LCD projector - 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 for a liquid crystal projector, and more particularly to a three-plate type projection zoom lens for a liquid crystal projector with improved chromatic aberration of magnification.

[0002]

2. Description of the Related Art Generally, in a three-plate type liquid crystal projector,
The liquid crystal panel for each color is illuminated by the light from the light source separated into three colors of R (red), G (green), and B (blue), and each image is combined by a dichroic mirror or a cross dichroic prism (XDP). Then, a method of enlarging and projecting on a projection surface with a projection lens is used. As a projection zoom lens used in a liquid crystal projector using such a liquid crystal panel, a long back focus is required for inserting a color synthesizing optical system. Furthermore, in order to obtain a large projection image at a short projection distance, it is necessary to widen the angle of the projection zoom lens, and in order to project the image displayed on the rectangular liquid crystal panel in a rectangular shape and without distortion, distortion (distortion aberration) ) Is required to be good.
Conventionally, as a wide-angle lens having a long back focus, a retrofocus type lens used as a wide-angle lens for a single-lens reflex camera is known.

[0003]

However, since the retrofocus type lens used in such a conventional single-lens reflex camera has a large emission angle and the luminous flux is not telecentric, it is used in a color liquid crystal projector. When it is used, there is a problem that color unevenness occurs in a region distant from the image optical axis projected on the projection surface. An object of the present invention is to solve the above-mentioned problems of the conventional example, and an object thereof is to make a luminous flux as telecentric as possible in a projection zoom lens for a liquid crystal projector so that chromatic aberration of magnification causes a liquid crystal panel screen. Is to improve the short-wavelength off-axis chromatic aberration in the high angle-of-view region in order to fit within one pixel.

[0004]

In order to achieve the above object, according to the present invention, there is provided a first lens, which is a positive lens, arranged in order from a projection surface, and a meniscus negative lens having a convex surface facing the projection surface. A certain second lens, a third lens that is a negative lens, a fourth lens that is a positive lens, a fifth lens that is a positive lens, a sixth lens that is a negative lens, and a meniscus negative lens that has a convex surface facing the projection surface. 7 lenses, an 8th lens that is a negative lens, a 9th lens that is a positive lens, a 10th lens that is a positive lens, an 11th lens that is a negative lens, and a 12th lens that is a final lens that is a positive lens. 5
A projection zoom lens for a liquid crystal projector in which a lens and a sixth lens, an eighth lens and a ninth lens, and an eleventh lens and a twelfth lens are cemented lenses, respectively, at a projection magnification of 66.67 times. The angle β12 of the paraxial ray immediately after the j-th lens is normalized by setting the angle β12 of the paraxial ray immediately after the twelfth lens to be 1.0, and βb is the Abbe number of the k-th lens glass material. Then, (1) β3 <-1.2 (2) β6> +0.5 (3) ν2, ν3> 50 (4) ν4, ν6 <32 (5) ν9, ν10> 50 (6) ν12 <26 Provided is a projection zoom lens for a liquid crystal projector, which satisfies the condition.

It is preferable that the cemented lens composed of the eleventh lens and the twelfth lens is formed as a color-extracting lens.

Further preferably, the back focus section is provided with a cross dichroic prism.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of a projection zoom lens group and an XDP of the present invention. The lens L1 is a positive lens, the lens L2 is a meniscus negative lens having a convex surface facing the projection surface, and the lens L3 is a negative lens in order from the projection surface 1 side.
The lens L4 is a positive lens, the lenses L5 and L6 are positive and negative cemented lenses, the lens L7 is a negative meniscus lens with a convex surface facing the projection surface, the lenses L8 and L9 are negative and positive cemented lenses, and the lens L10 is positive. The lens, the lens L11 and the lens L12 are composed of a negative and positive cemented lens and an XDP2 in this order.

Here, the lens L1 and the lens L2 constitute a first group, and hereinafter, the lens L3 is the second group, the lens L4 is the third group, the lenses L5 and L6 are the fourth group, and the lens L7 is the fifth group. The lens configuration includes a group L9, a lens L8 as a sixth group, a lens L9 as a seventh group, a lens L10 as an eighth group, and lenses L11 and L12 as a ninth group. Further, the lens system according to the present invention is divided into an auxiliary portion and a main portion for the sake of convenience. The lenses L1 to L4 are auxiliary parts, and the lenses L5 to L12 are main parts. The auxiliary section has a negative power as a whole to spread the light flux, while the main section has a positive power as a whole to converge the light flux. (Not shown). In this way, the long back focus required for projection zoom lenses for liquid crystal projectors is realized. It also plays the role of making the luminous flux of the main part as telecentric as possible. The main part plays an image forming function as a lens, and plays a role of aberration correction as a whole system in cooperation with the auxiliary part. The XDP has a role of illuminating the liquid crystal panel for each color by the light from the light source separated into R, G, and B colors, and synthesizing the respective images to guide them to the projection lens.

In each of the above lenses, the angle β12 of the paraxial ray immediately after the final lens L12 of the paraxial ray immediately after the j-th lens at a projection magnification of 66.67 is normalized to 1.0. When the angle is βj and the Abbe number of the k-th lens glass material is νk, the following six conditions are designed. First, the condition (1) is β3 <-1.2.
That is, the negative power up to the lens L3 is defined. It is difficult to secure the back focus unless the lens L3, that is, the surface number R6, which will be described later, has a certain negative power or more. In the case of this lens, β3 is −
1.2 is more positive, that is, the negative power is −
If the absolute value becomes smaller than 1.2, it becomes difficult to secure the required long back focus.

Next, the condition (2) is to set β6> +0.5, which defines the power up to the lens L6. Up to the lens L3, the negative power defined by the condition (1) is prepared and the back focus condition is adjusted, but this also causes a large negative distortion. Originally lens L1
In order to prepare for the negative distortion aberration that is strongly generated in the lens L2 and the lens L3 by generating positive distortion aberration in advance, this is not enough. In order to correct this residual distortion, the positive lens of the lens L4 and the cemented lens of the lens L5 and the lens L6 work effectively.

The lens L1, the lens L4, the cemented lens of the lens L5 and the lens L6, and the positive powers of the three groups spaced apart are required for all angles of view such as a low angle of view, an intermediate angle of view, and a high angle of view. This is because the distortion is well corrected in good balance. It is necessary that the power up to the lens L5 and the lens L6 has a positive power above a certain level against the negative power up to the lens L3. Condition (2) defines this. That is, β6 needs to be larger than +0.5. If it is smaller than this, the distortion cannot be corrected well, or the size of the entire lens becomes too large.

Next, the condition (3) is ν2, ν3> 50
And the Abbe numbers of the glass materials of the lenses L2 and L3 are defined. The negative lenses of the lenses L2 and L3 are necessary to secure the back focus as described above. However, when β immediately after the lens L3 is examined by wavelength, β of short wavelength (β short) is long wavelength. It is always smaller than β (β length), that is, the sign is negative and the absolute value is large. The absolute value of the difference [| βshort−βlength |] increases as the Abbe numbers of the lenses L1 and L2 decrease. Therefore, the lens L2,
To specify the Abbe number of L3 to be larger than a certain value,
This is important for suppressing overcorrection of chromatic aberration that occurs inevitably immediately after the lens L3 to a certain value or less. conditions
(3) defines the Abbe numbers of the lenses L2 and L3 to be 50 or more. When it is 50 or less, correction of chromatic aberration occurring immediately after the lens L3 becomes excessive, and it becomes difficult to balance aberrations as a whole.

Next, the condition (4) is ν4, ν6 <32
And the Abbe numbers of the lenses L4 and L6 are defined. First, although the lens L4 is a positive lens, its Abbe number is set to 32 or less, and an upper limit is set to regulate the Abbe number to a certain value or less. Normally, the positive power in the lens is
The chromatic aberration is corrected by increasing the Abbe number and decreasing the Abbe number for negative power, but the reverse provisions are specified. This is done in order to minimize the chromatic aberration of off-axis magnification.
This is for recovering the image height of the short wavelength which is too small due to the strong negative power of 2 and L3. The cemented lens of the lens L5 and the lens L6 has a positive total power, and the negative lens L6 defines its Abbe number to be 32 or less in order to correct chromatic aberration to the over side. If it is more than that, chromatic aberration cannot be corrected to the over side.

Next, the condition (5) is ν9, ν10> 5
0, which is the lens L that is the positive lens of the main part.
9, the Abbe number of the lens L10 is specified. These form the main part of the positive power of the present lens. Naturally, the Abbe number should be as large as possible and the occurrence of chromatic aberration should be minimized. Therefore, the Abbe number is specified to be larger than 50. If it is smaller than this, chromatic aberration is excessively generated, and the chromatic aberration balance of the entire system is lost.

The condition (6) is to satisfy ν12 <26, which is the main condition of the present invention. Up to the above condition (5), conventionally known so-called conventional means, but it is possible to perform color correction up to the axial and off-axis intermediate portions as described above, but with short off-axis high field angles. The wavelength is overcorrected, and the size of the short-wavelength image becomes too large. Therefore, the Abbe number of the positive lens of the lens L12 is defined as in condition (6). That is, the lens L12 is a positive lens and naturally has a positive power, but by defining as in the condition (6), the positive refracting power in the short wavelength region is made excessively larger than usual, and a short wavelength image is formed. The size was intentionally reduced to improve the chromatic aberration balance of the entire system at high angles of view even in the short wavelength region. In particular, the lens L11 and the lens L12 are cemented lenses, the combination thereof is not an achromatic type but a color-developing type, and the power of the lens L12 alone is further strengthened than the power allowed by the single lens to reduce the size of the short wavelength image. The degree is getting stronger. Abbe number of lens L12 is a condition (6)
If it is smaller, the effect of the present invention will not be sufficiently exhibited.

As described above, the lens structure as shown in FIG. 1 and the various conditions such as the condition (1) to the condition (6) are satisfied, so that a large back focus is obtained and
A lens system in which DP can be installed and chromatic aberration of magnification is well corrected can be realized. Therefore, to summarize the role of each of the above conditions, first, a long back focus required by the condition (1) was made possible. Next, condition (2)
Distortion aberration is well balanced by. conditions
By (3), it is possible to prevent overcorrection of chromatic aberration,
Condition (4) and condition (5) make it possible to balance off-axis chromatic aberration and on-axis chromatic aberration.

Further, by the condition (6), the Abbe number of the lens L12 is kept small, and the lens L11 and the lens L1 are
2 is a cemented lens, and the combination thereof is colored, whereby the degree of the lens L12 is further strengthened and the size of the image of short wavelength is reduced. However, this also causes a large amount of axial chromatic aberration to be undercorrected on the under side, so ν6 of condition (4), condition (5), and the balance between the glass material selection of lenses L7 and L8 and power distribution, etc. This achieves the overall aberration balance.

As described above, by adding the condition (6) in addition to the conditions (1) to (5), the positive refracting power particularly in the short wavelength region becomes larger than usual, and the image size at the short wavelength is increased. The liquid crystal projector has a high resolution over the entire screen, and as a result, it is possible to satisfactorily correct aberration balance in the entire system, especially off-axis chromatic aberration at short wavelengths in the high field angle range. It has become possible to provide a projection zoom lens for use in

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 2 is a cross-sectional view showing the surface number of the projection lens according to the embodiment of the present invention, and the thickness or surface interval of the lens. There are 1 to 24 surface numbers, each R1
Is represented by R24. Particularly, the 12th surface (R12) represents the diaphragm surface. The lens thickness or the surface distance is represented by D1 to D23. Table 1 shows design values of radius of curvature R of each surface, lens thickness or surface distance D, refractive index n of glass material, Abbe number ν, effective radius H of lens in order to satisfy the above conditions (1) to (6). It is a table.

[0020]

[Table 1]

Further, Table 2 shows that f = 35.07 to 41.82, F
Number Fno = 1: 2.3 to 1: 2.7, (magnification) MAG =-
0.015, If the diaphragm surface is 12 surfaces, it shows the relationship between the focal length and the lens spacing that changes due to zooming. The surfaces R23 to R24 in this embodiment are XDP, and the liquid crystal panel size is 0.9 inch. In the above embodiment, 45
It is designed with the second wavelength as a reference wavelength for three wavelengths of 0 nm, 550 nm, and 610 nm.

[0022]

[Table 2]

3A and 3B are aberration diagrams of the projection lens at the second wavelength of the present invention. FIG. 3A shows spherical aberration, FIG. 3B shows astigmatism, and FIG. 3C shows distortion aberration. Therefore, it can be said that the projection lens of the present invention satisfactorily corrects the aberration. Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments and can be appropriately modified without departing from the scope of the present invention. . For example, instead of XDP, two sets of two right-angled triangular prisms may be attached to each other, and the three primary colors may be combined.

[0024]

As described above, the projection zoom lens for a liquid crystal projector of the present invention is composed of 12 elements in 9 groups, and the normalized angle of the paraxial ray immediately after the lens at a predetermined position and the glass material Since the Abbe number is designed so as to satisfy the specified condition, it is possible to excellently correct the off-axis chromatic aberration of the projection zoom lens for the liquid crystal projector, especially at a short wavelength in a high angle field. Also, a long back focus can be secured.

[Brief description of drawings]

FIG. 1 is a sectional view of a projection zoom lens for a liquid crystal projector according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing the surface number of the projection lens of the embodiment of the present invention, and the thickness or surface interval of the lens.

FIG. 3 is an aberration diagram of the projection lens of the present invention.

[Explanation of symbols]

1 Projection plane 2 Cross dichroic prism (XDP) D1 to D23 Lens thickness or surface spacing L1 to L12 lenses R1 to R24 surface number

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-7-134244 (JP, A) JP-A-11-101940 (JP, A) JP-A-2000-137165 (JP, A) JP-A-2000-19400 ( JP, A) JP 11-95098 (JP, A) JP 2000-66098 (JP, A) JP 11-231215 (JP, A) JP 2-40607 (JP, A) JP 2000 -98222 (JP, A) JP-A-9-318876 (JP, A) JP-A-4-335610 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02B 9/00- 17/08 G02B 21/02-21/04 G02B 25/00-25/04

Claims (3)

(57) [Claims] 1. A first lens, which is a positive lens, arranged in order from the projection surface, a second lens which is a negative meniscus lens having a convex surface facing the projection surface, a third lens which is a negative lens, and a positive lens. 4 lenses, 5th lens which is a positive lens,
The sixth lens, which is a negative lens, the seventh lens, which is a meniscus negative lens with a convex surface facing the projection surface, and the eighth lens, which is a negative lens
A fifth lens, a ninth lens that is a positive lens, a tenth lens that is a positive lens, an eleventh lens that is a negative lens, and a twelfth lens that is a final lens that is a positive lens. 8 lens and 9th lens, and
In a projection zoom lens for a liquid crystal projector, wherein the eleventh lens and the twelfth lens are respectively cemented lenses, a paraxial ray immediately after the j-th lens at a projection magnification of 66.67 times, immediately after the twelfth lens. When the angle β12 of the paraxial ray of is normalized to be βj and the Abbe number of the k-th lens glass material is νk, (1) β3 <-1.2 (2) β6> +0 A projection zoom lens for a liquid crystal projector, which satisfies the following conditions: 5 (3) ν2, ν3> 50 (4) ν4, ν6 <32 (5) ν9, ν10> 50 (6) ν12 <26. 2. The projection zoom lens for a liquid crystal projector according to claim 1, wherein a cemented lens formed by the eleventh lens and the twelfth lens is formed as a color display. 3. The projection zoom lens for a liquid crystal projector according to claim 1, wherein the back focus portion is provided with a cross dichroic prism.