WO2008015938A1

WO2008015938A1 - Wide-angle lens for projection and projector with the same

Info

Publication number: WO2008015938A1
Application number: PCT/JP2007/064569
Authority: WO
Inventors: Takeshi Kitakata; Takahiro Sugiyama
Original assignee: Brother Kogyo Kabushiki Kaisha
Priority date: 2006-08-02
Filing date: 2007-07-25
Publication date: 2008-02-07
Also published as: JP2008039877A

Abstract

A wide-angle lens for projection, having the brightness of an aperture ratio of about 1:4.0 and a projection angle of not less than 120˚. The wide-angle lens has a first lens group (G1) and a second lens group (G2), arranged in that order from the projection surface side. The first lens group (G1) is constructed from three negative lenses and one joint lens of a negative lens and a positive lens, and the first lens group (G1) has negative power. The second lens group (G2) is constructed from one negative lens, three positive lenses, one joint lens of a negative lens and a positive lens, and one joint lens of two positive lenses and a negative lens, and the second lens group (G2) has positive power. The first lens group (G1) includes at least one aspheric lens. Also, the wide-angle lens satisfies the following conditional expression (1): 0.3 ≤ |F1/F2| ≤ 1.3, ...(1) where F1 is the composite focal length of the first lens group and F2 is the composite focal length of the second lens group.

Description

Specification

Wide angle lens for projection and projector provided with the same

Technical field

The present invention relates to a wide-angle lens used for a projection optical system and a projector equipped with the same.

Background art

[0002] Conventionally, various types of projection optical systems have been proposed. However, in many cases, the projection distance is around lm, and the projection angle is at most around 100 °.

[0003] In a projection optical system with a projection angle of around 100 °, the lens design is relatively easy. However, when the projection distance force is around Sim, a relatively large space is required for installing the projection optical system. Required.

However, in order to reduce the projection distance and obtain a projection image having an appropriate size, the projection angle of the projection lens must be large. That is, a wide-angle projection lens is required. This complicates the configuration of the projection lens and requires advanced lens design technology.

[0005] Further, Patent Document 1 below describes a wide-angle lens with a long back focus.

However, this lens cannot make the projection angle sufficiently large (for example, 120 ° or more).

Patent Document 1: Japanese Unexamined Patent Publication No. 2003-215448

Disclosure of the invention

Problems to be solved by the invention

The present invention has been made in view of such a situation. An object of the present invention is to provide a projection wide-angle lens having a brightness of about an aperture ratio of about 1: 4.0 and a projection angle of 120 ° or more, and a projector using the same.

Means for solving the problem

[0007] In the wide-angle lens according to the present invention, the first lens group and the second lens in order from the projection surface side. A group is arranged. The first lens group includes three negative lenses and one negative lens and one cemented lens obtained by cementing one positive lens, and has negative power. The second lens group includes one negative lens, three positive lenses, one negative lens and one positive lens cemented lens, two positive lenses and one negative lens. It has a positive power and is composed of a single cemented lens. The first lens group includes at least one aspheric lens. The wide-angle lens of the present invention further satisfies the following conditional expression (1).

0.3≤ I F / ¥

1 2 I ≤1. 3 (1)

Where F is the composite focal length of the first lens unit

F: Composite focal length of the second lens group

2

[0008] The wide-angle lens according to the present invention may further satisfy the following conditional expression (2):

2. 0≤F / F≤7. 0 (2)

b

F: Composite back focus of the first lens group and the second lens group

b

F: Composite focal length of the first lens group and the second lens group

The wide-angle lens according to the present invention can further satisfy the following conditional expression (3):

1. 5≤L / F≤6. 0 (3)

L: Air distance between the first lens group and the second lens group

F: Composite focal length of the first lens group and the second lens group

[0010] A projector according to the present invention includes a projection wide-angle lens having any one of the above-described configurations.

[0011] Each condition described above will be described below.

Conditional expression (1) is for obtaining a wide-angle projection lens having a projection angle of 120 ° or more, and for obtaining a required back focus by making the lens system a retrofocus type.

[0013] Now, if I F / F I in conditional expression (1) is larger than the upper limit of 1.3,

1 2

The composite focal length is too large. Then, in order to obtain a projection angle of 120 ° or more for a retrofocus lens, the entire lens system becomes very large. The product value will be significantly reduced.

[0014] Also, | F / F is lower limit 0.

When the value is smaller than 1 2 I 3, it is advantageous to obtain a projection angle of 120 °, but the combined focal length force of the first lens group becomes too small and the positive spherical aberration generated in the first lens group. The amount of coma becomes too large, which is not preferable.

Conditional expression (2) is a condition for obtaining a required back focus. In order to secure a sufficient amount of light for the subject projected in the projection optical system, it is necessary to illuminate the subject appropriately. This condition is to secure an air space that can be inserted with an illumination optical system to achieve the above-mentioned purpose.

[0016] Now, when the F / F in the conditional expression (2) is smaller than the lower limit of 2.0, insert the illumination optical system. B

This is not preferable because the air interval is too small and the illumination optical system cannot be inserted.

[0017] Also, when F / F is larger than the upper limit of 7.0, the space for inserting the illumination optical system b

Although the air gap can be secured sufficiently, the focal length of the first lens unit is set to be very small in relation to conditional expression (1), resulting in an increase in spherical aberration and coma.

Conditional expression (3) is a condition for attempting to secure an air gap between the first lens group and the second lens group for inserting a reflection mirror for bending the projection optical system.

[0019] Now, when the L / F of the conditional expression (3) is smaller than the lower limit of 1.5, the air interval becomes too small to insert the reflecting mirror.

[0020] When the L / F is larger than the upper limit of 6.0, the air space for inserting the reflecting mirror can be secured, but the projection optical system becomes too large and is generated in the first lens group. This is preferable because the chromatic aberration of magnification is increased.

The invention's effect

[0021] According to the invention of claim 1, a wide-angle lens used in a projection optical system, having a brightness of an aperture ratio of about 1: 4.0 and capable of a projection angle of 120 ° or more, and It is possible to provide a projector using this.

[0022] According to the invention of claim 2, by adopting conditional expression (2), a long synthetic back focus can be secured, and the illumination optical system can be easily inserted. Force, spherical aberration, An increase in coma aberration can be suppressed.

[0023] According to the invention of claim 3, by adopting conditional expression (3), it is possible to ensure a long air gap between the first lens group and the second lens group, and a reflecting mirror is provided at this gap. It becomes easy to insert the projection optical system, and the projection optical system can be bent. Moreover, it is possible to prevent the projection optical system from becoming too large, and to control the increase in chromatic aberration of magnification that occurs in the first lens group.

[0024] According to the projector of the present invention, the projection angle can be set to 120 ° or more, for example. As a result, a high-magnification image can be projected, and a large image can be projected even at a short projection distance.

BEST MODE FOR CARRYING OUT THE INVENTION

[0025] Embodiments of wide-angle lenses according to the present invention will be described based on Examples;! First, the lens configurations in Examples 1 to 3 are shown in FIGS. 1, 3, and 5, respectively. In the following, a configuration common to these embodiments will be described first, and then numerical examples in each embodiment will be described.

The wide-angle lens in each embodiment is configured by arranging a first lens group G and a second lens group G in order from the projection plane S side (see FIGS. 1, 3, and 5).

1 2

[0027] The first lens group G includes three negative lenses (see R to R in the figure) and one negative lens (R in the figure).

1 1 6

To R) and one positive lens (see R to R in the figure) cemented

7 8 8 9

It has a negative power.

7 9

[0028] The second lens group G includes one negative lens (see R to R in the figure) and three positive lenses (in the figure).

2 10 11

R to R, R to R, and R to R) and one negative lens (see R to R in the figure)

13 14 22 23 24 25 15 16 and one positive lens (see R to R in the figure), one cemented lens (R to R in the figure)

16 17 15

R), 2 positive lenses (see R to R and R to R in the figure) and 1 negative lens (

17 18 19 20 21

Consists of a single cemented lens (see R to R in the figure) cemented with R to R in the figure)

19 20 18 21

Thus, a so-called retrofocus type lens configuration having positive power is obtained.

The first lens group G includes at least one aspheric lens (R to R in the figure).

1 1 2 [0030] In FIG. 1, FIG. 3 and FIG. 5, symbol P denotes an illumination optical system prism, symbol LCD denotes an image element, and symbol GL denotes a protective glass for the image element. In the figure, R is the light intensity control. It is a dummy surface for clauses.

[0031] The wide-angle lens in each embodiment can be used as a projection lens of a projector. Here, the projector is capable of optically projecting an image on a projection surface such as a screen surface and includes not only a liquid crystal projector but also various projectors such as a DLP projector.

Example 1

FIG. 2 shows various aberration diagrams in the lens configuration of Example 1 (FIG. 1).

In the various aberration diagrams of FIG. 2, chromatic aberrations G, B, and R represented by spherical aberration are aberrations for green, blue, and red wavelengths, respectively, and astigmatism S is sagittal. ,

M is meridional.

In addition, Table 1 below shows design values and obtained characteristics of the lens of Example 1. The meanings of the symbols in Table 1 are as follows. The numbers in the left column of Table 1 indicate the projection plane side force and the order.

F: Composite focal length of the first lens group and the second lens group (mm)

F: Composite focal length of the first lens group (mm)

F: Composite focal length of the second lens group (mm)

2

F: Composite back focus (mm) of the first lens group and the second lens group

b

L: Air distance between the first lens group and the second lens group (mm)

R: radius of curvature (mm)

d: Lens thickness or air spacing (mm)

N: Refractive index of d-line (588nm)

d

V: Abbe number of d line

d

[0035] The aspherical expression is expressed by the following expression. x = cy ² / (l + ^-(k + D-c ² y ² ) + A + A ₆ y ⁶ + y ⁱ + A _w y ^l + A y ^l2 + A _u y ^u However, the sign of this expression The meaning is as follows.

X: Displacement from the lens apex

C: curvature y: Height from the optical axis

k: conical coefficient

A, A, A, A, A, A: coefficients in the order of each subscript

4 6 8 10 12 14

[table 1]

R d Nd Vd

1 oo 6.500 1.52998 55.80

2 34.599 11.096

3 59.494 4.000 1.83400 37.34

4 24.949 11.639

5 39.215 3.500 1.58930 62.56

6 15.306 10.532

7 -31.521 10.000 1.48749 70.44

8 22.300 10.000 1.60342 38.01

9 -35.782 18.346

0 19.664 1.000 1.80420 46.50 1 10.590 1.203

2 oo .000

3 12.219 6.500 1.58930 32.01 4 -20.618 .487

5 -29.563 5.557 1.83400 37.34 6 8.000 10.000 1.80518 25.46 7 18.200 .100

8 16.877 5.587 1.48749 70.44 9 -26.525 1.200 1.84666 23.78 0 16.827 8.294 1.48749 70.44 1 -17.200 .100

2 84.008 4.659 1.48749 70.44 3 -37.679 .100

4 34.036 4.680 1.48749 70.44 5 -111.501 2.500

6 oo 22.000 1.58913 61.25 7 oo 3.000

8 oo 3.000 1.48750 65.81 9 oo .483

0 oo

Projection distance 350.000

Projection angle 126.5 ^U

Aperture ratio 1: 4.0

F 5.173

FB 21.823

F1 -23.211

F2 26.826

18.346

ZF2 -0.865

Fb / F 4.218

L / F 3.546 As apparent from the lens characteristics in Table 1, the lens of Example 1 satisfies the conditional expressions (1) to (3) in the present invention.

[0038] As shown in Table 1, according to this example, a wide-angle lens having a brightness of about 4.0 aperture ratio and having a projection angle of 120 ° or more is obtained. be able to.

[0039] Further, according to the present embodiment, the combined back focus F can be long, and illumination optics b

There is also an advantage that the system can be easily inserted. In addition, the force S suppresses the increase in spherical aberration and coma.

Furthermore, according to the present embodiment, the air gap L between the first lens group G and the second lens group G is set to

1 2

It is possible to take a long time, and it is easy to insert the reflecting mirror at this interval, and there is an advantage that the projection optical system can be bent. Furthermore, it is possible to suppress an increase in chromatic aberration of magnification that occurs in the first lens group.

Example 2

FIG. 4 shows various aberration diagrams in the lens configuration of Example 2 (FIG. 3). Table 2 below shows the design values and the obtained characteristics of the lens of Example 2. The meanings of the symbols and aspherical expressions used in the second embodiment are basically the same as those in the first embodiment.

[0042] [Table 2]

R d Nd Vd

1 -267.046 6.500 1.50915 56.40

2 35.945 11.784

3 57.896 4.000 1.83400 37.34

4 23.653 10.741

5 33.077 3.500 1.80518 25.46

6 14.551 10.443

7 -44.757 10.000 1.48749 70.44

8 12.300 9.671 1.57300 32.01

9 -40.509 14.500

0 30.248 1.200 1.80420 46.50 1 10.353 1.229

2 oo .000

3 11.693 6.500 1.60342 38.01 4 -23.576 1.106

5 -35.291 5.553 1.63500 42.34 6 8.000 10.000 1.80518 25.46 7 38.400 .100

8 18.526 4.695 1.48749 70.44 9 -39.004 1.200 1.84666 23.78 0 17.611 7.733 1.48749 70.44 1 -21.818 .100 1.00000 .00 2 95.988 4.575 1.48749 70.44 3 -36.889 .100

4 40.074 4.677 1.48749 70.44 5 -42.100 5.310

6 oo 22.000 1.58913 61.25 7 oo 4.000

8 oo 3.000 1.48750 65.81 9 oo .499

0 oo

Projection distance 350.000

Projection angle 126.9 "

Aperture ratio 1: 4.0

F 5.130

FB 25.650

F1 -26.634

F2 24.306

14.500

F1 / F2 -1.095

Fb / F 4.999

L / F 2.826 [0043] In the wide-angle lens of Example 2, the same advantages as those of Example 1 can be obtained. The configuration and advantages of the second embodiment other than those shown in Table 2 are basically the same as those of the first embodiment, and thus description thereof is omitted.

Example 3

FIG. 6 shows various aberration diagrams in the lens configuration of Example 3 (FIG. 5). In addition, Table 3 below shows the design values and the obtained characteristics of the lens of Example 3. The meanings of the symbols and aspherical expressions used in the third embodiment are basically the same as those in the first embodiment.

[0045] [Table 3]

R d Nd Vd

1 -241.083 6.500 1.50915 56.40

2 35.212 11.043 1.00000 .00

3 45.232 4.000 1.83400 37.34

22.535 8.332 1.00000 .00

5 42.867 3.500 1.80518 25.46

6 14.657 11.903 1.00000 .00

7 -25.785 2.500 1.48749 70.44

8 35.641 9.358 1.60342 38.01

9 -40.917 24.506 1.00000 .00 0 18.257 1.200 1.58913 61.25 1 11.880 1.085 1.00000 .00 2 .000 .000 1.00000 .00 3 13.731 6.500 1.60342 38.01 4 -27.447 .803 1.00000 .00 5 -232.299 8.836 1.83400 37.34 6 7.353 6.366 1.58913 61.25 7 24.228 .100 1.00000 .00 8 14.660 8.087 1.48749 70.44 9 -14.065 1.200 1.84666 23.78 0 17.606 8.114 1.48749 70.44 1 -19.707 .100 1.00000 .00 2 71.856 4.965 1.48749 70.44 3 -31.584 .100 1.00000 .00 4 33.735 4.656 1.48749 70.44 5 -118.674 2.000 1.00000 .00 6 .000 20.000 1.58913 61.25 7 .000 2.000 1.00000 .00 8 .000 2.000 1.48750 65.81 9 .000 .299 1.00000 .00 0 .000 .000 1.00000 .00

Projection distance 350.000

Projection angle 127.0 "

Aperture ratio 1: 4.0

F 5.115

FB 18.212

F1 -12.397

F2 31.225

24.506

F1ZF2 -0.397

Fb / F 3.560

L / F 4.790 [0046] In the wide-angle lens of Example 3, the same advantages as those of Example 1 can be obtained. The configuration and advantages of the third embodiment other than those shown in Table 3 are basically the same as those of the first embodiment, and thus description thereof is omitted.

It should be noted that the present invention is not limited to the above-described embodiments, and various changes can be made without departing from the scope of the present invention.

Brief Description of Drawings

FIG. 1 is a lens configuration diagram of Example 1 of a wide-angle projection lens according to the present invention.

FIG. 2 is a diagram showing various aberrations of Example 1 of the wide-angle projection lens according to the present invention.

FIG. 3 is a lens configuration diagram of Example 2 of a wide-angle projection lens according to the present invention.

FIG. 4 is a diagram showing all aberrations of Example 2 of the wide-angle projection lens according to the present invention.

FIG. 5 is a lens configuration diagram of Example 3 of a wide-angle projection lens according to the present invention.

FIG. 6 is a diagram illustrating all aberrations of Example 3 of the wide-angle projection lens according to the present invention.

Explanation of symbols

[0049] G 1st lens group

G Second lens group

2

s Projection plane

GL video device protective glass

LCD picture element

P Prism for illumination optics

Claims

The scope of the claims

[1] The first lens group and the second lens group are arranged in order from the projection surface side.

The first lens group includes three negative lenses and one cemented lens obtained by cementing one negative lens and one positive lens, and has negative power.

The second lens group includes one negative lens, three positive lenses, one negative lens and a positive lens.

It is composed of one cemented lens that is joined with one lens, and one cemented lens that is joined with two positive lenses and one negative lens, and has positive power.

The first lens group includes at least one aspheric lens,

Furthermore, the wide-angle lens for projection characterized by satisfying the following conditional expression (1).

0.3≤ I F

1 / ¥ 2 I ≤1. 3 (1)

Where F is the composite focal length of the first lens unit

F: Composite focal length of the second lens group

2

[2] The wide-angle lens for projection according to claim 1, wherein the following conditional expression (2) is further satisfied.

2. 0≤F / F≤7. 0 (2)

b

F: Composite back focus of the first lens group and the second lens group

b

F: Composite focal length of the first lens group and the second lens group

[3] The projection wide-angle lens according to claim 1 or 2, further satisfying the following conditional expression (3):

1. 5≤L / F≤6. 0 (3)

L: Air distance between the first lens group and the second lens group

F: Composite focal length of the first lens group and the second lens group

[4] A projector comprising the projection wide-angle lens according to any one of claims 1 to 3.