JP2000098222A - Projection lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-sized projection lens wherein the fluctuation of the various kinds of aberration due to focusing is suppressed. SOLUTION: A projection lens 5 is constituted of a four-group that is, a first lens group 10, a second lens group 20, a third lens group 30 and a fourth lens group 40. A negative meniscus lens 50 whose convex surface is faced to a screen side is arranged at the end of the third lens group. Only the second lens group 20 positioned at the center of an optical system is moved along an optical axis at the time of executing focusing. When a focal distance at an entire optical system is set to be (f), and the synthetic focal distance of the second lens group 20 is set to be f2 and the focal distance of the negative meniscus lens 50 in the third lens group 30 is set to be f3m, respective conditions such as 0.86<=f2/f<=1.83 and 2.88<=|f3m*|/f<=7.46) are satisfied. The moving amount of a lens at a focusing time is reduced by applying an inner focus system, so that the fluctuation of the aberration due to the focusing is suppressed. Also, the focusing is executed without changing the entire length of the optical system. Therefor, the reduction of the entire length of the optical system is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection lens suitable for a liquid crystal projector for projecting an image displayed on a liquid crystal display on a screen.

[0002]

2. Description of the Related Art In a liquid crystal projector for projecting an image displayed on a liquid crystal display onto a screen, a projection lens having a focusing mechanism is used. There are various types of focus adjustment mechanisms.For projection lenses for liquid crystal projectors, the entire optical system is moved integrally on the optical axis, or the lens group located closest to the screen is moved on the optical axis. The method of making it dominant is the mainstream.

FIG. 22 shows a lens configuration of a conventional projection lens. The projection lens 70 has a three-group form of a first lens group 71, a second lens group 72, and a third lens group 73 in this order from the screen side. On the object side of the third lens group 73, a parallel glass 75 as a cross dichroic prism is arranged. In the projection lens 70, when performing focus adjustment, only the first lens group 71 located closest to the screen is moved on the optical axis. In addition,
In the projection lens 70, when performing focus adjustment, it is also possible to integrally move all optical systems from the first lens group 71 to the parallel glass 75 on the optical axis.

[0004]

However, in the conventional projection lens configured as described above, the amount of movement of the lens when performing focus adjustment is large, and the fluctuation of aberrations due to focusing is large. For this reason, it is difficult for a conventional projection lens to maintain a good balance of various aberrations in the entire focal range. In particular, since the curvature of field greatly fluctuates, it is difficult to set a wide focus adjustment range, and it cannot be mounted on a liquid crystal projector using a large-screen liquid crystal display having a large number of pixels. Further, in the conventional projection lens, since the entire length of the lens is increased at the time of focusing, the entire optical system is likely to be large.

The present invention has been made in view of the above circumstances, and has as its object to provide a small projection lens that suppresses fluctuations of various aberrations due to focusing.

[0006]

In order to achieve the above object, a projection lens according to the present invention comprises:
A first lens group including one or more negative lenses, one of the negative lenses being closest to the screen, a second lens group including two or more positive lenses, and a diaphragm;
A third lens group in which a meniscus-shaped negative lens having a convex surface facing the screen side is arranged rearward from the screen side;
The fourth lens group is composed of a meniscus-shaped compound lens having two lenses joined together, with the concave surface facing the screen, and a fourth lens group composed of two positive lenses. The lenses constituting the lens group are moved integrally on the optical axis, the focal length of the entire optical system is f, the combined focal length of the second lens group is f ₂ , and the third lens group is located at the last position from the screen side. Assuming that the focal length of the meniscus negative lens disposed at the tail is f _{3 m} , each condition of 0.86 ≦ f ₂ /f≦1.83 2.88 ≦ | f _3m | /f≦7.46 is satisfied. Is to do so.

[0007]

According to the present invention, the projection lens is constituted by a four-group system, and when focusing is performed, an inner focus system is employed in which only the second lens group located at the center of the optical system is moved on the optical axis. It is. According to this, it is possible to reduce the amount of movement of the lens at the time of focusing and to suppress fluctuation of aberration. Further, since the focus adjustment is performed without changing the overall length of the optical system, the overall length of the optical system can be reduced.

Further, the first lens group located closest to the screen includes two or more negative lenses, and one of these negative lenses is arranged closest to the screen, so that the focus area can be reduced. It is possible to make the incident angle uniform over the entire area and suppress the fluctuation of aberrations due to focusing.

Further, the second lens group moved at the time of focusing is constituted by two or more positive lenses, and the second lens group satisfies the conditional expression of 0.86 ≦ f ₂ /f≦1.83. It is possible to keep the refractive power of the group appropriately and keep the balance of various aberrations in a good condition over the entire focal range. If the upper limit of the conditional expression is exceeded, the second
The power of the lens group is weakened, and the amount of movement of the second lens group during focusing increases. For this reason, not only does the overall length of the optical system become longer, but also the fluctuation of the curvature of field accompanying focusing increases and cannot be suppressed. In addition, the power of the first lens group is also weakened as the power of the second lens group is weakened,
Sufficient light intensity cannot be obtained. If the required light quantity is to be ensured, the diameter of the front lens becomes large, and it becomes difficult to process the lens surface in a normal processing step, so that the manufacturing cost is increased. On the other hand, if the lower limit of the conditional expression is exceeded, the second
The power of the lens group becomes too strong, and it becomes difficult to correct aberrations in the entire optical system.

A meniscus-shaped negative lens having a convex surface facing the screen is disposed at the end of the third lens group from the screen side, and the conditional expression 2.88 ≦ | f _3m | /f≦7.46 is satisfied. This makes it possible to remove the coma flare and flatten the image surface. If the upper or lower limit of the conditional expression is exceeded, chromatic aberration of magnification and coma flare will increase, making it impossible to correct them.

Further, the fourth lens group is composed of four lenses, a meniscus-shaped compound lens having a concave surface facing the screen, and two positive lenses. This makes it possible to maintain a good balance of various aberrations.

[0012]

FIG. 1 shows a projection lens according to a first embodiment of the present invention. The projection lens 5 includes four lenses of a first lens group 10, a second lens group 20, a third lens group 30, and a fourth lens group 40 in this order from the screen side.
It is composed of group form. A parallel glass 6 as a cross dichroic prism is provided on the object side of the fourth lens group 40.
0 is arranged. In the projection lens 5, when performing focus adjustment, only the second lens group 20 is moved integrally on the optical axis, and the first lens group 10, the third lens group 30, the fourth lens group 40, and the parallel lens group are moved. The glass 60 remains fixed in position.

The first lens group 10 includes two or more negative lenses, and one of the negative lenses is disposed closest to the screen. The second lens group 20 includes two or more positive lenses. The third lens group 30 includes a stop SP, and a meniscus-shaped negative lens 50 whose convex surface faces the screen side from the screen side to the rear end is disposed. 4th
The lens group 40 is formed by joining two lenses, and has a meniscus compound lens 55 with a concave surface facing the screen.
And two positive lenses and a total of four lenses.

The projection lens 5 has a focal length f of the entire optical system, a composite focal length f ₂ of the second lens group 20, and a focal length f ₂ of the negative meniscus lens 50 in the third lens group 30.
When it is set to _{3 m} , it is configured to satisfy each condition of 0.86 ≦ f ₂ /f≦1.83 2.88 ≦ | f _3m | /f≦7.46.

"First Embodiment" The projection lens 5 of the first embodiment.
, The first lens group 10 includes, in order from the screen side, a meniscus-shaped negative lens 11 having a convex surface facing the screen side, a positive lens 12 having both convex surfaces facing the screen, and a meniscus-shaped negative lens 12 having a convex surface facing the screen side. It comprises four lenses, a lens 13 and a negative lens 14 having concave surfaces on both sides. The second lens group 20 is composed of two lenses: a positive meniscus lens 21 having a concave surface facing the screen and a positive lens 22 having both convex surfaces.

The third lens group 30 is a composite lens formed by joining two lenses, a meniscus-shaped positive lens 31 having a concave surface facing the screen and a meniscus-shaped negative lens 32 having a concave surface facing the screen. 33, a compound lens 36 formed by joining two lenses of a meniscus-shaped negative lens 34 having a convex surface facing the screen and a meniscus-shaped positive lens 35 having a convex surface facing the screen; And a meniscus negative lens 50 for the total of five lenses. Note that the stop SP is disposed between the two compound lenses 33 and 36.

The fourth lens group 40 includes a compound negative lens 55 formed by joining two lenses, a negative lens 41 having both concave surfaces and a positive lens 42 having both convex surfaces, and a positive negative lens having two convex surfaces. It is composed of a total of four lenses including lenses 43 and 44.

The specifications of the projection lens 5 of the first embodiment are as follows. f = 37.9 mm M = 1 / 28.25 to 1 / 18.52 Y = 22.25 ω = 30.51 ° F _NO = 2.46 L = 267.33 mm

In the above data, M is the projection magnification, Y is the image height, ω is the half angle of view, F _NO is the F number, and L is the total length of the optical system.

Further, the projection lens 5, "f ₂ / f" characteristic value in the present invention, "| f _3m | / f" values _{of, f 2 / f ≒ 1.39 |} f 3m | / f ３3.62.

Table 1 below shows the lens data of the projection lens 5. The surface number i is a number given to the surface of each lens in order from the object side, and the surface interval D represents the lens thickness or the air space between the next surface (unit: mm).

[0022]

[Table 1]

The projection lens 5 includes a short distance object (object distance 1000 mm) and a standard distance object (object distance 2700 m).
m), when focused on a long-distance object (object distance 7000 mm), the surface distance D8 between the first lens group 10 and the second lens group 20, and the surface distance between the second lens group 20 and the third lens group 30 D12 changes as shown in Table 2 below. The table also shows the focal length f when focusing on an object at each distance.

[0024]

[Table 2]

FIGS. 2 and 3 show aberration diagrams of the projection lens 5 when focusing on a short-distance object, FIGS. 4 and 5 show aberration diagrams when focusing on a standard-distance object, and FIGS. FIGS. 6 and 7 show aberration diagrams when focusing on. In addition,
In each of FIGS. 2, 4 and 6, (A) shows the spherical aberration,
(B) shows astigmatism, (C) shows distortion, and symbols S and T in the astigmatism diagram in (B) show aberrations with respect to a spherical image plane and a meridional image plane, respectively. ing. FIGS. 3, 5, and 7 are lateral aberration diagrams.
(B), (C), (D), and (E) are image height ratios (1.00), (0.90), (0.70), and (0.5), respectively.
0) and (0.00).

[Second Embodiment] FIG. 8 shows a second embodiment of the configuration of the projection lens according to the present invention. The same members as those of the projection lens 5 shown in FIG. I have. In the projection lens 6 of the second embodiment, the first lens group 10 and the second lens group 20 have the same configuration as the projection lens 5 of the first embodiment.

The third lens group 30 is a composite lens formed by joining two lenses of a negative meniscus lens 37 having a concave surface facing the screen and a positive meniscus lens 38 having a concave surface facing the screen. 39, a compound lens 36 formed by joining two lenses of a negative lens 34 and a positive lens 35, and a meniscus negative lens 50.
The stop SP is arranged between the two compound lenses 39 and 36.

The fourth lens group 40 includes a compound lens 5 formed by cementing two lenses, a negative lens 41 and a positive lens 42.
5, a meniscus-shaped positive lens 45 having a concave surface facing the screen, and a positive lens 44 having both convex surfaces. A parallel glass 60 is provided on the object side of the fourth lens group 40.
Is arranged.

The specifications of the projection lens 6 of the second embodiment are as follows. f = 44.28 mm M = 1 / 24.10-1 / 158.73 Y = 22.30 ω = 25.00 ° F _NO = 2.59 L = 214.98 mm

The projection lens 6 is configured such that each of the characteristic values satisfies f ₂ /f≒0.86|f _3m | /f≒2.88.

Table 3 shows the lens data of the projection lens 6.

[0032]

[Table 3]

A short-distance object (object distance 1000 m
m), when focusing on a standard distance object (object distance 2700 mm) and a long distance object (object distance 7000 mm), the surface distance D8 between the first lens group 10 and the second lens group 20, and the second lens group 20 Surface distance D12 with third lens group 30
Changes as shown in Table 4 below.

[0034]

[Table 4]

9 and 10 show aberration diagrams of the projection lens 6 when focusing on a short distance object, FIGS. 11 and 12 show aberration diagrams when focusing on a standard distance object, and FIGS. FIGS. 13 and 14 show aberration diagrams when focusing on.

Third Embodiment FIG. 15 shows a third embodiment of the configuration of the projection lens of the present invention. The same members as those of the projection lenses 5 and 6 shown in FIGS. Common symbols are given. In the projection lens 7 of the third embodiment, the first lens group 10 includes, in order from the screen side, a meniscus-shaped negative lens 11 having a convex surface facing the screen side.
And a positive meniscus lens 15 having a convex surface facing the screen, a negative meniscus lens 13 having a convex surface facing the screen, and a negative lens 14 having both concave surfaces. The second lens group 20 includes a meniscus-shaped positive lens 21 with the concave surface facing the screen.
And a meniscus-shaped positive lens 23 with the convex surface facing the screen.

The third lens group 30 is a composite lens formed by joining two lenses of a negative meniscus lens 51 having a concave surface facing the screen and a positive meniscus lens 52 having a concave surface facing the screen. 53, a composite lens 36 formed by joining two lenses of a meniscus-shaped negative lens 34 and a meniscus-shaped positive lens 35, and a meniscus negative lens 50. The stop SP is disposed between the two compound lenses 53 and 36. Also, the fourth
The lens group 40 has the same configuration as the projection lens 6 of the second embodiment, and a parallel glass 60 is disposed on the object side.

The specifications of the projection lens 7 of the third embodiment are as follows. f = 31.95 mm M = 1 / 27.54 to 1 / 222.20 Y = 22.00 ω = 35.00 ° F _NO = 2.60 L = 251.39 mm

[0039] The projection lens 7, each value of the characteristic value, f ₂ / f ≒ 1.83 | is configured such that the / f ≒ 7.46 | f _3m.

Table 5 shows the lens data of the projection lens 7.

[0041]

[Table 5]

A short distance object (object distance 800 m
m), when focusing on a standard distance object (object distance 2700 mm) and a long distance object (object distance 7000 mm), the surface distance D8 between the first lens group 10 and the second lens group 20, and the second lens group 20 Surface distance D12 with third lens group 30
Change as shown in Table 6 below.

[0043]

[Table 6]

FIGS. 16 and 17 show aberration diagrams of the projection lens 7 when focusing on a short-distance object, FIGS. 18 and 19 show aberration diagrams when focusing on a standard-distance object, and FIGS. FIGS. 20 and 21 show aberration diagrams when focusing on.

For comparison, FIGS. 23 and 24 show aberration diagrams when the conventional projection lens 70 shown in FIG. 22 is focused on a standard distance object. Also, the projection lens 7
FIGS. 25 and 26 show aberration diagrams when focusing on a short-distance object by moving the entirety of 0, and FIGS. 27 and 28 show aberration diagrams when focusing on an object at infinity. FIGS. 29 and 30 show aberration diagrams when only the first lens group 71 of the projection lens 70 is moved to focus on a short-distance object.
FIG. 31 and FIG. 32 show aberration diagrams when focusing on an object at infinity.

[0046]

As described above, according to the projection lens of the present invention, the entire optical system is constituted by a four-group system, and when performing focus adjustment, only the second lens group located at the center of the optical system is used. Lens is moved on the optical axis, so that the lens at the time of focusing is moved compared with the conventional projection lens which moves the entire optical system or moves the first lens group located closest to the screen side. Is small, and the fluctuation of aberration due to focusing is suppressed. Further, since the focus adjustment is performed without changing the total length of the optical system, the total length of the optical system can be reduced.

Further, the second lens group moved at the time of focusing is constituted by two or more positive lenses, and the combined focal length is adjusted so that the power of the second lens group is properly maintained and the focusing is performed. Can suppress the fluctuation of the aberration caused by. Further, a meniscus-shaped negative lens having a convex surface facing the screen side is arranged at the end of the third lens group from the screen side, and by adjusting the focal length of the meniscus negative lens, a frame associated with focusing is obtained. Deterioration of aberrations and chromatic aberration of magnification can be suppressed. As a result, it is possible to maintain a good balance of various aberrations in the entire focal range.

[Brief description of the drawings]

FIG. 1 is an optical path diagram of a first configuration example of a projection lens of the present invention.

2A and 2B are aberration diagrams when the projection lens of FIG. 1 is focused on a short-distance object, where FIG. 2A illustrates spherical aberration, FIG. 2B illustrates astigmatism, and FIG. 2C illustrates distortion. ing.

3A and 3B are lateral aberration diagrams when the projection lens of FIG. 1 is focused on a short-distance object, wherein FIG. 3A illustrates aberration at an image height ratio of 1.00, and FIG. 3B illustrates aberration at an image height ratio of 0.90. Aberration (C)
Represents aberration at an image height ratio of 0.70, and FIG.
50 shows the aberration at 50, and (E) shows the aberration at the image height ratio of 0.00.

4A and 4B are aberration diagrams when the projection lens of FIG. 1 is focused on a standard distance object, wherein FIG. 4A shows spherical aberration, FIG. 4B shows astigmatism, and FIG. 4C shows distortion. ing.

5A and 5B are lateral aberration diagrams when the projection lens of FIG. 1 is focused on a standard distance object, wherein FIG. 5A shows aberrations at an image height ratio of 1.00, and FIG. 5B shows aberrations at an image height ratio of 0.90. Aberration
(C) shows aberration at an image height ratio of 0.70, (D) shows aberration at an image height ratio of 0.50, and (E) shows aberration at an image height ratio of 0.00.

6A and 6B are aberration diagrams when the projection lens of FIG. 1 is focused on a long-distance object, where FIG. 6A shows spherical aberration, FIG. 6B shows astigmatism, and FIG. 6C shows distortion. ing.

7A and 7B are lateral aberration diagrams when the projection lens of FIG. 1 is focused on a long-distance object, wherein FIG. 7A illustrates aberration at an image height ratio of 1.00, and FIG. 7B illustrates aberration at an image height ratio of 0.90. Aberration (C)
Represents aberration at an image height ratio of 0.70, and FIG.
50 shows the aberration at 50, and (E) shows the aberration at the image height ratio of 0.00.

FIG. 8 is an optical path diagram according to a second configuration example of the projection lens of the present invention.

9 is an aberration diagram when the projection lens of FIG. 8 is focused on a short-distance object.

10 is a lateral aberration diagram when the projection lens in FIG. 8 is focused on a short-distance object.

FIG. 11 is an aberration diagram when the projection lens of FIG. 8 is focused on a standard distance object.

12 is a lateral aberration diagram when the projection lens of FIG. 8 is focused on a standard distance object.

13 is an aberration diagram when the projection lens of FIG. 8 is focused on a long-distance object.

14 is a lateral aberration diagram when the projection lens of FIG. 8 is focused on a long-distance object.

FIG. 15 is an optical path diagram according to a third configuration example of the projection lens of the present invention.

16 is an aberration diagram when the projection lens in FIG. 15 is focused on a short-distance object.

FIG. 17 is a lateral aberration diagram when the projection lens of FIG. 15 is focused on a close object.

18 is an aberration diagram when the projection lens of FIG. 15 is focused on a standard distance object.

19 is a lateral aberration diagram when the projection lens of FIG. 15 is focused on a standard distance object.

20 is an aberration diagram when the projection lens of FIG. 15 is focused on a long-distance object.

21 is a lateral aberration diagram when the projection lens of FIG. 15 is focused on a long-distance object.

FIG. 22 is an optical path diagram showing a configuration of a conventional projection lens.

FIG. 23 is an aberration diagram when the projection lens of FIG. 22 is focused on a standard distance object.

24 is a lateral aberration diagram when the projection lens in FIG. 22 is focused on a standard distance object.

25 is an aberration diagram when the entire projection lens in FIG. 22 is moved to focus on a short-distance object.

26 is a lateral aberration diagram when the entire projection lens of FIG. 22 is moved to focus on a short-distance object.

FIG. 27 is an aberration diagram when the entire projection lens of FIG. 22 is moved to focus on an object at infinity.

28 is a lateral aberration diagram when the entire projection lens of FIG. 22 is moved to focus on an object at infinity.

FIG. 29 is an aberration diagram when only the first lens group of the projection lens in FIG. 22 is moved to focus on a short-distance object.

30 is a lateral aberration diagram when only the first lens group of the projection lens in FIG. 22 is moved to focus on a short-distance object.

31 is an aberration diagram when only the first lens group of the projection lens in FIG. 22 is moved to focus on an object at infinity.

32 is a lateral aberration diagram when only the first lens group of the projection lens in FIG. 22 is moved to focus on an object at infinity.

[Explanation of symbols]

 5, 6, 7, 70 Projection lens 10, 71 First lens group 20, 72 Second lens group 30, 73 Third lens group 40, 74 Fourth lens group 50 Meniscus negative lens 60, 75 Parallel glass

Claims (1)

[Claims] 1. A first lens group including two or more negative lenses, one of these negative lenses being arranged closest to the screen, and a second lens group including two or more positive lenses, in order from the screen side. A third lens group including a two-lens group, a third lens group including a diaphragm, and a meniscus-shaped negative lens having a convex surface facing the screen side from the screen side to the rear end is joined to two lenses. The fourth lens group is composed of a meniscus-shaped compound lens directed to the side and two positive lenses.
The lenses constituting the lens group are moved integrally on the optical axis, the focal length of the entire optical system is f, the combined focal length of the second lens group is f ₂ , and the third lens group is located at the last position from the screen side. When the focal length of the meniscus negative lens arranged at the tail is f _{3 m} , the following conditions are satisfied: 0.86 ≦ f ₂ /f≦1.83 2.88 ≦ | f _3m | /f≦7.46 A projection lens characterized by satisfying.