JP2006171127A - Ultra wide-angle lens and projector provided with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultra wide-angle lens which has brightness of the about an F-number of 4 and allows a projection angle to be 130° or larger, and to provide a projector that uses the ultra wide-angle lens. <P>SOLUTION: In the ultra wide-angle lens, a first lens group G<SB>1</SB>which is composed of three negative lenses and has negative power, a second lens group G<SB>2</SB>which is composed of five positive lenses and two cemented lenses, and has positive power and a third lens group G<SB>3</SB>composed of one positive lens are arranged, in the order starting from the projection surface side. The first lens group G<SB>1</SB>and the second lens group G<SB>2</SB>, respectively include at least one aspheric lens. Further, the lens groups satisfy the conditional expression (1): 0.1≤¾F<SB>1</SB>/F<SB>2</SB>¾≤0.5 (1), where F<SB>1</SB>the combined focal length of the first lens group and F<SB>2</SB>is the combined focal length of the second lens group. The projector is provided with the ultra wide-angle lens as a projection lens. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a super wide-angle lens used in a projection optical system and a projector including the same.

  Conventionally, various types of projection optical systems have been proposed. However, in many cases, the projection distance is about 1 m, and the projection angle is at most about 100 °.

  A projection optical system with a projection angle of around 100 ° is relatively easy to design a lens, but if the projection distance is around 1 m, a relatively large space is required for installing the projection optical system.

  Even in such a conventional projection optical system, if the projection distance is simply reduced, projection is possible without requiring a large space.

  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 wider-angle projection lens is required. Then, the configuration of the projection lens becomes complicated, and advanced lens design technology is required.

Patent Document 1 listed below describes a wide-angle lens with a long back focus. However, this lens cannot make the projection angle sufficiently large (for example, 130 ° or more).
JP 2003-215448 A

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 F _NO = 1: 4.0 and a projection angle of 130 ° or more, and a projector using the same. And

The super wide-angle lens according to claim 1,
In order from the projection surface side
A first lens group having negative power, which is composed of three negative lenses;
A second lens group having a positive power and composed of five positive lenses and two cemented lenses;
A third lens group composed of one positive lens is arranged;
Each of the first lens group and the second lens group includes at least one aspheric lens;
The following conditional expression (1) is satisfied.
0.1 ≦ | F ₁ / F ₂ | ≦ 0.5 (1)
Where F _{1 is} the combined focal length of the first lens group, and F ₂ is the combined focal length of the second lens group.

The super wide-angle lens described in claim 2 is the one described in claim 1, and further satisfies the following conditional expression (2).
_{2 ≦ L A / F ≦ 10} (2)
Where F is the combined focal length of the entire lens system L _A is the combined back focus of the first lens group and the second lens group.

The super wide-angle lens described in claim 3 is the one described in claim 1 or claim 2, and further satisfies the following conditional expression (3).
2 ≦ L _B / F ≦ 10 (3)
Where F is the combined focal length of the entire lens system, and L _B is the air spacing between the first lens group and the second lens group.

  According to a fourth aspect of the present invention, there is provided a projector comprising the super wide-angle lens according to any one of the first to third aspects as a projection lens.

  Hereinafter, each of the above-described conditions will be described.

  Conditional expression (1) is for obtaining an ultra-wide projection lens having a projection angle of 130 ° or more, and for obtaining a required back focus by making the lens system a retrofocus type.

Now, when | F ₁ / F ₂ | in conditional expression (1) is larger than the upper limit of 0.5, the combined focal length of the first lens unit becomes too large. Then, in order to obtain 130 ° or more as the projection angle of the retrofocus lens, the entire lens system becomes very large, and as a result, the commercial value is significantly reduced.

When | F ₁ / F ₂ | is smaller than the lower limit of 0.1, it is advantageous for obtaining a projection angle of 130 °. However, the combined focal length of the first lens group becomes too small, and the first lens The amount of positive spherical aberration and coma generated in a group becomes too large, which is not preferable.

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

Now, when L _A / F in the conditional expression (2) exceeds the lower limit 2 and is small, the air interval for inserting the illumination optical system becomes too small, and the illumination optical system cannot be inserted, which is not preferable.

Further, when L _A / F is larger than the upper limit of 10, the air space for inserting the illumination optical system can be sufficiently secured, but the focal length of the first lens group is related to the conditional expression (1). As a result, the spherical aberration and the coma are increased.

  Conditional expression (3) is a condition in which an air interval for inserting a reflection mirror for bending the projection optical system is to be secured between the first lens group and the second lens group.

Now, when L _B / F in conditional expression (3) exceeds the lower limit 2 and is small, the air interval becomes too small and the reflection mirror cannot be inserted.

When L _B / F is larger than the upper limit of 10, the air gap for inserting the reflecting mirror can be secured, but the chromatic aberration of magnification generated in the first lens group is increased at the same time as the projection optical system becomes too large. This is not preferable.

According to the first aspect of the present invention, a wide-angle lens used in a projection optical system, having a brightness of about F _NO = 1: 4.0 and capable of a projection angle of 130 ° or more, and It is possible to provide a projector using this.

  According to the second aspect of the present invention, since the conditional expression (2) is adopted, the combined back focus can be long, and the illumination optical system can be easily inserted. In addition, increases in spherical aberration and coma can be suppressed.

  According to the third aspect of the present invention, the air space between the first lens unit and the second lens unit can be long, and it becomes easy to insert the reflection mirror at this space, and the projection optical system can be bent. It becomes possible. In addition, it is possible to prevent the projection optical system from becoming too large, and to suppress the increase in chromatic aberration of magnification occurring in the first lens group.

  According to invention of Claim 4, it becomes possible to set it as 130 degrees or more as a projection angle. Accordingly, it is possible to provide a projector capable of projecting a high-magnification image and capable of projecting a large image even at a short projection distance.

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

In the super wide-angle lens in each embodiment, a first lens group G ₁ , a second lens group G ₂ , and a third lens group G ₃ are arranged in order from the projection plane side (left side in FIGS. 1, 3, and 5). Configured.

The first lens group G ₁ is composed of three negative lenses and has negative power.

The second lens group G ₂ is composed of five positive lenses and two cemented lenses, and has a lens configuration of a retrofocus type loose said having a positive power.

  Each of the first lens group G1 and the second lens group G2 includes at least one aspheric lens.

The third lens group G ₃ is composed of one positive lens, a lens group having a positive power. The third lens group G ₃ has a condenser lens for miniaturizing the outer diameter of the effective use for the simultaneous lenses the amount of light of the projection optical system.

  The super wide-angle lens in each embodiment can be used as a projection lens for 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.

  Various aberration diagrams in the lens configuration (FIG. 1) of Example 1 are shown in FIG.

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

In addition, Table 1 below shows design values and obtained characteristics of the lens of Example 1. The meanings of symbols in Table 1 are as follows. The numbers in the left column in Table 1 indicate the order from the projection plane side.
F _NO : F number W: Projection angle (°)
u: Projection distance (mm)
F: Total focal length of the entire lens system (mm)
F ₁ : Composite focal length (mm) of the first lens group
F ₂ : Composite focal length (mm) of the second lens group
L _A : Composite back focus (mm) by the first lens group and the second lens group
L _B : Air spacing (mm) between the first lens group and the second lens group
r: radius of curvature (mm)
d: Lens thickness or air gap (mm),
N _d : Refractive index of d line (588 nm) ν _d : Abbe number of d line

但し、この式における符号の意味は以下の通りである。
Ｃ：曲率半径
ｙ：光軸からの高さ
Ｋ：円錐係数
Ａ_４、Ａ_６、Ａ_８、Ａ_１０、Ａ_１２、Ａ_１４：それぞれの添え字の次数における非球面係数 The aspherical formula is expressed by the following formula.

However, the meanings of the symbols in this equation are as follows.
C: radius of curvature y: height from the optical axis K: conic coefficient A ₄ , A ₆ , A ₈ , A ₁₀ , A ₁₂ , A ₁₄ : aspheric coefficient in the order of each subscript

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

  As shown in Table 1, according to this example, it is possible to obtain an ultra-wide-angle lens having a projection angle of 130 ° or more and a brightness with an F number of about 4.0.

Further, according to this embodiment, it is possible to take a synthetic back focus L _A long, there is an advantage that the insertion of the illumination optical system is facilitated. In addition, increases in spherical aberration and coma can be suppressed.

Further, according to this embodiment, the first lens group G ₁ and the air gap L _B between the second lens group G ₂ can be made long, it becomes easy to insert the reflecting mirror in this interval, the projection optical There is an advantage that the system can be bent. Furthermore, it is possible to suppress an increase in chromatic aberration of magnification occurring in the first lens group.

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

Also in the super wide-angle lens of the second embodiment, the same advantages as those of the first embodiment can be obtained. However, in Example 2, Synthesis back focus L _A and the air gap L _B is larger than that of Example 1. Since 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, description thereof will be omitted.

  Various aberration diagrams in the lens configuration (FIG. 5) of Example 3 are shown in FIG. In addition, Table 3 below shows design values and 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.

In the super wide-angle lens of the third embodiment, the same advantages as those of the first embodiment can be obtained. However, in Example 3, Synthesis back focus L _A and the air gap L _B is larger than that of Example 1. Since 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, description thereof will be omitted.

  In addition, this invention is not limited to an above-described Example, In the range which does not deviate from the summary of this invention, a various change can be added.

It is a lens block diagram of Example 1 of the super wide angle projection lens by this invention. FIG. 6 is a diagram illustrating all aberrations of Example 1 of the super-wide angle projection lens according to the present invention. It is a lens block diagram of Example 2 of the super wide angle projection lens by this invention. FIG. 9 is a diagram illustrating all aberrations of Example 2 of the super-wide angle projection lens according to the present invention. It is a lens block diagram of Example 3 of the super-wide-angle projection lens by this invention. FIG. 10 is a diagram illustrating all aberrations of Example 3 of the super-wide angle projection lens according to the present invention.

Explanation of symbols

G ₁ first lens group G ₂ second lens group G ₃ third lens group

Claims (4)

In order from the projection surface side
A first lens group having negative power, which is composed of three negative lenses;
A second lens group having a positive power and composed of five positive lenses and two cemented lenses;
A third lens group composed of one positive lens is arranged;
Each of the first lens group and the second lens group includes at least one aspheric lens;
An ultra-wide-angle lens characterized by satisfying the following conditional expression (1).
0.1 ≦ | F ₁ / F ₂ | ≦ 0.5 (1)
F ₁ : Composite focal length of the first lens group F ₂ : Composite focal length of the second lens group The super wide-angle lens according to claim 1, further satisfying the following conditional expression (2):
_{2 ≦ L A / F ≦ 10} (2)
Where F: total focal length of the entire lens system L _A : composite back focus of the first lens group and the second lens group The super-wide-angle lens according to claim 1 or 2, wherein the following conditional expression (3) is satisfied.
2 ≦ L _B / F ≦ 10 (3)
Where F: total focal length of the entire lens system L _B : air distance between the first lens group and the second lens group A projector comprising the super wide-angle lens according to claim 1 as a projection lens.

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