JP2007256712A - Wide-angle lens for projection, and projector with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wide-angle lens for projection having brightness of nearly an aperture ratio 1:4.0, and also, capable of attaining a projection angle of ≥120°, and to provide a projector equipped with the lens. <P>SOLUTION: A first lens group G<SB>1</SB>and a second lens group G<SB>2</SB>are disposed sequentially from a projection plane side. The first lens group G<SB>1</SB>consists of three negative lenses and one cemented lens obtained by joining two positive lenses and one negative lens, and has a negative power. The second lens group G<SB>2</SB>consists of three positive lenses, one negative lens, one cemented lens obtained by joining one positive lens and one negative lens, and one cemented lens obtained by joining two positive lenses and one negative lens, and has a positive power. The first lens group G<SB>1</SB>includes at least one aspherical lens. The wide-angle lens satisfies the following conditional expression (1): 0.3≤¾F<SB>1</SB>/F<SB>2</SB>¾≤1.2 ...(1), wherein F<SB>1</SB>represents composite focal length of the first lens group, and F<SB>2</SB>represents composite focal length of the second lens group. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a 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 about 100 ° at most.

  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.

  By the way, in order to obtain a projection image having a small projection distance and 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, 120 ° 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 wide-angle lens for projection having a brightness of an aperture ratio of about 1: 4.0 and a projection angle of 120 ° or more, and a projector using the same. To do.

In the wide-angle lens according to the present invention, the first lens group and the second lens group are arranged in order from the projection plane side. The first lens group includes three negative lenses and one cemented lens obtained by cementing two positive lenses and one negative lens, and has negative power. The second lens group includes three positive lenses, one negative lens, one cemented lens obtained by cementing one positive lens and one negative lens, two positive lenses, and one negative lens. It is composed of a single cemented lens and has positive power. 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 ≦ | F ₁ / F ₂ | ≦ 1.2 (1)
F ₁ : Composite focal length of the first lens group F ₂ : Composite focal length of the second lens group

The wide-angle lens according to the present invention can further satisfy the following conditional expression (2).
2.0 ≦ F _b /F≦8.0 (2)
However F _b: Synthesis back focus F of the first and second lens groups combined 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

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

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

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

Now, when | F ₁ / F ₂ | in the conditional expression (1) is larger than the upper limit 1.2, the combined focal length of the first lens unit becomes too large. Then, in order to obtain 120 ° 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 0.3, it is advantageous for obtaining a projection angle of 120 °. 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 F _b / F in conditional expression (2) exceeds the lower limit of 2.0 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 F _b / F is larger than the upper limit of 8.0, a sufficient air space for inserting the illumination optical system can be secured, but the focus of the first lens group is related to the conditional expression (1). The distance is set to be very small, resulting in an increase in spherical aberration and coma.

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

  Now, when L / F of conditional expression (3) is smaller than the lower limit of 1.5, the air interval becomes too small, and the reflection mirror cannot be inserted.

  When the L / F is larger than the upper limit of 6.0, the air gap for inserting the reflecting mirror can be secured, but the projection optical system becomes too large and at the same time the chromatic aberration of magnification generated in the first lens group. Is undesirably increased.

  According to the first aspect of the present invention, there is provided a wide-angle lens used in a projection optical system that has a brightness of an aperture ratio of about 1: 4.0 and can have a projection angle of 120 ° or more. It is possible to provide a projector using the projector.

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

  According to the invention described in claim 3, by adopting conditional expression (3), a long air space between the first lens group and the second lens group can be secured, and a reflecting mirror is inserted into this space. And the projection optical system can be bent. 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 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.

  Embodiments of a wide-angle lens according to the present invention will be described based on Examples 1 to 4. First, the lens configurations in Examples 1 to 4 are shown in FIGS. 1, 3, 5, and 7, respectively. In the following, configurations 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 ₁ and a second lens group G _{2 in} order from the projection surface S side (see FIGS. 1, 3, 5, and 7). Yes.

The first lens group _{G 1} has, three negative lenses (see _R 1 to R ₆ in the figure), two positive lenses (see _R 7 to R ₈ and _R 9 _{to R 10} in the figure) and a negative lens It is composed of a single cemented lens (see R _{7 to} R ₁₀ in the figure) in which one (see R _{8 to} R ₉ in the figure) is cemented, and has negative power.

The second lens group _{G 2} includes three positive lenses (see _{R 14 ~R 15, R 23 ~R} 24 and _R 25 _{to R 26} in the figure), _{R 11} ~ in one negative lens (FIGS and R reference _12), R in the positive lens one (see _R 17 _{to R 18} in the figure) and one negative lens (see _R 16 _{to R 17} in the figure) one cemented lens (FIG. _{16 to} R ₁₈ ), one positive lens (see R _{19 to} R ₂₀ and R _{21 to} R _{22 in the} figure) and one negative lens (see R _{20 to} R ₂₁ in the figure) This is a so-called retrofocus type lens configuration having positive power, and a cemented lens (see R _{19 to} R ₂₂ in the figure).

The first lens group G ₁ includes at least one aspherical lens.

  1, 3, 5, and 7, reference numeral P denotes an illumination optical system prism, reference numeral LCD denotes a video element, and reference numeral GL denotes a protective glass for the video element.

  The 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: Composite focal length (mm) of the first lens group and the second lens group
F ₁ : Composite focal length (mm) of the first lens group
F ₂ : Composite focal length (mm) of the second lens group
F _b : Composite back focus (mm) of the first lens group and the second lens group
L: Air distance (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
ｘ：レンズ頂点からの変位 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 coefficients A ₄ , A ₆ , A ₈ , A ₁₀ , A ₁₂ , A ₁₄ : aspheric coefficients in the respective subscript orders x: from the lens apex Displacement

  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 the present embodiment, it is possible to obtain a wide-angle lens having brightness with an aperture ratio of about 4.0 and capable of having a projection angle of 120 ° or more.

Further, according to this embodiment, it is possible to take a synthetic back focus F _b 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 can the take long between the second lens group G _2, it becomes easy to insert the reflecting mirror in this interval, the projection There is an advantage that the optical 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 wide-angle lens of the second embodiment, the same advantages as those of the first embodiment can be obtained. 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.

  Also in the wide-angle lens of the third embodiment, the same advantages as those of the first embodiment can be obtained. 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.

  FIG. 8 shows various aberrations in the lens configuration of Example 4 (FIG. 7). In addition, Table 4 below shows design values and obtained characteristics of the lens of Example 4. The meanings of symbols used in the fourth embodiment and aspherical expressions are basically the same as those in the first embodiment.

実施例４の広角レンズにおいても、実施例１と同様の利点を得ることができる。実施例４における、表４に示す以外の構成及び利点は、実施例１と基本的に同様なので説明を省略する。

Also in the wide-angle lens of the fourth embodiment, the same advantages as those of the first embodiment can be obtained. Since the configuration and advantages of the fourth embodiment other than those shown in Table 4 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 wide angle projection lens by this invention. FIG. 6 is a diagram illustrating all aberrations of Example 1 of the wide-angle projection lens according to the present invention. It is a lens block diagram of Example 2 of the wide angle projection lens by this invention. FIG. 10 is a diagram illustrating all aberrations of Example 2 of the wide-angle projection lens according to the present invention. It is a lens block diagram of Example 3 of the wide angle projection lens by this invention. FIG. 10 is a diagram illustrating all aberrations of Example 3 of the wide angle projection lens according to the present invention. It is a lens block diagram of Example 4 of the wide angle projection lens by this invention. FIG. 10 is a diagram illustrating all aberrations of Example 4 of the wide-angle projection lens according to the present invention.

Explanation of symbols

G ₁ 1st lens group G ₂ 2nd lens group S Projection surface GL Image element protective glass LCD Image element P Illumination optical system prism

Claims (4)

A first lens group and a 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 two positive lenses and one negative lens, and has negative power.
The second lens group includes three positive lenses, one negative lens, one cemented lens obtained by cementing one positive lens and one negative lens, two positive lenses, and one negative lens. Consists of a single cemented 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 ≦ | F ₁ / F ₂ | ≦ 1.2 (1)
F ₁ : Composite focal length of the first lens group F ₂ : Composite focal length of the second lens group The wide-angle lens for projection according to claim 1, further satisfying the following conditional expression (2):
2.0 ≦ F _b /F≦8.0 (2)
Where F _{b is} the combined back focus of the first lens group and the second lens group, and F is the combined focal length of the first lens group and the second lens group. The wide-angle lens for projection according to claim 1 or 2, wherein the following conditional expression (3) is satisfied.
1.5 ≦ L / F ≦ 6.0 (3)
Where L: air distance between the first lens group and the second lens group F: combined focal length of the first lens group and the second lens group The projector provided with the wide-angle lens for projection of any one of Claims 1-3.

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