JP2008241981A - Wide angle lens for projection - Google Patents

Abstract

Provided is a bright wide-angle lens for projection having an F-number of about 2.0 and a projection angle of 90 ° or more.
A first lens group G ₁ is composed of three negative lenses, and has a negative power. The second lens group G ₂ includes, and one negative lens, one three positive lens, and two cemented lens one negative lens one and a positive lens, a positive lens 2 sheets and a negative lens And has a positive power. The third lens group G ₃ is composed of one positive lens and has a positive power. The first lens group G ₁ includes at least one aspherical lens. Further, this lens satisfies the following conditional expression (1).
0.3 ≦ | F ₁ / F ₂ | ≦ 1.0 (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.
[Selection] Figure 1

Description

  The present invention relates to a wide-angle lens used in a projection optical system.

  Conventionally, various types of lenses have been proposed as projection optical systems. However, most of the wide-angle lenses having a projection angle of 90 ° or more have an F number of about 2.8 or 3.5.

  However, if the F number is about 2.8 or 3.5, the illumination of the usage environment must be dimmed or the illumination power of the projection apparatus must be increased.

  Dimming the lighting of the usage environment causes usability to deteriorate. Further, increasing the illumination power of the projection apparatus not only increases the amount of heat generated by the projection apparatus but also increases the cost.

In the projection lens, a lens having a smaller F number and a larger aperture is required.
However, when a bright wide-angle lens having an F number of about 2.0 is to be provided, the configuration of the projection lens becomes complicated, and an advanced lens design technique is required.

Moreover, although the wide angle lens with a large projection angle is described in the following patent document, the F number is not as bright as 3.5 and 4.0.
JP 2006-171127 A JP 2006-171128 A

  The present invention has been made in view of such a situation. An object of the present invention is to provide a bright wide-angle lens for projection having an F-number of about 2.0 and a projection angle of 90 ° or more.

In the wide-angle lens for projection according to claim 1, a first lens group, a second lens group, and a third lens group are arranged in order from the projection surface side. The first lens group is composed of three negative lenses and has negative power. The second lens group includes one negative lens, three positive lenses, two cemented lenses obtained by cementing one negative lens and one positive lens, two positive lenses, and one negative lens. It consists of a single cemented lens that is cemented and has positive power. The third lens group includes one positive lens and has positive power. The first lens group includes at least one aspheric lens. This wide-angle lens further satisfies the following conditional expression (1).
0.3 ≦ | F ₁ / F ₂ | ≦ 1.0 (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 wide-angle lens for projection according to claim 2 further satisfies the following condition (2) in the lens according to claim 1.
2.0 ≦ F _b /F≦6.0 (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 3 further satisfies the following condition (3) in the one according to claim 1 or 2.
1.5 ≦ L / F ≦ 6.0 (3)
Where L: the air gap between the first lens group and the second lens group F: the combined focal length of the first lens group and the second lens group.

  A projector according to a fourth aspect includes the wide-angle lens according to any one of the first to third aspects as a projection lens.

  Hereinafter, the above-described conditions will be described.

  Conditional expression (1) is for obtaining a wide-angle lens having an F number of 2.0 and a projection angle of 90 ° or more, and for obtaining a required back focus by making the lens system a retrofocus type.

When | F ₁ / F ₂ | of the present condition (1) is larger than the upper limit of 1.0, the combined focal length of the first lens group becomes too large. Then, in order to obtain an F number 2.0 of the retrofocus lens and a projection angle of 90 ° or more, 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 3.0, it is advantageous for obtaining an F number of 2.0 and a projection angle of 90 ° or more, but the combined focal length of the first lens group is The amount of positive spherical aberration and coma aberration generated in the first lens group becomes too small, which is not preferable.

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

When F _b / F is larger than the upper limit of 6.0, a sufficient air space for inserting the illumination optical system can be secured, but the focal length of the first lens group is related to conditional expression (1). As a result, the spherical aberration and coma increase.
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 is smaller than the lower limit of 1.5, the air interval becomes too small and the reflection mirror cannot be inserted.

  When 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 at the same time, the chromatic aberration of magnification generated in the first lens group It is not preferable because it is increased.

  According to the first aspect of the present invention, there is provided a bright wide-angle lens that is used in a projection optical system and has a brightness of F number 2.0 and a projection angle of 90 ° or more. Is possible.

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

  According to the third aspect of the present invention, it is possible to ensure a large air gap between the first lens group and the second lens group, and it becomes easy to insert the reflection mirror at this gap, and the projection optical system is bent. Is possible. In addition, it is possible to suppress an increase in chromatic aberration of magnification that occurs in the first lens group.

  Embodiments of a wide-angle lens for projection according to the present invention will be described based on Examples 1 to 6.

  First, lens configuration diagrams in Examples 1 to 6 are shown in FIGS. 1, 3, 5, 7, 9, and 11, 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 bright wide-angle lens in each example is configured by arranging a first lens group G ₁ , a second lens group G ₂ , and a third lens group G _{3 in} order from the projection surface S side.

The first lens group _{G 1} is composed of three negative lenses _(R 1 to R _6), and has a negative power. Furthermore, the first lens group _{G 1} includes at least one aspheric lens _(R 1 _{~R 2).} In Examples 1 to 3, the second lens (R _{3 to} R ₄ ) of the first lens group G ₁ is a biconcave lens, whereas in Examples 4 to 6, the lens is a concave meniscus. It is a lens. Accordingly, the obtained projection angles are different (described later).

The second lens group _{G 2} includes one negative lens _(R 10 _{~R 11),} 3 pieces of a positive lens _{(R 12 ~R 13, R 21} ~R 24), 1 negative lens and a positive lens 1 Two cemented lenses (R _{7 to} R ₉ , R _{14 to} R ₁₆ ) that are cemented together, and one cemented lens (R _{17 to} R ₂₀ ) that is composed of two positive lenses and one negative lens. The lens configuration is a so-called retrofocus type lens configuration.

The third lens group _{G 3} is composed of one positive lens _(R 25 _{~R 26),} a lens group having a positive power. The third lens group G _3, at the same time effectively utilizing the light amount of the projection optical system, and has a condenser lens for miniaturizing the outer diameter of the lens.

  Reference numeral LCD denotes a video element, and reference numeral GL denotes a protective glass of the video element. The bright wide-angle lens in each embodiment can be used as a projection lens for a projector. Here, the projector is not limited to a liquid crystal projector, and includes various projectors such as a DLP projector.

  Here, a schematic configuration of a projector that can use the wide-angle lens for projection according to the present embodiment will be described with reference to FIG. As this projector, a projector similar to the conventional one can be used.

  This projector includes a control unit 1, an illumination system 3, a projection lens 4, and an LCD element 5 as an image display element. These are generally housed in a housing (not shown).

  The control unit 1 includes a video signal input unit 11, an image processing unit 12, an LCD element drive unit 13, a light source control circuit 14, and a CPU 15 as main elements. The video signal input means 11 receives a video signal from video signal output means such as a personal computer or a television tuner. The image processing unit 12 is a part that generates a signal for driving the LCD element drive unit 13 based on the received video signal. The LCD element drive unit 13 drives the LCD element 5 based on a signal from the image processing unit 12. On the other hand, the light source control circuit 14 turns on and off the light source based on the ON / OFF signal input by the input means 16 and supplies voltage and power necessary for lighting the light source.

  The illumination system 3 includes a light source 31 and an illumination optical system 32 for light transfer, and can uniformly supply RGB three color rays to the LCD element 5.

  The projection lens 4 is for projecting an image on the screen S. As the projection lens 4, the projection lens of this embodiment can be used.

  The LCD element 5 is a part that generates an image to be projected by changing the transmission state of light rays from the illumination system 3.

  Since the existing technology can be basically used as the configuration of the projector described above, further detailed description is omitted.

  Various aberration diagrams in the lens configuration (FIG. 1) of Example 1 are shown in FIG. In the various aberration diagrams of FIG. 2, chromatic aberrations G, B, and R indicated by spherical aberration are spherical aberrations for green, blue, and red wavelengths, respectively, astigmatism S is sagittal, and M is meridional. In addition, Table 1 shows design values of Example 1 and obtained characteristics. The meanings of the symbols in Table 1 are as follows. The numbers in Table 1 indicate the order from the projection plane side. The same applies to the following tables.

F: Composite focal length F _{1 of} the first lens group and second lens group F ₁ : Composite focal length of the first lens group F ₂ : Composite focal length F _b of the second lens group F: between the first lens group and the second lens group Composite back focus L: Air distance R between the first lens group and the second lens group R: Radius of curvature d: Lens thickness or air distance N _d : Refractive index of d line (588 nm) V _d : Abbe number of d line

The aspherical formula is expressed by the following formula. The same applies to the following embodiments.

However, the meanings of the symbols in this formula are as follows.
x: displacement in the optical axis direction from the lens apex c: curvature y: height from the optical axis K: conical coefficients A ₄ , A ₆ , A ₈ , A ₁₀ : coefficients in the order of the subscripts, respectively

  As can be seen from the lens characteristics in Table 1, this lens satisfies the conditional expressions (1) to (3) in the present invention. The projection angle of this lens is 95 ° or more.

  FIG. 4 shows aberration diagrams 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.

  As can be seen from the lens characteristics in Table 2, this lens satisfies the conditional expressions (1) to (3) in the present invention. The projection angle of this lens is 95 ° or more.

  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.

  As can be seen from the lens characteristics in Table 3, this lens satisfies the conditional expressions (1) to (3) in the present invention. The projection angle of this lens is 95 ° or more.

  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.

  As can be seen from the lens characteristics in Table 4, this lens satisfies the conditional expressions (1) to (3) in the present invention. The projection angle of this lens is 90 ° or more.

  Various aberration diagrams in the lens configuration (FIG. 9) of Example 5 are shown in FIG. Table 5 below shows design values and obtained characteristics of the lens of Example 5.

  As can be seen from the lens characteristics in Table 5, this lens satisfies the conditional expressions (1) to (3) in the present invention. The projection angle of this lens is 90 ° or more.

  FIG. 12 shows various aberrations in the lens configuration of Example 6 (FIG. 11). In addition, Table 6 below shows design values and obtained characteristics of the lens of Example 6.

  As can be seen from the lens characteristics in Table 6, this lens satisfies the conditional expressions (1) to (3) in the present invention. The projection angle of this lens is 90 ° or more.

It is a lens block diagram of Example 1 of the wide-angle lens for projection in this invention. FIG. 6 is a diagram illustrating all aberrations of the wide-angle lens for projection according to Example 1 of the present invention. It is a lens block diagram of Example 2 of the wide-angle lens for projection in this invention. FIG. 10 is a diagram illustrating all aberrations of Example 2 of the wide-angle lens for projection according to the present invention. It is a lens block diagram of Example 3 of the wide angle lens for projection in this invention. FIG. 10 is a diagram illustrating all aberrations of Example 3 of the wide-angle lens for projection according to the present invention. It is a lens block diagram of Example 4 of the wide-angle lens for projection in this invention. FIG. 10 is a diagram illustrating all aberrations of Example 4 of the wide-angle lens for projection according to the present invention. It is a lens block diagram of Example 5 of the wide-angle lens for projection in this invention. FIG. 10 is a diagram illustrating all aberrations of Example 5 of the wide-angle lens for projection according to the present invention. It is a lens block diagram of Example 6 of the wide-angle lens for projection in this invention. FIG. 10 is a diagram illustrating all aberrations of Example 6 of the wide-angle lens for projection according to the present invention. It is a block diagram which shows the outline | summary of the projector in which the wide angle lens for projection in this invention is used.

Explanation of symbols

G ₁ : First lens group G ₂ : Second lens group G ₃ : Third lens group S: Projection surface GL: Cover glass of image element LCD: Image element

Claims (4)

In order from the projection surface side, a first lens group, a second lens group, and a third lens group are arranged,
The first lens group is composed of three negative lenses and has negative power;
The second lens group includes one negative lens, three positive lenses, two cemented lenses obtained by cementing one negative lens and one positive lens, two positive lenses, and one negative lens. It consists of a single cemented lens and has positive power,
The third lens group is composed of one positive lens and has a 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 | ≦ 1.0 (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 condition (2).
2.0 ≦ F _b /F≦6.0 (2)
However, F _b : Composite back focus of the first lens group and the second lens group F: Composite focal length of the first lens group and the second lens group The wide-angle lens for projection according to claim 1 or 2, further satisfying the following condition (3).
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   A projector comprising the wide-angle lens according to claim 1 as a projection lens.

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