JP2008268595A - Wide angle lens for projection and projector equipped therewith - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wide angle lens for projection capable of achieving improvement of molding property of a lens, to avoid the use of a lens whose radius of curvature is extremely small, and further to design a first lens to be as small as possible. <P>SOLUTION: The wide angle lens for projection is equipped with a first lens group G<SB>1</SB>, a second lens group G<SB>2</SB>and a third lens group G<SB>3</SB>arranged along an optical axis AX in order from a projection surface side. The first lens group G<SB>1</SB>has negative power. The second lens group G<SB>2</SB>has positive power. The third lens group G<SB>3</SB>has negative power. Furthermore, the first lens group G<SB>1</SB>is equipped with a first lens arranged on the projection surface side. The first lens is a negative meniscus aspherical plastic lens. Furthermore, the first lens is equipped with a first surface arranged on the projection surface side. The first surface is a flat surface in the vicinity of the optical axis AX. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

  There exists a thing of the following patent document 1 as a wide-angle lens for projection. This lens achieves a large angle of view by making the second surface of the second lens in the first lens group an aspheric surface and making this lens a meniscus type.

  However, in this lens, since the second lens is a meniscus type, D / H becomes large. Here, D: lens depth and H: lens radius. This can be read from Table 3 of Patent Document 1 and lens data on the eighth page and the 26th line onwards.

  That is, in the lens of Patent Document 1, since the first lens is a negative power spherical lens, the first surface of the second lens also has a spherical shape with the same radius of curvature. Furthermore, the second surface of the second lens must have a smaller radius of curvature than the first surface in order to have negative power. As the radius of curvature decreases, the lens depth (D) increases. Therefore, in the lens of Patent Document 1, the above-described D / H value becomes large.

Thus, when the value of D / H increases, the following inconvenience occurs.
-When the lens is manufactured, the resin as the lens material is difficult to reach the peripheral portion. Then, it becomes easy to produce distortion to a lens, and an optical characteristic deteriorates.
・ The temperature gradient in the lens mold is increased. Then, the peelability between the mold and the resin deteriorates particularly in the tail portion (near the periphery of the lens). For this reason, defects such as distortion are likely to occur in the molded lens.
It becomes difficult to uniformly deposit an antireflection film (for example, AR coating) on the lens.

  In the lens of Patent Document 1, as described above, the radius of curvature of the second surface of the second lens is small. For this reason, in this lens, optically reflected light from the aspherical surface is easily imaged in the vicinity of the stop. Since this image is projected as a ghost on the screen, so to speak, the image quality of the projected image deteriorates.

Further, in the lens of Patent Document 1, the first lens tends to be large because the second lens is aspherical. In particular, if the half angle of view is designed to be 60 ° or more, there is a problem that the first lens becomes too large.
WO2005 / 057267

  The present invention has been made in view of such a situation. A first object of the present invention is to improve the moldability of a lens. The second object of the present invention is to avoid the use of a lens having an extremely small radius of curvature. The third object of the present invention is to design the first lens as small as possible.

  The wide-angle lens for projection according to claim 1 includes a first lens group, a second lens group, and a third lens group that are arranged along the optical axis in order from the projection surface side. The first lens group has a negative power, the second lens group has a positive power, and the third lens group has a negative power. Furthermore, the first lens group includes a first lens disposed on the projection plane side. The first lens is a negative meniscus aspheric plastic lens. Furthermore, the first lens includes a first surface arranged on the projection surface side. The first surface is a flat surface in the vicinity of the optical axis.

  According to the present invention, the D / H value in each lens can be kept small by adopting the above configuration. In particular, by forming a flat surface on the first surface of the first lens, D / H can be reduced even when a negative meniscus lens is employed. If the vicinity of the optical axis of the first surface of the first lens is formed flat, the radius of curvature of the second surface can be set large, and therefore the value of D can be kept small. In addition, when the flat surface is formed in the vicinity of the optical axis, it is possible to reduce the influence on the image quality. Further, according to the present invention, since the lens configuration described above is employed, it is possible to avoid the use of a lens having an extremely small radius of curvature.

  Furthermore, according to the present invention, since the first lens is a negative meniscus aspheric plastic lens, it is possible to avoid the first lens from becoming excessively large even if it is a wide-angle lens.

  The wide-angle lens for projection according to claim 2 is the one according to claim 1, wherein the lower limit of the flat surface of the first surface is a radius of 2.5 mm from the optical axis, and The upper limit of the flat surface of the first surface is a radius of 10 mm from the optical axis.

  Here, when the lower limit of the flat surface of the first surface is smaller than the radius of 2.5 mm from the optical axis, D in the first lens tends to increase and the D / H value tends to increase. There is an inconvenience. Further, by forming a flat surface in the predetermined range in the vicinity of the optical axis of the first surface, there are the following advantages. That is, at the time of lens molding, the resin is poured from the lens periphery toward the center. Here, if the curvature in the vicinity of the optical axis of the lens is changed in a complicated manner in order to effectively perform aberration correction, the flow of the resin is deteriorated and the lens molding becomes difficult. On the other hand, by making the vicinity of the optical axis of the lens a flat surface, the flow of the resin can be made smooth and lens molding can be facilitated.

  In addition, if the upper limit of the flat surface of the first surface exceeds the radius of 10 mm from the optical axis, there is a disadvantage that the light beam has poor convergence and the spot shape is broken.

  According to the second aspect of the present invention, since the flat surface range is as described above, good aberration can be obtained.

The wide-angle lens for projection according to claim 3 is the one according to claim 1 or 2, wherein the ratio of the thickness of the first lens near the optical axis to the thickness near the periphery is as follows. The above conditions are satisfied.
0.7 ≦ D ₂ / D ₁ ≦ 2.0
Where D ₁ is the thickness of the first lens near the optical axis
D ₂ : thickness of the first lens near the periphery

According to the invention of claim 3, since the range of D ₂ / D ₁ is as described above, the moldability of the lens can be further improved.

  The wide-angle lens for projection according to claim 4 is the one according to any one of claims 1 to 3, wherein the angle of view at half angle is 40 ° or more.

  The wide-angle lens for projection according to claim 5 is the one according to any one of claims 1 to 4, wherein only the even order is used as the aspherical coefficient of the aspherical surface on the first surface of the first lens. It is what has been.

  According to the invention of claim 5, the shape of the first surface of the first lens can be easily molded with few inflection points.

  The wide-angle lens for projection according to a sixth aspect is the one according to any one of the first to fifth aspects, further having an F number in the range of 2.0 to 3.5. According to this, a bright lens can be obtained.

  A projector according to a seventh aspect includes the projection wide-angle lens according to any one of the first to sixth aspects.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the wide angle lens for projection which can improve the moldability of a lens, and a projector using the same. Further, according to the present invention, it is possible to avoid the use of a lens having an extremely small radius of curvature. Furthermore, according to the present invention, it is possible to avoid the use of a large first lens.

  Embodiments of a wide-angle lens for projection according to the present invention will be described based on Examples 1 to 3 below.

  Various aberration diagrams in the lens configuration (FIG. 1) of Example 1 are shown in FIG. In the various aberration diagrams of FIG. 2, G, B, and R in astigmatism and distortion are aberrations for green, blue, and red wavelengths, respectively. Astigmatism S (solid line) is sagittal, and T (dotted line) is meridional.

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.
r: radius of curvature (mm)
d: Distance between faces (mm)
N _d : Refractive index of d line (588 nm) ν _d : Abbe number of d line

The aspherical formula is expressed by the following formula.
However, the meanings of the symbols in this equation are as follows.
x: Displacement from the lens apex c: Curvature y: Height from the optical axis k: Conical coefficient A ₄ , A ₆ , A ₈ , A ₁₀ , A ₁₂ , A ₁₄ : Coefficient in the order of each subscript

In the present embodiment, the first lens group G ₁ has a negative power. The second lens group G ₂ includes a positive power. The third lens group G ₃ has a negative power.

The first lens group G ₁ includes first lenses (r _{1 to} r ₂ ) disposed on the projection surface side. The first lens is a negative meniscus aspheric plastic lens. Furthermore, the first lens includes a first surface (r ₁ ) disposed on the projection surface side. The first surface is a flat surface in the vicinity of the optical axis AX. Here, the flat surface means that the radius of curvature is 500 mm or more.

In this example, the lower limit of the range that is a flat surface on the first surface is a range of a radius of 2.5 mm from the optical axis, and the upper limit of the range that is a flat surface on the first surface is from the optical axis. The radius is in the range of 10 mm. In this embodiment, the distance from the optical axis AX to the periphery of the flat surface, indicated by reference numeral L ₁ in FIG. 1. In this embodiment, L ₁ = 15 mm.

Moreover, the ratio of the thickness of the first lens near the optical axis to the thickness near the periphery satisfies the following conditions. In this embodiment, D ₂ / D ₁ = 1.0.
0.7 ≦ D ₂ / D ₁ ≦ 2.0
D ₁ : thickness of the first lens in the vicinity of the optical axis (see FIG. 1)
D ₂ : thickness of the first lens near the periphery (see FIG. 1)

  Furthermore, in the wide-angle lens for projection according to the present embodiment, the angle of view at a half angle is 45 ° and is included in a range of 40 ° or more.

  Only the even order is used for the aspherical surface aspherical coefficient (see Table 1) on the first surface of the first lens of the present embodiment. When the odd order is used, inflection points are likely to be generated on the surface and the formability is deteriorated. However, by using only the even order, the surface shape can be made smooth and the formability can be improved.

  The F-number of the wide-angle lens of this example is 3.5, and is included in the range of 2.0 to 3.5.

FIG. 3 shows a spot distribution diagram in the lens of this example. According to this figure, the spot has no core and no large center of gravity, and it can be evaluated that the resolution is not so good. This is thought to be because the flat surface range is L ₁ = 15 mm, which is larger than 10 mm.

  Further, the D / H (see FIG. 1) of this example is about 0.26, which is smaller than 1. This is considered to be because a flat surface was formed on the first surface of the first lens.

  1, 4, and 7, reference numeral P denotes an illumination optical system prism, reference numeral LCD denotes a video display element, and reference numeral GL denotes a protective glass for the video display 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. A specific example of the projector will be described later.

  Various aberration diagrams in the lens configuration (FIG. 4) of Example 2 are shown in FIG. 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.

In this embodiment, the distance from the optical axis AX to the periphery of the flat surface, indicated by reference numeral L ₂ in FIG. In this embodiment, L ₂ = 10 mm.

Moreover, the ratio of the thickness of the first lens near the optical axis to the thickness near the periphery satisfies the following conditions. In this embodiment, D ₂ / D ₁ = 1.35.
0.7 ≦ D ₂ / D ₁ ≦ 2.0

  Further, in the wide-angle lens for projection according to the present embodiment, the half angle of view is set to 50 ° and is included in the range of 40 ° or more.

  The F-number of the wide-angle lens of this example is 2.0, which is included in the range of 2.0 to 3.5.

  FIG. 6 shows a spot distribution diagram in the lens of this example. According to this figure, it is a spot that is neatly condensed but has a large distortion, and it can be evaluated that the resolution is good but it is slightly distorted.

  Further, the D / H (see FIG. 4) of this example is about 0.57, which is smaller than 1. This is considered to be because a flat surface was formed on the first surface of the first lens.

  In this embodiment, reference numeral P denotes an illumination optical system prism, reference numeral LCD denotes a video display element, and reference numeral GL denotes a protective glass for the video display element.

  FIG. 8 shows various aberrations in the lens configuration of Example 3 (FIG. 7). 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.

In this embodiment, the distance from the optical axis AX to the periphery of the flat surface, indicated by reference numeral L ₃ in FIG. In this embodiment, L ₃ = 5 mm.

Moreover, the ratio of the thickness of the first lens near the optical axis to the thickness near the periphery satisfies the following conditions. In this embodiment, D ₂ / D ₁ = 0.8.
0.7 ≦ D ₂ / D ₁ ≦ 2.0

  Further, in the wide-angle lens for projection according to the present embodiment, the half angle of view is set to 50 ° and is included in the range of 40 ° or more.

  The F-number of the wide-angle lens of this example is 2.0, which is included in the range of 2.0 to 3.5.

  Further, FIG. 9 shows a spot distribution diagram in the lens of this embodiment. According to this figure, the spot shape is small. Therefore, it is possible to provide a lens with good light condensing property and small distortion.

  Further, the D / H (see FIG. 7) of this example is about 0.36, which is smaller than 1. This is considered to be because a flat surface was formed on the first surface of the first lens.

  In this embodiment, reference numeral P denotes an illumination optical system prism, reference numeral LCD denotes a video display element, and reference numeral GL denotes a protective glass for the video display element.

  Hereinafter, an example of a wide-angle projector to which the wide-angle lens of the above-described embodiment can be attached will be described with reference to FIGS.

  The projector PJ includes, as main elements, a housing 1 (see FIG. 1), a light source 2 (see FIG. 2), a light modulation element 3, a projection optical system 4, a video signal input means 5, and image processing. A circuit 6, a light modulation element drive circuit 7, a light source control circuit 8, an illumination optical system 9, a CPU 10, and a control panel 11 are provided.

  The housing 1 houses an internal mechanism in the projector PJ. Moreover, the housing | casing 1 is equipped with the leg part 1a (FIG. 10) for adjusting the projection angle in the height direction of a screen.

  The light source 2 generates a light beam for forming an optical image to be projected. As the light source 2, for example, a lamp or LED that generates white light is used, but the type of the light source is not particularly limited.

  The light modulation element 3 forms an optical image to be projected by modulating the light beam from the light source 2. The light modulation element 3 is, for example, a liquid crystal display element in a liquid crystal projector or a DMD (Digital Micromirror Device) element in a DMD projector. In the DMD element, the light flux from the light source 2 can be modulated on a pixel-by-pixel basis by controlling the inclination of a minute mirror corresponding to one pixel.

  As the projection optical system 4, the wide-angle lens for projection shown in Examples 1 to 3 of this embodiment can be used.

  The video signal input means 5 is a part that performs an interface for receiving a video signal input from the outside.

  The image processing circuit 6 and the light modulation element drive circuit 7 are parts for generating a drive signal for driving the light modulation element 3 based on the video signal received by the video signal input means 5.

  The light source control circuit 8 is a part that controls ON / OFF of the light source in accordance with an input from the control panel 11.

  The illumination optical system 9 transfers the light beam from the light source 2 to the light modulation element 3.

  The CPU 10 controls the operation of each unit such as the image processing circuit 6 in accordance with pre-installed computer software.

  The control panel 11 is exposed on the surface of the housing 1 and is a part where a command from the operator can be input.

  Since the configuration of the video signal input means 5 to the control panel 11 in the projector according to the present embodiment may be basically the same as that of the conventional art, further detailed description is 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 spot distribution map 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 spot distribution map of Example 2 of the wide angle projection lens by this 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 spot distribution map of Example 3 of the wide-angle projection lens according to the present invention. It is an external view which shows an example of the projector provided with the wide angle projection lens by this invention. It is a schematic block diagram in the projector of FIG.

Explanation of symbols

G ₁ 1st lens group G ₂ 2nd lens group G ₃ 3rd lens group GL Protective glass for image display element LCD Image display element P Prism for illumination optical system PJ Projector AX Optical axis

Claims (7)

A first lens group, a second lens group, and a third lens group, which are arranged along the optical axis in order from the projection surface side,
The first lens group has negative power, the second lens group has positive power, and the third lens group has negative power,
Furthermore, the first lens group includes a first lens disposed on the projection plane side,
The first lens is a negative meniscus aspheric plastic lens;
Furthermore, the first lens includes a first surface disposed on the projection surface side,
The wide-angle lens for projection, wherein the first surface is a flat surface in the vicinity of the optical axis.   The lower limit of the flat surface in the first surface is a radius of 2.5 mm from the optical axis, and the upper limit of the flat surface in the first surface is a radius from the optical axis. The wide-angle lens for projection according to claim 1, wherein the wide-angle lens for projection is in a range of 10 mm. 3. The projection according to claim 1, wherein a ratio between a thickness in the vicinity of the optical axis and a thickness in the vicinity of the peripheral edge of the first lens satisfies the following condition. Wide angle lens.
0.7 ≦ D ₂ / D ₁ ≦ 2.0
Where D ₁ is the thickness of the first lens near the optical axis
D ₂ : thickness of the first lens near the periphery   The wide-angle lens for projection according to any one of claims 1 to 3, wherein a half-angle angle of view is 40 ° or more.   5. The wide-angle lens for projection according to claim 1, wherein only the even order is used as the aspherical coefficient of the aspherical surface on the first surface of the first lens.   The wide-angle lens for projection according to claim 1, wherein the F number is in the range of 2.0 to 3.5.   The projector provided with the wide-angle lens for projection of any one of Claims 1-6.