JP5384415B2 - Wide angle lens for projection and projection display device - Google Patents

Description

  The present invention relates to a wide-angle lens for projection that is used as a projection lens for a projector device or the like, and is particularly suitable for a so-called front type that enlarges and projects an original image displayed on a light valve such as a liquid crystal display element on a screen. The present invention relates to a wide-angle lens for projection and a projection display device equipped with the same.

  A so-called front projection type projector that projects an image on a screen in front of the apparatus is increasingly used for school education, corporate training, presentation, and the like. Furthermore, as the projector market matures, the variety of projectors increases, and various types of projectors are used, ranging from large projectors for large-screen theaters to ultra-small projectors for mobile phones.

  However, in the data projection market, which is the oldest projection market, there is a strong demand for a bright, compact, high resolution, low cost product. In order to achieve such a requirement, a lens having a standard projection angle of view is optimal because the size of the entire lens can be minimized and the number of lenses can be relatively small.

  By the way, in the case of a wide angle of view lens, the number of lenses inevitably increases and the outer diameter tends to increase for correcting aberrations in a wide angle of view region, which increases costs. In the field of wide-angle lenses, many rear-type projection lenses are known. Among them, the one disclosed in Patent Document 1 below is an eight-element lens using two plastic aspheric lenses. F2.4 and angle of view 92 degrees are achieved.

Japanese Patent No. 398363 Japanese Patent No. 3625923

  In contrast to the rear type projection lens, the front type projection lens can be equivalent to the rear type in terms of angle of view, but generally requires a lens shift, so it is necessary to increase the image size. is there. As a result, since the front type needs to have a longer focal length than the rear type, it is slightly advantageous in securing the back focus, but the aberration is enlarged accordingly, so that high resolution is satisfied. This is a difficult problem in terms of aberration correction. The rear-type lens has the advantage that even when plastic aspherical lenses are used before and after the lens system, the entire lens system is housed in the housing, so that it takes a long time to reach a predetermined temperature and temperature compensation is easy. In the case of the front type, there is a problem that the temperature until the temperature difference before and after the plastic aspherical lens becomes a predetermined value is easily influenced by the environment and temperature compensation is difficult.

  The one disclosed in Patent Document 2 uses an aspheric lens for each of the front lens group and the rear lens group, and each aspheric lens is configured with a minimum refractive power so that the influence of temperature change is reduced. In addition, the front type lens is designed to cancel out the influence of the mutual temperature change and achieves F2.5 and an angle of view of 80 degrees, but the influence of the temperature change differs depending on the position of the arranged lenses. Therefore, it is not always possible to cancel the influence of the temperature change that occurs in the aspherical lens. Further, there is a strong demand for a wider angle and brighter than that of Patent Document 2.

  The present invention has been made in view of such circumstances, and is suitable for a front-type lens that is wide-angle, bright, compact, hardly affected by temperature changes, low cost, and good optical performance. It is an object to provide a wide-angle lens for projection and a projection display device.

In order to achieve the above object, a first wide-angle lens for projection according to the present invention includes:
In order from the enlargement side, a negative first lens group as a whole, a positive second lens group as a whole, and a positive third lens group as a whole are arranged,
The first lens group includes, in order from the magnification side, two negative lenses, a negative first lens made of a plastic material having at least one aspheric surface, and a negative second lens having a concave surface facing the reduction side. Composed of lenses,
The second lens group is composed of one positive third lens having a convex surface on the enlargement side,
The third lens group includes, in order from the magnifying side, a fourth lens composed of a negative meniscus lens having a concave surface facing the magnifying side, a fifth lens composed of a positive meniscus lens having a convex surface facing the demagnifying side, and a negative overall 5 lenses of a cemented lens having a refractive power and having a cemented surface with a concave surface facing the reduction side, and a positive eighth lens with a convex surface facing the magnification side. It is characterized by comprising a lens.

In the wide angle lens for projection according to the present invention, it is preferable that the following conditional expression (1) is satisfied.
2.2 <bf / ft (1)
However,
ft: focal length of the entire system bf: back focus

In the wide angle lens for projection according to the present invention, it is preferable that the following conditional expression (2) is satisfied.
_{2.5 <D 12 / ft <6.0} (2)
However,
F _G1 : Focal length of the first lens group D ₁₂ : Distance on the optical axis between the first lens group and the second lens group

In the wide angle lens for projection according to the present invention, it is preferable that the following conditional expression (3) is satisfied.
_{2.0 <F 1 / F 2 (} 3)
However,
F ₁ : Focal length of the first lens F ₂ : Focal length of the second lens

In the wide angle lens for projection according to the present invention, it is preferable that the following conditional expression (4) is satisfied.
F ₄ / F _G3 <−0.8 (4)
However,
F ₄ : Focal length of the fourth lens F _G3 : Focal length of the third lens group

In the wide angle lens for projection according to the present invention, it is preferable that the following conditional expression (5) is satisfied.
_{-5.0 <F G1 / ft <-1.0} (5)
However,
F _G1 : focal length of the first lens group ft: focal length of the entire system

In the wide angle lens for projection according to the present invention, it is preferable that the following conditional expression (6) is satisfied.
0.9 <(FHH3 + Dst) / F _Gr3 <1.1 (6)
However,
FHH3: distance on the optical axis from the most magnified surface position of the third lens group to the front principal point position of the third lens group Dst: the most magnified surface of the third lens group from the stop position Distance on the optical axis to the position F _Gr3 : Distance on the optical axis from the front synthetic focus position of the third lens group to the front principal point position of the third lens group

  In addition, a projection display device according to the present invention includes a light source, a light valve, an illumination optical unit that guides a light beam from the light source to the light valve, and any one of the projection wide-angle lenses described above. Is modulated by the light valve, and projected onto the screen by the wide-angle lens for projection.

  The “enlarged side” means the projected side (screen side), and the screen side is also referred to as the enlarged side for the sake of convenience when performing reduced projection. On the other hand, the “reduction side” means the original image display area side (light valve side), and the light valve side is also referred to as the reduction side for the sake of convenience in the case of reduced projection.

  In order to achieve the above object, the first and second wide-angle lenses for projection according to the present invention include, in order from the magnification side, a first lens group having a negative refractive power, and a second lens group having a positive refractive power. And a third lens group having a positive refracting power. The third lens group is a negative meniscus lens in which the fourth lens on the most magnified side has a concave surface facing the magnified side. The fifth lens adjacent to the reduction side of the fourth lens is a positive meniscus lens having a convex surface facing the reduction side.

  For example, in Patent Document 1 described above, since the fourth lens on the most magnified side of the third lens group has a biconcave shape, strong negative power is generated in this portion, and further, this strong negative power is generated. In order to cancel, the fifth lens adjacent to the reduction side is a biconvex lens. For this reason, it has been difficult to improve optical performance while maintaining good brightness.

  On the other hand, in the present invention, as described above, the fourth lens on the most magnified side of the third lens group is a negative meniscus lens having a concave surface on the magnified side. The generation of power can be mitigated, and accordingly, the fifth lens adjacent to the reduction side does not have to generate a strong positive power. As a meniscus lens, the generation of positive power in this portion is alleviated.

  Accordingly, it is possible to improve the optical performance while maintaining a wide angle and brightness without using a reduction-side aspherical surface, which has been conventionally required. Further, by using an eight-lens configuration and omitting the reduction-side aspheric surface, it is possible to achieve compactness and cost reduction.

  Further, the aspherical surface on the reduction side can be omitted, and it is not necessary to use a plastic lens on the reduction side, so that a lens system that is hardly affected by temperature changes can be obtained.

  In the third lens group, the sixth lens and the seventh lens are cemented with each other, and the cemented surface has a concave surface directed toward the reduction side. Can do.

1 is a detailed configuration diagram of a wide-angle lens for projection according to Embodiment 1. FIG. FIG. 3 is a diagram illustrating a locus of light rays incident on the wide-angle lens for projection according to the first embodiment. 6 is a detailed configuration diagram of a wide-angle lens for projection according to Embodiment 2. FIG. FIG. 6 is a diagram illustrating a locus of light rays incident on a wide-angle lens for projection according to Example 2. FIG. 6 is a diagram illustrating various aberrations (spherical aberration (i), astigmatism (ii), distortion (iii), and lateral chromatic aberration (iv)) of the wide-angle lens for projection according to Example 1; FIG. 6 is a diagram illustrating various aberrations (spherical aberration (i), astigmatism (ii), distortion (iii), and lateral chromatic aberration (iv)) of the wide-angle lens for projection according to Example 2. It is a conceptual diagram which shows a part of lens system used for description of conditional expression (6). 1 is a schematic configuration diagram of a projection display device according to an embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a lens configuration diagram of Example 1 to be described later. This lens will be described below as a representative example.

The wide-angle lens for projection according to the present embodiment is a mode including Examples 1 and 2 shown in FIGS. 1 and 3, and in order from the enlargement side (screen side), a first lens group G ₁ having negative refractive power, a second lens group G ₂ having a positive refractive power, and a third lens group G ₃ having a positive refractive power.

Here, the first lens group G ₁ includes, in order from the magnification side, a first lens L ₁ negative made of plastic material at least one surface is formed by an aspherical surface, a negative second having a concave surface facing the reduction side It is composed of two lenses of the lens L _2.

The second lens group G ₂ is composed of a positive third lens L _{3 1} Like a convex surface facing the magnification side.

The third lens group G ₃ includes, in order from the magnification side, a fourth lens L ₄ composed of a negative meniscus lens having a concave surface facing the magnification side, and a fifth lens L composed of a positive meniscus lens having a convex surface facing the reduction side. _{5. A} cemented lens having positive refractive power as a whole and having the cemented surface with the concave surface facing the reduction side, which is formed by cementing the sixth lens L ₆ and the seventh lens L ₇ (Examples 1 and 2 below) in the sixth lens L _6, which are composed of five lenses of the eighth lens L ₈ of the positive seventh lens L ₇ with biconcave lens having a convex surface directed toward the biconvex lens) and the magnification side.

As described above, the fourth lens L ₄ on the most magnifying side of the third lens group G ₃ is a negative meniscus lens having a concave surface facing the magnifying side, and alleviates the generation of negative power in this portion. To be able to. Along with the relaxed generation of power of the fourth lens L _4, also the fifth lens adjacent to the reduction side, since well without causing a strong positive power, positive having a convex surface facing the reduction side The lens aberration is reduced by the generation of positive power at this portion. Thereby, it is possible to improve the optical performance while maintaining the brightness at a wide angle without using an aspheric lens on the reduction side. At the same time, the lens system is composed of eight lenses and the aspherical surface on the reduction side can be omitted, so that compactness and cost reduction can be achieved. Further, by omitting the aspherical surface on the reduction side, the manufacturability does not decrease without using a plastic lens on the reduction side, so that a lens system that is hardly affected by temperature changes can be obtained.

Further, in the third lens group G _3, the sixth lens L ₆ and the seventh lens L ₇ are joined to each other, because its bonding face is set to be a concave surface facing the reduction side shape, the image plane It can be good.

Further, although not shown, for example, between the second lens group G ₂ and the third lens group G _3, (it is also allowed to mask part) it can be provided as appropriate aperture.

In focusing is configured to move the first lens group G ₁ in the optical axis direction, it is possible to perform focusing by moving the other lens.

  In addition, the wide-angle lens for projection according to the present embodiment receives image information on the image display surface 1 of a light valve (a reflective liquid crystal display panel (LCOS type), a transmissive liquid crystal display panel, or a DMD) disposed on the reduction side. The given luminous flux enters from the reduction side (right side in the figure) via the color synthesis optical system 2a and various filters 2b, and is projected on the screen arranged on the enlargement side (left side in the figure) by the projection wide-angle lens. The projection is enlarged.

In addition, it is preferable that the wide-angle lens for projection according to the present embodiment satisfies at least one of conditional expressions (1) to (6).
2.2 <bf / ft (1)
_{2.5 <D 12 / ft <6.0} (2)
_{2.0 <F 1 / F 2 (} 3)
F ₄ / F _G3 <−0.8 (4)
_{-5.0 <F G1 / ft <-1.0} (5)
0.9 <(FHH3 + Dst) / F _Gr3 <1.1 (6)
However,
ft: focal length of the entire system bf: back focus F _G1 : focal length of the first lens group G ₁ F _G3 : focal length of the third lens group G ₃ D ₁₂ : first lens group G ₁ and second lens group G _{2 on} the optical axis F ₁ : focal length of the first lens L ₁ F ₂ : focal length of the second lens L ₂ F ₄ : focal length of the fourth lens L ₄ FHH3: of the third lens group G ₃ from the most magnification side surface position, the distance on the optical axis to the front principal point of the third lens group G ₃ Dst: from stop position to the surface position of the most magnification side of the third lens group G ₃ on the optical axis distance in F _Gr3: from the front combined focal position of the third lens group G _3, the distance on the optical axis to the front principal point of the third lens group G ₃

  The conditional expression (1) is a conditional expression for defining a range of values obtained by normalizing the length of the back focus bf of the lens with the focal length of the entire system. By satisfying the conditional expression (1), It becomes easy to insert a color synthesis prism between the lens system and a light valve such as a liquid crystal display element.

In addition, it is preferable that the following conditional expression (1 ′) is satisfied instead of the conditional expression (1), and it is more preferable that the following conditional expression (1 ″) is satisfied.
2.4 ≦ bf / ft (1 ′)
2.7 ≦ bf / ft (1 ″)

Generally when the excessively increase the refractive power of the second lens group G ₂ may adversely affect the aberrations. To suppress this, together with allowed to exhibit the effect of the aspherical lens disposed in the first lens group G _1, the conditional expression (2), by satisfying the expression (5), the minimum adverse effect on the aberrations Correct so that

That is, the following conditional expression (2), by satisfying the expression (5), a first lens group G ₁ and the second distance lens group G _2, while limiting to the lens diameter is not increased, and adjust, the to optimize the power of the first lens group G _1, it is preferable to effect due to the refractive power of the second lens group G ₂ is configured to not extend across.

  If the upper limit of conditional expression (2) is exceeded, it becomes difficult to correct the image plane, and if the lower limit is exceeded, the lens diameter increases and the cost increases. If the upper limit of conditional expression (5) is exceeded, the lens diameter increases, and if the lower limit is not reached, correction of the image plane becomes difficult.

In addition, it is preferable to satisfy the following conditional expressions (2 ′) and (5 ′) instead of the above conditional expressions (2) and (5) from such inspection points, and the following conditional expressions (2 ″) , (5 ″) is more preferable.
_{3.0 <D 12 / ft <5.0} (2')
3.5 <D ₁₂ /ft<4.2 (2 ″)
−3.0 <F _G1 /ft<−1.5 (5 ′)
-2.1 <F _G1 /ft<-1.9 (5 ″)

Also, by way of this embodiment, since the number reduction of the lens unit which moves during focusing, it is preferable that both the first lens group G ₁ and a negative lens two lenses, of which the one aspherical lens . Furthermore, although it is difficult to correct distortion with a retrofocus lens, a plastic aspheric lens is provided on the enlargement side in order to enhance the aspheric effect. Under such a premise, it is preferable to satisfy the following conditional expression (3) in order to reduce the temperature change of the plastic lens.

That is, by satisfying the conditional expression (3), the negative refractive power of the first lens group G ₁ becomes small, the positive refractive power of the second lens group G ₂ becomes large. The temperature change of the projection display device after lighting, the number of temperature rise of around barrel of the third lens group G ₃ to block the light beam is intense, the lenses constituting the first lens group G ₁ is whole ambient temperature changes Because the movement is close, the influence can be reduced. Therefore, if the lower limit of conditional expression (3) is not reached, the temperature change of the plastic lens becomes too large.

In addition, it is preferable that the following conditional expression (3 ′) is satisfied instead of the conditional expression (3) based on such inspection points, and it is more preferable that the following conditional expression (3 ″) is satisfied.
_{3.0 <F 1 / F 2 (} 3')
3.5 <F ₁ / F ₂ (3 ″)

Further, the conditional expression (4) prescribes the focal length of the fourth lens to the focal length of the third lens group G _3. That is, in the present embodiment, in order to increase the back focus in the telecentric system, the first lens group G ₁ having a negative refractive power on the enlargement side (focus lens group), and the second lens having a positive refractive power on the reduction side, The third lens groups G ₂ and G ₃ are arranged, and the diameter of the on-axis light beam is large (F2.2) and the telecentric system is combined. lens diameter of the third lens group G ₃ becomes inevitably large. In the third lens group G ₃ region because there is no separation of the axial light flux and the peripheral light, thereby achieving a performance improvement by configuring with five lenses.

Under such circumstances, if the negative refractive power of the fourth lens L ₄ provided on the most enlargement side of the third lens group G ₃ is set to a relatively small numerical range satisfying the conditional expression (4), the axis This is preferable because the balance between the upper aberration and the peripheral aberration can be achieved. That is, if the upper limit of conditional expression (4) is exceeded, it will be difficult to balance axial aberration and peripheral aberration.

In addition, it is preferable that the following conditional expression (4 ′) is satisfied instead of the conditional expression (4) based on such inspection points, and it is more preferable that the following conditional expression (4 ″) is satisfied.
F ₄ / F _G3 <−1.2 ( _{4 ′} )
F ₄ / F _G3 <−1.4 (4 ″)

Further, the conditional expression (6), defines a ratio between _{F Gr3} and (FHH3 + Dst). That is, as shown in FIG. 7, FHH3 + Dst represents the distance from the stop to the front principal point position (main plane position) H of all lenses on the reduction side of the stop, while F _Gr3 represents the stop, the third lens group G ₃ is representative of the distance between the front combined focal position. Therefore, what is meant by the conditional expression (6), when the diaphragm is, it means that is disposed in the vicinity of the front focal point of the third lens group G _3, in which the match position and aperture the front focal position, Since the reduction side is in a telecentric state, the reduction side is brought into a state close to telecentricity by setting the conditional expression (6).

  Thus, if the conditional expression (6) is satisfied, it is preferable because the telecentricity on the reduction side can be obtained.

  That is, if the conditional expression (6) exceeds the upper limit or falls below the lower limit, the telecentricity cannot be obtained.

It should be noted that it is preferable to satisfy the following conditional expression (6 ′), more preferably to satisfy the following conditional expression (6 ″), instead of the conditional expression (6).
0.95 <(FHH3 + Dst) / F _Gr3 <1.08 (6 ′)
0.98 <(FHH3 + Dst) / F _Gr3 <1.02 (6 ″)

<Projection display device>
Next, an embodiment of a projection display device according to the present invention will be described. FIG. 8 is a configuration diagram showing the illumination optical system 30 and the projection lens 10, which are the main parts of the projection display device.

  As shown in FIG. 8, the illumination optical system 30 includes a light source 15, transmissive liquid crystal panels 11a to 11c as light valves, dichroic mirrors 12 and 13 for color separation, and a cross dichroic prism for color synthesis. 14, condenser lenses 16 a to 16 c, and total reflection mirrors 18 a to 18 c. A light source 15 is disposed in front of the dichroic mirror 12, and white light from the light source 15 passes through the illumination optical unit and the liquid crystal panels 11 a to 11 c respectively correspond to three color light beams (G light, B light, and R light). Then, the light is modulated and projected onto a screen (not shown) by a projection lens.

  Since this projection display apparatus uses the projection lens according to the present invention, it is possible to obtain a large screen with high resolution in which aberrations are well corrected.

  Specific examples of the wide-angle lens for projection according to the present invention will be described below. 3 and 4 showing the configuration of the second embodiment, members having the same functions and effects as those of the first embodiment are denoted by the same reference numerals as those used in FIGS.

<Example 1>
As shown in FIG. 1 (lens configuration diagram) and FIG. 2 (ray locus diagram), the wide-angle lens for projection according to Example 1 includes, in order from the enlargement side, a first lens group G ₁ having negative refractive power, a second lens group G ₂ having a positive refractive power, aperture stop 3 (it may be removed), and a third lens group G ₃ having a positive refractive power, the reduction side are telecentric _On the reduction side of the third lens group G3, an image display surface 1 of a light valve composed of a liquid crystal display panel or the like is disposed.

The first lens group G ₁ is, in order from the magnification side, a first lens (having negative refractive power on the optical axis Z) made of a plastic material whose both surfaces are aspheric and stronger on the reduction side. is composed of two lenses of a second lens L ₂ is a biconcave lens having a concave surface, the second lens group G ₂ is composed of a third lens L ₃ which is a biconvex lens.

Further, the third lens group G ₃ is composed, in order from the magnification side, a fourth lens L _4, which is a negative meniscus lens having a concave surface facing the magnification side, a is a positive meniscus lens having a convex surface directed toward the reduction side a fifth lens L _5, a sixth lens L _6, which is a biconcave lens, a seventh lens L ₇ having a biconvex lens, is constructed from the eighth lens L ₈ Metropolitan having a biconvex lens, and the sixth lens L ₆ No. constitute a cemented lens 7 lens L ₇ are joined to each other. In addition, the cemented surface of the cemented lens is configured to have a concave surface facing the reduction side.

Since each lens surface of the second lens L ₂ from the eighth lens L ₈ are all spherical, a cost advantage.

The shape of the aspherical surface is defined by the following aspherical surface formula. In the first lens L ₁ having an aspheric surface, the effect can be obtained even if any one of the surfaces is an aspheric surface, but a lens having both aspheric surfaces is more preferable. .

The curvature radius R (mm) of each lens surface of the wide-angle lens for projection according to Example 1, the center thickness of each lens, and the air space between each lens (hereinafter referred to as “axial upper surface space”) D (mm), each lens The values of the refractive index N _d and the Abbe number ν _d in the d-line are shown in the upper part of Table 1 (the data shown in Table 1 are actual sizes. In the uppermost row, the focal length, angle of view, Fno. And back focus (mm).

  In addition, as shown in Table 3, the wide-angle lens for projection according to Example 1 has conditional expressions (1) to (6), (1 ′) to (6 ′), and (1 ″) to (6 ″). ) Are all satisfied.

  Also, as shown in Table 1, the angle of view 2ω is 93.6 degrees, and Fno. Is a bright lens with a wide angle of 2.2. The back focus bf is 26.875 mm, which is a sufficiently large value.

<Example 2>
As shown in FIG. 3 (lens configuration diagram) and FIG. 4 (ray locus diagram), the wide-angle lens for projection according to the second embodiment has a configuration substantially similar to the wide-angle lens for projection according to the first embodiment.

Table 2 shows the values of the radius of curvature R (mm) of each lens surface of the wide-angle lens for projection according to Example 2, the axial top surface distance D (mm), the refractive index N _d of each lens at d-line, and the Abbe number ν _d. Shown in the top row. In the uppermost row, the focal length, angle of view, Fno. And back focus (mm).

  In addition, as shown in Table 3, the wide-angle lens for projection according to Example 2 has conditional expressions (1) to (6), (1 ′) to (6 ′), and (1 ″) to (6 ″). ) Are all satisfied.

  Also, as shown in Table 2, the angle of view 2ω is 93.5 degrees, Fno. Is a bright lens with a wide angle of 2.2. The back focus bf is 26.896 mm, which is a sufficiently large value.

  5 and 6 are aberration diagrams (spherical aberration (i), astigmatism) showing various aberrations (spherical aberration, astigmatism, distortion, and lateral chromatic aberration) of the projection wide-angle lens according to Examples 1 and 2. (Ii), distortion (iii) and lateral chromatic aberration (iv)). In these aberration diagrams, ω represents a half angle of view, the aberration diagram for spherical aberration represents the aberration curve for each wavelength of G (green), B (blue), and R (red), and the aberration diagram for magnification chromatic aberration. Shows aberration curves of B and R with respect to G. As shown in FIGS. 5 and 6, the wide-angle lenses for projection according to Examples 1 and 2 are well corrected for various aberrations including spherical aberration, distortion, and lateral chromatic aberration.

  The wide-angle lens for projection according to the present invention is not limited to the above-described embodiments, and various modifications can be made. For example, the radius of curvature R and the axial distance D between the lenses can be appropriately changed. Is possible.

  Further, the projection display device of the present invention is not limited to the above-described configuration, and various device configurations including the projection wide-angle lens of the present invention are possible.

  As described above, in this embodiment, the brightness is Fno. A telecentric and bright wide-angle lens having an angle of view of greater than or equal to 2.2 and exceeding 90 degrees can be obtained by using one aspheric lens.

DESCRIPTION OF SYMBOLS 1 Image display surface 2a Color synthetic | combination optical system 2b Various filters 3 Aperture (mask)
10 illumination optics 11a~11c liquid crystal panel 12, 13 dichroic mirror 14 cross dichroic prism 15 the light source 16a~16c condenser lens 18a~18c total reflection mirror G ₁ ~G ₃ lens group L ₁ ~L ₈ lens R ₁ to R ₁₈ lens curvature of the surface, such as a radius D ₁ to D ₁₈ axial distance Z optical axis

Claims (8)

In order from the magnification side, a first lens group having a negative refractive power as a whole, a second lens group having a positive refractive power as a whole, and a third lens group having a positive refractive power as a whole are arranged.
The first lens group includes, in order from the magnification side, two negative lenses, a negative first lens made of a plastic material having at least one aspheric surface, and a negative second lens having a concave surface facing the reduction side. Composed of lenses,
The second lens group is composed of one positive third lens having a convex surface on the enlargement side,
The third lens group includes, in order from the magnification side, a fourth lens composed of a negative meniscus lens having a concave surface facing the magnification side, a fifth lens composed of a positive meniscus lens having a convex surface facing the reduction side, and is positive as a whole. 5 lenses of a cemented lens having a refractive power and having a cemented surface with a concave surface facing the reduction side, and a positive eighth lens with a convex surface facing the magnification side. A wide-angle lens for projection, comprising a lens. The wide-angle lens for projection according to claim 1, wherein the following conditional expression (1) is satisfied.
2.2 <bf / ft (1)
However,
ft: focal length of the entire system bf: back focus The wide-angle lens for projection according to claim 1 or 2, wherein the following conditional expression (2) is satisfied.
_{2.5 <D 12 / ft <6.0} (2)
However,
F _G1 : Focal length of the first lens group D ₁₂ : Distance on the optical axis between the first lens group and the second lens group The wide-angle lens for projection according to claim 1, wherein the following conditional expression (3) is satisfied.
_{2.0 <F 1 / F 2 (} 3)
However,
F ₁ : Focal length of the first lens F ₂ : Focal length of the second lens The projection wide-angle lens according to claim 1, wherein the following conditional expression (4) is satisfied.
F ₄ / F _G3 <−0.8 (4)
However,
F ₄ : Focal length of the fourth lens F _G3 : Focal length of the third lens group The wide-angle lens for projection according to claim 1, wherein the following conditional expression (5) is satisfied.
_{-5.0 <F G1 / ft <-1.0} (5)
However,
F _G1 : focal length of the first lens group ft: focal length of the entire system The wide-angle lens for projection according to any one of claims 1 to 6, wherein the following conditional expression (6) is satisfied.
0.9 <(FHH3 + Dst) / F _Gr3 <1.1 (6)
However,
FHH3: distance on the optical axis from the most magnified surface position of the third lens group to the front principal point position of the third lens group Dst: the most magnified surface of the third lens group from the stop position Distance on the optical axis to the position F _Gr3 : Distance on the optical axis from the front synthetic focus position of the third lens group to the front principal point position of the third lens group A light source, a light valve, an illumination optical unit that guides the light beam from the light source to the light valve, and the wide-angle lens for projection according to any one of claims 1 to 7, and the light beam from the light source A projection display device, wherein light is modulated by the light valve and projected onto a screen by the wide-angle lens for projection.

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