JP2008309991A - Projection lens and projection display apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a wide-angle projection lens having high projection performance while securing a long back focus, capable of using an inexpensive light reflection mirror as an optical path bending component, whose manufacturing cost is reduced and whose various aberrations are sufficiently corrected. <P>SOLUTION: The projection lens is constituted by arraying a first group G<SB>1</SB>having negative refractive power and a second group G<SB>2</SB>having positive refractive power in order from an enlargement side, and the projection lens is nearly telecentric on the reduction side. The first group G<SB>1</SB>comprises at least six lenses, that is, aspheric lenses L<SB>1</SB>and L<SB>2</SB>, a negative lens L<SB>3</SB>with a concave surface facing the reduction side, a negative lens L<SB>4</SB>with a concave surface facing the reduction side, a biconvex lens L<SB>5</SB>and a negative lens L<SB>6</SB>with a concave surface facing the enlargement side (three-cemented lens composed of lenses L<SB>4</SB>, L<SB>5</SB>and L<SB>6</SB>). Further, the projection lens satisfies three conditional expressions (1) to (3). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a projection lens for enlarging and projecting display information from a light valve such as a transmissive or reflective liquid crystal display element or DMD (digital micromirror device), and more particularly to a rear projection display device. The present invention relates to a suitable projection lens and a projection display device using the same.

  Conventionally, as a projection display device, a projection lens is disposed on the same side as a viewer with respect to a screen, and a front-type device that forms an image of light emitted from the projection lens on a reflective screen, a projection lens, There is known a rear-type device that is arranged so that a viewer sandwiches a screen and images light emitted from a projection lens on a transmissive screen.

  Among these, in a rear projection display device, for example, a rear projection TV, the light source to the screen are housed in a cabinet, and image information is projected from the projection lens disposed on the back toward the screen disposed on the front of the cabinet. A configuration for projecting light carrying the light is well known.

  In recent years, various projection lenses have been proposed for application to such cabinet-type projection display devices.

  Projection lenses are required to be able to project large sizes at short projection distances, and in particular for rear projection projectors, there is a strong demand for thinner devices. There is a demand for a projection lens that can achieve this.

  In addition, in an optical system using a plurality of light valves for colorization, etc., in order to arrange a synthesis unit that synthesizes light beams from each light valve, to separate illumination light and projection light, and further to heat A large back focus is required to alleviate problems.

  In response to such demands, lenses described in the following Patent Documents 1 to 4 are known as lenses having a relatively long back focus and an angle of view on the enlargement side exceeding 100 degrees.

JP 2003-015033 A JP 2004-326079 A USP 7123426 USP 7126767

  By the way, in the projection display device, particularly the rear projection type device, it is considered useful to insert a light reflecting element into the projection lens for the purpose of bending the optical path at a predetermined position in order to make the device compact. It is done.

  However, the above Patent Documents 3 and 4 do not have the concept of inserting a light reflecting element into the optical path. In addition, in the above-mentioned Patent Documents 1 and 2, as a light reflecting element to be inserted into the optical path, a prism with a long optical path length is used instead of a light reflecting mirror in order to compensate for a narrow space, which increases the manufacturing cost. There was a problem.

  Further, in Patent Documents 1 and 2, the first lens on the most magnified side is an aspherical lens with weak power, and the distance from the aperture stop to the aspherical surface is secured, so that aberrations such as curvature of field and distortion are obtained. Although the correction is improved, in recent years when high image quality is required, a higher performance projection lens is required.

  The present invention has been made in view of such circumstances, and has a wide angle and high projection performance while ensuring a long back focus, and has a light reflection for bending an optical path in order to achieve a configuration suitable for downsizing. An object of the present invention is to provide a low-cost projection lens that can use an inexpensive light reflecting mirror as an element and correct various aberrations well, and a projection display device using such a projection lens.

The projection lens according to the present invention is
A projection lens in which a first lens group having a negative refractive power and a second lens group having a positive refractive power are arranged in order from the magnification side,
The distance between the first lens group and the second lens group is set to the maximum air distance in the projection lens, and the reduction side is configured to be substantially telecentric,
The first lens group includes, in order from the magnifying side, a first lens and a second lens that are aspherical lenses, a third lens that is a negative lens having a concave surface on the reduction side, and a negative lens that has a concave surface on the reduction side. A fourth lens, a fifth lens composed of a biconvex lens, and a sixth lens composed of a negative lens with a concave surface facing the enlargement side, and is composed of at least six lenses.
The following conditional expressions (1) to (3) are satisfied.
105 degrees <2ω (1)
15 <| f1 | / f (2)
15 <| f2 | / f (3)
here,
2ω: angle of view on the enlargement side f: focal length of the entire system f1: focal length of the first lens f2: focal length of the second lens

  In this case, it is preferable that the fourth lens, the fifth lens, and the sixth lens constitute a three-piece cemented lens.

Moreover, it is preferable that the following conditional expressions (4) to (6) are satisfied.
5.0 <Bf / f (4)
2.5 <f5 / f <10.0 (5)
45> νd5 (6)
here,
Bf: Air-converted back focus f5: Focal length of the fifth lens νd5: Abbe number of the fifth lens

Moreover, it is preferable that the following conditional expressions (7) and (8) are satisfied.
6.0 <d / f (7)
7.0 <F2 / f (8)
here,
d: the maximum air gap (the largest of the adjacent lens gaps)
F2: focal length of the second lens group

  Further, it is preferable that a reflection mirror is inserted between adjacent lenses to bend the optical path.

  In addition, it is preferable to correct the image plane curve accompanying the change in the projection distance by moving the first lens in the optical axis direction.

  Further, it is preferable that the image plane position correction accompanying the change in the projection distance is performed by changing an air interval between the first lens group and the second lens group.

  Furthermore, 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 the projection lens according to the present invention. The light beam is modulated by the light valve and projected onto the screen by the projection lens.

  Since the projection lens of the present invention has the above-described configuration, it can have a wide angle and high projection performance while ensuring a long back focus. In addition, when a light reflecting element for bending an optical path is used in order to achieve a configuration suitable for downsizing, the light reflecting element can be configured with an inexpensive light reflecting mirror, and the manufacturing cost can be reduced.

  Further, since the two lenses on the most magnification side are aspherical lenses and satisfy the conditional expressions (2) and (3), the large diameter located on the most magnification side of the first lens group, In addition, it is possible to regulate the power of the first lens and the second lens having an aspherical surface to be small, and two aspherical lenses having weak power are arranged at an enlargement side position spaced from the aperture stop. Therefore, various aberrations including field curvature and distortion can be greatly improved. Further, as these two lenses, it is possible to use an inexpensive material that is easily affected by a temperature change, for example, a lens made of plastic, so that the manufacturing cost can be reduced. In particular, it is possible to make a significant contribution to cost reduction by using a lens with a larger diameter on the enlarged side and two lenses made of plastic, and the weight is much larger than when glass is used. Can be reduced in weight.

  Further, the projection display device of the present invention uses the projection lens of the present invention, so that it is possible to widen the angle while ensuring a long back focus and to reduce the manufacturing cost.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1 shows a projection lens according to Example 1 described later, FIGS. 2 and 3 show a projection lens according to Example 2 described later, and FIG. 4 shows a projection lens according to Example 3 described later. Is shown. Among these, the lens shown in FIGS. 2 and 3 will be described below as a representative of this embodiment. In the figure, X represents the optical axis.

Projection lens of this embodiment, in order from the magnification side, a first lens group G ₁ having a negative refracting power and is the second lens group G ₂ and the sequence having a positive refractive power, a substantially telecentric reduction side It is said that. In the first lens group G ₁ , two aspherical lenses L ₁ and L ₂ having weak power are arranged on the most enlargement side, and three lenses are joined on the most reduction side. single cemented lens _L 4 ~L ₆ is arranged. Further, the second lens group _{G 2,} an aperture stop 3 (the possible features a mask), two three-element cemented lens _{L 9 ~L 11, L 13 ~L} 15 is disposed, the first between the lens group G ₁ and the second lens group G _2, are the largest adjacent lens distance (maximum air interval).

The three-piece cemented lenses L _{4 to} L ₆ of the first lens group G ₁ are formed by sandwiching a fifth lens L ₅ made of a biconvex lens between a fourth lens L ₄ made of a negative lens and a sixth lens L ₆ . Further, in the second lens group _{G 2,} 3 cemented lens _L 9 _{~L 11} is interposed therebetween in a ninth lens _{L 9} and the eleventh lens _{L 11} becomes the tenth lens _{L 10} made biconcave lens of a positive lens Further, the three cemented lenses L _{13 to} L ₁₅ are formed by sandwiching the fourteenth lens L ₁₄ made of a biconcave lens between the thirteenth lens L ₁₃ and the fifteenth lens L _{15 made} of a positive lens.

  In the projection lens of FIG. 2, a light beam incident from the right side of the paper and given image information on the image display surface 1 of the light valve is incident on the projection lens through the glass block 2, and the left side of the paper is projected by the projection lens. Is enlarged and projected. Although only one image display surface 1 is shown in FIG. 2 for ease of viewing, in the projection display device, a light beam from a light source is separated into three primary color lights by a color separation optical system, and each primary color is displayed. Some light valves are provided with three light valves so that a full-color image can be displayed. The glass block 2 can be used as a color synthesizing means such as a cross dichroic prism, whereby three primary color lights can be synthesized. In addition, it can replace with this glass block and can also arrange | position cover glass, such as a liquid crystal display element, in the position of this glass block 2. FIG.

Incidentally, FIG. 3, between the first lens group G ₁ and second lens group G ₂ of the projection lens 2, and the plate-like light reflecting mirror 4 as an optical path deflecting means for deflecting the optical path is disposed The structure of the case is shown. Incidentally, in the first lens group G ₁ and the second lens group G _2, when a large adjacent lens distance (large air gap) is provided, the light-reflecting mirror 4 of the plate-like and disposed in the gap May be.

Moreover, the following conditional expressions (1) to (7) are satisfied.
105 degrees <2ω (1)
15 <| f1 | / f (2)
15 <| f2 | / f (3)
5.0 <Bf / f (4)
2.5 <f5 / f <10.0 (5)
45> νd5 (6)
6.0 <d / f (7)
7.0 <F2 / f (8)
here,
2ω: angle of view on the enlargement side f: focal length of the entire system f1: focal length of the first lens L ₁ f2: focal length of the second lens L ₂ Bf: air-converted back focus (image display from the final surface of the reduction side lens) (It is the distance to the surface, and cover glass and glass block between them shall be converted into air)
f5: focal length of the fifth lens L ₅ νd5: the Abbe number of the fifth lens L ₅ d: (largest of adjacent lens distance) said maximum air gap
F2: a focal length of the second lens group _{G 2}

  With the configuration as described above, the projection lens of the present embodiment can have high projection performance at a wide angle while ensuring a long back focus. Moreover, an inexpensive light reflecting mirror can be employed as the light reflecting element for bending the optical path.

Also, most two lenses of the magnification side is an aspherical lens, moreover conditional expression (2), by which is configured to satisfy (3), located closest to the magnifying side of the first lens group G ₁ large The power of the first lens L ₁ and the second lens L ₂ having a diameter and an aspherical surface can be defined to be small, and the two powers are weak at the enlargement side position spaced from the aperture stop 3. Since an aspheric lens can be disposed, various aberrations including field curvature and distortion can be greatly improved.

Furthermore, in particular conditions (5), to satisfy (6), and a three-element cemented lens, one on the first lens group G _1, the chromatic aberration (especially by providing two in the second lens group G ₂ High-order chromatic aberration) can be satisfactorily corrected.

  Since each of the above components is set so as to be related to each other, these functions and effects can be obtained by satisfying at least all of the above conditional expressions (1) to (3). The significance of each of the conditional expressions (1) to (8) will be described.

  Conditional expression (1) indicates the lower limit of the angle of view on the enlargement side. If the lower limit is not reached, the light reflecting mirror for bending the optical path cannot be inserted or the lens back becomes too short.

Condition (2) to the total focal length, it prescribes the lower limit of the value of the ratio of the absolute value of the first lens focal length of L _1. The conditional expression (3) is, relative to the total focal length, prescribes the lower limit of the value of the ratio of the absolute value of the focal length of the second lens L _2. In either case, if the value is lower than the lower limit value, the power of the corresponding lens becomes too strong and it becomes difficult to obtain a plastic lens, so that the manufacturing cost increases.

  Further, by satisfying these conditional expressions (2) and (3), two aspherical lenses having low power can be arranged at positions away from the aperture stop 3, and field curvature and distortion can be reduced. Various aberrations including the beginning can be made favorable.

  Conditional expression (4) represents the lower limit of the value of the back focus Bf with respect to the focal length f of the entire system. Below this lower limit, the required back focus cannot be secured.

Note that, by replacing the conditional expression (4) with the following conditional expression (4 ′), the necessary back focus can be ensured more reliably.
6.5 <Bf / f (4 ′)

Conditional expression (5) defines the range of the value of the ratio of the focal length f of the entire system to the focal length f5 of the positive lens (fifth lens L ₅ ) of the first lens group G ₁ . If out of this range, chromatic aberration correction becomes difficult.

Condition (6) is obtained by defining the lower limit of the Abbe number νd5 the first lens group G ₁ having a positive lens (fifth lens L _5). If the lower limit is not reached, chromatic aberration correction becomes difficult.

  Conditional expression (7) defines the lower limit of the ratio of the focal length f of the entire system to the maximum air gap d. When the lower limit is not reached, it becomes impossible to insert a light reflecting mirror for bending the optical path between the lenses, or the lens back becomes too short.

Condition (8), to the focal length F2 of the second lens group G _2, a definition of the lower limit of the ratio of the values of the focal length f of the entire system. If the lower limit is not reached, the light reflecting mirror for bending the optical path cannot be inserted between the lenses, or the lens back becomes too short.

Further, the projection lens of this embodiment has three cemented lens _L 4 ~L ₆ in the first lens group _{G 1} is arranged, and the second lens group _{G 2,} 2 three-cemented lens _L 9 ~ By arranging L ₁₁ and L _{13 to} L ₁₅ , it is possible to make the entire system compact while satisfactorily correcting chromatic aberration (particularly higher-order chromatic aberration).

Further, the projection lens of this embodiment, at least two surfaces in the first lens group G _1, and to arrange at least one aspherical surface during the second lens group G _2, by which, the number of lenses The resolution can be improved while reducing.

Further, the projection lens of the present embodiment is configured so that the most magnification side lens and any lens in the second lens group G ₂ in the first lens group G ₁ is an aspherical lens, the correction of the field curvature due to the projection distance change, and the first lens L ₁ is the most magnification side lens in the first lens group G ₁ as carried out by moving in the optical axis direction. Furthermore, the image plane position correcting due to the change of the projection distance, and to perform by varying the air gap between the first lens group G ₁ and the second lens group G _2.

  Next, an embodiment of a projection display device according to the present invention will be described. FIG. 8 is a longitudinal sectional view of a projection display device according to an embodiment of the present invention, and FIG. 9 is a configuration diagram showing an example of the illumination optical system 10 shown in FIG.

  The projection display device shown in FIG. 8 is a rear projection display device that particularly exhibits the above-described effects of the projection lens, and guides the light source, the light valve, and the light flux from the light source to the light valve. An illumination optical unit (both included in the illustrated illumination optical system 10) and the projection lens are provided in the cabinet 8, and a light beam from a light source is optically modulated by a light valve to carry a light beam carrying image information. The projection lens and the rear mirror 6 are configured to project onto the rear surface of the screen 7 disposed at a predetermined distance. The viewer views the image enlarged and projected on the screen 7 from the front side (left side of the paper) of the screen 7.

  As shown in FIG. 9, the illumination optical system 10 includes transmissive liquid crystal panels 11a to 11c as light valves, dichroic mirrors 12 and 13 for color separation, a cross dichroic prism 14 for color synthesis, and a condenser. Lenses 16a to 16c and total reflection mirrors 18a to 18c are provided. Although the illustration of the front stage of the dichroic mirror 12 is omitted, the white light from the light source passes through the illumination optical unit and the liquid crystal panels 11a to 11c respectively correspond to the three color light beams (G light, B light, and R light). And is optically modulated and projected onto the screen 7 by the projection lens shown in FIG.

Since this projection type display apparatus uses the projection lens according to the present invention, it is possible to obtain a large screen with high resolution in which chromatic aberration is well corrected. Further, when a predetermined lens distance between (in the first lens group G ₁ and the second lens group G ₂ of the first lens group G ₁ and the second lens group G ₂ of the projection lens is large, the Since the mirror 4 for deflecting the optical path is disposed at the lens interval) and the optical path is bent at an acute angle, the height and thickness can be reduced. Further, since the mirror 4 is used as an element for deflecting the optical path, it is advantageous in terms of cost compared to the case of deflecting light using a prism. Instead of the prism capable of shortening the physical path length, it became possible to use a plate-shaped light reflecting mirror 4, between the first lens group G ₁ and the second lens group G ₂ This is because the spatial distance (or the distance between the lenses in each of the lens groups G ₁ and G ₂ ) can be greatly increased.

  Specific examples of the projection lens according to the present invention will be described below. In addition, in each Example, the same code | symbol is attached | subjected about the member which makes mutually the same effect.

<Example 1>
1, the projection lens according to Example 1, in order from the magnification side, a first lens group G ₁ having a negative refractive power, positive second lens group G ₂ and the sequence having a refractive power As a result, the reduction side is substantially telecentric.

The first lens group G ₁ includes, in order from the magnification side, a first lens L ₁ and a second lens L _{2 made of} an aspheric lens having a small refractive power, and a third lens L made of a negative meniscus lens having a concave surface facing the reduction side. _{3. A} fourth lens L _{4 made of} a negative lens having a concave surface facing the reduction side, a fifth lens L _{5 made of a} biconvex lens, and a sixth lens L ₆ made of a negative lens having a concave surface directed to the enlargement side. Three cemented lenses are arranged.

On the other hand, the second lens group G ₂ includes a seventh lens L ₇ formed of a positive lens, an aperture stop 3, the eighth lens L ₈ formed of a negative lens, a tenth lens L ₁₀ made biconcave lens of a positive lens comprising a cemented triplet consisting sandwiching ninth lens _{L 9} and the eleventh lens _{L 11,} a twelfth lens _{L 12} made of a small aspherical lens having refractive power, a fourteenth lens _{L 14} which is a biconcave lens positive lens and 3 cemented lens formed by interposing in thirteenth lens _{L 13} and the fifteenth lens _{L 15} made of, sixteenth lens _{L 16} which is a biconvex lens are arrayed.

The shape of each aspherical surface is defined by the following aspherical surface formula. The first lens L ₁ , the second lens L _2, and the twelfth lens L ₁₂ having an aspheric surface can obtain an effect even if any one of the surfaces is an aspheric surface. More preferably, the lens is aspherical.

  Although the projection lens according to Example 1 is configured to satisfy the conditional expressions (1) to (8), the lower limit value of the conditional expression (4) is set to a more preferable numerical value. Further, the above-described conditional expression (4 ′) is satisfied.

  FIG. 1 shows an image display surface 1 and a glass block 2 of the light valve.

The radius of curvature R of each lens surface of the projection lens according to Example 1 (standardized with a focal length of 1; the same in the following examples), the center thickness of each lens, and the air space between each lens (hereinafter “axis”) D) (referred to as “upper surface distance”) D (normalized with a focal length of 1; the same in the following examples), the refractive index N _d of each lens at the d-line and the Abbe number ν _d of each lens at the d-line. It is shown in the upper part of Table 1. In Table 1 and the following table, the surface number numbers indicate the order from the enlargement side, and the surface marked with * on the right side of the surface number is an aspheric surface. In Example 1 and Examples 2 and 3 below, the curvature radius R of these aspheric surfaces is shown as the value of the curvature radius R on the optical axis X in each table, but in the corresponding lens configuration diagram. In order to make the drawing easy to see, there are some leader lines that are not necessarily drawn from the intersection with the optical axis X.

The lower part of Table 1 shows the values of the constants K, A _{3 to} A ₁₂ corresponding to the aspheric surfaces. The lower part of Table 1 shows the projection distance (enlarged side conjugate position to lens first surface). Are shown).

  In Example 1, values corresponding to the conditional expressions (1) to (8) are as shown in Table 4 to be described later, and all the conditional expressions (1) to (8) are satisfied (conditional expression (4 ') Is also satisfied).

<Example 2>
The configuration of the projection lens according to Example 2 is as shown in FIG. 2 and is the same as that of the projection lens according to Example 1. Further, the projection lens according to Example 2, between the first lens group G ₁ and the second lens group G _2, have provided capable air space mirrors 4 for deflecting the optical path, FIG. 3 A mirror 4 can be provided as shown in FIG. The projection lens is configured to be telecentric on the reduction side.

The values of the curvature radius R of each lens surface of the projection lens according to Example 2, the axial distance D between each lens, the refractive index N _d of each lens at the d-line and the Abbe number ν _d at the d-line of each lens are 2 is shown in the upper part. The lower part of Table 2 shows the values of the constants K, A _{3 to} A ₁₂ corresponding to the respective aspheric surfaces, and the lower part of Table 2 shows the projection distance (enlarged side conjugate position to lens first surface). Are shown).

  In Example 2, the values corresponding to the conditional expressions (1) to (8) are as shown in Table 4 to be described later, and all the conditional expressions (1) to (8) are satisfied (conditional expression (4 ′)). Is also satisfied).

<Example 3>
The configuration of the projection lens according to Example 3 is as shown in FIG. 4 and is the same as that of Example 1.

The values of the radius of curvature R of each lens surface of the projection lens according to Example 3, the axial distance D between each lens, the refractive index N _d of each lens at the d-line, and the Abbe number ν _d of each lens at the d-line are 3 is shown in the upper part. The lower part of Table 3 shows values of constants K and A _{3 to} A ₁₂ corresponding to the respective aspheric surfaces. The lower part of Table 3 shows the projection distance (enlarged side conjugate position to lens first). The spacing between the surfaces is shown.

  In Example 3, values corresponding to the conditional expressions (1) to (8) are as shown in Table 4 described later, and all of the conditional expressions (1) to (8) are satisfied (conditional expression (4 ′)). Is also satisfied).

  FIGS. 5 to 7 are aberration diagrams illustrating various aberrations (spherical aberration, astigmatism, distortion, and lateral chromatic aberration) of the projection lenses according to Examples 1 to 3. FIGS. In these aberration diagrams, ω represents a half angle of view, the aberration diagram of spherical aberration shows aberration curves of d-line, F-line and C-line, and the aberration diagram of magnification chromatic aberration shows F-line and C-line with respect to d-line. The aberration curve is shown. As shown in FIGS. 5 to 7, in the projection lenses according to Examples 1 to 3, each aberration including distortion and lateral chromatic aberration was corrected satisfactorily, and the half angle of view was 55.9 to 56.0 degrees (see Table 4). (See each numerical value corresponding to conditional expression (1)), F number 2.50, and a wide-angle and bright projection lens. In addition, a sufficient back focus (refer to each numerical value corresponding to the conditional expression (4)), and an inter-lens air space sufficient to insert a light reflecting mirror (respective numerical values corresponding to the conditional expression (7) Reference) is secured.

  The projection lens according to the present invention is not limited to the above-described embodiments, and various modifications can be made. For example, the curvature radius R and the lens interval (or lens thickness) D of each lens can be changed as appropriate. 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 lens of the present invention are possible. As the light valve, for example, a transmissive or reflective liquid crystal display element, or a micro mirror element in which a large number of micro mirrors capable of changing the inclination are formed on a substantially flat surface (for example, manufactured by Texas Instruments). Digital micromirror device) can be used. Also, as the illumination optical system, an appropriate configuration corresponding to the type of light valve can be adopted.

FIG. 3 is a diagram illustrating the configuration of a projection lens according to Example 1 of the invention. The figure showing the structure of the projection lens which concerns on Example 2 of this invention. FIG. 2 is a diagram illustrating a configuration when a mirror that deflects an optical path is provided in the projection lens according to FIG. 2. The figure showing the structure of the projection lens which concerns on Example 3 of this invention. Various aberration diagrams of the projection lens according to Example 1 Various aberration diagrams of the projection lens according to Example 2 Various aberration diagrams of the projection lens according to Example 3 The figure showing schematic structure of the projection type display apparatus of this invention The figure showing the composition of the illumination optical system of a projection type display device

Explanation of symbols

1 Image display surface 2, 2a, 2b Glass block (cover glass)
3a mask 3,3b aperture stop 4 mirror 6 back mirror 7 screen 8 cabinet 10 an illumination optical system 11a~11c transmissive liquid crystal panel 12, 13 dichroic mirror 14 cross dichroic prism 16a~16c condenser lens 18a~18c total reflection mirror G _1, G ₂
Lens group L ₁ ~L ₁₆ lens R ₁ to R of curvature such as ₂₉ lens surface radius D ₁ to D ₂₈ lens spacing (lens thickness)
X optical axis

Claims (8)

A projection lens in which a first lens group having a negative refractive power and a second lens group having a positive refractive power are arranged in order from the magnification side,
The distance between the first lens group and the second lens group is set to the maximum air distance in the projection lens, and the reduction side is configured to be substantially telecentric,
The first lens group includes, in order from the magnifying side, a first lens and a second lens that are aspherical lenses, a third lens that is a negative lens having a concave surface on the reduction side, and a negative lens that has a concave surface on the reduction side. A fourth lens, a fifth lens composed of a biconvex lens, and a sixth lens composed of a negative lens with a concave surface facing the enlargement side, and is composed of at least six lenses.
A projection lens satisfying the following conditional expressions (1) to (3):
105 degrees <2ω (1)
15 <| f1 | / f (2)
15 <| f2 | / f (3)
here,
2ω: angle of view on the enlargement side f: focal length of the entire system f1: focal length of the first lens f2: focal length of the second lens   The projection lens according to claim 1, wherein the fourth lens, the fifth lens, and the sixth lens constitute a three-piece cemented lens. The projection lens according to claim 1, wherein the following conditional expressions (4) to (6) are satisfied.
here,
5.0 <Bf / f (4)
2.5 <f5 / f <10.0 (5)
45> νd5 (6)
here,
Bf: Air-converted back focus f5: Focal length of the fifth lens νd5: Abbe number of the fifth lens The projection lens according to claim 1, wherein the following conditional expressions (7) and (8) are satisfied.
6.0 <d / f (7)
7.0 <F2 / f (8)
here,
d: the maximum air gap (the largest of the adjacent lens gaps)
F2: focal length of the second lens group   The projection lens according to claim 1, wherein a reflection mirror is inserted between adjacent lenses to bend the optical path.   6. The projection lens according to claim 1, wherein the correction of an image plane curve accompanying a change in projection distance is performed by moving the first lens in the optical axis direction.   The image plane position correction associated with a change in the projection distance is performed by changing an air space between the first lens group and the second lens group. Projection lens. A light source, a light valve, an illumination optical unit that guides a light beam from the light source to the light valve, and a projection lens according to claim 1, wherein the light beam from the light source is converted into the light A projection display device, wherein light is modulated by a bulb and projected onto a screen by the projection lens.

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