JPH11305116A - Projection lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a projection lens having a wide angle, a short projection distance, a long back focus, and a telecentric property and capable of projecting light at high contrast, reducing various aberrations such as a distortion aberration. SOLUTION: In a whole system, 1st and 2nd lens groups 100, 200 arranged on the large conjugate side are allowed to have negative refractive power and 3rd and 4th lens groups 300, 400 arranged on the small conjugate side are allowed to have positive refractive power to form reverse telephoto type lens constitution and obtain a wide angle and a long back focus. A telecentric property is secured so that the front side focal distance of the small conjugate side lens group exists near to the position of an outgoing pupil in the large conjugate side lens group. A combined lens 202 in the rear side 2nd lens group 200 is formed by a negative (both concave) lens 203 and a positive lens 204 arranged from the large conjugate side and a combined lens 301 in the 3rd lens group 300 is formed by a meniscus lens 302 and a negative (concave) lens 303 arranged from the large conjugate side, so that an F value can be properly reduced and a light ray entering angle can be widened.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a projection lens, and is suitably applied to, for example, a projection lens provided in a projection device of a projection display device.

[0002]

2. Description of the Related Art In recent years, projection display devices have become widespread. As one of such projection display devices, there is known a so-called rear projection type display device which performs display by projecting image light from a rear side of a transmission type screen.

[0003] In the rear projection type projection display device as described above, for example, a light beam obtained by collimating light from a white light source by a reflector or the like is a color separation mirror, and red, green,
It is decomposed into light beams of three colors of blue. The three color light fluxes are applied to two-dimensional image display devices (for example, LCD; Liquor) formed in accordance with red, green, and blue (R, G, B) video electric signals.
id Crystal Display). Image light obtained on each of the two-dimensional image display elements corresponding to these red, green, and blue is
The color is synthesized into white by the color synthesizing optical system, and is enlarged and projected on a transmission screen through a projection lens.

As a lens having the same configuration, a wide-angle photographic lens for a single-lens reflex camera having a long back focus and a projection television for a CRT (Cathode Ray Tube) are used in consideration of limitations due to a quick return mirror. Many wide-angle projection lenses have also been proposed.

[0005]

In the structure of the projection display apparatus as described above, the two-dimensional image display element is not used because of the necessity of arranging an optical element such as a dichroic prism or a dichroic mirror as a color combining optical system. The so-called back focus, which corresponds to the distance to the rearmost end of the projection lens, must be secured longer.

Further, as a projection display device,
When an enlarged image is formed on the entire transmissive screen with one projection device, the projection distance (for example, the distance from the exit end of the projection lens to the transmissive screen via the mirror) is reduced in order to make the projection display device itself compact. It is necessary to shorten the beam length). For that purpose, it is necessary to obtain a large screen by widening the angle of the projection lens and increasing the divergence angle of the emitted light.

In order to transmit the light from the light source to the two-dimensional image display device and enlarge and project the image on the two-dimensional image display device onto the screen with high contrast, the angle from the two-dimensional image display device is almost vertical. Must use the luminous flux emitted by the light source. Further, in order to reduce color unevenness on the screen on which the image light is projected, it is preferable that the angle of the light beam hitting the coating surface of the dichroic prism or dichroic mirror used in the color synthesizing optical system is constant.

Therefore, it is necessary to have telecentricity so that the principal ray off the axis of the projection lens is perpendicular to the two-dimensional image display element. In this case, the lens is located at the center of the two-dimensional image display element. Although the two-dimensional image display element itself has a high contrast direction in only one direction while being symmetrical with respect to the optical axis passing through, it is necessary to make an angle to the light beam itself irradiated on the two-dimensional image display element. is there.

[0009] The two-dimensional image display element usually includes an LC.
Although a display device such as D is employed, since the LCD is driven by using the matrix electrodes, it is difficult to correct the distortion of the projection lens unlike the case of using a CRT. That is, in the case of a CRT, it is relatively easy to correct the distortion of the projection lens by using a raster shape correction function such as a pincushion distortion correction. Such a raster distortion correction is not usually performed in a display device to be performed. Given the circumstances above,
It is desirable that the distortion of the projection lens be as small as possible. However, this is an obstacle to widening the angle of the projection lens and obtaining a long back focus. In other words, it has been found that if telecentricity is given while ensuring a wide angle and a long back focus as the projection lens, the overall length of the lens or the diameter of the lens tends to increase.

Also, wide-angle photographic lenses for single-lens reflex cameras and projection lenses for projection televisions using CRTs have insufficient back focus, and the incident angle and exit angle of off-axis light beams are tight, resulting in poor telecentricity. At present, the amount of light is small.

[0011]

In order to solve the above-mentioned problems, the present invention has a wide angle of view, a short projection distance, a long back focus, a large amount of off-axis light, and telecentricity. An object is to obtain a projection lens with small aberrations.

Therefore, as a first configuration, a first lens group having a negative refractive power and an aspheric surface is formed in order from a large conjugate side to a small conjugate side;
A second lens group formed with at least a cemented lens and having at least a cemented lens and having a negative refractive power with the largest central air surface interval in the entire system; A third lens group including a cemented lens and formed such that the lens surface located on the largest conjugate side has a convex surface with respect to the smaller conjugate side, and a positive refraction separated by a required center air space. A projection lens is formed by arranging a fourth lens group having an aspherical surface with a power, and a back focus is BF, a combined focal length of the entire system is F, The center air surface distance between the first lens unit and the second lens unit is D1, the combined focal length of the first lens unit and the second lens unit is F12, and the third lens unit and the fourth lens unit are F4. Lens group The formed focal length as F 34, was be configured to satisfy BF / F> 2.3 0.7 <-F12 / F34 <2.0 D1 / F> 0.8 The condition.

With the above arrangement, the first and second arrangements located on the front side (large conjugate side) in the entire system of the projection lens.
By having the negative lens unit have negative refractive power and the third and fourth lens units disposed on the rear side (small conjugate side) having positive refractive power, a wide-angle lens having a long back focus can be obtained. Thus, an inverse telephoto lens configuration can be obtained. Then, telecentricity is given by providing a front (large conjugate side) focal length of the small conjugate side lens group near the exit pupil position of the large conjugate side lens group.

As a second configuration, a first lens group having a negative refractive power and an aspheric surface is formed in order from a large conjugate side to a small conjugate side, and A second lens group formed to have a negative refractive power at the largest central air surface distance and to have at least a cemented lens; and to have at least a cemented lens to have a positive refractive power and to have at least a cemented lens. And a fourth lens group having a positive refractive power and an aspheric surface are arranged to form a projection lens, and then a second lens group is formed. The cemented lens forming the third lens group is formed by arranging the negative lens and the positive lens from the large conjugate side to the small conjugate side, and the cemented lens forming the third lens group is the large conjugate side. It was be formed by arranging the positive lens and the negative lens toward the direction of al small conjugate side.

With this configuration, in the first to fourth lens groups, the cemented lens in the second lens group is formed by a negative lens and a positive lens from the large conjugate side, and the cemented lens in the third lens group. Is formed by a positive lens and a negative lens from the large conjugate side. This makes it possible to make the F-number appropriately small and widen the light capturing angle. Transmits angled light flux,
Enlarged projection on the screen becomes possible.

Further, under each of the first and second configurations,
0.1 <D3 / F <, where D3 is the center air surface distance between the third lens unit and the fourth lens unit, F3 is the focal length of the third lens unit, and F4 is the focal length of the fourth lens unit. By adopting a configuration that satisfies the conditional expression of 0.7 F3 / F4 <4.0, a long back focus is obtained while maintaining the height of paraxial rays emitted from the third lens group, The height of the outer chief ray is emitted to a higher position in the fourth lens group, and the telecentricity of the off-axis chief ray that enters the panel surface, which is assumed to be on the small conjugate side, is maintained. Also, various aberrations at this time are suppressed.

Further, under the first and second configurations, the cemented lens forming the second lens group is formed by a positive lens and a negative lens.
The Abbe numbers of these positive lens and negative lens are respectively V2
By satisfying the conditional expression of V2N−V2P> 25 as P and V2N, chromatic aberration is corrected.

In the first configuration, the cemented lens forming the third lens group is formed by a positive lens and a negative lens, and the focal length of the positive lens is F31. The refractive indices of these positive and negative lenses are N3P and N3N, and the Abbe numbers are V3P and V3P, respectively.
As V3N, the following conditional expression is satisfied: 2.0 <F31 / F <7.0 N3N-N3P> 0.08 V3P-V3N> 25 As a result, the third
After obtaining an appropriate value as the refractive index of the cemented lens forming the above lens group, appropriate color correction can be performed.

In the second configuration, the lens disposed on the largest conjugate side in the second lens group is a meniscus lens having a negative refractive power and convex on the larger conjugate side. D21 is the largest center air surface interval of the two lens groups, F12 is the combined focal length of the first lens group and the second lens group, F21 is the focal length of the largest conjugate side meniscus lens of the second lens group. Assuming that the focal length of the second lens group is F2, the following conditional expression is satisfied: 0.1 <-D21 / F12 <0.5 0.1 <F21 / F2 <1.7. Thereby, a favorable state of the off-axis aberration correction by the second lens group can be obtained.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a projection lens according to an embodiment of the present invention will be described. The projection lens of the present embodiment will be described as being provided in a projection device of a rear projection type projection display device employing an LCD as a two-dimensional image display element.

The following description will be made in the following order. 1. Configuration of projection display device 1-1. First example 1-2. Second example 1-3. Third example 2. Configuration of projection lens 2-1. Lens arrangement structure 2-2. Conditional expression 2-3. Numerical embodiments, etc.

1. Configuration of Projection Device 1-1. First Example FIG. 1 conceptually shows an internal structure as a first example of a projection display device on which the projection lens of the present embodiment can be mounted. In this figure, a lamp 1 as a light source, such as a metal halide lamp, is disposed at a focal position of a reflector 2 (parabolic mirror). Light emitted from the lamp 1 is reflected by the reflector 2, collimated so as to be substantially parallel to the optical axis, and emitted from the opening of the reflector 2. Of the light emitted from the opening of the reflector 2, unnecessary light in the infrared and ultraviolet regions is blocked by the IR-UV cut filter 3, and only light effective for display is arranged at the subsequent stage. It will be guided to the optical element.

In the subsequent stage of the IR-UV cut filter 3,
Subsequent to the multi-lens array 4, a multi-lens array 5 is provided. In this case, the multi-lens array 4 is a state in which a plurality of convex lenses having a similar outer shape equal to the aspect ratio of the effective aperture of each liquid crystal panel block, which is a light modulating means, are shifted in phase by, for example, ２. And has a flat shape arranged in a houndstooth check pattern. The multi-lens array 5 is of a plano-convex type in which a plurality of convex lenses 5a are formed on the side of the multi-lens array 4 facing the convex lenses. By arranging the multi-lens array 4 and the multi-lens array 5, I
The luminous flux passing through the R-UV cut filter 3 is efficiently
In addition, the light is uniformly applied to an effective opening of a liquid crystal panel block described later.

Between the multi-lens array 5 and the effective aperture of the liquid crystal panel block, the luminous flux from the lamp 1 is changed to red, green,
Dichroic mirrors 6 and 10 are arranged to separate blue light. In the example shown in this figure, first, the red light beam R is reflected by the dichroic mirror 6, and the green light beam G and the blue light beam B are transmitted. The traveling direction of the red light beam R reflected by the dichroic mirror 6 is turned by 90 ° by the mirror 7 and the red liquid crystal panel block 9
Is led to the condenser lens 8 in front of.

On the other hand, the green and blue luminous fluxes G and B transmitted through the dichroic mirror 6 are
Will be separated by That is, the green light flux G
Is reflected and bent in the traveling direction by 90 °, and guided to the condenser lens 11 in front of the liquid crystal panel 12 for green. Then, the blue light beam B passes through the dichroic mirror 10 and proceeds straight, and is guided to the condenser lens 17 in front of the blue liquid crystal panel 18 via the relay lens 13, the mirror 14, the inversion relay lens 15, and the mirror 16.

In this manner, the red, green, and blue luminous fluxes R, G, and B are supplied to the respective condenser lenses 8, 11, and 17 respectively.
Through the liquid crystal panel blocks 9, 12, and 18 for each color.
Is incident on. The liquid crystal panel blocks 9 and 1 of these colors
In Nos. 2 and 18, a liquid crystal panel is provided, and an incident-side polarizing plate for aligning the polarization direction of light incident on the front stage of the liquid crystal panel in a certain direction is provided. A so-called analyzer that transmits only light having a predetermined polarization plane of the emitted light is disposed at the subsequent stage of the liquid crystal panel, and the intensity of the light is modulated by a voltage of a circuit for driving the liquid crystal.

Generally, dichroic mirrors 6, 10
In order to make effective use of the above characteristics, the reflection and transmission characteristics of the P polarization plane are used. Therefore, the above-mentioned incident side polarizing plate in each of the liquid crystal panel blocks 9, 12, 18 is arranged so as to transmit a plane of parallel polarization in the plane of FIG. Each liquid crystal panel constituting the liquid crystal panel blocks 9, 12, 18 is, for example, of the TN type, and its operation is of, for example, a normally white type, and the analyzer is perpendicular to the plane of FIG. It is arranged to transmit polarized light.

Then, the liquid crystal panel blocks 9, 12, 1
The light flux of each color light-modulated by 8 is incident on each surface shown in a light combining element (cross dichroic prism) 19. This photosynthetic element is formed by combining reflection films 19a and 19b with a prism having a predetermined shape. The red light flux R in the photosynthesis element 19 is reflected by the reflection film 19.
a, and the blue light flux B is reflected by the reflection film 19b and is incident on the projection lens 20. The green light flux G is incident on the projection lens 20 so as to go straight through the light combining element 19 and pass therethrough. As a result, the light beams R, G, and B are incident on the projection lens 20 in a state of being combined into one light beam.

The projection lens 20 converts the light beam incident from the light combining element 19 into projection light and projects it on, for example, a transmission type screen 21. On the screen 21, an enlarged image obtained by the projection light projected from the projection lens 20 is displayed. For example, the viewer views the display image by looking at the screen 21 from a direction opposite to the direction where the projection lens 20 is arranged.

1-2. Second Example FIG. 2 conceptually shows an internal structure as a second example of a projection display device on which the projection lens of the present embodiment can be mounted. In this figure, the same parts as those in FIG.

In this case, the light beam B is reflected by the dichroic mirror 6A at the subsequent stage of the multi-lens array 5, and the light beam R and the light beam G are passed. The light beam B reflected by the dichroic mirror 6A is reflected by the mirror 7A, and further reflected by the condenser lens 8A.
, And after being light-modulated through the liquid crystal panel block 9A for blue, the light enters the photosynthesis element 19A from the illustrated direction.

The luminous flux R and luminous flux G passing through the dichroic mirror 6A are combined with the subsequent dichroic mirror 10A.
Is incident on. In this case, the dichroic mirror 10A
Then, the light beam R is reflected and the light beam G is allowed to pass. The light beam R reflected by the dichroic mirror 10A passes through the condenser lens 11A, is light-modulated via the liquid crystal panel block 12A for red light, and then enters the light combining element 19A from the illustrated direction.
The light beam G that has passed through the dichroic mirror 10A is converted into a relay lens 13A, a mirror 14A, and a reversing relay lens 1.
5A, condenser lens 17A via mirror 16A
To reach. Then, after passing through the condenser lens 17A and being light-modulated through the liquid crystal panel block 18A for green, the light is incident on the photosynthesizing element 19A from the illustrated direction.

The light combining element 19A also comprises a prism having a predetermined shape and reflection films 19A-a and 19A-b combined. Of the light beams of the respective colors incident on the photosynthesis element 19A, the light beam B is reflected by the reflection films 19A-b and is incident on the projection lens 20, and the light beam G is reflected by the reflection films 19A-a and is projected on the projection lens 20A. Is incident on. The light beam R passes through the light combining element 19A so as to go straight on and enters the projection lens 20. As a result, the light beams R, G, and B are combined into one light beam and incident on the projection lens 20.

1-3. Third Example FIG. 3 conceptually shows an internal structure as a third example of a projection display device on which the projection lens of the present embodiment can be mounted. In this figure, the same parts as those in FIGS. 1 and 2 are denoted by the same reference numerals, and the description is omitted.

In this case, the dichroic mirror 6B
Reflects the light flux G, and passes the light flux R and the light flux B. The light beam G reflected by the dichroic mirror 6B is reflected by the mirror 7B and the condenser lens 8
B, after passing through the liquid crystal panel block 9B for green, the light is incident on the photosynthesis element 19B from the illustrated direction.

The light beam R and the light beam B that have passed through the dichroic mirror 6B are incident on the dichroic mirror 10B, so that the light beam R is reflected and the light beam B passes. The light beam R reflected by the dichroic mirror 10B is incident on the photosynthesis element 19B from the illustrated direction via the condenser lens 11B and the liquid crystal panel block 12B for red. Dichroic mirror 1
The light beam B that has passed through 0B is incident on the photosynthesis element 19B from the illustrated direction through the relay lens 13B, the mirror 14B, the inversion relay lens 15B, the mirror 16B, the condenser lens 17B, and the liquid crystal panel block 18B for blue. Is done.

The light combining element 19B is also formed by combining a prism having a predetermined shape with reflection films 19B-a and 19B-b. Here, of the light beams of each color that have entered the light combining element 19B, the light beam G is the reflection film 19B-a.
The light beam B is reflected by the reflection film 19B-b, and the light beam R passes through the photosynthetic element 19B so as to go straight, and is incident on the projection lens 20 as one light beam. .

Although the projection display device according to the present embodiment has been described with reference to three examples, these are merely examples, and the internal configuration of the projection display device to which the projection lens according to the present embodiment can be mounted. In addition, various other things can be considered.

2. Configuration of projection lens 2-1. Lens Arrangement Structure Subsequently, a projection lens as the present embodiment will be described. Projection lenses according to the first to fifth embodiments described below are employed as the projection lens 20 in the projection display device shown in FIGS.

First, the lens structure of the projection lens 20 according to the first to fifth embodiments will be described. FIGS. 4, 5, 6, 7 and 8 show a projection lens 2 as a first, second, third, fourth and fifth embodiment, respectively.
FIG. 2 is a lens cross-sectional view conceptually showing an arrangement structure of a No. 0 lens. In these figures, the left side of the figure is the screen 21
Side (large conjugate side), and the right side is the liquid crystal panel block and photosynthesis element side (small conjugate side). In these drawings, common parts are denoted by the same reference numerals.

As shown in FIGS. 4 to 8, the projection lens 20 according to the first to fifth embodiments has a first lens group 100, a second lens group 200, The lens group 300 and the fourth lens group 400 are arranged in order.

In this case, the first lens group 100 includes one meniscus lens 101 having a convex shape on the large conjugate side, thereby having a negative refractive power. Also, this meniscus lens 101
It has an aspheric surface according to an aspheric coefficient in a numerical embodiment described later.

The second lens group 200 includes a meniscus lens 201 having a negative refractive power due to having a convex shape from the large conjugate side to the large conjugate side, and a cemented lens 202 arranged as shown in the figure. Consisting of Here, the bonding lens 202 is formed by arranging a biconcave lens (negative lens) 203 and a positive lens 204 from the large conjugate side, and bonding these.

The third lens group 300 has a positive refractive power by arranging a cemented lens 301 and a positive lens 304 as shown in the figure from the large conjugate side. The cemented lens 301 has a convex surface from the large conjugate side to the small conjugate side.
2 and a concave lens (negative lens) 303 having a concave surface on one side on a large conjugate side.
2 and the concave surface of the concave lens 303 having a large curvature.

The fourth lens group 400 is formed by arranging the positive lenses 401 and 402 from the large conjugate side.
The third lens group 300 has a positive refractive power at a certain center air plane distance. here,
The positive lens 402 has an aspheric surface according to an aspheric coefficient in a numerical embodiment described later.

2-2. Conditional Expressions In the projection lens 20 according to the first to fifth embodiments having the above configuration, the following conditional expressions (1) to (11).
Meets.

The back focus is BF, the combined focal length of the entire system is F, the center air surface distance between the first lens group 100 and the second lens group 200 is D1, and the combined focus of the first lens group 100 and the second lens group 200 is D1. Assuming that the distance is F12 and the combined focal length of the third lens unit and the fourth lens unit is F34, BF / F> 2.3 (1) 0.7 <-F12 / F34 <2.0 ... (2) D1 / F> 0.8 (3)

Third lens group 300 and fourth lens group 400
Is defined as D3, the focal length of the third lens group 300 is defined as F3, and the focal length of the fourth lens group 400 is defined as F4. 0.1 <D3 / F <0.7 (4) F3 /F4<4.0 (5)

The largest center air surface interval in the entire system in the second lens group 200 is D21, and the first lens group 100
The combined focal length of the second lens group 200 and F12 is
Assuming that the focal length of the largest conjugate side meniscus lens of the lens unit 200 is F21 and the focal length of the second lens unit 200 is F2, 0.1 <−D21 / F12 <0.5 (6) 0.1 <F21 / F2 <1.7 (7)

For the positive lens 204 and the biconcave lens (negative lens) 203 forming the cemented lens 202 in the second lens group 200, the Abbe number of the positive lens 204 is V
2P, the Abbe number of the biconcave lens (negative lens) 203 is V2
As N, V2N−V2P> 25 (8)

The meniscus lens 302 and the concave lens (negative lens) 303 forming the cemented lens 301 in the third lens group 300 are
02 is set to F31 and the meniscus lens 302
And the concave lens (negative lens) 303 are N3P and N
Assuming that 3N and Abbe numbers are V3P and V3N, 2.0 <F31 / F <7.0 (9) N3N-N3P> 0.08 (10) V3P-V3N> 25 ( 11)

Next, the above-mentioned conditional expressions will be described.
For example, as can be seen from the configurations shown in FIGS. 1 to 3, as the projection lens of the projection display device, it is necessary to use an optical element such as a dichroic mirror or a dichroic prism for color synthesis. is necessary. Here, it is necessary to obtain a large screen with a short projection distance in order to reduce the size of the projection display device, that is, to reduce the size of the housing, so that the angle of view of the projection lens 20 is widened. become.

Therefore, in the present embodiment, conditional expression (1)
Is satisfied, the angle of view of the projection lens 20 is widened. Here, when the value goes below the lower limit of the conditional expression (1), the space of the color composition system is lost.

In the conditional expression (2), in order to achieve the reverse telephoto type configuration, the combined focal length of the first lens group 100 and the second lens group 200, the third lens group 300 and the fourth lens group 400
Are defined. When the conditional expression (2) is satisfied, the size, the back focus, and the optical performance of the entire projection lens system are favorably maintained. Conversely, when the value exceeds the upper limit of the conditional expression (2), the inverse telephoto type configuration becomes weak. Therefore, it is difficult to maintain the back focus, and if it is intentionally lengthened, the overall length of the lens becomes longer, and the lens diameters of the first lens group 100 and the second lens group 200 become undesirably large. If the lower limit of conditional expression (2) is exceeded, the first lens group 10
0, the refracting power of the second lens group 200 increases, and curvature of field and distortion occur, making it difficult to correct.

Conditional expression (3) is a condition for reducing the diameter by reducing the diameter of the second lens group 200, and by increasing the center air surface distance between the first lens group 100 and the second lens group 200, This means that the second lens group 200 is arranged at a position where the height of the light beam emitted from the one lens group 100 is low. Here, if the lower limit value of conditional expression (3) is exceeded, the lens diameter of the second lens group 200 becomes large, and for example, the cost of parts is undesirably increased.

Also, conditional expressions (4) and (5) are
The distance between the center air surface of the third lens group 300 and the fourth lens group 400 is increased, and the back focus is lengthened by maintaining the height of paraxial rays emitted from the third lens group 300. Conditions for maintaining the telecentricity of the off-axis principal ray incident on the panel surface by emitting the principal ray to the high position of the fourth lens group 400, and the third lens group 300 in the entire lens system at that time. This defines the condition of the balance of the power of the fourth lens group 400. Here, when the values exceed the upper limits of conditional expressions (4) and (5), various aberrations including spherical aberration occur, and correction becomes difficult, which is not preferable.

Conditional expressions (6) and (7) show the arrangement of the lenses and the balance of the focal length in a state where the off-axis aberration is well corrected by the second lens group 200. In the first lens group 100, each off-axis light beam passes through a different part of the lens, and the aspherical lens changes the state of refraction of the light beam by a slightly different curved surface for each light beam. Second
In the vicinity of the lens on the liquid crystal panel side (small conjugate side) of the lens group 200, the rays from the on-axis ray to the off-axis light beam pass through almost the same lens surface and are emitted to the third lens group 300. The lens closest to the screen (large conjugate side) of the second lens group 200 guides light rays to the cemented lenses 202 and 301 in the second lens group 200 and the third lens group 300. Then, here, conditional expressions (8), (10), (1)
By using a material such as glass that satisfies 1) as a lens, chromatic aberration is corrected.

The conditional expression (6) defines the height of a light ray in the second lens group 200. By satisfying conditional expression (6), the negative meniscus lens 201 convex to the screen side (large conjugate side) closest to the screen side (large conjugate side) in the second lens group 200 and the central air surface thereafter By increasing the distance, the first lens group 10
The luminous flux from 0 is guided to the cemented lens in the second lens group 200 by a light beam having a gentle angle, so that the occurrence of aberration due to the refraction of the light beam on the surface is suppressed. If the upper limit of conditional expression (6) is exceeded, the screen side (large conjugate side) closest to the screen side (large conjugate side) in the second lens group 200 will be described.
The lens diameter of the negative meniscus lens or the first lens group 100 that is convex to the right increases. If the lower limit of conditional expression (6) is exceeded, off-axis aberrations will increase and correction will be difficult.

Conditional expression (7) is the focal length of the meniscus lens (negative lens) 201 that is closest to the screen side and convex to the screen side in the second lens group 200 that satisfies the conditional expression (6). It is a balance. If the upper limit of condition (7) is exceeded, this meniscus lens 20
Since the refractive power of the lens 1 becomes strong and the emitted light beam is refracted too much, the off-axis light beam diverges, and the diameter of the next lens (the meniscus lens 101) becomes undesirably large.
If the lower limit of the conditional expression (7) is exceeded, the refractive power of the meniscus lens 201 becomes weak. Therefore, the largest central air surface distance D21 (in the entire system in the second lens group 200 in the above conditional expression (6) Here, meniscus lens 20
1 and the center air surface distance between the cemented lens 202) become too narrow, and the positional balance between the on-axis ray and the off-axis ray cannot be maintained.

Conditional expression (9) indicates the refractive power of the meniscus lens 302 in the cemented lens 301 in the third lens group 300. For example, conditional expressions (10) and (11) for the meniscus lens 302 By using a glass that can satisfy the condition, appropriate color correction can be performed. When the value exceeds the upper limit of the conditional expression (9), the refractive power of the concave lens (negative lens) 303 in the cemented lens 301 must be increased. If the lower limit of conditional expression (9) is exceeded, the refractive power of the concave lens (negative lens) 303 in the cemented lens 301 will be weak, and chromatic aberration will be insufficiently corrected.

2-3. Numerical Embodiments and the Like Here, the projection lens 20 according to the first to fifth embodiments is described.
Numerical embodiments as shown in FIG. 9, FIG. 10, FIG. 11, FIG.
2 and FIG. In these figures,
m is the surface number of the lens surface counted from the screen 21 side (large conjugate side), ri is the i-th radius of curvature counted from the screen side, di is the i-th lens surface interval, and ni is the i-th refraction. The ratio, vi, indicates the i-th Abbe number.

The surface shape of the first surface and the sixteenth surface as an aspherical surface is such that, in an orthogonal coordinate system (X, Y, Z) where the origin is the center of the surface and the optical axis direction is Z, r is the center. When the curvature radius and K are conic constants A4, A6, A8, and A10, respectively, are the fourth, sixth, eighth, and tenth aspherical coefficients,

(Equation 1) Is represented by the following equation.

FIG. 14 shows a numerical example satisfying the above-mentioned conditional expressions (1) to (11) in the first to fifth embodiments.

Also, FIGS. 15, 16, 17, 18,
19 shows the spherical aberration, astigmatism, and distortion of the projection lens 20 according to the first to fifth embodiments. In order to obtain the results shown in the various aberration diagrams shown in these figures, although not shown in the numerical embodiments, the light combining element 19 (19A, 19B) has a center plane spacing of 35 mm (refractive index n = 1. 51633, Abbe number ν
= 64.0) is calculated.

The actual structure of the projection lens according to the first to fifth embodiments is not limited to those shown in FIGS. 4 to 8, but satisfies the conditional expressions described above. As long as it is possible, the number of lenses forming each lens group may be changed. In the above embodiment, the projection lens of the present invention is described as being provided in a projection device using a liquid crystal panel as a two-dimensional image display element in a rear projection type projection display device. Is not
For example, a wide-angle photographic lens for a single-lens reflex camera,
The present invention can be applied to a projection lens for a projection television using an RT.

[0066]

As described above, according to the present invention, the following effects can be obtained. First, according to the first aspect of the present invention, for example, a wide-angle lens having a long back focus, which is required when a projection lens is used in a projection display device, can be obtained, and an inverted telephoto lens configuration can be obtained. That is, a large screen can be obtained with a short projection distance. In addition, telecentricity is given by providing a front (large conjugate side) focal length of the small conjugate side lens group near the exit pupil position of the large conjugate side lens group.

According to the fifth aspect of the present invention, in the first to fourth lens groups forming the entire projection lens system,
The cemented lens in the second lens group is formed by a negative lens and a positive lens from the large conjugate side,
The bonded lens in the lens group is formed by a positive lens and a negative lens from the large conjugate side. As a result, the F-number can be made appropriately small and the light-intake angle can be widened, so that the angled light flux of the two-dimensional image display element can be appropriately transmitted and enlarged and projected on the screen with high contrast. Becomes possible.

Further, according to the second aspect of the present invention described in the first aspect and the sixth aspect of the invention described in the fifth aspect, the near lens output from the third lens group is provided. By maintaining the height of the axial ray, a long back focus is also ensured here. Further, the height of the off-axis chief ray is emitted to a high position of the fourth lens group, so that the telecentricity of the off-axis chief ray incident on the liquid crystal panel surface in the projection display device can be maintained. Further, various aberrations at this time can be suppressed, and a projection lens with high performance can be obtained.

According to the third and eighth aspects of the present invention, the chromatic aberration of the projection lens is properly corrected. Will be done.

Further, according to the invention described in claim 4 under the invention described in claim 1, after obtaining an appropriate value as the refractive index of the cemented lens forming the third lens group,
Appropriate color correction is made possible.

According to the invention described in claim 7 under the invention described in claim 2, it is possible to obtain a state in which the off-axis aberration by the second lens group is favorably corrected.

That is, according to the present invention, a wide angle, a short projection distance, a long back focus, and telecentricity can be achieved, especially in a projection device using a liquid crystal panel, in which high-contrast projection is possible. And a projection lens with few aberrations is realized. Then, for example, when the projection lens of the present invention is applied to a projection device using a liquid crystal panel as a two-dimensional image display element to form a projection display device, a thin type having a reduced depth and the like can be obtained. At the same time, good image quality is expected.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration (first example) of a projection display device including a projection lens according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration (second example) of a projection display device including a projection lens according to an embodiment of the present invention.

FIG. 3 is a diagram illustrating a configuration (third example) of a projection display device including a projection lens according to an embodiment of the present invention.

FIG. 4 is a lens cross-sectional view showing a structural example of a projection lens as a first embodiment.

FIG. 5 is a lens cross-sectional view illustrating a structural example of a projection lens as a second embodiment.

FIG. 6 is a lens cross-sectional view illustrating a configuration example of a projection lens as a third embodiment.

FIG. 7 is a lens cross-sectional view illustrating a configuration example of a projection lens as a fourth embodiment.

FIG. 8 is a lens cross-sectional view illustrating a configuration example of a projection lens as a fifth embodiment.

FIG. 9 is a diagram showing a numerical embodiment of the projection lens as the first embodiment.

FIG. 10 is a diagram showing a numerical embodiment of a projection lens as a second embodiment.

FIG. 11 is a diagram showing a numerical embodiment of a projection lens as a third embodiment.

FIG. 12 is a diagram showing a numerical embodiment of a projection lens as a fourth embodiment.

FIG. 13 is a diagram showing a numerical embodiment of a projection lens as a fifth embodiment.

FIG. 14 is a diagram showing numerical values corresponding to conditional expressions (1) to (11) in each of the first to fifth embodiments.

FIG. 15 is an aberration diagram showing a spherical aberration, an astigmatism, and a distortion of the projection lens as the first embodiment.

FIG. 16 is an aberration diagram showing a spherical aberration, an astigmatism, and a distortion of the projection lens as the second embodiment.

FIG. 17 is an aberration diagram showing a spherical aberration, an astigmatism, and a distortion of the projection lens as the third embodiment.

FIG. 18 is an aberration diagram showing a spherical aberration, an astigmatism, and a distortion of a projection lens as a fourth embodiment.

FIG. 19 is an aberration diagram showing spherical aberration, astigmatism, and distortion of a projection lens as a fifth embodiment.

[Explanation of symbols]

1 lamp, 2 reflector, 3 IR-UV cut filter, 4,5 multi-lens array, 6,6A, 6B
Dichroic mirror, 7,7A, 7B mirror,
8, 8A, 8B Condenser lens, 9, 9A, 9B
Liquid crystal panel block, 10, 10A, 10B dichroic mirror, 11, 11A, 11B condenser lens, 12, 12A, 12B Liquid crystal panel block, 1
3, 13A, 13B relay lens, 14, 14A, 1
4B mirror, 15, 15A, 15B Inverting relay lens, 16, 16A, 16B mirror, 17, 17A,
17B Condenser lens, 18, 18A, 18B
Liquid crystal panel block, 19, 19A, 19B Photosynthesis element, 19a, 19b, 19A-a, 19A-b, 19B
-A, 19B-b Reflective film 20 Projection lens, 21
Screen, 100 first lens group, 101 meniscus lens, 200 second lens group, 201 meniscus lens, 202 stuck lens, 203 biconcave lens,
204 positive lens, 300 third lens group, 301 bonded lens, 302 meniscus lens, 303 concave lens, 304 positive lens, 400 fourth lens group, 4
01 positive lens, 402 positive lens

Claims (8)

[Claims] 1. A first lens group having a negative refractive power and an aspheric surface formed in order from a large conjugate side to a small conjugate side, and the largest center air surface distance in the entire system. A second lens group formed having at least a cemented lens and having a negative refractive power at a distance; and a second lens group having a positive refractive power and having at least a cemented lens and having the largest conjugate side. A third lens group formed such that the lens surface located at a convex surface with respect to the small conjugate side has a positive refractive power at a required center air surface interval, and has an aspheric surface. A back focus is BF, a combined focal length of the entire system is F, a center air surface distance between the first lens group and the second lens group is D1, The above The composite focal length of the lens group unit and the second lens F12, and the fourth the third lens group
Where F34 is the combined focal length of the lens group of (1), and the following conditional expression is satisfied: BF / F> 2.3 0.7 <-F12 / F34 <2.0 D1 / F> 0.8 . 2. A center air surface distance between the third lens group and the fourth lens group is D3, a focal length of the third lens group is F3, and a focal length of the fourth lens group is F4. The projection lens according to claim 1, wherein the following conditional expression is satisfied: 0.1 <D3 / F <0.7 F3 / F4 <4.0. 3. The bonded lens forming the second lens group is formed by a positive lens and a negative lens, and the Abbe numbers of the positive lens and the negative lens are defined as V2P and V2N, respectively. The projection lens according to claim 1, wherein the following conditional expression is satisfied: V2N-V2P> 25. 4. The cemented lens forming the third lens group is formed by a positive lens and a negative lens. The focal length of the positive lens is F31. The refractive index of each lens is N3
2. A conditional expression of 2.0 <F31 / F <7.0 N3N-N3P> 0.08 V3P-V3N> 25, where P, N3N and Abbe's number are V3P and V3N, respectively. The projection lens according to 1. 5. A first lens group having a negative refractive power and an aspherical surface, and the largest central air surface distance in the whole system, in order from a large conjugate side to a small conjugate side. A second lens group formed to have a negative refractive power and having at least a cemented lens, and a second lens group having a positive refractive power and having at least a cemented lens. 3 and a fourth lens group having a positive refractive power and an aspheric surface are arranged. The cemented lens forming the second lens group has a large conjugate. A negative lens and a positive lens are arranged and formed from the side to the small conjugate side, and the cemented lens forming the third lens group is positive from the large conjugate side to the small conjugate side. A projection lens, wherein a lens and a negative lens are arranged and formed. 6. The distance between the center air surface of the third lens group and the fourth lens group is D3, the focal length of the third lens group is F3, and the focal length of the fourth lens group is F4. The projection lens according to claim 5, wherein the following conditional expression is satisfied: 0.1 <D3 / F <0.7 F3 / F4 <4.0. 7. The second lens group, wherein the lens disposed on the largest conjugate side has a negative refractive power and is a meniscus lens convex on the larger conjugate side. The largest center air surface spacing in
1. The combined focal length of the first lens group and the second lens group is F12, the focal length of the largest conjugate side meniscus lens of the second lens group is F21, and the focal length of the second lens group is F12. 6. The projection lens according to claim 5, wherein F2 satisfies the following conditional expression: 0.1 <-D21 / F12 <0.5 0.1 <F21 / F2 <1.7. 8. The bonded lens forming the second lens group is formed by a positive lens and a negative lens, and the Abbe numbers of the positive lens and the negative lens are V2P and V2N, respectively. The projection lens according to claim 5, wherein the following conditional expression is satisfied: V2N-V2P> 25.