JPH06235884A - Projection optical system - Google Patents

Abstract

PURPOSE:To obtain the projection optical system which efficiently illuminates a liquid crystal display element and which is adequate to a liquid crystal projector capable of obtaining a good projection image. CONSTITUTION:The projection optical system is provided with a positive meniscus first lens L1 whose convex face faces on a first conjugate point side having a longer distance, an entirely negative combined lens obtained by combining a positive meniscus second lens L2 whose convex face faces on the first conjugate point side with a negative meniscus third lens L3 whose convex face faces on the first conjugate point side, a negative meniscus fourth lens L4 whose convex face faces on the side of a second conjugate point having a shorter distance, a positive meniscus fifth lens L5 whose convex face faces on the second conjugate point side, and a positive Fresnel lens FL in order from the 1st conjugate point side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection optical system, and more particularly to a projection optical system suitable for enlarging and projecting image information displayed on a liquid crystal display device or the like onto a screen surface.

[0002]

2. Description of the Related Art Conventionally, a plurality of images having color information, such as liquid crystal light valves, are illuminated by predetermined color lights, optically superposed, and then projected onto a screen surface by a projection lens. Various projection type display devices (liquid crystal projectors) have been proposed.

FIG. 8 is a schematic view of a main part of an optical system of a conventional projection type display device.

In FIG. 1, reference numerals 1, 2 and 3 denote liquid crystal light valves, on the surface of which an image (black and white image) based on predetermined color information is formed.

The light flux from the white light source 14 is separated by the dichroic mirrors 8 and 9 using the reflecting mirror 13 into colored light based on the color information, for example, red (R), green (G) and blue (B) colored light. To do. The liquid crystal light valves 1, 2 and 3 based on the color information corresponding to each color light are illuminated using the condenser lenses 4, 5 and 6 (the liquid crystal light valve 1 is via the total reflection mirror 7).

After the light flux from the liquid crystal light valve 3 is bent by the total reflection mirror 12 and the light flux from the liquid crystal light valves 1 and 2 passes through the dichroic mirror 10, the dichroic mirror 11 produces red, green and Images based on the three color lights of blue are combined to form a color image, which is then projected by a projection lens 15 onto a screen (not shown).

FIG. 9 is a schematic view of a main part of a projection type display device when a color image is displayed on a single liquid crystal display element and an image is projected.

In the figure, the liquid crystal display element 16 is illuminated with a light beam from a light source 19 using a reflecting mirror 18 and a condenser lens 17. Then, the liquid crystal display element 16 is projected by the projection lens 20 onto a predetermined surface (screen surface).

[0009]

Since the projection lens 20 of the projection type display device shown in FIG. 9 has a relatively short back focus as compared with the projection lens 15 shown in FIG. 8, the size of the entire device can be reduced.

However, of the illumination light that illuminates the liquid crystal display element 16, the luminous flux that illuminates the peripheral portion of the liquid crystal display element enters the liquid crystal display element at a large angle. Therefore, there is a problem in that contrast unevenness occurs over the entire liquid crystal display element.

Besides, as the number of pixels of the liquid crystal display element increases, the aperture ratio of the liquid crystal display element decreases.

In order to improve this, there has been proposed a liquid crystal display element member in which a microlens array 26 is provided corresponding to each pixel 27 of the liquid crystal display element 16 as shown in FIG.

However, in the liquid crystal display element member to which the microlens array is added, if the light flux is not incident on the liquid crystal display element substantially perpendicularly, the light flux is eclipsed as shown in FIG. 11 and the aperture ratio is lowered. There was a point.

Further, as shown in FIG. 10, since the light flux is diffused by the microlens array 26, the light utilization efficiency of the whole must be improved unless the F-number of the projection lens is made bright for the liquid crystal display element to which the microlens array is not added. However, there was a problem that

According to the present invention, by appropriately setting the lens configuration, a light flux emitted substantially vertically from a projected image of a liquid crystal display element or the like illuminated substantially vertically over the entire screen is efficiently condensed and on a predetermined surface. An object of the present invention is to provide a projection optical system capable of obtaining a bright and high-quality projected image.

[0016]

The projection optical system of the present invention comprises:
A meniscus-shaped positive first lens having a convex surface directed toward the first conjugate point side and a meniscus-shaped positive second lens having a convex surface directed toward the first conjugate point side in order from the first conjugate point side having the longer distance; First
A negative cemented lens as a whole in which a negative meniscus lens having a convex surface facing the conjugate point side is cemented, and a negative meniscus lens having a convex surface facing the second conjugate point side having a shorter distance. It is characterized by having a lens, a positive meniscus fifth lens having a convex surface facing the second conjugate point, and a positive Fresnel lens.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic view of a main part of an embodiment in which the projection optical system of the present invention is applied to a liquid crystal projector, and FIGS. 2, 3 and 4 are numerical values of the projection optical system of the present invention described later. It is a principal part sectional view of the optical system of Examples 1, 2, and 3. FIG.

In the figure, L is a light source, which emits white light, for example. M is a reflecting mirror such as a concave mirror or a parabolic mirror, which collects the light flux from the light source L and illuminates the liquid crystal display element LA as the projection target with a substantially vertical light flux.

The liquid crystal display element LA is made of, for example, a color liquid crystal or a black and white liquid crystal. FL is a Fresnel lens that projects the light flux emitted from the liquid crystal display element LA into the projection lens L.
It is deflected in the P direction.

The projection lens LP has a lens structure shown in FIGS. 2 to 4, and projects the image information displayed on the liquid crystal display element LA on the screen surface S in an enlarged manner with high optical performance.

In the figure, the first side having a long distance on the screen surface S side.
The liquid crystal display element LA side corresponds to the second conjugate point side having a short distance on the conjugate point side. The projection lens LP and the Fresnel lens FL form one element of the projection optical system.

In this embodiment, the Fresnel lens FL is arranged close to the liquid crystal display element LA, and the light flux emitted from the entire screen of the liquid crystal display element LA in a substantially vertical direction is deflected to the projection lens LP.

That is, a telecentric system is set,
Thereby, the light flux is extracted under the same condition over the entire surface of the liquid crystal display element LA. The image information displayed on the liquid crystal display element LA can be projected by the projection lens LP with the same contrast over the entire screen.

Further, the Fresnel groove of the Fresnel lens FL is positioned on the side of the second conjugate point, so that aberrations such as image plane distortion and distortion of the projected image by the projection lens LP are easily corrected.

When a liquid crystal plate with a microlens array is used as a liquid crystal display element in the present embodiment, since the incident angle of the illumination light flux can be made substantially constant over the entire screen, the change of the aperture ratio depending on the position of the liquid crystal ( Peripheral dimming) can be prevented.

As shown in FIGS. 2 to 4, the projection lens LP of the present embodiment has a lens configuration of 5 elements in 4 groups, whereby the image information of the liquid crystal display element LA is transferred to the Fresnel lens F.
The image is enlarged and projected on the screen surface S via L with high image quality. (Note that SP in FIGS. 2 to 4 is a diaphragm.) In particular, by configuring the projection lens LP with a small number of lenses, such as five lenses of a predetermined shape, as described above, F It is as bright as the number 2.5, and it also corrects various aberrations such as spherical aberration and coma in a well-balanced manner to obtain high optical performance.

In order to obtain high optical performance over the entire projection screen in the projection lens LP according to this embodiment, the following conditions should be satisfied.

(1-1) The average values of the refractive indices and Abbe numbers of the materials of the first, second, and fifth lenses are Np and νp, respectively, and the refractive indices and the Abbe numbers of the materials of the third and fourth lenses. Supposing that the average values of Nn and νn are -0.02 <Np-Nn <0.015 ... (1), 15 <νp-νn <30 ... (2) is there.

Conditional expression (1) is mainly for maintaining good optical performance around the screen. If the upper limit of conditional expression (1) is exceeded, the image plane curvature will be overcorrected, and if the lower limit is exceeded, on the contrary, the image plane curvature will be undercorrected.

Conditional expression (2) is mainly for favorably correcting axial and lateral chromatic aberration. If the upper limit of conditional expression (2) is exceeded, axial chromatic aberration and lateral chromatic aberration will be overcorrected, and if the lower limit is exceeded, axial chromatic aberration and lateral chromatic aberration will be undercorrected.

(1-2) The focal length of the i-th lens is f
i, the radius of curvature of the i-th lens surface counting from the first conjugate point side is Ri, and the focal length of the entire system is f, 0.2 <R4 / f <0.5 (3) The condition is −1.6 <f ₄ /f<−0.8 (4).

Conditional expression (3) is mainly for favorably correcting chromatic aberration. If the upper limit of conditional expression (3) is exceeded, axial chromatic aberration and lateral chromatic aberration will be overcorrected, and if the lower limit is exceeded, axial chromatic aberration and lateral chromatic aberration will be undercorrected.

Conditional expression (4) is mainly for favorably correcting distortion. If the upper limit of conditional expression (4) is exceeded, the distortion will be overcorrected, and if the lower limit is exceeded, the distortion will be undercorrected.

[0034] (1-3) wherein the distance between the fifth lens and the Fresnel lens D10, when the focal length of the Fresnel lens was _{f 6, 0.5 <D10 / f} <0.7 ‥‥‥ ( 5) It is necessary to satisfy the condition of 0.6 <f ₆ / f <1.5 (6).

Conditional expression (5) is a condition for effectively exhibiting the optical action of the Fresnel lens. When the upper limit of conditional expression (5) is exceeded and the Fresnel lens and the image surface (liquid crystal display element) are too close to each other, moire is likely to occur in the projected image. If the lower limit is exceeded and the image is too far from the Fresnel lens, the refracting power of the Fresnel lens must be increased in order to make the projection optical system a telecentric system, resulting in a large amount of coma and distortion. So not good.

Conditional expression (6) is for maintaining a good telecentric system. When the value exceeds the upper limit value or the lower limit value of the conditional expression (6), the incident angle of the off-axis chief ray to the image plane becomes large, and the telecentric system is broken, which is not preferable.

Next, numerical examples of the present invention will be shown. In the numerical examples, Ri is the radius of curvature of the i-th lens surface in order from the first conjugate point side, Di is the i-th lens thickness and air gap from the first conjugate point side, and Ni and νi are the first conjugate points respectively. From the side, the refractive index and the Abbe number of the glass of the i-th lens are in order. R11 and R12 are Fresnel lens data.

Table 1 shows the relationship between the above-mentioned conditional expressions and various numerical values in the numerical examples.

Numerical Example 1 f = 113.12 F _NO = 1: 2.5 2 ω = 51.9 ° R 1 = 55.77 D 1 = 7.95 N 1 = 1.65844 ν 1 = 50.9 R 2 = 119.22 D 2 = 0.20 R 3 = 28.68 D 3 = 7.90 N 2 = 1.69680 ν 2 = 55.5 R 4 = 39.99 D 4 = 2.30 N 3 = 1.69895 ν 3 = 30.1 R 5 = 21.76 D 5 = 16.10 R 6 = (aperture) D 6 = 11.70 R 7 =- 30.03 D 7 = 2.00 N 4 = 1.67270 ν 4 = 32.1 R 8 = -45.49 D 8 = 1.25 R 9 = -146.60 D 9 = 7.25 N 5 = 1.65844 ν 5 = 50.9 R10 = -40.27 D10 = 67.50 R11 = ∞ D11 = 2.00 N 6 = 1.49171 ν 6 = 57.4 R12 = Fresnel surface Fresnel surface data Conjugation point on large conjugate side 244 Conjugation point on small conjugate side −244 <Numerical example 2> f = 112.37 F _NO = 1: 2.5 2ω = 52.2 ° R 1 = 58.10 D 1 = 7.47 N 1 = 1.69680 ν 1 = 55.5 R 2 = 119.53 D 2 = 0.20 R 3 = 28.56 D 3 = 7.93 N 2 = 1.69680 ν 2 = 55.5 R 4 = 39.39 D 4 = 2.30 N 3 = 1.69895 ν 3 = 30.1 R 5 = 21.89 D 5 = 16.21 R 6 = (aperture) D 6 = 12.01 R 7 = -30.07 D 7 = 2.00 N 4 = 1.67270 ν 4 = 32.1 R 8 = -45.57 D 8 = 1.40 R 9 = -141.47 D 9 = 6.99 N 5 = 1.69680 ν 5 = 55.5 R10 = -41.70 D10 = 66.61 R11 = ∞ D11 = 2.00 N 6 = 1.49171 ν 6 = 57.4 R12 = Fresnel surface Fresnel surface data Large conjugate side conjugate point 244 Small conjugate side conjugate point −244 <Numerical example 3> f = 111.98 F _NO = 1: 2.5 2ω = 52.3 ° R 1 = 58.11 D 1 = 7.96 N 1 = 1.60524 ν 1 = 60.7 R 2 = 130.41 D 2 = 0.20 R 3 = 28.74 D 3 = 7.62 N 2 = 1.77582 ν 2 = 49.6 R 4 = 40.33 D 4 = 2.30 N 3 = 1.70385 ν 3 = 30.1 R 5 = 21.69 D 5 = 15.45 R 6 = (aperture) D 6 = 12.52 R 7 = -30.27 D 7 = 2.00 N 4 = 1.67714 ν 4 = 32.1 R 8 = -46.04 D 8 = 1.40 R 9 = -141.69 D 9 = 7.07 N 5 = 1.69948 ν 5 = 55.5 R10 = -41.78 D10 = 66.89 R11 = ∞ D11 = 2.00 N 6 = 1.49354 ν 6 = 57.4 R12 = Fresnel surface Fresnel surface data Large conjugate side Conjugate point 244 Conjugate point on small conjugate side -244

[0040]

[Table 1]

[0041]

As described above, according to the present invention, by appropriately setting the lens configuration, the luminous flux emitted substantially vertically from the projected image of the liquid crystal display element or the like illuminated substantially vertically over the entire screen is efficiently produced. It is possible to achieve a projection optical system that collects light well and obtains a bright and high-quality projected image on a predetermined surface.

[Brief description of drawings]

FIG. 1 is a schematic view of a main part of an embodiment when the present invention is applied to a liquid crystal projector.

FIG. 2 is a sectional view of an essential part of an optical system according to Numerical Example 1 of the present invention.

FIG. 3 is a sectional view of an essential part of an optical system according to Numerical Example 2 of the present invention.

FIG. 4 is a sectional view of an essential part of an optical system according to Numerical Example 3 of the present invention.

FIG. 5 is an aberration diagram of Numerical example 1 of the present invention.

FIG. 6 is an aberration diagram of Numerical example 2 of the present invention.

FIG. 7 is an aberration diagram of Numerical example 3 of the present invention.

FIG. 8 is a schematic view of a main part of an optical system of a conventional color liquid crystal projector.

FIG. 9 is a schematic view of a main part of an optical system of a conventional color liquid crystal projector.

FIG. 10 is an explanatory view of a liquid crystal display device having a conventional microlens array.

FIG. 11 is an explanatory view of a liquid crystal display device having a conventional microlens array.

[Explanation of symbols]

 L, 14, 19 Light source M, 13, 18 Reflecting mirror LA, 1, 2, 3, 16 Liquid crystal display element FL Fresnel lens LP, 15, 20 Projection lens S Screen surface

Claims (5)

[Claims] 1. A positive meniscus lens having a convex surface facing the first conjugate point side in order from the first conjugate point side having a longer distance, and a meniscus positive lens having a convex surface facing the first conjugate point side. The second cemented lens is a negative cemented lens as a whole in which the second lens and the negative third meniscus lens having a convex surface directed toward the first conjugate point are cemented together, and the convex surface is directed toward the second conjugate point side having a shorter distance. A projection optical system comprising a negative meniscus fourth lens, a positive meniscus fifth lens having a convex surface facing the second conjugate point, and a positive Fresnel lens. 2. The projection optical system according to claim 1, wherein the Fresnel lens is provided with a Fresnel groove on the second conjugate point side. 3. The average values of the refractive index and the Abbe number of the materials of the first, second, and fifth lenses are Np, νp, and the third and third, respectively.
The average value of the refractive index and Abbe number of the material of the fourth lens is N
The projection optical system according to claim 1 or 2, wherein the condition of -0.02 <Np-Nn <0.01515 <νp-νn <30 is satisfied, where n and νn. 4. The focal length of the i-th lens is fi,
The radius of curvature of the i-th lens surface counted from the conjugate point side is R
i, where f is the focal length of the entire system, the condition 0.2 <R4 / f <0.5 −1.6 <f ₄ /f<−0.8 is satisfied. 1, 2 or 3 projection optical systems. 5. The distance between the fifth lens and the Fresnel lens D10, when the focal length of the Fresnel lens was _{f 6, 0.5 <D10 / f} <0.7 0.6 <f 6 / 4. A condition satisfying f <1.5 is satisfied.
Or the projection optical system of 4.