KR910005257B1 - Projection image display apparatus - Google Patents

Abstract

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Description

Projection Image Display

1 and 2 are side cross-sectional views showing the structure of a conventional projection television.

3 is a characteristic diagram showing emission spectra of phosphors.

4 is a plan view illustrating chromatic aberration and the like.

5 is a plan view showing a lens structure.

6 to 10 are characteristic diagrams showing MTF characteristics of each embodiment.

11 is a characteristic diagram showing central MTF characteristics.

12 is a characteristic diagram showing the deterioration characteristics of MTF due to temperature change.

13 is a side sectional view showing a set configuration according to the present invention.

14 is a plan view showing an example of another lens configuration of the present invention.

15 to 20 are characteristic views showing the characteristics of the respective embodiments shown in FIG.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lens for use in a projection television, and more particularly to a projection image display device suitable for projecting an enlargement of an image appearing in a CRT.

As the image reproducing surface of a television receiver is enlarged and a demand for reducing the force-rich image that cannot be obtained with a small screen is intensified, the image reproduced on the fluorescent surface of the CRT is enlarged by a projection optical system such as a lens reflector. So-called projection televisions have become widely available for obtaining large screen reproduced images.

In such projection type televisions, various improvements have been made so far, and as a result, there is a great progress compared to several years ago. The role of the lens in this projection television is very large. As described above, since the lens disclosed in US Patent Publication No. 4348081 is composed of three lenses, a high luminance of F number 1.0 is achieved. This design is designed to make the best use of asphericity, which is the greatest advantage of plastic lenses. In addition, since the lens is suitable for mass production of three small components and plastic lenses, the cost is also low.

The structure of the set using this lens is shown in FIG. 1 and FIG. 2 (side cross-sectional view).

Although the image on the CRT 4 is enlarged and projected on the screen 6 by the lens 5, the mirrors 1 and 2 are arranged for compactness, respectively. 2 shows the compact set by providing the mirror 3 in the lens. And 7 in FIGS. 1 and 2 are cabinets. It is no exaggeration to say that the projection-type television has been greatly developed by the lens disclosed in US Patent No. 4348081. However, it is still inferior in image quality, compactness, and price compared with a direct-view television. Each problem is described.

(1) Image quality: Focus, brightness and contrast are mentioned as important image quality items of projection TV. In terms of focus, the lens is generally evaluated by MTF (Modulation Transfer Function), but the above-described US Patent Publication No. 4348081 is very good. However, in the actual CRT, the luminescence spectrum characteristics of the phosphor have a distribution as shown in FIG. 3, and considering this, the MTF becomes worse, especially compared to the projection type television glass lens generally used in the low frequency region. Fall behind This is because consideration of chromatic aberration improvement has not been considered for this lens. On the contrary, a large MTF improvement is expected by improving chromatic aberration. In addition, since all of these lenses are made of plastic lenses, when the temperature changes, the refractive index changes, resulting in a decrease in focus.

As can be seen from the set using this lens, as shown in FIG. 1 and FIG. 2, if a compact set is to be realized, many mirrors must be arranged.

Because of this. ① Reduces brightness by causing mirror reflection loss. ② There is a problem that scattered light is generated and large trajectory is lowered.

(2) Compactness: Conventionally, there was a tendency to increase the mirror in the set to achieve compactness, but there is a limit to the phenomenon, and compactness requires shortening of the projection distance and the length of the lens, and at the same time the mirror arrangement It is also necessary to reconsider.

Further, the projection distance and lens length of the lens described in US Patent No. 4348081 are about 1200 to 1300 mm and about 200 mm, respectively, when the magnification is about 9 to 10 times using a 45-inch screen.

(3) As described above, in the vertical technique, it is unavoidable to increase the cost due to the arrangement of complicated mirrors and large lenses.

The object of the present invention is to shorten the projection distance and the length of the lens, to improve the quality of the focus, brightness, contrast, etc., to realize a compact set, and to achieve a cost reduction. To provide a device.

In order to achieve the above object, a lens having a configuration capable of realizing a short focal length described below is used. On the screen side, the (a) screen side phenomena are connected at the center and diverged at the periphery, (b) biconvex lenses, (c) convex and (d) centers of curvature at the center of the screen. It is arranged as a CRT glass lens having a fluorescent surface that has a large radius of curvature as it moves to the periphery or has an aspheric shape with a center of curvature at the electron gun side.

Embodiments of the present invention will be described in detail with reference to the drawings.

In order to solve the problems described above, the present invention reduces the focal length by about 35%. In order to shorten the projection distance with a constant magnification, it is necessary to increase the angle of view, and the half angle of view of the conventional Japanese patent application No. 54-115645 is about 25 degrees, but this needs to be increased by 40% to 35 degrees. It is very difficult to achieve this while maintaining the amount of light in the center and the periphery. On the contrary, if the angle of view is increased and the projection distance can be shortened, the focal length can be shortened, and the lens can be miniaturized and the chromatic aberration can be reduced, which can greatly contribute to the development of plastic lenses.

Here, the relationship between shortening of the focal length and reduction of the focus shift due to chromatic aberration and temperature change will be described.

In FIG. 4 (plan view or side view), the lens 5 is strongly worked at the distance of the focal length F, and the distance between the fluorescent surface and the lens is a and the distance from the lens to the screen is b.

If the radius of curvature of both sides of the lens is set to r ₁ , r ₂

in (ii)

Here, although the shape changes due to thermal expansion and the focal length is changed due to temperature change, it is very small compared with the effect due to the change in refractive index, and when the plastic lens cylinder is used, the elongation and cancellation of the lens cylinder Therefore, the contribution by the term containing Δr _{1 and} Δr ₂ is omitted. Further, the drop Δd of the spot diameter on the screen 6 is given by the following equation using the F number and the magnification M of the lens. (i) using the insider (iii),

That is, the increase _Δ d of the spot diameter due to chromatic aberration or temperature change is proportional to the focal length f. That is, the focal length is reduced by 35%, and the increase in spot diameter due to chromatic aberration and temperature change is also reduced by 35%. In particular, this lens is very effective because the MTF of the center of the screen is dominated only by chromatic aberration.

In the case of the plastic lens, the focus shift is the biggest problem due to the temperature change, but it is very effective to reduce this by 35%. The following describes how the MTF characteristic of the actual screen center changes with temperature. A typical configuration of this lens is shown in FIG.

In FIG. 5, reference numeral 10 denotes a first lens having a surface S1 opposite to the screen 6 where the central portion having the lens axis is focused and the peripheral portion having the lens distal distance is diverging. 1 a biconvex lens having a surface S3 opposite the surface S2 of the lens 10, 30 a concave lens having a surface S5 opposite the surface S4 of the lens 20, 40 a surface of the lens 30 A liquid crystal layer made of a silicone gel disposed between S6 and the surface S7 of the shielded glass 50 sealed by the sealing material 42, 60 is between the surface S8 and the surface S9 of the fluorescent surface 22 of the CRT 4. The fixed coolant 70 denotes the diaphragm, 80 denotes the lens 10 and 20, a lens barrel supporting the diaphragm 70, and 90 denotes a radiator. In this embodiment, the lenses 10, 20 and 30 are made of plastic material.

The surface S9 is planar with respect to the fluorescent surface 22, and the surface S10 coated with the phosphor is curved such that the fluorescent surface 22 acts as a lens. The center of curvature with respect to the center of the surface S10 is arranged on the screen side of the projection system, and the radius of curvature of the corners of the center is increased in accordance with the increase in the semi-radial distance of the sections at the lens side to reduce the field curvature. Aperture 70 is used to reduce aberrations and to increase brightness in the periphery of the lens system.

Lens data corresponding to Examples 1 to 5 are shown in Tables 1-5. The characteristic of these lenses is that they are arranged in order as follows on the screen side.

(a) The first lens, i.e., the lens having the screen side shape in the center portion and the diverging action in the periphery portion, has a very strong aspherical shape, as can be seen in FIG. 5 (plane to side view).

(b) biconvex second lens

(c) concave third lens

(d) A CRT glass lens having a fluorescent surface having a center of curvature at the center and a radius of curvature as it moves to the periphery, or a plane having a center of curvature at the electron gun side.

TABLE 1

TABLE 2

TABLE 3

TABLE 4

TABLE 5

The present invention shortens the projection distance from the front end of the lens to the screen by using this lens and the CRT tube, so that the optical system can be made simple and a compact set can be realized. Next, the features of the present invention will be described. The explanation is given when the star image on the 4.5-inch CRT is magnified 10 times with the lens to obtain a 4.5-inch image on the screen.

(1) have the following relationship: a plane shape of the first lens and the second lens of the screen side, when hayeoteul a radius of curvature near the center as r _1, r _2.

0.9r ₂ <r ₁ <1.1r ₂

As in the present invention, in order to realize a short projection distance, it is necessary to shorten the focal length and increase the power. This condition separates the two convex lenses from the power of the whole, and reduces the aberration occurring in the power lens. Moreover, if this condition is achieved, the distance between a 1st lens, a 2nd lens, and a 3rd lens will necessarily become narrow, and it is indispensable to realize a compact lens.

(2) The relationship between the surface interval T ₁₂ of the first lens and the second lens and the focal length f of the entire lens has the following relationship.

0.2f <T ₁₂ <0.4f

This is to make all the lens systems compact and to remove astigmatism in relation to the condition of (1). At the same time, the aperture of the second lens can be enlarged, so that the increase in the amount of ambient light that becomes a problem when a wide angle of view is prevented.

(3) between the second lens and the interval T ₂₃ and the focal length f of the whole of the third lens has the following relationship.

0.35f <T ₂₃ <0.45f

This is a condition necessary to reduce distortion and coma aberration.

If T ₂₃ greatly deviates from the lower limit, it is necessary to increase the curvature of the concave lens in order to reduce the petzval, but at the same time, high-order coma aberration occurs.

(4) The relationship between the thickness t ₂ of the second lens and the focal length f as a whole has the following relationship.

0.25f <t ₂ <0.35f

If this upper limit is exceeded as t ₂ , (1) cooling time at the time of lens shaping takes place, resulting in a cost increase. ② There is a problem that it costs materials. Below the lower limit, it is impossible to secure the thickness of the lens edge peripheral portion of the lens peripheral portion, and when the lens is assembled into the lens barrel, deformation may occur when an external force is applied to the peripheral portion of the lens by thermal expansion or the like.

(5) A second lens side clamp board is provided between the first lens and the second lens.

In general, in this type of lens, the aberration of the central root is easy to correct, and the F number can be reduced, so that it can be set to 1.0 or less.

However, in this case, the center on the screen is very bright, and conversely, the periphery becomes difficult to darken. In particular, when the angle of view is enlarged as in the present lens, as is generally known, the amount of light in the peripheral portion is very small in proportion to cos ⁴ θ when the angle of view is θ.

In consideration of such a situation, a clapboard was provided in order to reduce the number of peripheral parts and increase the amount of light.

(6) The fluorescent surface of the CRT is an aspherical surface, and as the shape thereof, the center of curvature near the center side is on the screen side, and the radius of curvature is large as it moves to the periphery, or the surface shape has a center of curvature on the electron gun side. have.

Generally, a lens has aberration called image curvature, and this condition is for reducing this aberration.

The upper surface curvature generally bends toward the object in the center root, i.e., in the tertiary aberration region, but in the peripheral, i.

The said dimension corresponding to Examples 1-5 is put together in Table 6 as a table | surface, and is based on this invention.

TABLE 6

Each dimension in the embodiment of the present invention

The results of the MTFs corresponding to Examples 1 to 5 shown in Table 1 to Table 5 are shown in Figs. 6 to 10 (all characteristic diagrams). Their values are 1 p1 / mm on the CRT.

In this MTF calculation, the emission spectrum distribution of the phosphor was also taken into consideration. The wait of each wavelength is as shown in Table 7.

TABLE 7

Wavelength of phosphor

The result of the screen-oriented MTF is shown in FIG. 11 (characteristic diagram) in comparison with US Patent Publication No. 4348081. Here, A is the characteristic of the lens of this invention, and B shows the thing of a conventional example.

In each of the embodiments, the F number was 0.91, which was high in luminance, and exhibited good MTF characteristics.

In addition, the ambient light quantity ratio is 30% as that of the lens used in a projection-type television having a small angle of view. In this way, compared with the conventional method, although the F-number was decreased to greatly improve the angle of view, the MTF characteristics could be significantly improved without lowering the brightness of the surroundings. 12 shows the characteristics of the MTF change with respect to the temperature change by the lens. A is the characteristic of the lens of this invention, B is a conventional example.

Although all are plastic lens structures, it can be seen that the MTF decrease due to temperature change is halved compared with conventional plastic lenses.

According to this embodiment, the following effects are obtained by using the lens described above.

(1) The lens length and aperture are very small, which makes it possible to lighten the weight and greatly reduce the cost.

(2) The focus of the center can be greatly improved.

In addition, this lens has a shorter projection distance, and a compact set is realized regardless of the reduction in the lens length. An example is shown in FIG. 13 (side cross-sectional view).

The projection system of FIG. 13 is depicted as follows. This projection system consists of a cabinet 110 having a top side 112, a bottom side 114, a front side 116, and a back side 118. In addition, the screen 6 shown in FIG. 4 is fixed to the upper part of the front side. The mirror 91 is inclined to the screen with the lower edge 119 of the mirror positioned away from the lower edge 121 of the screen 6 and away from the screen. The upper edge 123 of the projection system 124 is also located between the lower edge 121 of the screen and the lower edge 119 of the reflective mirror. This projection system 122 is composed of the CRT 4 and projection system 124 according to FIG.

As can be seen in FIG. 13, the projection system 124 is mechanically coupled to the CRT 4 by a coupling mechanism. The image projected in the projection system 122 is magnified via the mirror 91. Light at the upper edge 123 of the projection system 124 closest to the screen 6 is projected to the upper corner 125 of the mirror 91 and reflected at the top 127 of the screen 6. Similarly, light at the upper corner 129 of the projection system 124 closest to the lower edge 119 of the mirror 91 is reflected at the mirror 91 at the lower edge 121 of the screen 6. It consists of only one mirror 91 in a set, and has a very simple structure. As a result,

(1) The width and height of the set can be reduced to achieve compactness.

(2) By having one mirror in the set, the reflection loss of 10% of light can be loaded per piece.

(3) Cost reduction by reducing the number of mirrors and the pedestal supporting them.

(4) Since the conventional set is composed of many mirrors, various unnecessary lights are generated, which causes a problem of lowering the contrast as compared with the case of the lens alone.

The set using this lens can greatly reduce such unnecessary light, and can greatly improve contrast.

Another embodiment of the present invention is shown in FIG. The lens 20 of FIG. 5 may be separated into two lenses 22 and 24 as shown in FIG. In this embodiment the lens 22 is a weak power convex convex lens. The lens 24 preferably uses glass material to supply strong power and to reduce spherical aberration in which the other lenses 10, 22 and 30 are made of plastic material.

Lens data corresponding to Examples 6 to 11 are shown in Tables 6 to 13. The characteristics of these lenses are arranged as follows on the screen side in order.

(a) The side surface of the screen has an extreme aspheric shape, as can be seen in FIG.

(b) a convex concave-convex lens having the convex surface on the screen side and the concave surface on the CRT side;

(c) convex lenses,

(d) concave lenses,

(e) A CRT glass lens having a fluorescent surface having a center of curvature at the center of the screen and having a large radius of curvature or a plane having a center of curvature at the electron gun side as it moves toward the periphery.

TABLE 8

TABLE 9

TABLE 10

TABLE 11

TABLE 12

TABLE 13

As a feature of this lens,

(1) Aspherical surface amount on the screen side of the first lens

The relationship between ΔPa and the spherical amount ΔP _S has the following relationship.

0.5 _△ Ps <Pa <1.5 _△ P _S

Where ΔPa and ΔP _S

In terms of

rm and Zm are axial deviations from the center and the radial distance of the outermost circumference of the lens, respectively. In fact, _Δ Ps and _Δ Pa for Examples 1 to 6 are shown in Table 14.

TABLE 14

Aspheric amount of the first lens

By doing in this way, aberration by the light ray near the lower limit of the largest angle of view is improved, and it is especially useful for ensuring the amount of surrounding light.

(2) 0 <t <0.04f has a relationship between the spacing t of the said 2nd lens and the 3rd lens, and the focal length f of the whole.

As can be seen from the results of the MTF of the examples shown in Table 8 to Table 13, as the distance t is increased, the MTF of the outermost circumference slightly decreases, which is a level that can be practically used within this range. Increasing t further makes it unacceptable.

(3) A clap board for blocking light is provided between the first lens and the second lens toward the second lens side.

In general, in this type of lens, the value of the central root is easy to correct, the F number can be reduced, and the value can be set to 10 or less. However, in this case, as the image on the screen, the center is very bright, and conversely, the periphery appears dark. In particular, when the angle of view is enlarged as in the present lens, as is generally known, the amount of light in the peripheral portion becomes very small in proportion to cos ⁴ θ when the angle of view is θ. In consideration of such a thing, this clapboard was prepared so that the amount of light at the center part could be slightly reduced to reduce the aberration of the peripheral part and increase the amount of light.

The results of the MTF corresponding to the lenses shown in Table 8 in Table 8 are shown in FIGS. 15 to 20 (characteristic diagrams).

In the calculation of this MTF, the emission spectrum distribution of the phosphor was also taken into consideration. The weight of each wavelength is as showing in Table 7 mentioned above.

Also, the results of the screen-oriented MTF are shown in FIG. 12 (characteristic diagram) in comparison with Japanese Patent Application No. 54-115645. A is the present invention, and B is a characteristic of the conventional example. In all the examples, the F number is 0.93 and the focal length is 73 to 76 mm. The ambient light ratio is 30% in the 90% band of view, similar to the lens generally used in conventional projection televisions. In this way, the screen was wider and the F number was greatly improved than in the prior art.

In the examples shown in Tables 8 to 11, the second lens is made of glass, and has a design in which focus deterioration is small with respect to temperature change.

According to the present invention, the following effects are obtained by using the lens described above.

(1) Lens length, aperture are very small and can be reduced in weight, and it becomes drastic cost reduction.

(2) The focus of the center can be greatly improved.

In addition, this lens has a shorter projection distance, and a compact set can be realized regardless of the shortening of the lens length. An example is shown in FIG. 13 (side cross-sectional view).

There is only one mirror 2 in the set, and the structure is very simple. As a result, the width and height of the set (1) can be reduced to achieve compactness.

(2) The return loss of 10% of light per piece can be reduced by having one mirror in a set. As a result, the brightness is improved.

(3) Since the conventional set is composed of many mirrors, various unnecessary lights are generated, which causes a problem of lowering the contrast as compared with the case of the lens alone.

The set using this lens can greatly reduce such unnecessary light, and can significantly improve contrast.

Claims (1)

Cabinet 110, the screen (6) provided on the front of the cabinet, the fluorescent screen is provided in the lower side of the cabinet in the direction of the upper side of the cabinet 4, the inclined to the upper rear portion of the cabinet, the Braun tube A reflection mirror 91 for reflecting light from the fluorescent surface toward the screen and an optical projection provided on the fluorescent surface of the cathode ray tube, and projecting the light from the fluorescent surface onto the screen through a reflecting mirror; The projection apparatus is configured to include three lenses of an aspherical convex lens 10 having a small power, a convex lens having a large power, and a negatively concave lens 30 having a small power on the screen side. The edge portion 123 is located between the lower edge portion 121 of the screen and the lower edge portion 119 of the reflection mirror, and the room of the central optical axis of the optical projection apparatus. The fragrance is a projection-type image display device which corresponds to the upper back direction of the cabinet facing the fluorescent surface of the CRT.

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