JPH0719029B2 - Projection screen - Google Patents

Description

The present invention relates to a projection screen suitable for a rear projection TV.

Figure 1 shows the basic configuration of the optical system of a rear projection TV. In the figure, 1a, 1b and 1c are CRTs, and 2a, 2b and 2c are projection lenses. Further, 3 is a screen, which is made of an acrylic material.

FIG. 2 shows a horizontal sectional structure of the screen 3 in the prior art. 4 is a Fresnel surface, the action of which is the lens 2a
It is to refract and converge the input light diverging from 2 c to the periphery of the screen 3 into almost parallel output light. However, in the conventional example, the Fresnel lens surface was not provided on the exit surface side as in the same figure, but was provided on the entrance surface side. However, in that case, there was a drawback that the incident light in the peripheral portion was eclipsed by the vertical sectional view of the Fresnel lens. In order to improve this, the same drawing shows a configuration in which the Fresnel lens surface is formed on the exit surface. Reference numeral 5 is a lenticular lens surface, which diverges the light emitted from the lenticular sheet 7a in the direction of ± 45 ° in a microscopic manner, and a normal image is displayed on the screen even when viewing the screen from an oblique direction. To make it visible. 6 is on the output side of the wrench quiller sheet 7a,
The black strip surface is formed to face the concave portion of the lenticular lens surface 5, and is for reducing the reflectance of the screen surface with respect to external light illumination or the like to improve the contrast. See US Pat. No. 3,830,55 for details of its construction.
Since it is described in the specification No. 6, detailed description is omitted.

By the way, the relative luminance characteristic when viewing this type of screen from the front (0 °) or the horizontal oblique direction (± α °) is as follows:
The tendency is as shown in the figure, and the following two problems have been conventionally recognized. In the figure, the solid line G is the luminance characteristic for green, the dotted line R is the luminance characteristic for red, and the dashed-dotted line is the luminance characteristic for blue.

The first problem is a problem common to all colors, and the directional characteristics exhibit a bimodal property, and therefore the brightness when viewed from the front is insufficient.

The second problem relates to the difference between red and blue, and when viewed from an oblique direction, the balance between red R and blue B is lost and white appears to be colored.

The first problem is due to the fact that the lenticular lens on the entrance surface has large negative spherical aberration, as shown in FIG. 15 of USP 3,830,556.
Due to this, the screen of the prior art not only causes the above-mentioned first problem, but also cannot increase the area ratio of the black draft strip, and therefore the image contrast is insufficient. Had. Further, USP 3,830,556 does not show a correct quantitative derivation method of the horizontal directional characteristic of the screen. According to the same publication, the horizontal directional characteristic is interpreted as being proportional to the increment of the horizontal emission angle (α in FIG. 3 of the present application): Δα divided by the increment of the input light quantity. But this idea is wrong. The present invention has found that a correct solution based on the optical principle should use Δ (sinα), that is, cosα · Δα, instead of Δα.

The second problem is that the concentration angle where the red and blue lenses look into the screen has a size of about ± 7 degrees due to the structure. However, since this must be accepted as a prerequisite, it is desirable to take some measures on the screen side.

As described above, the conventional screen has a number of drawbacks.

The object of the present invention is to look the brightest when viewed from the front,
Moreover, it is to provide a screen having excellent horizontal directional characteristics that can be viewed from the left and right 45 ° directions.

Another object of the present invention is to provide a screen capable of providing a beautiful image with higher contrast by increasing the ratio of the area occupied by the black draft strip.

Another object of the present invention is to provide a correct law and method for quantitatively deriving the horizontal directional characteristic of the screen.

Another object of the present invention is to provide a screen that can reproduce a beautiful white color when viewed from an oblique direction.

In order to achieve the above-mentioned object, the present invention forms the lenticular sheet input interface by a part of the convex surface in the major axis direction of the ellipsoid whose eccentricity is equal to the reciprocal of the refractive index of the lens medium, and It is characterized in that the output interface is provided at the focus position of the elliptical surface farther from the input interface.

Hereinafter, the present invention will be described with reference to examples. First, FIG. 4 shows an essential part of the first embodiment of the present invention. With reference to the same figure, a countermeasure for the first problem of the conventional technique will be described. This figure shows the structure of a lenticular lens corresponding to the unit surface of the lenticular lens surface 5 of FIG.

In FIG. 4, the input surface of the unit surface is formed so as to be a part of the elliptical shape. Further, the output side interface is provided at the position of the focal point F on the elliptic surface farther from the input surface. Now take the x and y coordinates as shown in Fig. 4, and calculate the eccentricity e of the ellipse. If (n is equal to the refractive index of the material forming the lenticular lens 7b), the ellipse shape in the figure is expressed by the following equation (1).

Thus, the eccentricity e of the ellipse Is equal to, all light incident parallel to the major axis of the ellipse will have a focal point F farther from the input surface, as shown in the figure.
Converge to. Therefore, without impairing the transmission of incident light,
The ratio of the area occupied by the black-and-white strip can be increased, and thus a more beautiful image with an improved contrast ratio can be provided. The lenticular lens 7b is made of an acrylic material, and its refractive index n is about 1.5.

In the equation (1), if the unit of x and y is selected to be the unit of millimeter, the dimension of the elliptical surface becomes a dimension almost suitable as the lenticular lens surface for a screen.

According to the calculation, if an elliptical surface in the range of y = ± 0.63 mm is selected as the unit surface, the output light can be expanded to ± 45 degrees as a result. At this time, the directivity characteristic becomes as shown in FIG. 5, and a desired single-peak characteristic is obtained.

Next, the reason why the single peak characteristic as shown in FIG. 5 is obtained will be described. Generally, the following equation (2) is established from the characteristics of the ellipse and Snell's law.

Here, θ represents the inclination angle of the output light with respect to the x-axis, and y represents the height of the input light.

In the equation (2), the relative luminance, that is, the horizontal directional characteristic is a correct equation found by the present inventor: Then, a horizontal directional characteristic as shown in FIG. 5 can be obtained by drawing a graph with this as the vertical axis and the tilt angle θ as the horizontal axis.

Therefore, if the mold for molding the lenticular sheet is made so that the relation of the above formula (1) is established and the single-pitch characteristic as shown in FIG. Even if a rounded portion is generated, it is possible to prevent the remarkable double-mine characteristic as in the prior art from occurring.

As can be seen from the above description and FIGS. 4 and 5, the lenticular lens surface on the incident side is required in order to obtain the unilateral horizontal directional characteristic aimed at by the present invention and to obtain a desired divergence angle of ± 45 degrees or more. The width of the unit surface of 1.26 / (1
It is necessary to select + 1 / n) times or more. This will be clear from FIG.

Next, a second embodiment of the present invention will be described with reference to FIG. This embodiment solves both the above-mentioned first and second problems. The difference from FIG. 4 is that the lenticular lens surface 5 faces the output side interface and the same as the lenticular surface 5. Of the curved surface of the incident side lenticular lens surface, that is, the point where the lenticular lens surface is formed, and the light non-passage portion near the boundary where the unit strips of the output side lenticular lens surface are adjacent to each other. The point is that a black draft is formed symmetrically with respect to the axis.

When the lenticular sheet 7b having such a structure is used in place of the lens 7a in FIG. 2, the red and blue input lights are incident on the lenticular lens surface 5 with an inclination of ± 7 degrees as shown in FIG. Although incident, the light is refracted so as to be substantially parallel light from a part of the elliptical surface which is the output surface, that is, the emission side lenticular lens surface 8 and is output.

Therefore, when red and blue input lights as described in FIG. 3 are viewed from an oblique direction, the balance between the red and blue luminances is prevented from being disturbed, and white is seen even from an oblique direction. It reduces the appearance of color.

Although the above-described examples have been described assuming an ideal case, it is not always necessary to form a mathematically strict elliptical surface in the production of the lenticular sheet according to the present invention, and a unimine directivity and It is natural that a slight deviation from the ellipsoidal surface can be allowed as long as the lens is capable of converging to the focal point.

As described above, according to the first embodiment of the present invention, when viewed from the front, it is brighter (about 1.
There is a big effect that you can enjoy images.

Further, in the present invention, the unit surface of the lenticular lens surface is formed by a part of an elliptic cylindrical surface, and the ellipticity of the ellipse is formed so as to be substantially equal to the reciprocal of the refractive index n of the plate medium, and the light is emitted. ± 45 degrees or more because the position of the side lenticular surface is near the focal point of the entrance side elliptic cylinder surface and the width of each unit surface is about 1.26 / (1 + 1 / n) times the thickness of the lenticular lens plate. There is an effect that it is possible to obtain a unimine directional characteristic having a horizontal divergence angle of.

Here, in the lenticular sheet 7b of FIG. 6, the thickness of the lenticular lens plate is equal to the apex of the lenticular lens surface 5 and the exit side lenticular lens surface 8.
Is the distance between the vertices of.

Further, according to the second embodiment of the present invention, the shape of the light passage portion of the exit side lenticular surface is made substantially the same as a part of the elliptic cylinder surface, and each unit fine part of the exit side lenticular lens surface is formed. Since the black strips are formed symmetrically with respect to the optical axis of the incident side lenticular lens in the light non-passing portions near the boundary where the strips are adjacent to each other, horizontal color shift can be reduced and the contrast ratio can be reduced. There is an effect that it can be improved, the manufacturing is simple, and the productivity is improved.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a basic configuration of an optical system of a rear projection TV, FIG. 2 is a sectional view of a conventional screen, FIG. 3 is a characteristic diagram showing directional characteristics of a conventional screen, and FIG. FIG. 6 is a sectional view of a main part of the first embodiment of the present invention, FIG. 5 is a characteristic diagram showing horizontal directional characteristics of the screen of FIG. 4, and FIG.
The figure is a cross-sectional view of an essential part of a second embodiment of the present invention. 1 ... CRT, 2 ... projection lens, 3 ... screen,
4 ... Fresnel lens surface, 5 ... Lenticular lens surface, 6 ... Black strip surface, 7b ... Lenticular sheet

Claims (2)

[Claims] 1. A projection transmissive screen used in a projection television system, wherein the projection transmissive screen is arranged on a side closer to the projection light source and on a side farther from the projection light source. And a lenticular sheet having a vertical striped lenticular lens surface on the incident surface side, each unit surface of the lenticular lens on the incident surface side is formed of a part of an elliptic cylindrical surface, and The eccentricity of the ellipse is formed to be substantially equal to the reciprocal of the refractive index n of the plate medium, and the width of each unit surface is approximately 1.26 / (1 + 1 / n) times the thickness of the light transmitting portion of the lenticular sheet. By doing so, horizontal directional characteristics with a horizontal divergence angle of ± 45 degrees or more are obtained, and the exit surface of the lenticular sheet is placed near the focal point of the entrance-side elliptic cylinder surface. The projection screen is characterized in that black strips are formed substantially symmetrically with respect to the optical axis of each unit surface of the incident side lenticular lens in the light non-passing portion. 2. The projection surface according to claim 1, wherein the exit surface of the lenticular sheet is formed in a shape substantially equal to a part of the entrance-side elliptic cylinder surface. screen.