JPH0766144B2 - Transmissive screen - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a lenticular lens used in a transmissive screen, and more particularly to a transmissive screen with a small color shift suitable for projection of a projection television.

[Conventional technology]

The following two methods are known as methods for defining the directional characteristics of the horizontal and vertical directions of the light emitted from the transmissive screen.
Forming Design of Convex Cylindrical Lens Formed on Lenticular Sheet Optimizing the type and mixing ratio of the diffusing agent mixed in the lenticular sheet, but increasing the mixing ratio of the diffusing agent, which will be described later, causes the following problems. That is, the diffusing agent increases the reflection of light and reduces the amount of light emitted from the emission surface.

It is not possible to control the individual directional characteristics in the horizontal and vertical directions. For this reason, the control of the directional characteristics is performed by using the above-described method mainly based on the shape design of the convex cylindrical lens and optimizing the mixing ratio of the diffusing agent.

As an example of the lenticular sheet which adopts the conventional directional control method described above, as described in JP-A-58-221833, a synthetic resin which is a lenticular sheet base material.
The ratio of the light-scattering substance mixed with 100% by weight, and
It defines the particle size. Further, this shape eliminates spherical aberration of the incident surface and the convex cylindrical lens as shown in FIG. 4, and arranges the emitting surface at a position equal to the focal length of the convex cylindrical lens. In addition, JP-A-58-20
As described in No. 5140, the center of the convex cylindrical lens is arranged. Therefore, the incident light a, b, c, d, e, f parallel to the optical axis of the incident surface converges at almost one point on the emitting surface.
For the reasons described above, the area of the non-light-collecting portion of the emission surface can be made large, and by applying the coating film of the light absorber on the non-light-collecting portion, an image with less contrast deterioration with respect to external light can be obtained. effective. However, in the above-mentioned prior art, no consideration was given to a light beam obliquely incident on the convex cylindrical lens on the incident surface.

[Problems to be solved by the invention]

Problems when the above-described conventional lenticular sheet is used in a projection television will be described with reference to the drawings. FIG. 3 is a cross-sectional view showing the optical system of the projection television. The arrangement of the cathode ray tube and the projection lens 34 is such that the green cathode ray tube 32 is at the center and the blue cathode ray tube 31,
The red cathode ray tube 33 is arranged inline laterally.
Therefore, in order to obtain a regular image on the screen, the following is structurally required. That is, a blue cathode ray tube
31, the projection lens 34, the red cathode ray tube 33, and the projection lens 34 do not face the Fresnel (lens) sheet 35, and the light is obliquely incident at an angle β ₁ (hereinafter referred to as a concentration angle). Further, the light emitted from the Fresnel sheet 35 and incident on the incident surface of the lenticular sheet 36 has a concentrated angle β ₁ as shown in FIG.
It will have an inclination with respect to the green projection light. However,
The convex cylindrical lens formed on the lenticular sheet according to the related art does not consider light incident from an oblique direction. Next, the mechanism of one example of the prior art will be described. In general, when the lens surface is formed in an elliptical shape where the reciprocal of the refractive index of the material forming the lens is the eccentricity, the rays parallel to the optical axis converge to the focal position without aberration. By utilizing this property, the shape of the convex cylindrical lens, which is the incident surface of the lenticular sheet, is made elliptical. At this time, when the height from the optical axis to the incident ray is h as shown in FIG. 7, the thickness t of the screen and the emission angle θ ₃ are calculated by the following equations.

General formula of ellipse t = a + ae −− (2) Now, if eccentricity e = 1 / n ₁ then t ′ = a− (a ² −y ² / (1−e ² )) ^1/2 −− ( 3) n ₁ sin θ ₂ = n ₂ sin θ ₃ Substituting equation (4) into equation (5), since y = h, However, n _{1 is} the refractive index of the screen material, n _{2 is} the refractive index of the air, h is the incident ray height, e is the eccentricity, and a = t / (1 + e). The thickness t can be obtained by determining the pitch of the lens and the emission angle θ _{3 of the} light ray passing through the outermost portion. FIG. 5 is a lateral cross-sectional view showing the shapes of the entrance surface and the exit surface as an example of the conventional technique. The light parallel to the optical axis of the elliptical convex cylindrical lens is converged to one point on the exit surface as shown by the solid line, and the exit angle of each ray can be controlled, but the light that is obliquely incident by the convergence angle β ₁ is However, they do not converge at one point and the emission angle of the emitted light cannot be controlled. Similar to FIG. 5, FIG. 6 shows that the entrance / exit surface has an elliptical shape and the concentration angle β ₁ is 8.9.
Degree, the effective diameter of the entrance lens is 1.2 (mm), the effective diameter of the exit lens is 0.6 (mm), and the lens surface spacing is 1.5 (mm)
The directional characteristic in the case of is calculated by optical calculation. For example, as shown in FIG. 3, when the screen is viewed obliquely from the left, blue image light is emphasized and so-called color shift occurs. Further, conventionally, as a technical means for preventing the deterioration of the contrast against external light, as shown in FIG. 5, a convex projection is provided on the non-focus portion of the emission surface on the viewing side, and a light absorber is applied to the surface of this projection. A so-called "black stripe" is provided.

At this time, according to the conventional technique, the shape of the convex cylindrical lens on the exit surface and the shape of the above-mentioned projection change significantly. For this reason, it becomes difficult to shape the shape of the convex cylindrical lens with sufficient accuracy when manufacturing the lenticular sheet. An object of the present invention is to improve the shape accuracy of the lenticular lens described above and to reduce the color shift that occurs when a transmissive screen is used in a projection television.

[Means for solving problems]

The above object, the distance l ₁ between the elliptical shape as image light incident surface S ₁ emitting surface S ₂ is shown a lens shape of the image light incident surface S ₁ by the following equation (7) as shown in Figure 1 (1 ) To (6) compared with the thickness t determined to be 0.9t <l ₁ <1.0. Further, the absolute value of the second derivative of the equation showing the shape of the image light exit surface S ₂ corresponding to the convex cylindrical lens on the incident surface is smaller near the center than the absolute value of the second derivative of the equation (7), and Distance l ₃ is In this point, the radius of curvature R _{3 in the} vicinity of increasing l ₃ > l is achieved by making the shape gradually smaller as l ₃ increases.

Where a ² (1-e ² ) = b ^{2 where} e = 1 / N ₂ N ₂ : refractive index of sheet material y: minor axis x: major axis coincides with lens center axis [Operation] According to the present invention According to the transmissive screen using the lenticular sheet, for the green image light incident parallel to the optical axis of each convex cylindrical lens on the image light incident surface, the shape of the convex cylindrical lens on the incident surface and the emission surface By optimizing the distance, almost spherical aberration is eliminated and the light is converged on the exit surface of the corresponding convex cylindrical lens. Further, the distribution of the blue and red image light that is obliquely incident on each cylindrical lens on the incident surface and is emitted from the lens surface is improved by optimizing the shape of the outgoing surface.

〔Example〕

An embodiment of the present invention will be described in detail below with reference to the drawings.
FIG. 2 shows the shape of a lenticular lens which is an embodiment of the present invention. The lens pitch P ₀ is 1.2 (mm), which is the same as the conventional lenticular lens, and the design values are assumed when the refractive index of the screen material is 1.56 and the effective diameter L ₁ of the exit surface is 0.56 mm and the lens diameter L ₂ is 0.7 mm. Show. First, how to read data will be described. A positive sign of the curvature judgment R _D indicates that the center of curvature of the lens surface is located on the optical axis in the direction from the entrance surface 23 to the exit surface 22.

Here, the aspherical surface coefficient is a coefficient when the surface shape is expressed by the following equation.

However, the height of the lens surface when the optical axis direction is X and the radial direction of the lens is Y axis (representing a function of Y, R _D represents a radius of curvature, and n represents an arbitrary natural number). Therefore, CC, A
If the respective coefficients of D, AE, AF, AG, ..., A are given, the height of the lens surface, that is, the shape is determined according to the equation (8).

In the table below, as coefficients, only CC, AE, AF, AG, and AH are shown, that is, only coefficients up to the 10th order are shown, but it is not limited to this, and coefficients above the 12th order May be similarly set. Even in such a case, a lens surface that is axially symmetric with respect to the optical axis can be obtained.

t ₁ = 1.47 (mm) L ₁ = 0.56 (mm) L ₂ = 0.7 (mm) P ₀ = 1.2
(Mm) The entrance surface has an elliptical shape and is optimally designed by the lens intervals (1) to (7). Therefore, the image light incident parallel to the optical axis of the lens converges near the point on the optical axis of the exit surface with almost no influence of spherical aberration. On the other hand, the image light that is obliquely incident on the incident surface by the concentration angle β ₁ is refracted on the incident surface and then on the exit surface from the optical axis. Converge to a position distant by. Therefore, the aspherical amount of the convex cylindrical lens is increased to The light distribution of the emitted light is optimized by greatly changing the shape in the vicinity, and good directional characteristics are obtained.

Further, as shown in FIG. 2, the lenticular sheet of this embodiment is superior to the screen of the prior art also in formability for the following reasons.

The drop t ₃ from the projection 25 on the exit surface to the lower end of the lens surface is small.

The convex cylindrical lens on the exit surface has a large average curvature and a small amount of depression t ₂ .

Since the flat portion (L ₂ −L ₁ ) / 2 exists between the projection 25 formed on the exit surface and the effective portion L ₁ of the convex cylindrical lens on the exit surface, the transferability of the lens surface is improved.

Furthermore, by providing the light-shielding layer formed by the light absorber 14 on the flat portion of the protrusion 25, it is possible to obtain a screen with less contrast deterioration against external light. The value of the second derivative of the shape shown in equation (8) is compared with the value of the second derivative of the lenticular lens surface having an elliptical shape in which the eccentricity is the reciprocal of the refractive index of the material of the lenticular sheet, which is a conventional technique. And shown in FIG. The absolute value of the second derivative of the lens surface of the prior art is larger in the vicinity of the central axis than the absolute value of the second derivative of the shape of the present invention, and is shown in FIG. It is getting bigger in the vicinity.

〔The invention's effect〕

 According to the present invention, the following effects can be expected.

The color shift defined by the difference between the red image light and the blue image light can be greatly reduced by the shape of the convex cylindrical lens on the emission surface.

There is a joint between the projection 25 formed on the exit surface and the effective diameter L ₁ of the convex cylindrical lens on the exit surface. For this reason, it becomes possible to mitigate the formation error in this portion, and the formability of the lenticular sheet is improved.

Also, since the convex cylindrical lens on the entrance surface converges the light on the exit surface with almost no aberration, the area of the non-focusing part on the exit surface is increased, and by forming a light-shielding layer provided by a light absorber in this part, Contrast deterioration with respect to external light can be significantly reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a horizontal cross-sectional view of an essential part of a lenticular sheet of the present invention in the horizontal direction of the screen, and FIG. 2 is a horizontal cross-sectional view of an embodiment of the lenticular sheet of the present invention in the horizontal direction of the screen. The figure shows a cross-sectional view in the horizontal direction of the screen showing the optical system of the projection TV.
4 and 5 are horizontal sectional views of a conventional lenticular sheet in the horizontal direction of the screen, FIG. 6 is a characteristic diagram showing a directional characteristic when the conventional lenticular sheet is combined with a Fresnel lens sheet, and FIG. 7 is a cylindrical lens. 9 is a cross-sectional view of FIG. 8 and FIG. 8 is a diagram comparing the values of the second-order derivatives of the lens shapes. 21,36,51,61 …… Lenticular lens, 22 …… Exit surface, 23 …… Injection surface, 24,42 …… Light absorber, 25 …… Protrusion, 3
1 …… blue cathode ray tube, 32 …… green cathode ray tube, 33 …… red cathode ray tube, 34 …… projection lens, 35 …… Fresnel lens,
42 ... Light absorber, 38 ... Viewer, N ₁ , n ₂ …… Air refractive index, N ₂ , n ₁ …… Lenticular sheet material refractive index, β
₁ ... incident angle, β ₂ ... refraction angle, β ₃ ... exit angle, R ₂ ...
… Central radius of curvature, R ₃ … peripheral radius of curvature.

Claims (6)

[Claims] 1. A transmissive screen comprising a Fresnel sheet and a lenticular sheet, which transmits image light incident from the image generation source side and emits the image light to the image viewing side, wherein the image light generation source side of the lenticular sheet is provided. The sheet shape is a shape in which a plurality of _first lenticular lenses S ₁ having the screen screen vertical direction as the longitudinal direction are continuously arranged horizontally in the screen screen, and the shape of the image viewing side screen surface of the lenticular sheet is Second with the screen screen vertical direction as the longitudinal direction
A plurality of lenticular lenses S ₂ are arranged continuously in the horizontal direction of the screen screen substantially facing the _first lenticular lens S ₁ , and at least the horizontal direction of the screen of the first lenticular lens S ₁ is Either one of the cross-sectional shape and the cross-sectional shape of the second lenticular lens S _{2 in} the horizontal direction of the screen screen is a shape given as a function of the distance from the optical axis of the lenticular lens, and the axis is relative to the optical axis. A symmetric shape, a value obtained by substituting the distance near the optical axis of the lenticular lens into a function obtained by second-order differentiation of the function, and a light obtained by second-order differentiation of the function of the lenticular lens. A transmissive screen, which is different from a value obtained by substituting a distance of a portion away from the axis. 2. The transmission screen according to claim 1, wherein the function is X, where X is a distance along the direction of the optical axis of the lenticular lens, and X is a distance from the optical axis in the lens radial direction. When Y AF / Y ⁸ ＋ AG ・ Y ¹⁰ ＋ ・ ・ ・ ＋ A ・ Y ²ⁿ …… (1) A transmissive screen. However, R _D : radius of curvature, n: any natural number, CC, AD, AF, AG, AH,…, A: aspherical coefficient 3. The transmissive screen according to claim 1, wherein the predetermined distance is 1.
l is A transmissive screen characterized in that Where l ₁ is the distance between the image light incident surface and the exit surface, N _{2 is} the refractive index of the sheet material, and β _{1 is} the incident angle of the image light. 4. The transmission screen according to claim 3, wherein the slope of the function obtained by quadratic differentiating the equation (1) showing the shape of the lenticular lens is the predetermined distance l.
A transmissive screen that is characterized by turning from negative to positive in the vicinity. 5. The transmissive screen according to claim 4, wherein protrusions are provided at boundary portions between the _second lenticular lenses S ₂ , and the surface portions of the protrusions each have a finite width. A projection screen comprising a light absorbing layer and a connecting portion provided between the protrusion and the second lenticular lens S ₂ . 6. The transmissive screen according to claim 5, wherein the distance l ₁ between the image light incident surface and the image light emission surface is 0.9t <l ₁ <1.0t. Transmissive screen. However, t = a + ae, and a and e are elliptic general formulas, respectively. Is an arbitrary constant and eccentricity.