JP2996779B2 - Rear projection screen - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is mainly used for a projection apparatus having three TV projectors installed adjacent to each other for projecting red, green, and blue TV images on the back of a screen. In particular, a rear projection screen having a rearwardly formed rearward lens element formed as a convex lens for light incident from the rear and having a stripe forming portion opposed to the rearwardly facing lens element therebetween, and The invention relates to a rear projection screen consisting of a screen with a masking stripe extending in the front direction.

[0002]

BACKGROUND OF THE INVENTION Typically, a rearward facing lens element has its focal length measured (as viewed in a horizontal cross section through the screen) between the highest point of the rearward facing lens element and the stripe formation perpendicular to the screen surface. It is formed so as to correspond to the distance set. This is achieved by forming the lens as an ellipse or an elliptical enlargement, again in plan view. Accordingly, these known lens elements have the characteristic that light from the rear, which is incident perpendicularly and parallel to the screen surface, is focused on the center of the stripe forming portion that can be formed as a forward facing convex lens. .

[0003]

Such collimated light rays incident on the highest part of the rearward facing lens element pass through the screen almost as is. These rays dominate in the output light pattern of the stripe formation, since the energy loss when passing through the screen is negligible. On the other hand, light rays incident on the side portions of the rearward facing lens element experience a considerable energy loss when passing through the screen. This is due to the fact that these rays are incident on the surface of the side part at a relatively large angle of incidence, resulting in a considerable reflection. As described above, even when such a ray enters the stripe forming portion that can be formed as a convex lens from behind, the same can be said because the incident angle increases. The reflection loss in the latter case is greater than the reflection loss due to the light rays incident on the screen.
This is because in the latter case, the light rays travel from a material with a higher refractive index to a material with a lower refractive index (from the screen material into the air). It is generally envisioned that the light rays incident on the side portion of the rearward facing lens element proximate the mid-plane of the screen will suffer an energy loss of about 50%. As a result, the image projected on the back of the screen is radiated as clearer to a viewer located in a direction perpendicular to the front of the screen than a viewer obliquely viewing the image from the side of the screen. Technically speaking, this screen has a distinct "peak gain".

Accordingly, an object of the present invention is to provide a screen capable of obtaining a screen image having substantially the same light intensity when viewed from a direction perpendicular to the front and obliquely from the side.

[0005]

SUMMARY OF THE INVENTION In accordance with the present invention, it is an object of the present invention to make the focal length of the top portion of the rearward facing lens element shorter than the focal length of the side portion of the rearward facing lens element, and furthermore, the focal length of the top portion. This is achieved by making the distance shorter than the distance between the highest point of the rearward facing lens element, measured perpendicular to the screen plane, and the stripe formation.

[0006]

In this way, rays which are incident from the rear onto the top of the rear-facing lens element and which travel perpendicular to the screen surface cross each other in the screen material before leaving the stripe formation. If the stripe forming part is flat,
This diffusion will be further enhanced as the light rays travel from higher index materials to smaller materials.
If the stripe forming portion is formed as a forward facing convex lens, diffusion can be further accelerated by setting the focal point of the top portion between the forward facing lens and those focal points. This is because the forward facing lens functions as a concave lens. However, the focal length of the top portion and the convex lens facing forward may be selected such that the focal points of the two lenses are the same. Thus, in the latter case, the forward facing convex lens does not affect the diffusion of parallel rays incident on the top portion of the backward facing lens element.

This can be avoided because the diffusion of light rays that produces a distinct "peak gain" is caused by the structure described above. And, as a result of the improved energy spread in the horizontal direction with respect to the output light, both viewers looking straight at the screen from the front and viewers looking at the screen diagonally from the front can receive images projected with almost the same illuminance. Can be. In other words, a screen with an improved viewing state in the horizontal direction is formed.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the accompanying drawings.

Reference numerals 1, 2, and 3 in FIG. 1 denote three projectors that project a TV image on the back of the projection screen 4. Each projector projects a black-and-white TV image, and a filter is placed in front of the projector 1 so that the image projected by the projector on the screen 4 becomes red. A filter is provided in front of the projector 2 so that the image projected by the projector on the screen 4 becomes green, and a filter is used for the projector 3 so that the image of the projector becomes blue. These three colors are represented by R, G and B, respectively. The three projectors 1, 2, 3 are installed alongside the optical axis 7 of the central projector, which is at right angles to the center of the screen. Since each projector has a lateral spread, it cannot be installed so that the optical axes 6 and 8 are aligned with the axis 7, but instead the three optical axes are 7 ° next to each other.
To form an angle. Making these 7 ° angles even smaller is difficult due to the size of the projector. On the other hand, the angle of 7 ° can be increased to 10 ° as a result of the development of more powerful projectors and improved functions in the horizontal direction. The optical axis is directed to the center of the screen 4, and the projector is configured so that images projected on the back of the screen 4 cover each other as much as possible. This allows the viewer to view a higher quality and larger image corresponding to the image generated by the color TV picture tube from the front of the screen. The curved frame in FIG. 1 indicates the position of the viewer.

The screen shown in FIG. 1 comprises two screens, a front screen A and a rear screen B. "Front" means closest to the viewer's position, as well as "front" and "back"
Means a seat facing the viewer's position and a seat facing the back.

The front of the front screen A has a masking
It has a stripe 22 and a stripe forming part 23 positioned therebetween and extending in the vertical direction at the position where the screen is used. In the embodiment of the screen 4 shown in FIG. 1, the stripe forming part 23 has an edge 2 along its side.
4 and is formed as a forward facing convex lens. The edge 24 is substantially perpendicular to the screen surface and forms the side boundary of the masking stripe 22.

The front screen A has a rearwardly extending vertically extending lens element 25 on its rear surface, which is arranged immediately behind each stripe forming portion 23. These lenses 25 are mainly used to bend light from behind, so that the light is output through the stripe forming portion 23 on the front surface of the screen.

The rear screen B is formed as a Fresnel lens 27 whose front surface collimates the light coming from behind. Three projectors 1 with optical axes 6, 7, 8;
When a few are oriented toward the center of the screen and the optical axis of projector 2 is at right angles to the screen, the light from the three projectors will increase in angle of incidence as the distance from central optical axis 7 increases. Incident on the back of. However, this is corrected by the action of the Fresnel lens.

Even if the screen A is generally used as described with reference to FIG. 1, in the following figures, light incident on the screen A from the rear, that is, light perpendicular to the screen surface, that is, light from the projector 2 Only the direction is shown. With respect to the light from the projectors 1 and 3, even if they were collimated by the Fresnel lens B, the light from the projectors 1 and 3 continued to form, for example, the above-mentioned 7 ° angle with respect to the green light incident perpendicularly to the back of the screen A. But the situation is the same.

FIG. 2 is a partial cross-sectional view of a known embodiment of the screen A. A ray 30 which is incident perpendicularly to the middle plane of the screen at the highest point 31 of the rearward facing lens element 25 (upward in the projection of FIG. 2) passes through the screen as it is. The energy of the output beam is slightly reduced compared to the energy of the input beam. When the screen is made of acrylic resin, the light beam undergoes about 7% light energy loss as a result of reflection as it passes from the air into the acrylic resin and from the acrylic resin into the air. Light rays 33, 34 that are perpendicularly incident on the back of the screen and pass through the front side of the rearward facing lens element 25 close to the screen midplane suffer significantly more energy loss than light rays 30 after passing through the screen. This is due to the fact that the rays 33, 34 are incident on the surface side at a fairly large angle of incidence, resulting in a relatively large reflection from the surface side. However, screen A
Are formed such that none of the light rays incident on the surface side are totally reflected.

Further, partial reflection also occurs when the light beams 33 and 34 strike the inside of the stripe forming portion 23.
Also here, since the incident angle is relatively large, a large reflection occurs accordingly. Regarding the light ray 33, when the light ray is incident on the deepest part of the surface side part 35 substantially at the center of the two lens elements 25, the energy loss is 30 to 50% in total.
Go up. Much of this is due to the large refraction that occurs when the light beam 33 exits the stripe formation 23. The corresponding loss when ray 33 enters lens element 25 was calculated to be 15-20%, depending on the magnitude of the refraction at the time of incidence and the magnitude of the angle of incidence. Also, when light diffusing particles are incorporated into the screen for image reproduction, or when the lens surface is frosted for image reproduction, light rays are attenuated as they pass through the screen.

The various losses experienced by rays 30, 33, 34 and intermediate ray 36 are shown in FIG. 2, where the output rays are indicated by arrows. As a result, the output vector of ray 30 is longer than the output vector of ray 36, because the output vector of ray 36 is longer than the output vector of ray 34, and furthermore, the output vector of ray 33 is the shortest. You can see that.

The light energy diffused in the horizontal direction is shown in the graph of FIG. The energy of the light beam 30 is maximum and can be read as 8 from the graph. From the vectors and graphs described above, a viewer looking at the screen at a right angle from the front (bottom of FIG. 2) will receive much more light energy due to the aforementioned reflection losses than if the screen were viewed diagonally forward. You can see what you can do. Technically speaking,
This means that the screen has gained a fairly large "peak gain".

FIG. 4 shows a cross-sectional view of the screen of FIG. 2, in which the stripe forming portion 23 is planar and no masking stripes are shown. f1 indicates the focal length of the lens element 25, and b2 indicates the pitch of the screen.

To illustrate the operation of the present invention, it must be recognized that it is not possible to measure the energy of a single light beam passing through lens element 25. Of course, any measuring instrument has a certain size of measurement object.
Here, it is assumed that the measuring device can measure a spherical angle of +/- 1 °. Therefore, instead of a single ray set on the optical axis of the lens element 25, the ray 40 in the plane shown in FIG.
It is appropriate to target a light flux limited between the light beam 41 and the light beam 41. The luminous flux between rays 40 and 41 is 0.40 m
+/− 1 to the radius of curvature of the top of lens element 25 of m
It corresponds to a width b1 = 0.04 mm corresponding to the top part of the lens element 25 giving a displacement of ° and a pitch b2 of 1.0 mm. FIG. 5 shows the light intensity curve of the lens element 25 as a function of the viewing angle, which corresponds to the graph of FIG. It can be seen that the light energy decreases as you look diagonally. For a typical screen, the loss is about 18-20% at maximum refraction. If the screen of FIG. 4 is provided with a forward-facing convex lens corresponding to FIG. 2, the loss is greater for the maximum refracted ray, ie about 3
It increases by 0 to 40%. As a result, the total loss through the screen at the point of maximum refraction is about 50%.

The present invention starts from this point.
According to the present invention, the energy diffusion curves shown in FIG. 5 are equalized. FIG. 6 shows a cross section of the screen of the present invention corresponding to FIG. 4 showing a conventional screen. Here, the radius of curvature for the top portion 45 of the lens element 25 is about 10
% Has been reduced. Looking again at the luminous flux enclosed by rays 40 and 41, it can be seen that the rays intersect each other at focal point 44 in screen A because the more convex top lens portion 45 has a focal length f3. . Thereby, the luminous flux defined by the light rays 40 and 41 is wider than in the case of FIG. 4 and is only beta in FIG.
In, the spread angle for the light beam is increased by delta beta. At the same time, a "dilution" of the light intensity occurs at a right angle on the screen surface, so that the graph of FIG. 7 is saddle shaped due to the "dilution".

The difference between FIG. 4 and FIG. 6 can be explained as follows.

In FIG. 4, the light meter is moved from the top of the lens element 25, for example 2f1 in the shadow area between the rays 40 and 41.
It is assumed that the exposure meter indicates the value of E1 at this time. This experiment was repeated in FIG.
At the same distance from the top of the lens element 25,
The light meter indicates a value of E2 smaller than E1.

In both cases, when the lens element 25 is irradiated with the same energy in the same area, that is, between the rays 40 and 41, the intensity at the point at the same distance from the top (2f1) of the lens element is as shown in FIG. Is lower. This is because the light of FIG. 4 is spread over a larger angle, ie, beta + deltabeta.

As described above, the energy of the light output close to the optical axis of the lens element 25 decreases, and conversely, as can be seen from FIG. 7, the energy increases toward both sides of the axis. The half-value angle in FIG. 5 increased from alpha to alpha + delta alpha because the peak gain decreased. (Half value is defined as half the peak gain, which is considered to be substantially the light energy transmitted at right angles to the screen.) In FIG. 8, the light trail of an embodiment of the screen according to the present invention is: It is shown in plan view. In this case, the intermediate lens element 25 is illuminated over its entire width with parallel rays directed perpendicular to the back of the screen. The top lens portion 45 collects light incident therethrough at the focal point 44 (focal length f3), so that this portion of the light is diffused again. On top of this light, light entering the lens element 25 through lens portions 51 and 52 (focal length f1) located on the side of the top lens portion 45 and focused on the forward facing lens 23. . As a result, as shown in FIG. 8, a substantially hemispherical reflection vector band 50 that draws a curved portion over the wide-angle region is formed, and constant light energy appears in the wide-angle region. FIG. 9 shows the light energy after the light has passed through the lens portion 25, including the top lens portion 45, and it can be seen that the curve is saddle shaped. FIG. 10 shows the light energy diffused when the light passes through the forward convex lens 23. From FIG. 10, it can be seen that the graph is smoothed by the loss in the forward convex lens 23, and that the internal reflection is greatest at the side surface portion. Thus, a constant light intensity is obtained at various viewing angles.

The focal point of the lens 23, labeled 46, is very close to the surface of the top lens portion 45 and slightly offset inward. Thereby, in the present embodiment, the lens 23
Has approximately the same focal length as defined for the lens side portions 51, 52 (FIG. 8), 54, 56 and 55, 57 (FIG. 11). In other words, if the rearward facing lens element 25 did not have a more convex top portion 45, the focal length of the forward facing convex lens 23 would be at the highest position of the rearward facing lens element 25. This fact is illustrated in FIGS. 8 and 11, where the dashed line represents the configuration that the rearward facing lens element 25 would have if the top portion 45 had not been present.

Computer calculations have shown that the lens side portions 51, 52 compensate for the focus in the screen member, and that this arrangement does not change the color shift.

For the screen embodiment according to the present invention, preferred dimensions are shown in FIGS. FIG.
From FIG. 1, it can be seen that a uniform viewing state can be obtained when the screen is viewed from the front at a right angle or from the side at an angle of 45 °. Top lens part 45 is 80 °
And has a radius R3 of 0.35 mm over the square.
On each side of the top lens portion 45 there is provided a short side lens portion 54, 55 having a radius R2 of 0.40 mm and laterally defined from the top lens portion 45 by a radius forming a 90 ° angle with each other. I have. Side lens part 5
4 and 55 are followed by side portions 56, 57, respectively. Its radius of curvature R1 is 0.84 mm, and its center is located symmetrically with respect to the optical axis of each lens element 25, that is, at a distance of 0.30 mm therefrom. Further, their centers are displaced 0.24 mm from the intersection between adjacent lens elements 25 toward the center. In addition, the screen has a forward convex lens 23 having a radius of curvature R4 of 0.40 mm. The screen pitch is 1.0 mm, and the tangent to the inner portions of the lens side portions 56, 57 forms a vertex angle of 38 °. Thus, as can be seen from FIG. 12, the height of the lens element 25 (including the top lens portion 45) is 0.48 mm. Top lens part 4
The distance between the surface of the front convex lens 23 and the surface of the front convex lens 23 is 1.18 mm, and when the screen is conventionally formed as shown by the broken line in FIG. Is 1.1
5 mm.

With respect to the width of the top lens 45, the length of the arc is smaller than 1/3 of the length of the lens element 25 including the length of the top lens element 25, and Must be greater than 1/20 of the arc length.

Regarding the lengths of the radii R1, R2, and R3 described above, the following examples are given in the case of a screen having a pitch of 1.0. Example 1 R1 = 0.84 mm R2 = 0.40 mm R3 = 0.35 mm Example 2 R1 = 0.90 mm R2 = 0.43 mm R3 = 0.40 mm Example 3 R1 = 0.80 mm R2 = 0.38 mm R3 = 0. 33 mm These radii must meet the condition that R2 is greater than R3 and less than R1.

[0031]

As described above, according to the present invention,
There is provided a rear projection screen that can obtain a screen image having substantially the same luminous intensity when viewed from the front right angle direction or from an oblique side.

[Brief description of the drawings]

FIG. 1 is a perspective view schematically showing a preferred use example of an embodiment of a rear projection screen according to the present invention.

FIG. 2 is a horizontal sectional view passing through a part of a known screen.

FIG. 3 is a graph showing energy diffusion of light passing through the screen shown in FIG. 2;

FIG. 4 is a horizontal cross-sectional view showing a part of a known screen in order to illustrate a problem motivating the present invention.

5 is a graph showing energy diffusion of light passing through the screen shown in FIG.

FIG. 6 is a horizontal sectional view passing through a part of one embodiment of the screen according to the present invention.

FIG. 7 is a graph showing the energy spread of a part of the light exiting the screen according to FIG.

FIG. 8 is a horizontal sectional view of a part of another embodiment of the screen according to the present invention.

FIG. 9 is a graph showing the energy spread of a part of the light exiting the screen according to FIG.

FIG. 10 is a graph showing the total energy spread of light exiting the screen according to FIG. 8;

FIG. 11 is a view corresponding to FIG. 8 and showing an example of each dimension of the screen.

FIG. 12 is an enlarged view similarly showing each dimension of the screen.

[Explanation of symbols]

 1, 2, 3 Projector 4 Screen 6, 7, 8 Optical axis 22 Masking stripe 23 Stripe forming part 24 Edge 25 Backward lens element 30, 33, 34, 36, 40, 41 Light beam 45 Top lens part 54, 55, 56, 57 Side lens

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G03B 21/62

Claims (3)

(57) [Claims] 1. Three TVs disposed adjacent to each other for projecting red, green, and blue TV images on the back of a screen.
A rear projection screen mainly used in a projection apparatus having a projector (1, 2, 3), wherein a vertically extending rearward-facing lens element formed as a convex lens for light (30, 33, 34) incident from behind. (2
5) at the rear, and the rearward facing lens element (2)
5) A screen (A) with a vertically extending masking stripe (22) in front of it having a stripe formation (23) opposite to 5), the top of said rearward facing lens element (25). Part (4
5) has a focal length (f3) shorter than the focal length of the side portion (54, 56; 55, 57) of the rearward facing lens element (25), and the focal length (f3) of the top portion (45) is The distance between the highest part of the rearward facing lens element (25) and the stripe forming part (23) is shorter than the distance (f1) measured perpendicular to the screen surface;
A rear projection screen characterized by the following. 2. A focal length (f1) of a side portion (54, 56; 55, 57) of the rearward facing lens element (25) is:
2. Rear projection screen according to claim 1, characterized in that the distance between the highest part of the rearward facing lens element (25) and the stripe forming part (23) substantially corresponds to the distance measured perpendicular to the screen plane. . 3. The stripe forming portion is formed as a forward convex lens (23), and the focal length of the lens (23) is set to a side portion (5) of the rearward facing lens element (25).
4. The rear projection screen according to claim 1, wherein the rear projection screen substantially corresponds to a focal length of 4, 56; 55, 57).