JPS63231433A - Transmission type screen - Google Patents

Abstract

PURPOSE:To decrease the uneven colors over the entire part of a screen so that the uniformity of colors can be assured by constituting the screen of Fresnel lenses which change focal lengths in an inclination direction according to the degree of diagonal incidence of video light. CONSTITUTION:The color uniformity is obtd. only at the point of the focal length conforming to the projection distance of a screen to be diagonally entered with the video light even if an ordinary circular Fresnel lens is used. The position in the perpendicular direction of the Fresnel screen 1 is divided to, for example, 10 parts A-J in this embodiment and the focal lengths of the Fresnel lenses in the respective parts A-J are set at the projection distances aA-aJ in the case of rectangular projections. The screen is constituted by joining such Fresnel lenses A-J to one piece. The difference in white balance, i.e., uneven colors according to the places on a diagonal incident video projector screen are thereby considerably decreased and the color uniformity is assured.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is applicable to a video projector which uses, for example, red, green, and blue CRTs as light sources and obtains an enlarged image on a screen through an optical system equipped with lenses and mirrors. This relates to a transmissive screen.

BACKGROUND OF THE INVENTION In recent years, attempts have been made to make image light obliquely incident on a screen, especially in transmissive video projectors, in order to make them more compact, mainly to reduce the depth of the cabinet.

Figure 7 shows its configuration.
The image light from T5 via the lens 4 is reflected by the mirror 6 so as to be incident obliquely.

The solid line in FIG. 6a and the ray development diagram thereof are shown in FIG.

In this case, as the screen 1, a screen having at least one surface mainly having a prism structure is used as a means for polarizing light.

On the other hand, if this is done only, the angles at which the image lights from the three CRTs 6 of red, green, and blue are incident on the screen 1 are different, which particularly impairs color uniformity. Of course, a lenticular screen has been added to cope with this problem, but it is insufficient and cannot withstand practical use.

Therefore, attempts have been made to improve the uniformity by using a circular Fresnel lens on the other side of the screen, as in the case of vertical projection (screen where the image light is incident at right angles). Figure 3 a, b.

The structure of the Fresnel lens and the relationship between the incident light 2 and the output light 3 in the case of CK direct projection are shown, and FIG. 4 shows the color unevenness improvement mechanism in the case of vertical projection. Figure 4a
This is an enlarged version of the person's part.

Figure 0 is υ, Figure b is when Fresnel is not used,
Figure 0 shows the effect when using Fresnel. By deflecting the optical axes of all R, G, and B image lights toward the observer T side by the action of the circular Fresnel lens,
The brightness ratio of red, green, and blue can be made almost the same between the center of the screen and the rest of the screen, improving color uniformity across the screen.

Here, the general formula of the Fresnel lens is shown below.

θ= arctan ((sin θ, + sin θ,)
/, "niτkoku-0°8θ)) θ, = arc tan (y/a > θ2=!Lrc
tan (y/b) where θ is the inclination angle of the Fresnel lens, y is the image height on the screen, a is the distance from the light source to the screen, and b is the distance from the screen to the convergence point of the light rays (observer). .

Further, N is the refractive index of the screen. FIG. 5 shows a drawing for the above explanation.

However, as shown in Figure 7, for a screen where the image light is obliquely incident, even if the same circular Fresnel lens as above is used, in the vertical direction on the screen, there is only one point whose focal length corresponds to the projection distance. Basically, it cannot be improved.

Problems to be Solved by the Invention As a screen for a video projector with oblique incidence,
As mentioned above, when a screen with a constant focal length for vertical projection is used, there is a problem in that the color unevenness over the entire surface of the screen is so great that it is not practical.

In view of the above conventional problems, the present invention aims to provide a transmission type screen which is an oblique incidence screen and can reduce color unevenness over the entire screen and ensure color uniformity.

Means for Solving the Problems In order to solve the above problems, the transmission screen of the present invention is equipped with a Fresnel lens configuration that changes the focal length in the oblique direction depending on the degree of oblique incidence of the image light. be.

According to the present invention, with the above-described configuration, it is possible to significantly reduce differences in white balance depending on the location on a video projector screen of oblique incidence, and to significantly reduce color unevenness, thereby ensuring color uniformity. At the same time, brightness uniformity can also be improved.

Embodiment 1 A screen according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the structure of a Fresnel screen in one embodiment of the present invention. a is a side sectional view.

B is a front view, and C is a drawing showing the relationship between the incident light 2 on the screen 1 and the emitted light 3 from the screen 1. Here, not only the emitted light 3 but also the function of a prism screen that obliquely deflects the incident light 2 is shown as a light ray.

Here, the vertical position on the screen 1 is divided into 10 parts, for example, from Mu to J, and the focal length of the Fresnel lens in each part from Mu to J is the projection distance a in the case of right-angle projection, ~
It is composed of Fresnel lenses of the form of a tortoise, and the screen as a whole has a structure in which five to J of these are joined into one piece. Of course, it is necessary to consider the 7-Resnel lens in accordance with the output characteristics of the prism screen, or conversely, to consider the prism screen in accordance with the characteristics of the Fresnel lens.

Furthermore, if the incident light to the lenticular screen disposed on the output light side is to be parallel light, the projection distance a may be set to the focal length f.

FIGS. 2a, b, and o show the structure of a Fresnel lens in a second embodiment, in which a Fresnel lens processing similar to that shown in FIG. 1 is applied to a single screen plate. Unlike the first embodiment, there is no discontinuity in the vertical direction, resulting in a smooth surface.

Like a circular Fresnel lens in the case of orthogonal projection1
Instead of making the inclination angle of two circles constant, we created a Fresnel lens screen that has a structure that changes continuously according to the projection distance a, depending on the vertical position even within the same circle. It is something. In other words, even within the same circle, θ is not constant, but varies as θ 2θ′, θ′, etc. depending on the position in the vertical direction.

Alternatively, a spiral circle configuration may be used.

Furthermore, as a third embodiment, whereas in the case shown in FIGS. 1 and 2, the direction of the Fresnel processing is reversed at the vertical center of the screen, the Fresnel processing is performed in the same direction over the entire circle. In this case as well, step 1.
The same effects as in the second embodiment can be obtained. Of course, the angle θ is changing at this time. However, in this case, the emitted light is directed in the same direction at one end of the screen in the vertical direction and the other end, although the outgoing angle is different, so that the position of the observer 7 is lower than the position of the screen 1.

Effects of the Invention As described above, the present invention provides a screen for use in a video projector having a configuration in which image light from a CRT is incident obliquely on the screen.

It is possible to reduce color unevenness and significantly improve the uniformity of one color.

[Brief explanation of drawings]

FIGS. 1a, b, and c are side sectional views and front views of a transmission type Fresnel screen according to the first embodiment of the present invention, and schematic diagrams showing their functions, and FIGS. C is a side sectional view, front view, and partially sectional perspective view of a transmission type Fresnel screen in the second embodiment of the present invention;
Figures a, b, and c are a side sectional view and front view of a conventional 7-Renel screen, and a schematic diagram showing its function; Figures 4a, b,
Is c the mechanism of the color unevenness improvement effect of the 7 renel screen in the case of orthogonal projection? - Figure 6 is a schematic diagram showing the general formula of a Fresnel lens. Figure 6 a and b are vertical and horizontal views of the light ray expansion of a video projector with oblique incidence. Figure 7 is a diagram showing the general formula of a Fresnel lens. FIG. 2 is a side view of the configuration of a video projector. 1... Screen, 2... Incident light, 3
...Outgoing light, 4...Lens, 6...
...CRT, 6...Mirror, 7...
Observer. Name of agent: Patent attorney Toshio Nakao and one other person ((b) Amendment to figure procedure June 11, 1988 Patent Application No. 66346, 1988 2. Name of the invention Transparent screen 3. Relationship with the person making the amendment Case Patent application Location: 1006 Kadoma, Kadoma City, Osaka Prefecture Name name
(582) Matsushita Electric Industrial Co., Ltd. Representative Tani
Akio I 4 Agent 571 Address 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (1)

[Claims] Image light is obliquely incident and projected from a plurality of light sources of different colors, and the focal length of the Fresnel lens is changed depending on the projection distance from each light source to the screen. Transparent screen.