JPH0345987A - Back project type display device - Google Patents

Abstract

PURPOSE:To improve the contrast of an image by providing a means which cuts off unnecessary light at a screen-side position of a projection lens. CONSTITUTION:Cathode-ray tubes(CRT) 3 exclusively for red, green, and blue are arranged succeesively and one lens 2 is arranged in front of each CRT 3. Images displayed on the CRTs 3 are projected on a screen 1 at an angle thetaof incidence slantingly from above. Then a light shield means 6 is constituted by a painting resin such as methacryl or metal such as aluminum or iron in black and projection parts 6a are constituted on the light shielding surface so that, for example, unnecessary light (a1) is converged while reflected several times. Therefore, the unnecessary light (a1), etc., which is reflected in the lens barrel of a projection lens 2 is cut off by the light shielding means 6 and never incident on the screen 1. Consequently, the contrast of the image can be im proved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a rear projection type display device that displays an image by enlarging and projecting a display image of a CRT, LC, etc. onto a transmission screen from the back side using a lens.

[Prior Art 1] Conventionally, there has been known an oblique incidence type rear projection display device as shown in FIG. 6, in which an image from a display device such as a CRT is projected obliquely onto a screen at an angle. In the figure, 31 is a screen, 32 is a projection lens, and 33
is a CRT, 34a and 34b are mirrors, and 35 is a cabinet, and the image displayed on the tube surface of the CRT 33 enters the screen 31 via the mirrors 34a and 34b by the lens 32 at an angle of incidence θ. is projected. Of course, the angle of incidence θ. =O
Also known is a normal incidence type in which image light is projected perpendicularly to the screen 3I.

The former was devised because the depth of the cabinet 35 can be made considerably smaller than the latter.

Problem to be Solved by the Invention 1 However, in the above conventional example, as shown in FIG. Therefore, an object of the present invention is to solve the above problem by forming a single-frame image capturing system. An object of the present invention is to provide a rear projection type display device in which the contrast of an image is improved by preventing unnecessary light from entering on a screen.

[Means for Solving the Problems] In the present invention for solving the above problems, an image display section such as a CRT that displays an image, a projection lens for projecting this displayed image, and a convergence of this projection lens are provided. A screen is provided at a position of a surface (common convergence surface in an in-line three-tube type, etc.), and a light shielding means for blocking unnecessary light is provided at a position on the screen side of the projection lens.

[Embodiment] Fig. 1 shows the overall configuration of the first embodiment of the present invention, in which 1 is a screen, 2 is a projection lens, and 3 is a CRT.
, 4a and 4b are reflecting mirrors, 5 is a cabinet, and 6 is a light shielding means.

In Figure 1, the CRT3 is red (R) in the vertical direction of the drawing.
, 8 (G), and those dedicated to blue (B) are arranged side by side (in-line 3-tube type), and lens 2 is also connected to each CIIT3.
One of each is placed on the front of the. The image displayed on this CRT 3 is projected through each lens 2, and mirrors 4a,
After reflection at 4b, the light is projected onto the screen 1 at an angle of incidence θ (representative value at the center) from diagonally above.

In this embodiment, a Tsuisochi high-brightness CRT for projection is used as the CRT 3, and the lens 2 has an aperture of φ120 mm and an F1.
2 is used. The projection distance from the front of the lens 2 to the screen l is 1500 mrn, the screen size is 50 inches diagonally with an aspect ratio of 16:9,
At this time, the incident angle θ at the center of the screen is set to 30 degrees, and the depth L is 450 mm.

In the above configuration, the screen l is composed of eccentric Fresnel lenses 1α and lβ and a double lenticular sheet lγ shown in FIG. 5(a). Eccentric Fresnel lens 1
α and lβ are formed by a large number of concentric prisms with their centers eccentrically placed above the screen l in FIG. Furthermore, the prism forming surfaces 1a' and 1β' of both Fresnel lenses lα and lβ are directed toward the image light output side, that is, the viewing side.

The plane is facing the back side.

Moreover, the eccentric Fresnel lenses 1a and 1β are.

Light transmittance of 90% or more and refractive index of approximately 1 with a thickness of 0.5 to 5 mm
．． It is made of 5-layer methacrylic resin.

The double lenticular sheet ly may have a black stripe, which widens the left and right viewing angle.
The in-line arrangement of T3 prevents color shift and reflection of external light, and is designed to provide better image and viewing characteristics.

Since the screen 1 is formed as described above, even for oblique incidence with a large incident angle θ, the image light is divided into two stages to the optimum viewing position by the two decentered Fresnel lenses 1α and Iβ that distribute the power. They are separated and refracted gradually and effortlessly. Therefore, reflection loss at the prism can be reduced compared to the case of using a single decentered Fresnel lens.Furthermore, the inclination of the non-lens parts (ineffective parts) of the decentered 7 Fresnel lenses la and lβ can be made to be approximately along the traveling direction of the image light. With this structure, there is almost no vignetting of the light beam in the non-lens portion, and therefore moiré phenomena between the repeating periodic structures caused by this will hardly occur.

The mirrors 4a and 4b are surface mirrors with a reflectance of 9.0 to 100%, which change the direction of the projection light from the CRT 3 and the projection lens 2 twice and project it onto the screen l.

Next, the light shielding means 6, whose enlarged cross section is shown in FIG. There is. The protrusion 6a is configured to converge light, such as unnecessary light a, while reflecting it several times. Therefore, unnecessary light a reflected inside the lens barrel of the projection lens 2, etc.
The light such as 1 is blocked by the light blocking means 6 and does not enter the screen 1.

Next, a second embodiment shown in FIG. 3 will be explained.

In the first embodiment, the light shielding means 6 was provided at a position directly along the projection light projected from the projection lens 2, but in the second embodiment, the light shielding means 16 was provided at a position that was reflected by the mirror 4b and onto the screen l. It is provided at a position along the projection light just before it enters. Even if it is installed in such a position, the unnecessary light at that is reflected inside the lens barrel of the projection lens 2 will be removed from the screen l.
The other points are the same as in the first embodiment, in that the contrast of one image is improved by blocking light immediately before the light enters the light beam.

Although the above two embodiments are rear projection display devices of an oblique incidence type, the concept of the present invention is also applicable to a display device of a normal incidence type in which the angle of incidence on the screen 1 is 0 degrees.

FIG. 4 shows a third embodiment of a rear projection display device using a normal incidence system. In the third embodiment, the image light from the mirror 2 is reflected by one reflecting mirror 4c and is projected onto the screen 11 on the rear side. It is configured so that the light is incident perpendicularly to the center representative []. Moreover, since the screen 11 does not need to refract and deflect the projection light upward, it is also possible to use a concentric Fresnel lens 11 (2) as shown in FIG. 11β such as error sheets and diffusion plates
It is made up of. The light shielding means 26 is a lens 2
It is provided at a position directly along the projection light projected from. Other points are substantially the same as the first embodiment.

By the way, the mirror arrangement and lens arrangement adopted in the above example
Although an optical layout such as a CRT arrangement is effective in making the cabinet 5 thinner, it is not limited to this layout.

[Effects of the Invention] As explained above, according to the configuration of the present invention, since the light shielding member is provided on the screen side of the projection lens, the light is reflected within the lens barrel of the projection lens and directly enters the screen. Unwanted light is blocked. Therefore, the contrast of the image on the screen is improved and a high quality image can be observed from the viewing side of the screen.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram of the first embodiment of the present invention, FIG. 2 is an enlarged sectional view of the light shielding means of the first embodiment, FIG. 3 is an overall configuration diagram of the second embodiment of the invention, and FIG. The figure is an overall configuration diagram of a third embodiment of the present invention, FIGS. 5(a) and 5(b) are schematic diagrams of an eccentric Fresnel lens and a concentric Fresnel lens used in the above embodiment, respectively, and FIG. 6 is a conventional 1 is an overall configuration diagram of an oblique-incidence type rear projection type image display device.

Claims (1)

[Claims] 1. A rear projection display device having an image display section for displaying an image, a projection lens for projecting the displayed image, and a screen disposed at the convergence surface of the projection lens. A rear projection type display device, characterized in that a light shielding means for shielding unnecessary light is provided at a position on the screen side of the projection lens. 2. The rear projection type display device according to claim 1, wherein a protrusion is formed on a light shielding surface of the light shielding means on the projection lens side. 3. The rear projection type display device according to claim 1, wherein the light shielding means is provided at a position along the projection light projected from the projection lens. 4. The rear projection type display device according to claim 1, wherein the light shielding means is provided at a position along the projection light just before it enters the screen.