JPH09211413A - Overhead projector in common use for liquid crystal projector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain the brightness with the same screen size at a level similar to the level of' a large-size panel and to embody bright videos of a high contrast even if a small-size TFT liquid crystal panel of a low cost is used in a method for arranging the liquid crystal panel on the Fresnel lens face of an OHP. SOLUTION: The small-size liquid crystal panel 8 is arranged in a Fresnel lens part 4. This projector is provided with a means for converging the diffusion angle of the light source light projected to the Fresnel lens part 4 and adapting the light source light to the area of the liquid crystal panel 8 by switching an optical means 7. The light source light increased in the light quantity by the convergence is projected to the small-size liquid crystal panel 8 via the Fresnel lens and the video light generated in the liquid crystal panel is projected via a projecting lens 5 and a mirror 6 to the screen.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overhead projector (OHP), and more particularly to an overhead projector that also serves as a liquid crystal projector.

[0002]

2. Description of the Related Art Conventionally, an OHP liquid crystal panel has been constructed by arranging an OHP Fresnel lens having the same size as the lens.

[0003]

Therefore, a large liquid crystal panel has been required. The use of a TFT liquid crystal panel that can realize a bright and high-contrast screen is costly because it is expensive.

Further, in the structure in which a small liquid crystal panel is arranged in the Fresnel lens portion, only a part of the light source light of the whole can be used, so that an image of a dark liquid crystal screen with a low light utilization rate is obtained.

An object of the present invention is to eliminate the above-mentioned conventional drawbacks. In the OHP, a small liquid crystal panel is arranged in the Fresnel lens portion, and at that time, the light source light is in a portion other than the small liquid crystal panel. It is also an object of the present invention to provide an overhead projector which also serves as a liquid crystal projector and which can prevent a large loss of light from the light source as well as being prevented from being projected and reducing the light utilization rate.

[0006]

Therefore, in the overhead projector that also serves as the liquid crystal projector of the present invention, when it is used as a liquid crystal projector, a small liquid crystal panel is arranged in the Fresnel lens portion and the optical system means is switched. By providing a means for narrowing down the diffusion angle of the light source light projected on the Fresnel lens part and condensing it in a small area adapted to the area of the liquid crystal panel, the light source light whose light amount is increased by narrowing it down is Fresnel lens The image light generated by the liquid crystal panel is projected on a small liquid crystal panel via a projection lens and a mirror.

According to the present invention, when the OHP is used, the light amount equivalent to the light amount of the light source light projected on the Fresnel lens is projected on the small liquid crystal panel, so that the light source can be used even if the small TFT type liquid crystal panel is used. Bright and high-contrast images can be realized without significantly reducing the amount of light.

In the present invention, the expensive large TF is used by the method of disposing the liquid crystal panel on the Fresnel lens surface of the OHP.
By using a low-cost small-sized TFT liquid crystal panel instead of the T-type liquid crystal panel, a bright and high-contrast screen image can be realized at low cost.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION A detailed description will be given below with reference to an embodiment of the present invention.

FIG. 1 is a sectional view showing the configuration of an overhead projector that also serves as a liquid crystal projector according to the present invention.

As shown in the figure, the overall structure of the embodiment of the present invention is similar to the conventional OHP in basic structure, and the light source light 2 generated by the light source lamp 1 is reflected by a mirror 3 to generate Fresnel. The image is projected on the lens 4 and the characters on the OHP sheet arranged on the Fresnel lens 4 or the image on the liquid crystal panel is enlarged and projected on a screen (not shown) via the projection lens 5 and the mirror 6.

In the apparatus of the present invention, a particularly novel component is a light source light provided by, for example, a detachable or movable condenser means (condenser lens in the embodiment) 7 disposed between the light source lamp 1 and the Fresnel lens 4. 2 is narrowed down and the irradiation area to the Fresnel lens 4 portion is projected as a small area corresponding to the display surface of the small TFT liquid crystal panel 8 arranged on the Fresnel lens 4. Reference numeral 9 denotes a polarization converter used in a liquid crystal projector, which converts one of the P-wave component and the S-wave component, which is the polarization component of the light source light, to match the polarization direction of the liquid crystal panel, By using only one polarization component, it is possible to prevent either polarization component from being blocked by the polarizing plate portion of the liquid crystal panel. Further, in the figure, reference numeral 10 denotes light source light when OHP is used, and illuminates the entire Fresnel lens. Reference numeral 11 denotes a light source light when the liquid crystal panel is used, which is focused and illuminates only the small liquid crystal panel portion.

[0013]

According to the present invention, when a TFT liquid crystal panel capable of realizing a bright and high-contrast image is used, a TFT liquid crystal panel significantly smaller than the Fresnel lens size is used without reducing the image brightness. Can be used.

[Brief description of drawings]

FIG. 1 is a configuration cross-sectional view of an embodiment of the present invention.

[Explanation of symbols]

 1 Light source lamp 2 Light source light 3 Mirror 4 Fresnel lens 5 Projection lens 6 Mirror 7 Condensing lens 8 TFT small liquid crystal panel 9 Polarization converter

Claims (6)

[Claims] 1. A light source, a Fresnel lens that receives light from the light source, a projection lens that projects light that has passed through the Fresnel lens, and optics that is provided between the light source and the Fresnel lens and that narrows the area projected on the Fresnel lens. An overhead projector that also serves as a liquid crystal projector and is equipped with a means. 2. The overhead projector also used as a liquid crystal projector according to claim 1, further comprising a liquid crystal panel smaller than the Fresnel lens installed in the vicinity of the Fresnel lens, the liquid crystal panel receiving the squeezed light. 3. The overhead projector also serving as a liquid crystal projector according to claim 1, wherein the optical means is a movable lens. 4. The overhead projector that also serves as a liquid crystal projector according to claim 2, wherein the liquid crystal panel is a TFT liquid crystal panel. 5. The overhead projector also serving as a liquid crystal projector according to claim 2, further comprising a polarization conversion means provided between the light source and the liquid crystal panel. 6. An OH which projects a light source light generated by a light source lamp onto a Fresnel lens and is arranged on the Fresnel lens.
An overhead projector for enlarging and projecting an image of a P sheet or a liquid crystal panel onto a screen via a projection lens and a mirror, wherein the light source is narrowed down by a detachable condensing means arranged between a light source lamp and a Fresnel lens, An overhead projector that also functions as a liquid crystal projector, characterized in that a projection area for a part is projected onto the liquid crystal panel surface as an area corresponding to the display surface of the liquid crystal panel placed on the Fresnel lens.