JPH0756119A - Polarizing screen for projector - Google Patents

Abstract

PURPOSE:To provide a polarizing screen capable of obtaining a video having high contrast even though projected light from a liquid crystal projector has any kind of plane of polarization. CONSTITUTION:This polarizing screen 31 for a projector is constituted of a reflection type screen 41, a polarizing plate 42, and a 1/2 wavelength plate 43; and is set in a state where the surfaces are in a perpendicular direction. The polarizing plate 42 is arranged on the surface on the projector side of the reflection type screen 41 so that the axis of polarization of the polarizing plate 42 faces in the perpendicular direction. The 1/2 wavelength plate 43 is arranged on the projector side from the polarizing plate 42, and the plane of polarization of projected and polarized light is rotated to be aligned with the direction of the axis of polarization of the polarizing plate 42.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projector screen, and more particularly to a projector polarizing screen for projecting polarized projection light.

[0002]

2. Description of the Related Art A liquid crystal projector is characterized in that it can easily display a large screen. However, when an attempt is made to project in a bright place such as a room illuminated by an interior light, the contrast of projection light with respect to external light such as illumination light is lowered, and the projected image becomes significantly hard to see.

A polarizing plate is well known as a means for adjusting the light transmittance. For example, JP-A-63-81314
Is equipped with two polarizing plates, which can be rotated relative to each other according to the brightness of the outside light to adjust the light transmittance, thereby improving the visibility of the screen. It is disclosed. Also in the case of a liquid crystal projector device, a polarizing plate may be provided on the screen surface in order to improve the reduction in contrast. Such a screen is generally known as a polarizing screen.

FIG. 3 shows the configuration of the polarizing screen described in JP-A-63-267073, JP-A-61-38976 and JP-A-3-5147 and the positional relationship with the liquid crystal projector and the ceiling lamp. is there. The polarizing screen 11 is installed vertically to the floor, and the liquid crystal projector 12 is arranged so that the projection light enters the polarizing screen 11 vertically. Further, there is a ceiling lamp 13 on the upper side, and its illumination light is incident on the polarizing screen 11 obliquely from above.

The polarizing screen 11 is a reflection type screen 2.
A polarizing plate 22 is arranged on the surface of No. 1 so that its polarization axis is in a direction perpendicular to the floor, and a polarization component in a direction different from the vertical direction cannot pass through the polarizing plate 22. The external light that passes through the polarizing plate 22 and enters the reflective screen 21 is about half of the original light. Therefore, the external light reflected by the reflective screen 21, transmitted through the polarizing plate 22 and reaching the observer is greatly reduced.

On the other hand, the liquid crystal projector 12 projects projection light polarized in the direction perpendicular to the floor. As such a projector, Japanese Patent Application Laid-Open No. 4-151193 discloses a liquid crystal projector in which a polarization plate of projection light is controlled by a wave plate to be in a vertical direction. As another example of using a wave plate to rotate the plane of polarization, there is a projector device disclosed in Japanese Utility Model Laid-Open No. 2-83524. In this projector device, a wave plate is arranged between the rear projection screen and a polarizing plate installed on the projection light incident side, and the polarization plane of the projection light is rotated so that the reflected light on the screen does not return to the incident side. In order to prevent the deterioration of contrast.

As described above, since the projection light of the liquid crystal projector 12 is polarized in the polarization axis direction of the polarizing plate 22, most of it is incident on the reflection type screen 21. Most of the projection light that has entered the reflective screen 21 is reflected, and further passes through the polarizing plate to reach the observer. That is, by providing the polarizing plate 22, the external light is greatly reduced, but the projected light is hardly reduced. Therefore, the contrast of the projection light with respect to the external light is higher than in the case where the polarizing plate 22 is not provided, and an image that is easy to see even in a bright place can be obtained.

By the way, the polarizing plate 2 of the polarizing screen 11
No. 2 is arranged so that its polarization axis is perpendicular to the floor, for the following reason. As described above, most of the external light such as the ceiling light enters the polarizing screen 11 from the obliquely upper direction. Of this incident light,
Only the polarized component in the direction perpendicular to the floor passes through the polarizing plate 22 and reaches the reflective screen 21. That is, the external light that enters the reflective screen 21 is only the P-polarized component. In general, the P-polarized component has a characteristic that its reflectance is lower than that of the S-polarized component according to Brewster's law. Therefore, among the polarized components of the external light, the polarized component in the direction perpendicular to the floor is less reflected than the polarized component in the other direction is incident on the reflective screen 21. , Higher contrast images can be obtained. For the above reasons
In a polarizing screen, it is common to arrange polarizing plates so that the polarization axis is in the vertical direction.

[0009]

As described above, in the conventionally proposed polarizing screen, the polarizing axis of the polarizing plate is perpendicular to the floor in order to obtain a high-contrast image. Therefore, when used in a liquid crystal projector that projects projection light having a polarization plane different from the vertical direction, there is a problem that the brightness of the entire screen is reduced.

Therefore, an object of the present invention is to provide a polarizing screen which can obtain a high-contrast image regardless of the polarization plane of the projection light of the liquid crystal projector.

[0011]

According to a first aspect of the present invention, there is provided a reflection type screen which projects projection light emitted from a projector and polarized in one direction, and a reflection type screen which is disposed on a surface of the reflection type screen on the projector side. A polarizing screen for a projector is provided with a polarizing plate and a polarization plane rotating means which is disposed on the projector side of the polarizing plate and matches the polarization plane of projection light with the polarization direction of the polarizing plate.

That is, according to the first aspect of the invention, the polarizing screen for the projector is provided with the polarization plane rotating means, and the plane of polarization of the projection light of the projector is rotated so that it can be aligned with the polarization axis of the polarizing plate. It is possible to create a polarizing screen for a projector that can obtain a high-contrast image for the liquid crystal projector regardless of the direction of the polarization plane of light.

According to a second aspect of the present invention, a reflection type screen which projects the projection light emitted from the projector and polarized in one direction, a polarizing plate arranged on the surface of the reflection type screen on the projector side, and the polarization plate A half-wave plate arranged on the projector side of the plate as a polarization plane rotating means for aligning the polarization plane of the projection light with the polarization direction of this polarizing plate;
The projector polarization screen is provided with a rotation angle varying means for varying the rotation angle of the polarization plane by the half-wave plate.

That is, in the invention described in claim 2, since the polarizing screen for the projector is provided with the half-wave plate and the rotation angle varying means for varying the rotation angle of the polarization plane, the projection light of the projector is changed. Regardless of the direction of the plane of polarization, it is possible to adjust the rotation angle of the plane of polarization on the spot to obtain a high-contrast image.

According to the third aspect of the present invention, a reflection type screen which is installed vertically on the floor and projects projection light emitted from the projector and polarized in one direction, and a polarization axis on the projector side surface of the reflection type screen. A polarizing plate arranged so as to be perpendicular to the floor, and a ½ wavelength plate as a polarization plane rotating means arranged on the projector side of this polarizing plate to match the polarization plane of the projection light with the polarization direction of this polarizing plate. The projector polarization screen is provided with a rotation angle varying means for varying the rotation angle of the polarization plane by the half-wave plate.

That is, according to the third aspect of the invention, a polarizing plate is arranged on the surface of the reflection type screen so that the polarization axis is in the direction perpendicular to the floor, and the light is reflected by the reflection type screen rather than in another direction. It reduces the ambient light.

[0017]

EXAMPLES The present invention will be described in detail below with reference to examples.

FIG. 1 shows a configuration of a polarizing screen for a projector in one embodiment of the present invention and a positional relationship with a liquid crystal projector and a ceiling lamp. The projector polarization screen 31 is installed vertically to the floor, and the liquid crystal projector 32 is arranged so that an image can be projected almost vertically thereto. The liquid crystal projector 32 is equipped with a polarizing plate and is 45 ° from the vertical direction.
It is designed to project linearly polarized light having a rotated plane of polarization. Further, a ceiling lamp 33 is provided in a room where these are placed, and light emitted from the ceiling light 33 enters the polarizing screen 31 for the projector as external light.

The projector polarization screen 31 comprises a reflection type screen 41, a polarizing plate 42, and a half-wave plate 43. The reflection type screen 41 is a screen that almost completely reflects the light that is incident perpendicularly thereto. The polarizing plate 42 has its polarization axis perpendicular to the floor,
It is arranged on the surface of the reflective screen 41 on the projector side and transmits only polarized light having a vertical polarization plane. Therefore, as it is, the light projected by the liquid crystal projector 32 hardly reaches the reflection type screen 41. Therefore, the plane of polarization of the projection light projected from the liquid crystal projector 32 is rotated by the half-wave plate 43 so as to coincide with the polarization axis of the polarizing plate 42.

FIG. 2 shows the rotation of the plane of polarization by the half-wave plate 43. 1/2 wave plate 4
3 is arranged on the projector side of the polarizing plate 42 so that its slow axis 51 is 22.5 ° with respect to the vertical direction. In general, the half-wave plate has the property of rotating the plane of polarization of incident linearly polarized light in a direction symmetrical to the slow axis. Therefore, the polarization direction 5 inclined by 45 ° from the vertical direction
The projected polarized light having a polarization plane of 2 is converted into polarized light having a vertical polarization plane by the half-wave plate 43. This one
Most of the polarized light emitted from the / 2 wavelength plate 43 reaches the reflection type screen 41 because its polarization plane coincides with the polarization axis 53 of the polarizing plate 42.

In this way, the light incident on the reflection type screen 41 is almost completely reflected and re-enters the polarizing plate 42 from the side opposite to the above. Also in this case, since the polarization direction of the reflected light matches the polarization axis direction of the polarizing plate 42, most of the reflected light passes through the polarizing plate 42. The transmitted light is 1
It passes through the / 2 wavelength plate 43 and reaches the observer.

On the other hand, since the external light emitted from the ceiling lamp 33 has an indefinite polarization state, the polarization state does not change even if it passes through the ½ wavelength plate 43, and enters the polarizing plate 42 as indefinite polarization. Since the polarizing plate 42 transmits only the polarized component in the vertical direction, the external light reaching the reflective screen 41 is about half of the incident light. The external light that has reached the reflective screen 31 is reflected here, and most of it is reflected by the polarizing plates 42 and
It passes through the / 2 wavelength plate 43 and reaches the observer.

As described above, most of the projection light having the plane of polarization inclined by 45 ° from the vertical direction is provided with the half-wave plate 43, so that most of the projection light is polarized screen 3 for the projector.
It is reflected at 1 and reaches the observer. When this projected light is decomposed into a polarized light component having a vertical polarization plane and a polarized light component having a horizontal polarization plane, the square root of the original projected light is halved. This is 1.4 times brighter than the case. On the contrary,
Only half of the external light reaches the observer. As a result, a high-quality image with high contrast can be obtained.

In this embodiment, the case where the plane of polarization of the projection light of the liquid crystal projector makes an angle of 45 ° with the vertical direction has been described. However, in the present invention, the plane of polarization makes an angle of θ with the vertical direction. Applicable for cases. In that case, the 1/2 wavelength plate may be arranged so that its slow axis forms an angle of θ / 2 with the vertical direction. In addition, a transparent substrate made of optical glass or the like is installed on the projector side of the polarizing plate so that it can be rotated in a plane parallel to the polarizing screen, and a 1/2 wavelength plate is attached on the substrate as the rotation angle varying means. You may attach it. In this case, it is possible to adjust the image contrast to be the highest while rotating the half-wave plate.

Further, the projector to which the polarizing screen for a projector of the present invention can be applied is not limited to the liquid crystal projector. It can also be applied to a projector or the like in which outgoing light of a CRT is polarized in one direction.

Further, although the half-wave plate is used as the polarization plane rotating means in this embodiment, a means utilizing the Faraday effect may be used.

[0027]

As described above, according to the invention of claim 1, the polarization plane of the projection light of the projector is rotated by the polarization plane rotating means so that the plane of polarization of the projection light can be aligned with the polarization axis of the polarizing plate. There is an effect that it is possible to prepare a polarizing screen for a projector that can obtain a high-contrast image for the liquid crystal projector regardless of the direction of polarization of the projection light.

Further, according to the second aspect of the invention, since the rotation angle changing means changes the rotation angle of the polarization plane of the half-wave plate, the polarization plane of the projection light of the projector is in any direction. However, there is an effect that a high-contrast image can be obtained by adjusting the rotation angle of the polarization plane on the spot.

Further, according to the third aspect of the invention, since the polarizing plate is arranged on the surface of the reflection type screen so that the polarization axis is in the direction perpendicular to the floor, the reflection type screen is arranged rather than in other directions. It is possible to reduce the external light reflected by the screen, and it is possible to obtain an image with higher contrast.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration of a polarizing screen for a projector of the present invention and an arrangement with respect to a liquid crystal projector and a ceiling lamp in an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing rotation of a polarization plane of linearly polarized light that passes through a half-wave plate used in an example of the present invention.

FIG. 3 is a schematic explanatory diagram showing a configuration of a conventional polarizing screen for a projector and an arrangement with respect to a liquid crystal projector and a ceiling lamp.

[Explanation of symbols]

 31 Polarizing Screen for Projector 32 Liquid Crystal Projector 41 Reflecting Screen 42 Polarizing Plate 43 1/2 Wave Plate (Polarizing Plane Rotating Means)

Claims (3)

[Claims] 1. A reflection type screen for projecting projection light emitted from a projector and polarized in one direction, a polarizing plate arranged on the surface of the reflection type screen on the projector side, and arranged on the projector side of the polarizing plate. A polarization screen for a projector, comprising: a polarization plane rotating means for matching the polarization plane of the projection light with the polarization direction of the polarizing plate. 2. A reflection type screen which projects projection light emitted from a projector and polarized in one direction, a polarizing plate arranged on the surface of the reflection type screen on the projector side, and arranged on the projector side of this polarizing plate. A half-wave plate for matching the polarization plane of the projected light with the polarization direction of the polarizing plate; and a rotation angle varying means for varying the rotation angle of the polarization plane by the half-wave plate. Characteristic polarized screen for projector. 3. A reflection type screen for projecting projection light emitted from a projector installed vertically on the floor and polarized in one direction, and a polarization axis perpendicular to the floor on the projector side surface of the reflection type screen. And a half-wave plate arranged on the projector side of this polarizing plate to match the polarization plane of the projection light with the polarization direction of this polarizing plate, and the polarization plane by this half-wave plate And a rotation angle varying means for varying the rotation angle of the polarizing screen for a projector.