JPH0876248A - Projection device - Google Patents

Abstract

PURPOSE: To improve the picture quality by a projection device condensing, enlarging and projecting picture light from a picture display device with a projection lens, and to make the device small in size and light in weight concurrently. CONSTITUTION: The picture light 3 emitted from a light source 5 and transmitted through a liquid crystal display panel (picture display device) 6 is condensed by a Fresnel lens 8 and made incident on the projection lens 7, and enlarged and projected on a screen 2 by the lens 7. By arranging the Fresnel lens 8 between the panel 6 and the lens 7, the condensing rate of the picture light is improved without using a large-diameter projection lens and the quality of a video is made high. The Fresnel surface 8a of the Fresnel lens 8 is arranged to face the panel 6 side, so that various kinds of aberration such as laternal aberration, astigmatism and distortion aberration are suppressed to the minimum. Since a light and thin lens made of a polyacrylate is used as the Fresnel lens 8, the size and the weight of the device are hardly increased even in the case of adding the Fresnel lens 8. The device is made light in weight and small in size in comparison with the case that the diameter of the lens 7 is made large in order to improve the condensing efficiency to the same degree.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection device.

[0002]

2. Description of the Related Art As a projection device for enlarging and projecting a television image or a video image, an image signal is received from a television, a VTR (video tape recorder) or the like, an image is displayed on a liquid crystal display panel, and the image displayed on the liquid crystal is displayed. Liquid crystal projectors that use a projection lens to magnify and project on a screen have become widespread.

In addition, a transmissive screen is provided on the front surface of a main body case that houses a light source, a liquid crystal display panel, a projection lens, a projection mirror, etc., and an image displayed on the liquid crystal display panel is magnified by the projection lens, and the projection mirror is used. A liquid crystal projection television is also in widespread use as a rear-type projection device that reflects light on the screen and projects it from the back of the screen.

In all of this type of projection device, light emitted from a light source is guided to an image display device such as a liquid crystal display panel, and image light transmitted through the image display device is condensed by a projection lens to be enlarged and projected. This is common in that the image quality is improved by using a large-diameter projection lens to increase the efficiency of condensing the image light from the image display device.

[0005]

However, since the conventional projection device uses a large-diameter projection lens to collect the image light from the image display device with high efficiency, an attempt is made to improve the image quality of an image. Since the device becomes large, it is difficult to realize high image quality and at the same time reduce the size and weight of the device. Therefore, an object of the present invention is to provide a compact and lightweight projection device that can realize high-quality images.

[0006]

In order to achieve the above object, the present invention relates to a projection device for condensing and projecting image light from an image display device by a projection lens, the image display device and the projection lens. And a Fresnel lens with the Fresnel surface facing the image display device side.

[0007]

In the projection device of the present invention, the image light from the image display device is condensed by the Fresnel lens and enters the projection lens. Therefore, the condensing rate of the image light can be increased without using a large-diameter projection lens, and the image quality of the image can be improved. As the Fresnel lens can be made of light and thin material such as acrylic, the addition of the Fresnel lens does not increase the size and weight of the device, and the same increase in light collection efficiency can be achieved by increasing the diameter of the projection lens. Compared to the case where it is realized, it can be made lighter and smaller. In addition, by arranging the Fresnel lens with its Fresnel surface facing the image display device side, lateral aberration and astigmatism are compared to the case where the plane side of the Fresnel lens is arranged facing the image display device side. Various aberrations such as aberrations and bending aberrations can be suppressed to be small.

[0008]

Embodiments of the projection apparatus according to the present invention will be described below. [Embodiment 1] FIG. 1 is a perspective view showing a usage pattern of a liquid crystal projector as an example of a projection apparatus to which the present invention is applied.
FIG. 2 is a side view conceptually showing the optical system in FIG. 1. In FIG. 1, reference numeral 1 is a liquid crystal projector, and 2 is a reflective screen. By installing the liquid crystal projector 1 on the same side of the screen 2 as the observer and projecting image light 3, an image is displayed on the front surface of the screen 2. 4 is projected. That is, in this usage pattern, the observer sees the reflected light from the screen 2.

As shown in FIG. 2, the liquid crystal projector 1 is provided with a light source 5, a liquid crystal display panel 6 as an image display device (chart generator), and a projection lens 7 with their optical axes aligned. A Fresnel lens 8 is arranged between the liquid crystal display panel 6 and the projection lens 7.

The light source 5 comprises a lamp 9 for emitting white light, which is arranged at the focal point of an umbrella-shaped reflector 10, and a reflecting surface 10a of the reflector 10 facing the liquid crystal display panel 6 and provided at the rear of the projector body 1a. ing.

The liquid crystal display panel 6 is the projector body 1
It is provided in the middle part of a. This liquid crystal display panel 6
Is a transmissive display device in which liquid crystal is enclosed between two transparent glass plates on which transparent electrodes are arranged, and the drive voltage applied to the transparent electrodes on both sides is controlled for each pixel to change the alignment state of liquid crystal molecules. By doing so, the image is displayed.

The projection lens 7 is formed by combining a plurality of lenses including a condenser lens 11 and an exit lens 12, and the exit lens 12 side is provided so as to protrude from the front surface of the projector body 1a.

The Fresnel lens 8 is arranged so that the Fresnel surface 8a faces the liquid crystal display panel 6 side as shown in FIG. The Fresnel lens 8 is a plano-convex circular type acrylic lens, and its refractive index is 1.492.

In the liquid crystal projector 1 configured as described above, the light emitted from the light source 5 passes through the liquid crystal display panel 6 and is directed by the Fresnel lens 8 to the vicinity of the entrance pupil of the condenser lens 11 of the projection lens 7. The light is collected and emitted from the emission lens 12 toward the screen 2. As a result, the image displayed on the liquid crystal display panel 6 is enlarged and projected on the screen 2, and the observer observes it by reflected light.

As described above, in the liquid crystal projector 1 of the present embodiment, the image light from the liquid crystal display panel 6 is condensed by the Fresnel lens 6 and is made incident on the projection lens 7, so that the projection lens 7 is condensed. It is possible to increase the image light condensing rate without increasing the diameter of the lens 11 and achieve high image quality.

By arranging the Fresnel lens 8 with the Fresnel surface 8a side facing the liquid crystal display panel 6, lateral aberration is increased as compared with the case where the plane 8b side of the Fresnel lens 8 is arranged toward the liquid crystal display panel 6. Various aberrations such as astigmatism and aberration are suppressed to be small.

For example, assuming that the focal length of the Fresnel lens 8 is 60.4 mm in FIG. 3 and parallel rays are collected at one point with no aberration, the formula expressing the inclination angle of each prism of the Fresnel lens 8 is:

[Equation 1] (See FIG. 5). Fresnel lens 8 when the maximum height is 38.1 mm, the distance from the image display surface (chart surface) of liquid crystal display panel 6 to the first surface of Fresnel lens 8 is 7 mm, and there is a diaphragm on rear focal point F. The respective aberration diagrams of the virtual image 6'of the liquid crystal display panel 6 due to are as shown in FIGS.

Similarly, considering the case where the plane 8b side of the Fresnel lens 8 is directed to the liquid crystal display panel 6 as shown in FIG. 4, the expression representing the inclination angle of each prism of the Fresnel lens 8 is

[Equation 2] Becomes The aberration diagrams of the virtual image of the liquid crystal display panel 6 by the Fresnel lens 8 in this case are as shown in FIGS.

Aberration diagrams by the Fresnel lens 8 arranged as shown in FIG. 3 (FIGS. 6 and 7) and aberration diagrams by the Fresnel lens 8 arranged as shown in FIG. 4 (FIGS. 8 and 9) are compared. Then, the absolute value of each aberration is obviously smaller than that of the other aberration (both spherical aberrations are 0). This also holds true for a Fresnel lens other than the type that condenses a parallel light beam at one point without aberration. When the Fresnel surface 8a side faces the liquid crystal display panel 6, the flat surface 8b side faces the liquid crystal display panel 6. Each aberration can be made smaller than that.

Therefore, according to the liquid crystal projector 1 of this embodiment, since the Fresnel lens 8 is arranged with its Fresnel surface 8a side facing the liquid crystal display panel 6, the aberration of the Fresnel lens 8 can be easily adjusted by the projection lens 7. Can be offset
By using the thin and light Fresnel lens 8 at a lower cost than spherical lenses and aspherical lenses, it is possible to easily realize a high quality liquid crystal projector with little aberration.

[Embodiment 2] FIG. 10 is an external perspective view of a liquid crystal projection television as another example of a projection apparatus to which the present invention is applied, and FIG. 11 is a cutaway rear view showing the internal structure of the liquid crystal projection television shown in FIG. FIG. 12 is a cutaway side view of the same. As shown in FIG. 10, the liquid crystal projection television 14 is provided with a transmissive screen 16 for displaying a projection image from the back side on the front upper half of a vertically long device case 15.

Inside the liquid crystal projection television 14, as shown in FIGS. 11 and 12, a light source 13, a dichroic mirror 17, a liquid crystal display panel 18 are provided in the lower half of the equipment case 15. An optical mechanical module 22 including a Fresnel lens 19, a projection lens 20, and a cooling fan 21 is provided, and a projection mirror 23 is provided in the upper half of the device case 15. A power supply unit 24 is provided at the bottom of the device case 15, and a speaker 25 is provided at the side.

The light source 13 comprises a lamp 26 that emits white light at the focal point of a reflector 27. In this case, the reflector 27 is installed in the lower left part of the main body case 15 with the reflecting surface 27a of the reflector 27 facing the right side. ing. That is, the light source 13 emits white light emitted from the lamp 26 to the reflector 2
It is reflected by 7 and irradiated to the right in the figure,
A dichroic mirror 17 is arranged on the optical axis.

In order to reflect the light from the light source 13 upward, the dichroic mirror 17 is arranged in an inclined posture of 45 ° upward to the right in the figure. A liquid crystal display panel 18, which is an image display device, a Fresnel lens 19, and a projection lens 20 are arranged above the dichroic mirror 17 with their optical axes aligned. Also in this case, the Fresnel lens 19 is arranged with its Fresnel surface 19a facing the liquid crystal display panel 18 side.

In the liquid crystal projection television 14 configured as described above, the light emitted from the light source 13 is reflected upward by the dichroic mirror 17 and enters the liquid crystal display panel 18. Then, the image light transmitted through the liquid crystal display panel 18 is condensed by the Fresnel lens 19 and enters the projection lens 20. The image light magnified by the projection lens 20 and projected upward is reflected by the projection mirror 23 and then projected on the screen 3 from the rear side, and an image by the transmitted light is displayed on the front surface of the screen 3.

Also in the liquid crystal projection television 14, the image light from the liquid crystal display panel 18 is condensed by the Fresnel lens 19 and is incident on the projection lens 20, so that the diameter of the condenser lens of the projection lens 20 is increased. It is possible to increase the image light condensing rate and improve the image quality of the image without performing the above.

Also in this case, by arranging the Fresnel lens 19 with the Fresnel surface 19a side facing the liquid crystal display panel 18, the aberration of the Fresnel lens 19 can be easily canceled by the projection lens 20, and a spherical lens or an aspherical surface can be used. By using the thin and light Fresnel lens 19 at a lower cost than the lens, it is possible to easily realize a high quality liquid crystal projection television with little aberration.

The case where the present invention is applied to a liquid crystal projector and a liquid crystal projection television has been described above as an example. However, the present invention is not limited to the above embodiments, and an image display device other than the liquid crystal display panel is used. It goes without saying that it can also be applied to other projectors and projection televisions.

[0029]

In summary, according to the present invention, since the Fresnel lens is provided between the image display device and the projection lens, the image light from the image display device is condensed by the Fresnel lens and is incident on the projection lens. Therefore, it is possible to increase the image light condensing rate without using a large-diameter projection lens and achieve high image quality. Also,
The Fresnel lens can be made of light and thin material such as acrylic, so the addition of the Fresnel lens does not increase the size and weight of the device, and the same increase in light collection efficiency can be achieved by increasing the diameter of the projection lens. Compared to the case where it is realized, it can be made lighter and smaller. In addition, by arranging the Fresnel lens with its Fresnel surface facing the image display device side, lateral aberration and astigmatism can be reduced compared to the case where the plane side of the Fresnel lens is arranged facing the image display device side. It is possible to suppress various aberrations such as aberrations and bending aberrations to be small.

[Brief description of drawings]

FIG. 1 is a perspective view showing a usage pattern of a liquid crystal projector as an example of a projection apparatus to which the present invention is applied.

FIG. 2 is a side view conceptually showing the optical system in FIG.

FIG. 3 is a side view showing an arrangement of Fresnel lenses and an image formation state thereof in the present invention.

FIG. 4 is a side view showing an arrangement of Fresnel lenses and an image formation state thereof in a comparative example with the present invention.

FIG. 5 is a diagram showing a Fresnel surface formed by zone-dividing a curved surface Z represented by a theoretical formula and moving and arranging the surface inclination of each zone on a reference plane.

FIG. 6 is a diagram showing lateral aberration of the Fresnel lens in the case of FIG.

FIG. 7 is a diagram showing spherical aberration, astigmatism, and non-planar aberration of the Fresnel lens in the case of FIG.

FIG. 8 is a diagram showing lateral aberration of the Fresnel lens in the case of FIG.

9 is a diagram showing spherical aberration, astigmatism, and non-planar aberration of the Fresnel lens in the case of FIG.

FIG. 10 is an external perspective view of a liquid crystal projection television as another example of the projection apparatus to which the present invention is applied.

11 is a cutaway rear view of the liquid crystal projection television shown in FIG.

12 is a cutaway side view of the liquid crystal projection television shown in FIG.

[Explanation of symbols]

 1 Liquid crystal projector as an example of a projection device 3 Image light 6 Liquid crystal display panel as an image display device 7 Projection lens 8 Fresnel lens 8a Fresnel surface 18 Liquid crystal display panel as an image display device 19 Fresnel lens 19a Fresnel surface 20 Projection lens

Claims (1)

[Claims] 1. A projection device for condensing and projecting image light from an image display device by a projection lens, the Fresnel lens having a Fresnel surface between the image display device and the projection lens. A projection device, wherein the projection device is arranged toward the device side.