JPS6329726B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a projection device for a slide device, and is capable of projecting an image with sufficient contrast on a screen in a natural manner even in the presence of external light.

In conventional projection devices, such as slide devices, the projection light from the slide device is diffusely reflected by the reflective surface of the screen, so if outside light is present, this outside light is also diffusely reflected by the screen, causing the image on the screen to The disadvantage was that the contrast was reduced. Therefore, it was usually necessary to use the device in a darkened environment. Also, screens with directivity were used.

Also, if you try to forcefully obtain sufficient contrast under normal lighting, you must make sure that the reflected brightness from outside light matches the black level of the image, and in order to project an image with a white level, , the light source needs to be extremely bright, which is wasteful in terms of power and gives a very unnatural appearance. Generally, the relationship between the reflected brightness L of the white level due to the image on the screen and the reflected brightness L due to external light can be expressed as shown in FIG. In FIG. 1, the vertical axis shows the reflected brightness (relative value), the horizontal axis shows the time axis (t), and for simplicity, L is assumed to be twice l. As can be seen from Figure 1, the lowest level of the image in this case does not go below 1 due to external light, so the brightness of the image, which should normally change from O to L, only changes from 1 to L. become. The contrast (L/l) at this time is 2.

In consideration of the above-mentioned points, the present invention aims to provide a projection device that can obtain sufficient contrast even when the surroundings are bright and can produce a natural-looking projected image.

An embodiment in which the present invention is applied to, for example, a slide device will be described below. FIG. 2 shows a schematic configuration of an embodiment of the present invention, and in FIG.
P is a slide device. The slide device P consists of a light source 1, a film 2, and a lens 3. An image of the film 2 is magnified by the light source 1 and projected onto a screen S by the lens 3.

As shown in FIG. 3, the screen S is made up of opposing glass plates 4A and 4B and spacers 5A and 5.
A field-effect nematic liquid crystal 6 is filled in the sealed space formed by the glass plates 4A and 4B, and plate-shaped electrodes 7 and 8 are adhered to the entire surfaces of the glass plates 4A and 4B that face each other. . The electrode 7 on the front side of the screen S is a transparent electrode, and the electrode 8 on the back side is a black electrode.

Then, the light from the light source 1 of the slide device P is intermittently projected onto the screen S, and in synchronization with this, the screen S intermittently has a reflective function. For this reason, the driving pulse from the driving source 9 is applied to the light source 1 of the slide device P and the screen S.
so that it is supplied to the electrodes. In other words, at the same time that the light source 1 of the slide device P is turned on, an operating voltage is applied between the electrodes 7 and 8 of the screen S, and as a result, the liquid crystal 6 becomes cloudy, and a projected image is displayed on the screen S only at this moment. .

In the configuration of the embodiment of the present invention described above, the duty factor of the drive pulse from the drive source 9 is 25
%, as shown in FIG. 4A, the case will be explained using an example in which the reflected brightness becomes L' which is four times (brightness of 8) when the light from the slide device P is projected. At this time, the luminance reflected by external light is 1, as indicated by l'. During the period when the drive pulse is not supplied to the screen S, the liquid crystal 6 is not clouded and becomes a black surface, so that the reflection from external light is also reflected during the period when the screen S has a reflective function. only occurs. Here, the human eye perceives the integral value of light as brightness, so as shown in Figure 4B,
The reflected luminance L'' of the screen S due to the slide device P, which is perceived by the human eye, has a brightness of 2 as in FIG. 1, but the reflected luminance l'' due to external light has a brightness of 1/4. In other words, the contrast is from 2 to (2/0.25
=8).

As is clear from the above, according to the present invention, the contrast can be improved without increasing power consumption, and there is no need to abnormally increase the brightness of the white level of the image that can be perceived by the eye, so the image will not look unnatural. It won't happen.

In addition, the light source 1 of the slide device P and the screen S
It is desirable that one cycle of the drive pulse be 20 ms or less in order to avoid flickering.
Further, as the light source 1 of the slide device P, an incandescent light bulb, a xenon lamp, a strobe, etc. can be used.

Furthermore, although the embodiment of the present invention described above is a case in which the present invention is applied to a projection device that uses a reflective screen, the present invention can also be applied to a projection device that uses a transmissive screen. . Fifth
The figure shows an outline of the configuration in that case. The screen S in FIG. 5 has, for example, the same configuration as shown in FIG. A light absorption plate 10 coated with a film is arranged. In this case, the light absorption plate 10 does not block the optical path of the projection light from the slide device P to the screen S, and when the audience 12 views the screen S,
The screen S is arranged at a position where it becomes black.

Then, the liquid crystal 6 of the screen S becomes cloudy in synchronization with the projection of the light from the light source of the slide device P, as described above. When the present invention is applied to such a transmission type screen, the contrast can also be improved.

[Brief explanation of drawings]

Figure 1 is a schematic diagram used to explain the present invention, Figure 2 is a schematic diagram used to explain the present invention.
The figure is a configuration diagram showing an outline of one embodiment of the present invention.
The figure is a cross-sectional view of a screen used in an embodiment of the present invention, FIG. 4 is a schematic diagram used to explain an embodiment of the present invention, and FIG. 5 is a cross-sectional view of a screen used in an embodiment of the invention. This is a conceptual diagram of an example of application. P is a slide device, S is a screen, 1 is a light source, 6 is a liquid crystal, 7 is a transparent electrode, 8 is a black electrode, and 9 is a driving source.

Claims (1)

[Claims] 1. A screen filled with liquid crystal between plate-shaped electrodes, a projector that projects image light from an image light source onto this screen, and a light provided approximately parallel to the screen and on the opposite side from the viewer. The image light source is an absorption plate, and by supplying driving pulses in synchronization with the electrodes of the projector and the screen, the image light from the image light source is intermittently projected onto the screen, and the image light is projected. A projection device in which the liquid crystal is in a cloudy state only during a period of time, and the liquid crystal is in a light transmitting state during a period in which the image light is not projected.