Optics: image projectors – Distortion compensation
Patent
1992-11-13
1995-06-06
Cuchlinski, Jr., William A.
Optics: image projectors
Distortion compensation
353 70, 353 77, 362308, G03B 2114
Patent
active
054226910
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a projection type displaying apparatus for displaying video images, computer images, and so forth, in particular, relates to a projection type displaying apparatus for obliquely projecting these images from the rear of a screen with a liquid crystal light bulb or the like.
RELATED ART
Recently, an enlarging and projecting technique which uses a displaying device having a transmitting or reflecting type dot matrix liquid crystal (hereinafter this device is referred to as a light bulb) and which enlarges and projects an image of the light bulb on a screen is gaining popularity. This is because the image displayed by a Braun tube (CRT) has a limitation of the image size. To display a large image, the size of the Braun tube should be proportionally increased. The practical limitation of the image size of the Braun tube is at most 40 inches. Thus, to accomplish the need of such a large image, the enlarging and projecting technique is being used.
On the other hand, to provide a large light bulb, it should be produced without defects. However, it is not easy to produce a large light bulb which is free of defects. Even if such a light bulb were produced, it would become very expensive.
By using a transmitting (or reflecting type) light bulb, an image thereof can be enlarged and projected impressively without the restriction of the screen size.
From the above-mentioned point of view, a display type displaying apparatus which is equipped with an in-cabinet optical system which enlarges an image of a light bulb and projects the enlarged image from the rear of a screen disposed in front of the cabinet has been provided. The user can see the enlarged image from the front of the cabinet of the apparatus.
In a conventional rear projection type displaying apparatus using such a light bulb, as disclosed in Japanese Utility Patent Laid-Open Publication Serial No. HEI 1-85778, rays of light are radiated from a light source to a transmitting type liquid crystal light bulb. An image displayed on the liquid crystal light bulb is enlarged by a projection lens. The optical path of the resultant light is changed by a reflection mirror so as to guide it to the rear of a screen. In this construction, the entire projection optical system can be housed in a cabinet. Thus, the apparatus becomes portable. Moreover, even in a well-illuminated room, the user can see images on the screen.
However, in the conventional display type rear projection displaying apparatus, the optical path of rays of light which are transmitted through the light bulb is changed by the reflection mirror. The resultant rays of light are guided to the rear of the screen. Thus, unless the rays of light are projected in such a way that the optical axis thereof is perpendicular to the screen, the resultant image has a distortion such as a trapezoidal distortion. Therefore, this distortion largely restricts installation conditions of the reflection mirror. In other words, the volume of the projection optical system, in particular, the depth between the projection optical system and the screen (thickness of the cabinet) increase. Thus, the cabinet of the rear projection type displaying apparatus cannot become thin.
As a means for solving the above-mentioned problem, an oblique projection technique is known. As disclosed in U.S. Ser. No. 751,347 to T. Scheimpflug, when an image of an oblique object passes through a lens, a trapezoidal distortion takes place in the resultant image. As shown in FIG. 13, an image of an oblique object plane 43 passes through a lens 44. Thus, the resultant image is formed on an oblique image plane by the lens 44 in such a way that the prolonged line of the object plane 43 intersects with the prolonged line of the lens 44. Now, the point of intersection of the perpendicular line of the image side focal point f of the lens 44 and the prolonged line of the image plane 45 is referred to as g. A square image ABCD on the object plane 43 shown in FIG. 14 passes through the lens 44. Thus, an image
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Ishikawa Masaki
Ninomiya Noboru
Shinozaki Junichiro
Tanimoto Akihito
Cuchlinski Jr. William A.
Dowling William C.
Seiko Epson Corporation
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