Oblique projection optical system

Details Oblique projection optical system Oblique projection optical system

1999-11-23

2001-04-24

Dowling, William (Department: 2851)

Optics: image projectors

Distortion compensation

For projection axis inclined to screen

Reexamination Certificate

active

06220712

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
This Application is based on Patent Application No. 10-335472 filed in Japan, the content of which is hereby incorporated by reference.
FIELD OF THE INVENTION
The present invention relates to an oblique projection optical system, and specifically relates to an oblique projection optical system for projecting in an oblique direction from a primary image surface to a secondary image surface, and is suitable for image projection devices, and image reading devices.
BACKGROUND OF THE INVENTION
Projection devices which enlarge and project an image displayed on, for example, a liquid crystal display onto a screen are well known. There have been various proposals for projection devices which project an image from an oblique direction onto a screen for the purpose of making a more compact projection device while enlarging the screen. This type of oblique projection device is advantageous in that the projection optical system does not block the field of view of the observer since the projection optical system is arranged at a position removed from the center of the screen. However, the oblique projection devices also produce so-called trapezoid distortion in the projection image. There have also been various proposed projection optical systems to correct this trapezoid distortion. For example, Japanese Laid-Open Patent Application Nos. HEI 5-119283 and HEI 5-134213 disclose projection optical systems which are partially eccentric to correct the trapezoid distortion.
The projection optical systems disclosed in Japanese Laid-Open Patent Application Nos. HEI 5-119283 and HEI 5-134213 are not adequately satisfactory from the perspectives of compactness and high performance.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an improved oblique projection optical system.
Another object of the present invention is to provide an oblique projection optical system which has a wide field angle and high magnification, and which achieves a compact overall length of the optical system and lens diameter while providing sufficient inclination projection angle.
These objects are attained by an oblique projection optical system for enlarging and projecting in an oblique direction from a primary image surface to a secondary image surface, said oblique projection optical system being provided with two or more mutually eccentric lenses, wherein an intermediate real image is not formed between the primary image surface and the secondary image surface, and wherein conditional equations (1) through (3) below are satisfied when rays connecting the screen center of the primary image surface and the screen center of the secondary image surface are center screen rays:
15°<&thgr;
oi
<40°  (1)
20°<&thgr;
o
<50°  (2)
0°≦&thgr;
i
<5°  (3)
where,
&thgr;
oi
represents an angle formed between the primary image surface (I
1
) and the secondary image surface (I
2
),
&thgr;
o
represents an angle formed between a line normal to the secondary image surface (I
2
) and center screen ray, and
&thgr;
i
represents an angle formed between a line normal to the primary image surface (I
1
) and the center screen ray.


REFERENCES:
patent: 4455067 (1984-06-01), Hoppmann et al.
patent: 5032022 (1991-07-01), Sato et al.
patent: 5274406 (1993-12-01), Tejima et al.
patent: 5302983 (1994-04-01), Sato et al.
patent: 5475534 (1995-12-01), Okajima et al.
patent: 5703663 (1997-12-01), Fujioka et al.
patent: 5709445 (1998-01-01), Takamoto
patent: 5820240 (1998-10-01), Ohzawa
patent: 5947576 (1999-09-01), Sato et al.
patent: 5986806 (1999-11-01), Sugawara
patent: 5-119283 (1993-05-01), None
patent: 5-134213 (1993-05-01), None
patent: 6-186496 (1994-07-01), None
patent: 7-151994 (1995-06-01), None

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