Image-forming optical system

Details Image-forming optical system Image-forming optical system

2002-01-14

2004-08-03

Schwartz, Jordan M. (Department: 2873)

Optical: systems and elements

Lens

With field curvature shaping

C359S650000, C359S651000

Reexamination Certificate

active

06771427

ABSTRACT:

TECHNICAL FIELD
The present invention relates to an imaging optical system capable of reading an image from an oblique direction and of projecting an image.
BACKGROUND ART
Imaging optical systems relating to oblique image reading or image projection (hereinafter referred to simply as “oblique-incidence imaging optical systems”) are classified into oblique-incidence imaging optical systems of a decenter system and oblique-incidence image-forming optical systems of a tilt system.
FIG. 24
illustrates the basic principle of the oblique-incidence imaging optical system of the decenter system. In this oblique-incidence imaging optical system of the decenter system, an object plane
4
and image plane
2
, which are conjugate planes, are basically parallel to each other, and the optical axis
3
A of an image-forming optical system
30
is perpendicular to both the object plane
4
and the image plane
2
. To realize an oblique-incidence imaging optical system, for example, an image detecting region
201
included in the image plane
2
is shifted below the optical axis
3
A. Consequently, an image pick-up region
401
included in the object plane
4
is shifted upward as viewed in
FIG. 24 and a
oblique-incidence image-forming optical system can be realized without using any special optical system. The decenter system is advantageous in that any excessive distortion does not occur. However, the same system is disadvantageous in that the image circle of the image-forming optical system
30
must be large to displace the optical axis
3
A, the correction of aberration is difficult and the imaging optical system.
30
is large.
FIG. 25
illustrates the basic principle of the tilt system. The tilt system differs greatly from the decenter system in that the optical axis
3
A of an imaging optical system
30
is oblique to an object plane
4
, and an image plane
2
is oblique to the optical axis
3
A. Respective prolongations of the image plane
2
, the object plane
4
and the principal plane of the imaging optical system
30
intersect on a line A of intersection to meet Scheimpflug's principle, i.e., an imaging condition for the tilt system. The tilt system is advantageous in that the imaging optical system
30
is not excessively large and resolving power is comparatively high. The same system is disadvantageous in that a new distortion occurs.
FIG. 26
shows a typical example of such a distortion, which can be readily understood from the examination of imaging magnification illustrated in FIG.
25
.
Oblique-incidence imaging optical systems are classified into those of the decenter system, those of the tilt system and those of a composite system having the characteristics of both the decenter and the tilt system. The image-forming optical system must meet predetermined conditions about particulars including resolving power and distortion required of the optical system. Various devices have been proposed to solve problems in those systems and efforts have been made to provide optical systems answering purposes. Some examples of prior art optical system will be described.
FIGS.
27
(
a
) and
27
(
b
) show a projection lens for a projector disclosed in JP-A No. Hei 05-273460 in a sectional view. A projection lens
30
consisting of refracting optical elements, and an image-forming device
2
are moved perpendicularly to the optical axis
3
A of the projection lens
30
relative to each other to realize an oblique-incidence imaging optical system. To avoid moving a condenser lens
301
disposed near the image-forming device
2
, the optical axis of the projection lens
30
is tilted when moving the projection lens
30
. Therefore, it is considered that this oblique-incidence imaging optical system is basically of the decenter system and uses tilting for the degree of freedom of correction. This optical system achieves image projection in a maximum field angle 2&ohgr;of about 51°.
FIG. 28
shows a projector disclosed in U.S. Pat. No. 5,871,266 to the applicant of the present invention patent application in a sectional view. The projector includes, as essential components, an illuminating system
1
including a light source, an image-forming device
2
including a liquid-crystal display or the like, and an imaging system
3
. The illuminating system
1
and the imaging system
3
are optimized to realize an oblique-incidence imaging optical system. In a concrete example, the imaging system
3
comprises only a small number of reflecting mirrors. A light beam emitted by the illuminating unit
1
is decomposed into light beams of three primary colors by dichroic mirrors
2
a
and
2
b
to illuminate three reflecting image-forming devices
2
g
,
2
h
and
2
i
. Light beams reflected by the reflecting image-forming devices
2
g
,
2
h
and
2
i
are combined by the dichroic mirrors
2
a
and
2
b
, and the light beams travel toward the imaging system
3
. The imaging system
3
has three reflecting mirrors
3
a
,
3
b
and
3
d
. The light beams from the reflecting image-forming devices
2
g
,
2
h
and
2
i
are reflected by the reflecting mirrors
3
a
,
3
b
and
3
d
to form an image on a screen
4
, not shown. In this specification, the significance of the oblique-incidence imaging optical system included in the projector is discussed minutely. An example applied to a thin rear projection display capable of achieving image projection in a maximum field angle 2&ohgr; exceeding 100°. This rear projection display is, basically, of the decenter system.
Although such an epoch-making projector can be realized, the system disclosed in U.S. Pat. No. 5,871,266 has some disadvantages. The reflecting mirrors of the imaging system, as compared with refracting optical elements, must be formed in a high surface accuracy, which will be readily understood from the imagination of the state of reflection of imaging light by the reflecting mirrors. For example, suppose that a light beam emitted by the image-forming device to be focused on a point on a screen forms a spot in a region of a reflecting surface. If the region has a form error of &lgr;/4, where &lgr; is, for example, 0.55 &mgr;m, a wave aberration of about &lgr;/2 is produced. This wave aberration causes a non-negligible reduction in the resolving power of the imaging optical system. Thus, the accuracy of the catoptric system is affected significantly by waviness errors in the reflecting surface.
Another disadvantage of the system is the incidence angle of a light beam from the image-forming device. As stated in claims, a divergent light beam diverging at a divergence angle of 8° or below is used to realize a simple oblique-incidence imaging optical system. In this patented invention, all the systems including an illuminating system are optimized to enhance the efficiency of light. However, the system has only a narrow application field because of various restrictions on the size of an available light source, and the size and costs of the device.
An invention disclosed in JP-A No. Hei 10-206791 relates to a projector of the decenter system. As shown in
FIG. 29
, this invention includes an imaging system
30
employing decentered optical elements and free-form surfaces to increase the degree of freedom of design, and realizes a projection system having a maximum field angle 2 &ohgr; exceeding 68°. The imaging system
30
is used as an imaging system for oblique projection as shown in FIG.
30
. In
FIG. 30
, two conjugate planes
2
and
4
are substantially parallel. Although such decentered optical elements are employed, the field angle is not increased and, on the other hand, difficulty in fabricating and assembling parts is enhanced.
Some known optical systems of the decenter system have been described by way of example. Known optical systems of the tilt system will be described hereinafter.
FIG. 31
illustrates an invention disclosed in U.S. Pat. No. 5,274,406 relating to a projector particularly for a rear-projection display. This projector includes a symmetric projection lens
30
consisting of refracting optical elements shown

Affiliated with

Also associated with

Rating

Image-forming optical system does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Image-forming optical system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Image-forming optical system will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3301846