Optical: systems and elements – Compound lens system – With curved reflective imaging element
Reexamination Certificate
2000-12-13
2003-10-14
Lester, Evelyn (Department: 2873)
Optical: systems and elements
Compound lens system
With curved reflective imaging element
C359S365000, C359S431000, C359S432000, C359S433000, C359S678000, C359S716000, C359S720000, C359S726000, C359S737000, C359S739000, C359S834000, C359S837000
Reexamination Certificate
active
06633431
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an optical system, and particularly to an optical system having a reflecting optical element for forming the image of an object on the surface of a predetermined plane in a video camera, a still video camera, a copier or the like.
2. Related Background Art
Heretofore, optical systems comprised of refracting lenses alone are known as zoom optical systems, and these are generally such that refracting lenses provided with rotation-symmetrical spherical surfaces or rotation-symmetrical aspherical surfaces with respect to an optical axis are successively disposed in the direction of the optical axis and magnification change is effected by changing the spacing therebetween.
On the other hand, there is also known the zooming technique of moving a plurality of reflecting surfaces relative to one another to thereby vary the imaging magnification or focal length of a photo-taking optical system.
As shown in
FIG. 6
of the accompanying drawings, in a cassegrainian reflector disclosed, for example, in U.S. Pat. No. 4,812,030, the spacing from a concave mirror
101
to a convex mirror
102
and the spacing from the convex mirror
102
to an imaging plane
103
are changed relative to each other to thereby effect magnification change.
FIG. 7
of the accompanying drawings shows another example disclosed in U.S. Pat. No. 4,812,030. An object beam
138
from an object impinges on a first concave mirror
131
and is reflected by the surface thereof and becomes a convergent beam and travels toward the object side and impinges on a first convex mirror
132
, and is reflected toward the imaging plane side thereby and becomes a substantially parallel beam and impinges on a second convex mirror
134
, and is reflected by the surface thereof and becomes a divergent beam and impinges on a second concave mirror
135
, and is reflected thereby and becomes a convergent beam and is imaged on an imaging plane
137
. The spacing between the first concave mirror
131
and the first convex mirror
132
is changed and also the spacing between the second convex mirror
134
and the second concave mirror
135
is changed to thereby change the focal length of an entire mirror optical system.
Also, in U.S. Pat. No. 4,993,818, the image formed by the Cassegrainian reflector shown in
FIG. 6
is secondary-imaged by another mirror optical system provided at a rear stage, and the imaging magnification of this mirror optical system for secondary imaging is changed to thereby effect the magnification change of the entire optical system.
These optical system of the reflection type have required a great number of constituent parts, and to obtain necessary optical performance, it has been necessary to accurately assemble the respective optical parts. Particularly, the accuracy of the relative positions of the reflecting mirrors is severe and therefore, the adjustment of the position and angle of each reflecting mirror has been necessary.
As a method of solving this problem, there has been proposed, for example, a method of making mirror systems into a block to thereby avoid the incorporation errors of the optical parts occurring during the assembly thereof.
FIG. 8
of the accompanying drawings shows an embodiment of the reflecting optical system disclosed in Japanese Patent Application Laid-Open No. 09-258106 (corresponding to U.S. Pat. No. 5,999,311). A beam from an object passes through lenses (R
1
-R
2
) which are a first optical element B
1
and a stop R
3
, and thereafter enters a second optical element B
2
. In the second optical element B
2
, the beam is refracted by a fourth surface R
4
, is reflected by a fifth surface R
5
, a sixth surface R
6
, a seventh surface R
7
and an eighth surface R
8
, is refracted by a ninth surface R
9
, and emerges from the second optical element B
2
. At this time, the beam is primary-imaged on an intermediate imaging plane near the sixth surface.
Next, the beam enters a third optical element B
3
. In the third optical element B
3
, the beam is refracted by a tenth surface R
10
, is reflected by an eleventh surface R
11
, a twelfth surface R
12
, a thirteenth surface R
13
and a fourteenth surface R
14
, is refracted by a fifteenth surface R
15
, and emerges from the third optical element B
3
.
Next, the beam enters a fourth optical element B
4
. In the fourth optical element B
4
, the beam is refracted by a sixteenth surface R
16
, is reflected by a seventeenth surface R
17
, an eighteenth surface R
18
, a nineteenth surface R
19
, a twentieth surface R
20
and a twenty-first surface R
21
, is refracted by a twenty-second surface R
22
, and emerges from the fourth optical element B
4
. The beam having emerged from the fourth optical element B
4
is finally imaged on an imaging plane R
28
, i.e., the photographing surface of an image pickup medium such as a CCD.
The movement of each optical element resulting from the magnification changing operation will now be described. In case of magnification change, the first optical element B
1
which is a first optical unit, the stop R
3
, the third optical element B
3
which is a third optical unit and a block B
5
are fixed and are not moved. The second optical element B
2
which is a second optical unit is moved in Z plus direction from the wide angle end toward the telephoto end in parallelism to the incidence reference axis of this optical element. Also, the fourth optical element B
4
which is a fourth optical unit is moved in Z plus direction from the wide angle end toward the telephoto end in parallelism to the incidence reference axis of this optical element. A filter, cover glass and the twenty-eighth surface R
28
which is the final imaging plane are not moved in case of focal length change.
The spacing between the second optical element B
2
and the third optical element B
3
is narrowed by the magnification change from the wide angle end toward the telephoto end, the spacing between the third optical element B
3
and the fourth optical element B
4
is widened, and the spacing between the fourth optical element B
4
and the twenty-third surface R
23
is widened.
That is, use is made of a plurality of optical elements comprising reflecting surfaces which are a plurality of curved surfaces and flat surfaces formed integrally with one another, and the relative position of at least two of the plurality of optical elements is appropriately changed to effect zooming, whereby the downsizing of the entire mirror optical system is achieved and yet the disposition accuracy (assembly accuracy) of the reflecting mirrors incidental to the mirror optical system is loosened.
Also, by adopting a construction in which the stop is disposed most adjacent to the object side of the optical system and the object image is formed at least once in the optical system, a reduction in the effective diameter of the optical system is achieved in spite of being a reflection type zoom optical system of a wide angle of view, and appropriate refractive power is given to a plurality of reflecting surfaces constituting the optical elements and the reflecting surfaces constituting each optical element are eccentrically disposed, whereby the optical path in the optical system is bent into a desired shape to thereby achieve the shortening of the full length of the optical system in a predetermined direction.
However, in the prior-art optical system comprising refracting optical elements alone, it is often the case that the entrance pupil is deep at the back of the optical system, and this leads to the problem that the greater is the spacing to the incidence surface located most adjacent to the object side as viewed from the stop, the larger becomes the effective diameter of the beam on the incidence surface with the enlargement of the angle of view.
Also, in both of the optical systems having the magnification changing function disclosed in the above mentioned U.S. Pat. No. 4,812,030 and the above-mentioned U.S. Pat. No. 4,993,818, the number of constituent parts such as reflecting mirror
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