Optical: systems and elements – Prism – With reflecting surface
Reexamination Certificate
1999-02-23
2002-02-26
Nguyen, Thong (Department: 2872)
Optical: systems and elements
Prism
With reflecting surface
C359S365000, C359S431000, C359S630000
Reexamination Certificate
active
06351338
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an optical unit and an optical system using the same, and particularly is suitable for a video camera or a still video camera and a copying apparatus or the like utilizing an optical unit comprising a plurality of reflecting surfaces each having a curvature constructed integrally with one another.
2. Related Background Art
There have heretofore been proposed various photographing optical systems utilizing the reflecting surface of a concave mirror, a convex mirror or the like.
FIG. 6
of the accompanying drawings is a schematic view of the essential portions of a so-called mirror optical system (reflecting optical system) comprising a concave mirror and a convex mirror.
In the mirror optical system of
FIG. 6
, an object light beam
124
from an object is reflected by a concave mirror
121
and travels toward the object side while being converged, and is reflected by a convex mirror
122
, whereafter it is imaged on an image plane
123
.
This mirror optical system is based on the construction of a so-called Cassegrainian reflector, and is directed to shorten the full length of the optical system by bending the optical path of a telephoto lens system of a great full lens length comprised of a refracting lens by the use of two reflecting mirrors opposed to each other.
Also in an objective lens system constituting a telescope, for a similar reason, there are known a number of systems for shortening the full length of the optical system by the use of a plurality of reflecting mirrors, besides the Cassegrainian type.
As described above, by using a reflecting mirror instead of the lens of a photo-taking lens of a great full lens length, the optical path is efficiently bent to thereby provide a compact mirror optical system.
Generally, however, in a mirror optical system such as a Cassegrainian reflector, there is the problem that a part of the object ray of light is eclipsed by the convex mirror
122
. This problem is attributable to the fact that the convex mirror
122
is present in the passage area of the object light beam
124
.
In order to solve this problem, there has also been proposed a mirror optical system in which a reflecting mirror is made eccentric and used to avoid the other portion of the optical system shielding the passage area of the object light beam
124
, i.e., separate the principal ray
126
of the light beam from an optical axis
125
.
FIG. 7
of the accompanying drawings is a schematic view of the essential portions of a mirror optical system disclosed in U.S. Pat. No. 3,674,334, and this mirror optical system separates the principal ray of an object light beam from an optical axis to thereby solve the above-noted problem of eclipse. The mirror optical system of
FIG. 7
has, in the order of passage of the light beam, a concave mirror
131
, a concave mirror
133
, and they are originally reflecting mirrors rotation-symmetrical with respect to an optical axis
134
, as indicated by dot-and-dash lines in FIG.
7
. Of these mirrors, use is made of only the upper side of the concave mirror
131
relative to the optical axis
134
as viewed in the plane of the drawing sheet, only the lower side of the convex mirror
132
relative to the optical axis
134
as viewed in the plane of the drawing sheet, and only the lower side of the convex mirror
133
relative to the optical axis
134
as viewed in the plane of the drawing sheet to thereby construct an optical system in which the principal ray
136
of the object light beam
135
is separated from the optical axis
134
. This eliminates the eclipse of the object light beam
135
.
FIG. 8
of the accompanying drawings is a schematic view of the essential portions of a mirror optical system disclosed in U.S. Pat. No. 5,063,586. The mirror optical system of
FIG. 8
solves the above-noted problem by making the central axis itself of a reflecting mirror eccentric relative to an optical axis and separating the principal ray of an object light beam from the optical axis.
When in
FIG. 8
, the vertical axis of an object surface
141
is defined as an optical axis
147
, the central coordinates of the respective reflecting surfaces of a convex mirror
142
, a concave mirror
143
, a convex mirror
144
and a concave mirror
145
in the order of passage of the light beam and the central axes (axes passing through the centers of the reflecting surfaces and the centers of curvature of those surfaces)
142
A,
143
A,
144
A and
145
A are decentering or eccentric relative to the optical axis
147
. In
FIG. 8
, the amount of eccentricity at this time and the radius of curvature of each surface are appropriately set to thereby prevent the eclipse of the object light beam
148
by each reflecting mirror, and efficiently form an object image on an imaging plane
146
.
Besides the aforementioned patents, U.S. Pat. No. 4,737,021 and U.S. Pat. No. 4,265,510 disclose a construction in which use is made of a part of a reflecting mirror rotation-symmetrical with respect to an optical axis to avoid eclipse, or a construction in which the central axis itself of a reflecting mirror is made eccentric relative to an optical axis to thereby avoid eclipse.
Now, as a catadioptric optical system using both of a reflecting mirror and a refracting lens and having a focal length changing function, there are, for example, the deep sky telescopes of U.S. Pat. No. 4,477,456 and U.S. Pat. No. 4,571,036. These use a parabolic reflecting mirror as a main mirror and use an Elfre eyepiece mirror to make the magnification variable.
Also, there is known the zooming technique of moving the plurality of reflecting surfaces constituting the above-described mirror optical system relative to one another to thereby vary the imaging magnification (focal length) of the photo-taking optical system. For example, in U.S. Pat. No. 4,812,030, in the construction of the Cassegrainian reflector shown in
FIG. 6
, there is disclosed the technique of varying the spacing from the concave mirror
121
to the convex mirror
122
and the spacing from the convex mirror
122
to the image plane
123
relative to each other to thereby effect the focal length change of the photo-taking optical system.
FIG. 9
of the accompanying drawings shows another embodiment disclosed in the same publication. In
FIG. 9
, an object light beam
158
from an object impinges on a first concave mirror
151
and is reflected by the surface thereof and becomes a convergent light beam and travels toward the object side. The convergent light beam impinges on a first convex mirror
152
, by which it is reflected toward the imaging plane side and becomes a substantially parallel light beam (and parallel to the optical axis
159
) and impinges on a second convex mirror
154
, and is reflected by the surface thereof and becomes a divergent light beam impinges on a second concave mirror
155
, by which it is reflected and becomes a convergent light beam and is imaged on an image plane
157
. In this construction, the spacing
153
between the first concave mirror
151
and the first convex mirror
152
is varied and also the spacing
156
between the second convex mirror
154
and the second concave mirror
155
is varied to thereby effect zooming and vary the focal length of the 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 secondarily formed by another mirror optical system provided at the subsequent stage, and the imaging magnification of this mirror optical system for secondary imaging is varied to thereby effect the focal length change of the entire photo-taking system.
These photo-taking optical systems of the reflection type have many required constituents, and to obtain the necessary optical performance, it has been necessary to assemble respective optical parts with good accuracy. Particularly, the accuracy of the quickly retracted positions of the reflecting mirrors is severe and therefore, the adjustment of the position and angle
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Nguyen Thong
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