Optical: systems and elements – Compound lens system – With curved reflective imaging element
Reexamination Certificate
2001-08-16
2002-10-01
Henry, Jon (Department: 2872)
Optical: systems and elements
Compound lens system
With curved reflective imaging element
C359S431000, C359S432000, C359S433000, C359S435000, C359S731000, C359S396000, C359S016000
Reexamination Certificate
active
06459530
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a variable magnification optical system and an image pickup apparatus using the same and, more specifically, to an optical arrangement suitable for use in a video camera, a still video camera, a copying machine and the like which are arranged to realize variation of magnification by using an optical unit having decentered reflecting surfaces, as a magnification varying optical unit.
2. Description of Related Art
It is known that an optical system of the type which is composed of only refracting lenses has been provided as a variable magnification optical system. In such a conventional optical system, refracting lenses each having a spheric surface or aspheric surface of rotational symmetry are rotationally symmetrically arranged with respect to the optical axis.
In addition, various photographing optical systems using reflecting surfaces such as concave mirrors or convex mirrors have heretofore been proposed, and an optical system using both a reflecting system and a refracting system is also well known as a catadioptric system.
FIG. 37
is a schematic view of a so-called mirror optical system which is composed of one concave mirror and one convex mirror. In the mirror optical system shown in
FIG. 37
, an object light beam
104
from an object is reflected by a concave mirror
101
and travels toward an object side while being converged, and after having been reflected by a convex mirror
102
and having been refracted by a lens
110
, the object light beam
104
forms an image of the object on an image plane
103
.
This mirror optical system is based on the construction of a so-called Cassegrainian reflecting telescope, and is intended to reduce the entire length of the optical system by bending, by using the two opposed reflecting mirrors, the optical path of a telephoto lens system which is composed of refracting lenses and has an entire large length.
For similar reasons, in the field of an objective lens system which constitutes part of a telescope as well, in addition to the Cassegrainian type, various other types which are arranged to reduce the entire length of an optical system by using a plurality of reflecting mirrors have been known.
As is apparent from the above description, it has heretofore been proposed to provide a compact mirror optical system by efficiently bending an optical path by using reflecting mirrors in place of lenses which are commonly used in a photographing lens whose entire length is large.
However, in general, the mirror optical system, such as the Cassegrainian reflecting telescope, has the problem that part of an object ray is blocked by the convex mirror
102
. This problem is due to the fact that the convex mirror
102
is placed in the area through which the object light beam
104
passes.
To solve the problem, it has been proposed to provide a mirror optical system which employs decentered reflecting mirrors to prevent a portion of the optical system from blocking the area through which the object light beam
104
passes, i.e., to separate a principal ray of the object light beam
104
from an optical axis
105
.
FIG. 38
is a schematic view of the mirror optical system disclosed in U.S. Pat. No. 3,674,334. This mirror optical system solves the above-described blocking problem by using part of reflecting mirrors which are rotationally symmetrical about the optical axis.
In the mirror optical system shown in
FIG. 38
, a concave mirror
111
, a convex mirror
113
and a concave mirror
112
are arranged in the order of passage of the light beam, and these mirrors
111
,
113
and
112
are reflecting mirrors which are rotationally symmetrical about an optical axis
114
, as shown by two-dot chain lines in FIG.
38
. In the shown mirror optical system, a principal ray
116
of an object light beam
115
is separated from the optical axis
114
to prevent shading of the object light beam
115
, by using only the upper portion of the concave mirror
111
which is above the optical axis
114
as viewed in
FIG. 38
, only the lower portion of the convex mirror
113
which is below the optical axis
114
as viewed in
FIG. 38
, and only the lower portion of the concave mirror
112
which is below the optical axis
114
as viewed in FIG.
38
.
FIG. 39
is a schematic view of the mirror optical system disclosed in U.S. Pat. No. 5,063,586. The shown mirror optical system solves the above-described problem by decentering the central axis of each reflecting mirror from an optical axis and separating the principal ray of an object light beam from the optical axis. As shown in
FIG. 39
in which an axis perpendicular to an object plane
121
is defined as an optical axis
127
, a convex mirror
122
, a concave mirror
123
, a convex mirror
124
and a concave mirror
125
are arranged in the order of passage of the light beam, and the central coordinates and central axes
122
a
,
123
a
,
124
a
and
125
a
(axes which respectively connect the centers of reflecting surfaces and the centers of curvature thereof) of the reflecting surfaces of the respective mirrors
122
to
125
are decentered from the optical axis
127
. In the shown mirror optical system, by appropriately setting the amount of decentering and the radius of curvature of each of the surfaces, each of the reflecting mirrors is prevented from shading an object light beam
128
, so that an object image is efficiently formed on an image plane
126
.
In addition, U.S. Pat. Nos. 4,737,021 and 4,265,510 also disclose an arrangement for preventing the shading problem by using part of a reflecting mirror which is rotationally symmetrical about an optical axis, or an arrangement for preventing the shading problem by decentering the central axis of the reflecting mirror from the optical axis.
One example of a catadioptric optical system which uses both a reflecting mirror and a refracting lens and has a magnification varying function is a deep-sky telescope such as that disclosed in each of U.S. Pat. Nos. 4,477,156 and 4,571,036. The deep-sky telescope uses a parabolic reflecting mirror as a primary mirror and has a magnification varying function using an Erfle eyepiece.
Another variable magnification optical system is known which varies the image forming magnification (focal length) of a photographing optical system by relatively moving a plurality of reflecting mirrors which constitute part of the aforesaid type of mirror optical system.
For example, U.S. Pat. No. 4,812,030 discloses an art for performing variation of the magnification of the photographing optical system by relatively varying the distance between the concave mirror
101
and the convex mirror
102
and the distance between the convex mirror
102
and the image plane
103
in the construction of the Cassegrainian reflecting telescope shown in FIG.
37
.
FIG. 40
is a schematic view of another embodiment disclosed in U.S. Pat. No. 4,812,030. In the shown embodiment, an object light beam
138
from an object is made incident on and reflected by a first concave mirror
131
, and travels toward an object side as a converging light beam and is made incident on a first convex mirror
132
. The light beam is reflected toward an image forming plane by the first convex mirror
132
and is made incident on a second convex mirror
134
as an approximately parallel light beam. The light beam is reflected by the second convex mirror
134
and is made incident on a second concave mirror
135
as a diverging light beam. The light beam is reflected by the second concave mirror
135
as a converging light beam and forms an image of the object on an image plane
137
. In this arrangement, by varying the distance between the first concave mirror
131
and the first convex mirror
132
and the distance between the second convex mirror
134
and the second concave mirror
135
, zooming is performed and the focal length of the entire mirror optical system is varied.
In the arrangement disclosed in U.S. Pat. No. 4,993,818, an image formed by the Cassegrainian refle
Araki Keisuke
Nanba Norihiro
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