Zoom lens

Details Zoom lens Zoom lens

1997-02-11

2003-02-18

Schwartz, Jordan M. (Department: 2873)

Optical: systems and elements

Lens

With variable magnification

C359S729000, C359S731000, C359S733000

Reexamination Certificate

active

06522475

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to zoom optical systems and an image pickup apparatus using the same and, more particularly, to an optical system which comprises a plurality of optical elements of two types, one of which has a plurality of reflecting surfaces and the other of which has refracting surfaces alone, wherein, of the plurality of optical elements, at least two optical elements move in differential relation to effect zooming (to vary magnification). Still more particularly, this invention relates to zoom optical systems suited to be used in video cameras, still video cameras or copying machines.
2. Description of Related Art
The zoom optical systems for the image pickup apparatus have been known as constructed with refracting elements or lenses alone. These lenses are of the spherical or aspheric form of revolution symmetry and arranged on a common optical axis so that their surfaces take revolution symmetry with respect to the optical axis.
In the field of art of photographic objectives, there have been many previous proposals for utilizing reflecting surfaces such as convex or concave mirrors. It has been also known to provide an optical system which makes use of a reflecting system and a refracting system in conjunction. This optical system is well known as the catadioptric system.
FIG. 23
is a schematic diagram of an optical system composed of one concave mirror and one convex mirror, or so-called mirror optical system.
In the mirror optical system shown in
FIG. 23
, an axial light beam
104
coming from an object is reflected by the concave mirror
101
. While being converged, the light beam
104
goes toward the object side. After having been reflected by the convex mirror
102
, the light beam
104
forms an image on an image plane
103
.
This mirror optical system is based on the configuration of the Cassegrain type of reflecting telescope. The aim of adopting it is to shorten the total length of the entire optical system compared with the long physical length of the refracting telescope, as the optical path is folded by using two reflecting mirrors as arranged in opposed relation.
Even for the objective lens system constituting part of the telescope, for the same reason, the Cassegrain type and many other types have come to be known which differ in the number and the construction and arrangement of reflecting mirrors in order to ever more shorten the total length of the entire system.
Up to now, effort has been made to shorten the total length of the photographic lens as it is usually unduly long. For this purpose, instead of some of its lens elements, mirrors are used to efficiently fold up the optical path. A compact optical system of mirror type is thus obtained.
In the Cassegrain type reflecting telescopes or like mirror optical systems, however, the use of the convex mirror
102
leads, in general case, to a problem that the object light beam
104
is shaded in part. This is attributable to the fact that the back of the convex mirror
102
lies within the domain of passage of the object light beam
104
.
To solve this problem, the mirror may be decentered, thus permitting the domain of passage of the object light beam
104
to be cleared of the obstruction of the other parts of the optical system. In other words, the principal ray
106
of the object light beam
104
is set off from an optical axis
105
. Such a mirror optical system, too, has previously been proposed.
FIG. 24
is a schematic diagram of a mirror optical system disclosed in U.S. Pat. No. 3,674,334, which has solved the above-described problem of shading in such a way that the mirrors of revolution symmetry with respect to the optical axis are cut off in part.
The mirror optical system shown in
FIG. 24
comprises, in the order in which the light beam encounters, a concave mirror
111
, a convex mirror
113
and a concave mirror
112
. In the prototype design, these are of the forms shown by the double-dots and single-dash lines, or of revolution symmetry with respect to the optical axis
114
. In actual practice, the concave mirror
111
is used in only the upper half on the paper of the optical axis
114
, the convex mirror
113
in only the lower half and the concave mirror
112
in only a lower marginal portion, thereby bringing a principal ray
116
of the object light beam
115
away from the optical axis
114
. The optical system is thus made free from the shading of the object light beam
115
.
FIG. 25
is a schematic diagram of another mirror optical system disclosed in U.S. Pat. No. 5,063,586. In this mirror optical system, the mirrors are so arranged that their central axes set themselves off the optical axis of the system. By this arrangement, a principal ray of the object light beam is dislocated from the optical axis, thus solving the above-described problem.
In
FIG. 25
, an object to be photographed lies in a plane
121
. Assuming that a line perpendicular to the plane
121
is an optical axis
127
, it is found that, as the light beam encounters a convex mirror
122
, a concave mirror
123
, a convex mirror
124
and a concave mirror
125
successively in this order, the centers of area of their reflecting surfaces and their central axes (the lines connecting those centers with the respective centers of curvature of these reflecting surfaces)
122
a
,
123
a
,
124
a
and
125
a
are decentered from the optical axis
127
. In
FIG. 25
, the amounts of decentering of such parameters and the radii of curvature of all the surfaces are appropriately determined to prevent the object light beam
128
from being shaded by the back of any one of the mirrors. An object image is thus formed on a focal plane
126
with high efficiency.
In addition, U.S. Pat. Nos. 4,737,021 and 4,265,510 even disclose similar systems freed from the shading effect either by using partial mirrors of revolution symmetry with respect to the optical axis or by arranging the central axes themselves of the mirrors in decentered relation from the optical axis.
Meanwhile, the catadioptric optical system using both of reflecting mirrors and refracting lenses can be made to have the function of varying the image magnification. As an example of this optical system, mention may be made of deep sky telescopes disclosed in, for example, U.S. Pat. Nos. 4,477,156 and 4,571,036, in which the image magnification is made variable by using a parabolic mirror in the main mirror in conjunction with the Erfle eye-piece.
It is also known to provide another zooming technique which moves two mirrors constituting part of the above-described mirror optical system in differential relation. By this technique, the image magnification (or focal length) of the optical system for photography is made variable.
For example, U.S. Pat. No. 4,812,030 discloses application of such a zooming technique to the Cassegrain type reflecting telescope shown in
FIG. 23
, wherein the separation from the concave mirror
101
to the convex mirror
102
and the separation from the convex mirror
102
to the image plane
103
are made variable relative to each other. Thus, a mirror optical system for photography capable of zooming is obtained.
FIG. 26
shows another example of an application disclosed in the above U.S. Pat. No. 4,812,030. Referring to
FIG. 26
, a light beam
138
from an object encounters a first concave mirror
131
and is reflected from its surface, becoming a converging light beam. The converging light beam goes toward the object side, and encounters a first convex mirror
132
. Here, the light beam is reflected toward the image side, becoming an almost parallel light beam. The almost parallel light beam goes to a second convex mirror
134
and is reflected therefrom, becoming a diverging light beam. The diverging light beam encounters a concave mirror
135
. Here, the light beam is reflected and becomes a converging light beam, focusing an image on an image plane
137
.
In this optical system, the separation between the first concave mirror
131
and the first convex mirror
132
is m

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