Optical system

Details Optical system Optical system

2002-02-27

2004-07-06

Spector, David N. (Department: 2873)

Optical: systems and elements

Lens

Asymmetric

C359S678000

Reexamination Certificate

active

06760164

ABSTRACT:

This application claims benefit of Japanese Application Nos. 2001-56473 and 2001-332290 filed in Japan on 3.1.2001 and 10.30,2001, the contents of which are herein incorporated by this reference.
BACKGROUND OF THE INVENTION
The present invention relates generally to an optical system, and more particularly to an optical system used with an image pickup optical system having zooming (scaling) and focusing functions, etc.
Zoom image pickup optical systems constructed of free-form surface prisms, for instance, are disclosed in JP-A's 08-292372, 11-317894 and 11-317895.
However, the optical system of JP-A 08-292372 is designed for zooming or scaling by movement of a plurality of prisms. This requires an increase in size to provide sufficient space for the movement of the prisms in the system. Moreover, high accuracy needed for a mechanism for precise linear movement of the prisms makes the system structurally complicated providing obstacles to assembling the system and increased cost.
Similarly, the zooming or scaling mechanism of JP-A 11-317894, and JP-A 11-317895 has the same structural problem because of the movement of transmitting lens optical element.
With the prior art, it is thus impossible to achieve any zoom (scaling) optical system of smaller size because of the required space for movement of the optical element. This optical element itself has aberration problems, and renders optical parameters so likely to vary by large amounts that it may not be used.
Ordinary control of zooming (scaling) or focusing is generally carried out by moving several optical elements in an optical system along the optical axis. However, problems with this control mode are that it is difficult to move the optical elements completely parallel to the optical axis, causing tilting and decentration of the optical elements and, hence, degradation of images. Especially when a zooming (scaling) optical system is designed for an image pickup system of smaller size, very stringent, if not impossible, accuracy is imposed on the movement.
SUMMARY OF THE INVENTION
In view of such problems of the prior art, one object of the present invention is to provide an optical system of so simplified construction that its focal length, image-formation position, etc. can be controlled by bending the optical system to shift a light beam passing through the optical system and thereby making selective use of an arbitrary portion of the optical system.
According to one aspect of the invention, this object is achieved by the provision of an optical system, characterized in that said optical system is transformed to bend an optical axis thereof, so that paraxial amounts thereof can be varied.
According to another aspect of the invention, there is provided an image-formation optical system comprising at least two optical elements, characterized in that said at least two optical elements are mutually decentered, thereby varying the properties of said optical system.
Preferably in this embodiment, the optical system should be constructed of a first optical element located on the object side thereof for forming a primary image and a second optical element for projecting the primary image onto an image plane of the optical system. This second optical element is decentered by rotation with the center of rotation defined by the vicinity of the primary image.
Preferably in this embodiment, at least one of the first and second optical elements should be formed of an optical element having at least one rotationally asymmetric surface.
In this case, said at least one rotationally asymmetric surface may be defined by a continuous surface.
If the second optical element is decentered by rotation with respect to the first optical element, it is then possible to vary at least one of the focal length, image-formation position (focus), image-formation magnification and principal point of the optical system.
According to a specific preferred embodiment of the invention, there is provided an optical system comprising at least two optical elements, each having a rotationally asymmetric free-form surface, or a first optical element located on the object side of the optical system for forming a primary image and a second element for projecting the primary image, wherein the second optical element is decentered with the center of rotation defined by the vicinity of the primary image so that a light beam incident on the second optical element is reflected and bent at an arbitrarily selected central portion of the second optical element for zooming (scaling) at the second optical element, and the second optical element has an angle &thgr; of rotation run-out that satisfies the following condition:
0°<&thgr;<90°  (1)
Preferably in this embodiment, the optical system should satisfy the following condition:
0.5<|
Fy/Fx|<
2  (2)
Here Fx is the focal length of the optical system in an X direction and Fy is the focal length of the optical system in a Y direction provided that the direction of decentration of the optical system defines a Y-axis direction, a plane parallel with an axial chief ray defines a Y-Z plane and a direction perpendicular to the Y-Z plane defines the X-direction.
Why the aforesaid arrangements are used in the invention, and what is achieved thereby is now explained.
FIG. 1
is a schematic view illustrative of how light rays behave in a meridional section of an optical element S at which some large coma occurs with substantially well corrected spherical aberration, curvature of field, astigmatism, longitudinal chromatic aberration and chromatic aberration of magnification. With some considerable coma occurring, rays {circle around (
1
)}, {circle around (
2
)} and {circle around (
3
)} emanating at different angles of view from an object O are incident on an image plane I at different positions. Accordingly, as aperture positions P
1
, P
2
and P
3
of this optical element S displace substantially vertically with respect to an optical axis (note that an optical axis is defined by an axial principal ray passing through the center of an entrance pupil and arriving at the center of the image plane; however, the optical axis used herein is defined by an axial principal ray passing through the center of each aperture P
1
, P
2
, P
3
and arriving at the center of the image plane), the rays {circle around (
1
)}, {circle around (
2
)} and {circle around (
3
)} passing through the optical element S vary in position and angle, so that they are incident on the image plane I at different heights H
1
, H
2
and H
3
. Consequently, the image-formation magnification of the object O on the image plane I varies. In other words, zooming (scaling) can be effected by shifting each aperture substantially vertically to the optical axis. On the same principles, the image-formation position and principal point, too, can be controlled by shifting the pupil position substantially vertically to the optical axis. It is here noted that since the aperture positions are displaceable vertically to the direction coming out of the paper, for instance, zooming (scaling) may be carried out by displacement within the plane of the paper and focusing may be effected by displacement in the direction coming out of the paper.
As an optical system having at least two optical elements S
1
and S
2
as typically shown in FIG.
2
(
a
) is decentered as shown in FIG.
2
(
b
), an aperture A located on the object side of the first optical element S
1
is projected by the first optical element S
1
as an aperture image A′ in the vicinity of the second optical element. Then, as the first and second optical elements S
1
and S
2
are relatively transformed (decentered), the projected image A′ for the aperture A projected by the first optical element S
1
is shifted with respect to the second optical element S
2
. On the other hand, it is possible to construct the second optical element S
2
with at least one rotationally asymmetric optical surface; it is possible to construct an optical element whose power varies on a

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