Optical: systems and elements – Lens – Single component with multiple elements
Reexamination Certificate
2000-07-26
2002-01-01
Schwartz, Jordan M. (Department: 2873)
Optical: systems and elements
Lens
Single component with multiple elements
C359S720000, C359S730000
Reexamination Certificate
active
06335837
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical element used in optical devices such as video cameras, digital cameras, still video cameras, copiers, and so on.
2. Related Background Art
Various proposals have been made heretofore about optical systems making use of reflecting surfaces such as concave mirrors, convex mirrors, and so on.
FIG. 7
is a schematic diagram of a so-called mirror optical system consisting of one concave mirror and one convex mirror.
In the mirror optical system in the same figure, object light
104
from an object is reflected by the concave mirror
101
toward the object while being coverged, then is reflected by the convex mirror
102
, and thereafter is focused on the image plane
103
. Numeral
105
designates the optical axis of this optical system.
This mirror optical system is based on the structure of the so-called Cassegrain reflecting telescope and is designed for the purpose of decreasing the entire length of the optical system by folding optical paths of a telescope lens system of long entire length composed of refracting lenses by use of two reflecting mirrors opposed to each other.
In the objective systems for telescopes, there are a lot of known types of optical systems for decreasing the entire length of the optical system by use of a plurality of reflecting mirrors, in addition to the Cassegrain type, for the same reason.
As described, the compact mirror optical systems have been constructed heretofore by efficiently folding the optical paths by use of the reflecting mirrors instead of lenses in the taking lenses of long entire length.
In these reflective optical systems, optical components need to be assembled with accuracy in order to achieve desired optical performance. Particularly, since errors in relative position accuracy of the reflecting mirrors strongly affect the optical performance, it is important to accurately adjust the position and angle of each reflecting mirror.
A solution to this issue is a proposal of a method of avoiding assembly errors of the optical components during assembly by constructing the mirror system with reflectors of one block.
For example, in the case of non-coaxial optical systems, the optical systems in a well-corrected state of aberration can be constructed by introducing the concept of the reference axis and making constituent surfaces of rotationally asymmetric, aspherical surfaces; Japanese Patent Application Laid-Open No. 9-5650 describes the design method thereof and Japanese Patent Applications Laid-Open No. 8-292371 and Laid-Open No. 8-292372 describe design examples thereof.
Such non-coaxial optical systems are called offaxial optical systems (which are optical systems defined as optical systems including curved surfaces (offaxial surfaces) the normal to which at an intersection with the reference axis is off the reference axis, where the reference axis is taken along a ray passing the center of the image and the center of the pupil, and in which the reference axis is in the folded state).
In the offaxial optical systems, the constituent surfaces are normally not coaxial and no eclipse occurs even at the reflecting surfaces, which facilitates construction of the optical systems using the reflecting surfaces. These optical systems also have such features that routing of optical paths is relatively free, an integral optical system can be formed readily by a method of integral molding of the constituent surfaces, and so on.
FIG. 8
is a schematic diagram to show an embodiment of the reflecting optical system disclosed in Japanese Patent Application Laid-Open No. 8-292371.
In
FIG. 8
, numeral
10
designates an optical element having a plurality of curved, reflecting surfaces, which is constructed of a transparent body of glass or the like. The optical element
10
has a concave refracting surface (entrance surface)
11
of negative refractive power, four reflecting surfaces comprising a concave mirror
12
, a reflecting surface
13
, a reflecting surface
14
, and a concave mirror
15
, and a convex refracting surface (exit surface)
16
of positive refractive power, which are formed in surfaces of the optical element
10
and in order named according to passage of rays from the object.
Numeral
2
denotes a stop (entrance pupil) placed on the object side of the optical element
10
,
3
an optical corrector such as a quartz low-pass filter, an infrared cut filter, or the like, and
4
a final image plane, in which an image pickup surface of an image pickup device (imaging medium) such as CCD or the like is located. Numeral
5
indicates the reference axis of the photographing optical system (which is an axis passing the center
6
of the stop
2
and normally entering the center of the image plane
4
). Numeral
6
represents the center of the stop
2
.
The two refracting surfaces both are rotationally symmetric, spherical surfaces and all the reflecting surfaces are surfaces symmetric with respect to only the YZ plane.
The imaging action will be described next. The light
1
from the object is regulated in the amount of incident light by the stop
2
and thereafter is incident to the entrance surface
11
of the optical element
10
. The light is reflected by the surfaces
12
,
13
and thereafter once forms an image near the surface
13
. Then the light is reflected successively by the surfaces
14
,
15
and emerges from the exit surface
16
. The light again forms an image on the final image plane
4
through the optical corrector
3
. The object rays form the intermediate image near the surface
7
and pupil rays form an intermediate image between the surface
14
and the surface
15
.
In this embodiment the direction of the reference axis of incidence to the optical element
10
is parallel and identical to the direction of the reference axis of emergence therefrom. The reference axis including incidence and emergence all lies on the plane of the drawing (the YZ plane).
As described, the optical element
10
functions as a lens unit having desired optical performance and positive refractive power as a whole, based on the refractive powers of the entrance and exit surfaces and the refractive powers of the curved reflectors therein.
The invention disclosed in Japanese Patent Application Laid-Open No. 8-292371 decreased the effective diameter of the optical system even in the reflecting optical system of wide angle of view by the structure in which the stop was placed closest to the object in the optical system and in which the object image was formed at least once in the optical system, and also decreased the entire length of the optical system in the predetermined direction by bending the optical paths in the optical system into the desired shape by the structure in which the reflecting surfaces forming the optical element were provided with their respective, appropriate, refractive powers and in which the reflecting surfaces forming the optical element were placed in the non-coaxial relation.
Japanese Patent Application Laid-Open No. 8-292371 also discloses an example of the reflecting optical system wherein the entrance reference axis and the exit reference axis are not within a common plane, through free routing of optical paths.
FIG. 9
is a schematic diagram of the main part of such a reflecting optical system as disclosed in Japanese Patent Application Ladi-Open No. 8-292371. In
FIG. 9
, numeral
10
designates an optical element having one reflecting plane and a plurality of curved, reflecting surfaces, which is constructed of a transparent body of glass or the like. The optical element
10
has a convex refracting surface (entrance surface) R
2
of positive refractive power, six reflecting surfaces of a reflecting plane R
3
, a concave mirror R
4
, a convex mirror R
5
, a concave mirror R
6
, a reflecting surface R
7
, and a concave mirror R
8
, and a convex refracting surface (exit surface) R
9
of positive refractive power, which are arranged in the order named according to passage of rays from the object and in surfaces of
Akiyama Takeshi
Aratani Michiharu
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Schwartz Jordan M.
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