Optical: systems and elements – Single channel simultaneously to or from plural channels
Reexamination Certificate
1998-03-06
2003-04-08
Schwartz, Jordan M. (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
C359S627000, C359S620000
Reexamination Certificate
active
06545810
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an image pickup optical system and an image pickup apparatus using the same. More particularly, the present invention relates to an optical system which is most suitable for an image pickup apparatus designed to form an image relatively small in size and in which at least one reflecting surface having an image-forming power required for image formation is decentered. The present invention also relates to an image pickup apparatus using such an optical system.
There has heretofore been known a compact reflecting decentered optical system as disclosed in Japanese Patent Application Unexamined Publication Number [hereinafter referred to as “JP(A)”] 59-84201. This is an invention of a one-dimensional light-receiving lens comprising a cylindrical reflecting surface; therefore, two-dimensional imaging cannot be effected with this conventional optical system. JP(A) 62-144127 discloses an optical system wherein the identical cylindrical surface is used twice to effect reflection in order to reduce spherical aberration in the above-mentioned invention.
JP(A) 62-205547 discloses the use of an aspherical reflecting surface as a reflecting surface, but makes no mention of the configuration of the reflecting surface.
U.S. Pat. Nos. 3,810,221 and 3,836,931 both disclose an example in which a rotationally symmetric aspherical mirror and a lens system having a surface which has only one plane of symmetry are used to constitute a finder optical system of a reflex camera. In this example, however, the surface having only one plane of symmetry is utilized for the purpose of correcting the tilt of a virtual image for observation.
JP(A) 1-257834 (U.S. Pat. No. 5,274,406) discloses an example in which a surface having only one plane of symmetry is used for a reflecting mirror to correct image distortion in a rear projection type television. In this example, however, a projection lens system is used for projection onto a screen, and the surface having only one plane of symmetry is used for correction of image distortion. An example of a back-coated mirror type decentered optical system using an anamorphic surface and a toric surface as an observation optical system is also disclosed. However, the decentered optical system is not sufficiently corrected for aberrations, including image distortion.
None of the above-described prior arts use a surface having only one plane of symmetry as a back-coated mirror to form a folded optical path.
JP(A) 8-292368, 8-292371 and 8-292372 each disclose an image pickup optical system (i.e. a fixed focal length optical system or a zoom optical system) using a surface having only one plane of symmetry as a reflecting surface. However, the disclosed image pickup optical system has an unfavorably long optical path length from an entrance surface of an optical system constituent element including a rotationally asymmetric surface to an exit surface thereof or from a rotationally asymmetric surface of the optical system that is closest to the object to a rotationally asymmetric surface thereof that is closest to the image (in an example, image formation takes place once in the course of travel of light along the optical path). This causes the optical system to increase in size. Therefore, there is no merit in using rotationally asymmetric surfaces, which are difficult to produce.
In the conventional rotationally symmetric optical systems, a transmitting rotationally symmetric lens having refracting power is assigned to exert the required refracting power. Therefore, many constituent elements are needed for aberration correction. In the conventional decentered optical systems, however, an imaged figure or the like is undesirably distorted and the correct shape cannot be recorded unless the formed image is favorably corrected for aberrations, particularly rotationally asymmetric distortion.
In a rotationally symmetric optical system comprising a refracting lens which is formed from a surface rotationally symmetric about an optical axis, a straight-line optical path is formed. Therefore, the entire optical system undesirably lengthens in the direction of the optical axis, resulting in an unfavorably large-sized image pickup apparatus.
SUMMARY OF THE INVENTION
In view of the problems associated with the prior arts, an object of the present invention is to provide a compact image pickup optical system capable of providing a clear image of minimal distortion even at a wide field angle and also provide an image pickup apparatus using such an image pickup optical system.
To attain the above-described object, the present invention provides an image pickup optical system for forming an image of an object on a surface of an image pickup device. The image pickup optical system has at least a rear optical unit on the image side of a pupil plane. The rear optical unit has at least one reflecting surface decentered such that the whole surface is tilted with respect to an axial principal ray defined by a light ray emanating from the center of the object and passing through the center of the pupil to reach the center of the image. The reflecting surface has a rotationally asymmetric surface configuration that corrects rotationally asymmetric decentration aberrations caused by decentration, thereby reducing rotationally asymmetric aberrations of the object image.
In this case, the reflecting surface may be formed from a totally reflecting surface or a semitransparent reflecting surface so as to have both transmitting and reflecting actions. The reflecting surface may be formed from a coated mirror surface.
It is desirable for the rear optical unit to further have at least a second reflecting surface disposed to face the first reflecting surface.
Moreover, assuming that a direction in which the axial principal ray travels until it reaches a first surface of the optical system is defined as a Z-axis direction, and a Y-axis direction is taken in the plane of decentration of decentered surfaces, and further an axis constituting an orthogonal coordinate system in combination with the Y- and Z-axes is defined as an X-axis, and further that the axial principal ray and a light ray which is parallel to the axial principal ray at a slight distance d in the Y-axis direction are made to enter the optical system from the entrance surface side thereof, and the sine of an angle formed between the two rays in the YZ-plane at the exit side of the optical system is denoted by NA′yi, and further that a value obtained by dividing NA′yi by the distance d between the parallel rays, i.e. NA′yi/d, is defined as a power Py in the Y-axis direction of the optical system, and p is an optical path length from a point at which the axial principal ray enters a constituent element of the optical system disposed closest to the object and having a rotationally asymmetric surface to a point at which the axial principal ray exits from a constituent element of the optical system disposed closest to the image and having a rotationally asymmetric surface, it is desirable to satisfy the following condition:
0.1
<p×Py
<8 (1)
First of all, a coordinate system used in the following description will be explained.
As shown in
FIG. 12
, it is assumed that a light ray passing through the center of an object point and passing through the center of a stop
1
to reach the center of an image plane
8
is defined as an axial principal ray
2
. It is also assumed that an optical axis defined by a straight line along which the axial principal ray
2
travels until it intersects the first surface of the optical system is defined as a Z-axis, and that an axis perpendicularly intersecting the Z-axis in the decentration plane of decentered surfaces constituting the image pickup optical system is defined as a Y-axis, and further that an axis perpendicularly intersecting the Z-axis and also perpendicularly intersecting the Y-axis is defined as an X-axis.
In general, a spherical lens system comprising only a spherical lens is arranged su
Takada Katsuhiro
Togino Takayoshi
Olympus Optical Co,. Ltd.
Pillsbury & Winthrop LLP
Schwartz Jordan M.
Thompson Tim
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