Optical: systems and elements – Lens – With reflecting element
Reexamination Certificate
1999-09-24
2001-03-13
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
With reflecting element
C359S837000
Reexamination Certificate
active
06201648
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical system and, more particularly, to a decentered optical system having power, which comprises a decentered reflecting surface.
There has heretofore been known a compact reflecting decentered optical system as disclosed in Japanese Pat. Appln. Laid-Open (KOKAI) No. 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 the conventional optical system. Japanese Pat. Appln. Laid-Open (KOKAI) No. 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. Japanese Pat. Appln. Laid-Open (KOKAI) No. 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.
Japanese Pat. Appln. Laid-Open (KORAI) No. 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 back 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.
Japanese Pat. Appln. Laid-Open (KOKAI) No. 7-333551 discloses an example of a back-coated mirror type decentered optical system using an anamorphic surface and a toric surface as an observation optical system. However, the decentered optical system is not sufficiently corrected for aberrations, including image distortion.
None of the above-described prior art use a surface having only one plane of symmetry as a back-coated mirror to form a turn-back optical path.
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 aberrations of the formed image are favorably corrected and, particularly, rotationally asymmetric distortion is favorably corrected.
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 whole optical system undesirably lengthens in the direction of the optical axis, resulting in an unfavorably large-sized apparatus.
In view of the problems associated with the prior art, an object of the present invention is to provide a compact optical system capable of providing a clear image of minimal distortion even at a wide field angle.
SUMMARY OF THE INVENTION
To attain the above-described object, the present invention provides a decentered optical system including at least one curved surface with a rotationally asymmetric surface configuration having no axis of rotational symmetry in nor out of the surface, wherein rotationally asymmetric aberrations due to decentration are corrected by the rotationally asymmetric surface.
According to a first aspect of the present invention, there is provided a decentered optical system including at least one rotationally asymmetric surface having no axis of rotational symmetry in nor out of the surface, wherein, assuming that a light ray emanating from the center of an object point and passing through the center of a pupil to reach the center of an image is defined as a principal ray, and that a Y-axis is taken in the decentration plane of the surface, and an X-axis is taken in a direction perpendicularly intersecting the Y-axis, and further an axis constituting an orthogonal coordinate system in combination with the X- and Y-axes is defined as a Z-axis, and further that the principal ray and a light ray which is parallel to the principal ray at a slight distance d in the X-axis direction are made to enter the optical system from the entrance side thereof, and the sine of an angle formed between the two rays as projected on the XZ-plane at the exit side of the optical system is denoted by NA′X, and further that a value obtained by dividing the distance d between the parallel rays by NA′X is denoted by FX, and the focal length in the X-axis direction of that portion of the rotationally asymmetric surface on which the axial principal ray strikes is denoted by FXn, the following condition is satisfied to correct rotationally asymmetric aberrations due to decentration by the rotationally asymmetric surface:
−1000
<FX/FXn<
1000 (1-1)
According to a second aspect of the present invention, there is provided a decentered optical system including at least one rotationally asymmetric surface having no axis of rotational symmetry in nor out of the surface, wherein, assuming that a light ray emanating from the center of an object point and passing through the center of a pupil to reach the center of an image is defined as a principal ray, and that a Y-axis is taken in the decentration plane of the surface, and an X-axis is taken in a direction perpendicularly intersecting the Y-axis, and further an axis constituting an orthogonal coordinate system in combination with the X- and Y-axes is defined as a Z-axis, and further that the principal ray and a light ray which is parallel to the principal ray at a slight distance d in the Y-axis direction are made to enter the optical system from the entrance 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′Y, and further that a value obtained by dividing the distance d between the parallel rays by NA′Y is denoted by FY, and the focal length in the Y-axis direction of that portion of the rotationally asymmetric surface on which the axial principal ray strikes is denoted by FYn, the following condition is satisfied to correct rotationally asymmetric aberrations due to decentration by the rotationally asymmetric surface:
1000
<FY/FYn<
1000 (2-1)
According to a third aspect of the present invention, there is provided a decentered optical system including at least one rotationally asymmetric surface having no axis of rotational symmetry in nor out of the surface, wherein, assuming that a light ray emanating from the center of an object point and passing through the center of a pupil to reach the center of an image is defined as a principal ray, and that a Y-axis is taken in the decentration plane of the surface, and an X-axis is taken in a direction perpendicularly intersecting the Y-axis, and further an axis constituting an orthogonal coordinate system in combination with the X- and Y-axes is defined as a Z-axis, and further that the principal ray and a light ray which is parallel to the principal ray at a slight distance d in the X-axis direction are made to enter the optical system from the entrance side thereof, and the sine of an angle formed between the two rays as projected on the XZ-plane at the exit side of the optical system is denoted by NA′X, and a value obtained by dividing the distance d between the parallel rays by NA′X is denoted by FX, and further that the principal ray and a light ray which is parallel to the principal ray at a slight distance d in the Y-axis direction are made to enter the optical system from the entrance side thereof, and the
Epps Georgia
Olympus Optical Co,. Ltd.
Pillsbury Madison & Sutro LLP
Schwartz Jordan M.
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