Optical: systems and elements – Single channel simultaneously to or from plural channels – By surface composed of lenticular elements
Reexamination Certificate
1999-09-27
2001-11-27
Ben, Loha (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By surface composed of lenticular elements
C359S629000, C359S631000, C359S633000, C359S637000, C359S720000, C359S729000
Reexamination Certificate
active
06324012
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical system and an image pickup apparatus incorporating it and, more particularly, to those suitably applicable to image pickup apparatus of cameras, video cameras, still video cameras, etc. adapted to form an object image on a surface of an image pickup element by use of an optical system having off-axial reflecting surfaces a normal to which does not coincide with a reference axis.
2. Related Background Art
Viewing optical systems and optical systems for distance measurement and photometry used in the cameras, video cameras, etc. are often constructed so as to make use of rays passing through an image pickup optical system in order to avoid the influence of parallax. This method is generally called the TTL method.
On the other hand, there are conventionally known optical systems making use of an optical element of one block including many reflecting surfaces. Examples of such optical elements are a pentagonal roof prism, a Porro prism, etc., used in the finder system of a camera, and optical prisms, such as color separation prisms or the like, for separating light from a taking lens, for example, into three-color beams of red, green, and blue and forming an object image based on each color beam on a corresponding image pickup element surface.
An optical system of a single-lens reflex camera using the pentagonal roof prism will be described as a typical example of the optical system of the TTL method using an optical prism, referring to the sectional view illustrated in FIG.
1
.
In
FIG. 1
, rays passing through the image pickup optical system
101
are reflected by a reflecting mirror
102
to form a primary image of an object on matt
103
. After that, the light is guided via a viewing optical system composed of a condenser lens
104
, an erecting prism (pentagonal prism)
105
, and an eyepiece
106
, to the eye. During photography, the reflecting mirror
102
is retracted out of the optical path, and an object image is formed on an image pickup surface
108
on which a photosensitive film, an image pickup element, or the like, is placed. The light reflected by the reflecting mirror
102
is also utilized for distance measurement and photometry in some cases.
The structure illustrated in
FIG. 1
, however, requires a sufficiently large space for the reflecting mirror
102
to be set in the optical path. For that reason the image pickup optical system is needed to have a large back focus, which increases the number of lenses in the image pickup optical system and increases the size of the image pickup optical system. The reflecting mirror
102
heretofore was a plane mirror having no optical power and was not utilized for correction for aberration.
Meanwhile, it has been clarified recently as to non-coaxial, optical systems that an optical system of well-corrected aberration can be constructed by introducing the concept of the reference axis and making its component surfaces of asymmetric, aspherical surfaces; for example, Japanese Patent Application Laid-Open No. 9-5650 discloses a design method thereof and Japanese Patent Applications Laid-Open No. 8-292371 and Laid-Open No. 8-292372 (both corresponding to U.S. Pat. No. 5,825,560) describe design examples thereof. Such non-coaxial, optical systems are called off-axial, optical systems (which are optical systems defined as optical systems including a curved surface (off-axial curved surface) a normal to which at an intersecting point of the component surface with the reference axis does not lie on the reference axis, where the reference axis is assumed to run along a ray passing the center of the image and the center of the pupil, the reference axis being of a bent shape).
In these off-axial, optical systems, the component surfaces are normally non-coaxial and do not bring about an eclipse even if they are reflective surfaces. Therefore, it is easier to construct an optical system of reflective surfaces. They also have such features that routing of the optical path is relatively free and that it is easier to construct an integral optical system by the technique of integrally molding the component surfaces.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an optical system constructed of such an off-axial, optical system so as to realize downsizing of the whole optical system while being arranged to have no parallax between its optical paths, where the optical system is provided with an optical path (for example, the viewing optical path, the optical path for distance measurement and photometry, etc.) other than the photographing optical path.
For accomplishing the above object, an optical system according to a first aspect of the present invention comprises:
an optical element having a plurality of reflective surfaces integrally formed, wherein at least one reflective surface out of the plurality of reflective surfaces of the optical element is a curved surface a normal to which does not coincide with a reference axis at an intersecting point therewith;
an image pickup element to which light successively reflected by the plurality of reflective surfaces is incident; and
optical means for making at least part of light that ought to enter the image pickup element, travel in an optical path different from an optical path toward the image pickup element.
The light made to travel in the different optical path by the optical means is utilized for a purpose other than image pickup by the image pickup element.
An image pickup apparatus according to a second aspect of the present invention is characterized by comprising the optical system according to the first aspect of the present invention.
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Aratani Michiharu
Hoshi Hiroaki
Ben Loha
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
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