Photography – With exposure objective focusing means – focusing aid – or... – Optical detail with photoelement system
Reexamination Certificate
2000-10-24
2002-04-09
Adams, Russell (Department: 2851)
Photography
With exposure objective focusing means, focusing aid, or...
Optical detail with photoelement system
C396S113000, C250S201800
Reexamination Certificate
active
06370333
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multipoint focus detecting apparatus which can determine a focus state at each of a plurality of focus detection zones, and which is suitable for an optical instrument such as an SLR camera.
2. Description of the Prior Art
In recent years, SLR cameras provided with a multipoint focus detecting unit for determining a focus state (defocus) at each of a plurality of focus detection zones (focusing points) have been developed. In the optical system of a conventional multipoint focus detecting unit, in addition to the central focus detection zone arranged over the optical axis, one or more off-center focus detection zones are arranged away from the optical axis, and light bundles which form an object image which are passed through the central and off-center focus detection zones are respectively deflected by corresponding mirrors to be incident on corresponding light receiving elements arranged in a horizontal line. For instance, a light bundle of an object image that is passed through the horizontally-elongated central focus detection zone is deflected once by a mirror to be focused on a corresponding horizontally-elongated array of light receiving elements. The image observed through the horizontally-elongated central focus detection zone is divided into two, by a corresponding pair of separator lenses, to be formed as two separate images on the corresponding horizontally-elongated array of light receiving elements. At the same time, another light bundle of the object image which is passed through a vertically elongated off-center focus detection zone is deflected twice by two mirrors to be focused on a corresponding horizontally-elongated array of light receiving elements. The image observed through the vertically-elongated off-center focus detection zone is divided into two by a corresponding pair of separator lenses to be formed as two separate images on the corresponding horizontally-elongated array of light receiving elements. The central and off-center pairs of separator lenses are arranged away from the central and off-center light receiving elements by a predetermined distance.
FIG. 4
is a developed view of an optical path of a conventional multipoint focus detecting apparatus, showing optical paths thereof. Note that none of the aforementioned deflecting mirrors are, for clarity, shown in
FIG. 4. A
field mask
101
, positioned in a plane located at a position optically equivalent with a film surface (i.e., a focal plane of the photographing lens), is provided with two focus detection apertures
101
a
and
101
b
which respectively determine two off-center focus detection zones (e.g., a left focus detection zone and a leftmost focus detection zone) arranged away from the center of the field of view. A light bundle La, which is passed through the aperture (e.g., the aforementioned left focus detection zone)
101
a
and a condenser lens
103
a
, is firstly deflected by a prism
105
a
in an outward direction (i.e., in a downward direction as viewed in FIG.
4
), and is subsequently deflected by a prism
107
a
in a direction to be substantially parallel to the optical axis O of a photographing lens (not shown). Subsequently, the light bundle passes through a separator mask
109
a
provided as an exit-pupil dividing device and a pair of separator lenses
11
a
to be incident on a corresponding line sensor
113
a
, so that a couple of object images (a couple of light distributions) are formed on the line sensor
113
a.
On the other hand, a light bundle Lb, which is passed through another aperture (e.g., the aforementioned leftmost focus detection zone)
101
b
, that is positioned farther from the optical axis O than the aperture
101
a
, and a condenser lens
103
b
, is firstly deflected by a prism
105
b
in an inward direction (i.e., in an upward direction as viewed in FIG.
4
), and is subsequently deflected by a prism
107
b
in a direction to be substantially parallel to the optical axis O. Subsequently, the light bundle passes through a separator mask
109
b
provided as an exit-pupil dividing device, and a pair of separator lenses
111
b
to be incident on a corresponding line sensor
113
b
, so that a couple of object images (a couple of light distributions) are formed on the line sensor
113
b
. Each of the line sensors
113
a
and
113
b
extends in a direction normal to a surface of the drawing of
FIG. 4
, and the two light bundles which are passed through the two separator masks
109
a
and
109
b
are incident on the two line sensors
113
a
and
113
b
to be formed as two object images thereon, respectively.
Among the light bundle Lb that is passed through the focus detection aperture
101
b
, for instance, there is a stray light bundle Lb′ that is incident on the separator mask
109
a
, rather than the separator mask
109
b
. If the line sensor
113
a
receives such a stray light bundle that is passed through the focus detection aperture
101
b
, the object image of the stray light bundle is formed on the line sensor
113
a
. This deteriorates the precision in detection of the multipoint focus detecting apparatus. In some cases, the multipoint focus detecting apparatus cannot determine a focus state due to such a stray light bundle.
SUMMARY OF THE INVENTION
The present invention has been made in view of the aforementioned problems that reside in conventional multipoint focus detecting apparatuses, and an object of the present invention is to provide a multipoint focus detecting apparatus which can prevent any stray light which may cause a focus detection error from occurring.
To achieve the object mentioned above, according to an aspect of the present invention, a multipoint focus detecting apparatus of a camera is provided, including a plurality of exit-pupil dividing devices for dividing an exit pupil of a photographing lens into a plurality of detection sub-zones, the plurality of detection sub-zones corresponding to a plurality of arrays of light receiving elements arranged in a second direction orthogonal to a first direction in which the exit pupil is divided by each of the plurality of exit-pupil dividing devices; a plurality of pairs of light distribution forming devices, each of the pairs of light distribution forming devices receiving light bundles which are passed through a corresponding pair of the plurality of detection sub-zones to form a corresponding pair of light distributions, respectively, relative positions of which vary in accordance with a variation in position of a focal point of the photographing lens; a focus detection zone determining device that is positioned in a plane located substantially at a position optically equivalent with a focal plane of the photographing lens to determine the plurality of focus detection zones, at least two light bundles which are respectively passed through corresponding at least two of the plurality of focus detection zones being respectively incident on corresponding at least two of the plurality of exit-pupil dividing devices after intersecting each other; and a light intercepting member which is positioned in a vicinity of an intersection between the at least two light bundles so that each of the at least two light bundles is not incident on any of the plurality of arrays of light receiving elements other than a corresponding one of the plurality of arrays of light receiving elements.
Preferably, at least one condenser lens positioned between the focus detection zone determining device and the plurality of exit-pupil dividing devices is included so that the light bundles which are respectively passed through the plurality of focus detection zones pass through the at least one condenser lens.
In an embodiment, each of the plurality of exit-pupil dividing devices includes a separator mask having at least two apertures.
In an embodiment, each pair of the plurality of pairs of light distribution forming devices includes a pair of separator lenses.
Preferably, each of the plurality of arrays of light receiv
Adams Russell
Asahi Kogaku Kogyo Kabushiki Kaisha
Greenblum & Bernstein P.L.C.
Smith Arthur A
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