Photography – With exposure objective focusing means – focusing aid – or... – Optical detail with photoelement system
Reexamination Certificate
2000-10-24
2002-05-21
Adams, Russell (Department: 2851)
Photography
With exposure objective focusing means, focusing aid, or...
Optical detail with photoelement system
C396S121000, C396S111000, C359S618000
Reexamination Certificate
active
06393219
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. A typical conventional exit-pupil-dividing multipoint focus detecting unit is provided with a plurality of exit-pupil dividing devices, a plurality of pairs of light distribution forming devices and a plurality of array type photoelectric conversion sensors (e.g., CCD line sensors). Each exit-pupil dividing device functions to divide the exit pupil of a photographing lens into two detection sub-zones. Each exit-pupil dividing device is composed of, e.g., a separator mask having a pair of apertures. Each pair of light distribution forming devices receive light bundles which are passed through the corresponding aforementioned two detection sub-zones to form a corresponding pair of light distributions, respectively, whose relative positions vary in accordance with the variation in position of the focal point of the photographing lens. Each pair of light distribution forming devices are composed of, e.g., a pair of separator lenses. The plurality of array type photoelectric conversion sensors are arranged in a direction orthogonal to the direction in which the exit pupil of the photographing lens is divided by each of the aforementioned exit-pupil dividing devices. The conventional exit-pupil-dividing multipoint focus detecting unit is further provided with an opaque field mask (focus detection zone determining plate) having a plurality of apertures which determine the plurality of focus detection zones, respectively. The field mask is positioned in a plane located at a position optically equivalent with a film surface (i.e., a focal plane of the photographing lens). Each of the plurality of apertures of the field mask determines the size of the bundle of rays which are incident on the corresponding separator mask (the exit-pupil dividing device). However, the size of each array type photoelectric conversion sensor is generally smaller than that of the corresponding focus detection zone, while the space between two adjacent array type photoelectric conversion sensors is generally narrower than that between the corresponding two adjacent focus detection zones. For this reason, the conventional exit-pupil-dividing multipoint focus detecting unit is further provided between the field mask and the exit-pupil dividing devices with at least one condenser lens (sometimes with at least one prism) for converging each of the object light bundles which are respectively passed through the focus detection zones (i.e., the apertures) of the field mask and for deflecting each object light bundle in a direction of passing through the corresponding separator mask (the exit-pupil dividing device) so that the light distribution of the object light bundle (i.e., a object image) is formed on the corresponding array type photoelectric conversion sensor via the corresponding pair of separator lenses (the corresponding pair of light distribution forming devices).
FIGS. 5A
,
5
B and
5
C each show a diagram of fundamental elements of a focus detection optical system of a conventional multipoint focus detecting apparatus. In each of these drawings, reference numerals
101
,
102
and
103
represent the exit pupil of a photographing lens, the entrance pupil of the focus detection optical system and the aforementioned field mask, respectively.
In the focus detection optical system of a conventional multipoint focus detecting apparatus shown in
FIG. 5A
, two object light bundles which are passed through two focus detection zones (i.e., two apertures) of the field mask
103
are converged and deflected by a rotationally-symmetrical condenser lens
111
toward two separator masks (the aforementioned exit-pupil dividing devices)
113
and
114
, respectively, so that the light distribution of each object light bundle (i.e., a object image) is formed on the corresponding line sensor (the aforementioned array type photoelectric conversion sensor)
117
or
118
via the corresponding pair of separator lenses (the corresponding pair of light distribution forming devices)
115
or
116
. In this conventional multipoint focus detecting apparatus shown in
FIG. 5A
, more than one focus detection zone of the field mask
103
are covered by a single condenser lens, i.e., the rotationally-symmetrical condenser lens
111
. Since the condenser lens
111
has the same power in both horizontal and vertical directions and is rotationally symmetrical about the optical axis thereof, neither the light distribution of the object light bundle formed on each of the two line sensors
117
and
118
nor the distortion thereof can be corrected by the condenser lens
111
, even though the exit pupil
101
and the entrance pupil
102
are successfully made to coincide with each other in both horizontal and vertical directions by the condenser lens
111
. Therefore, neither the area of each focus detection zone of the field mask
103
nor the space between the two focus detection zones of the field mask
103
can be made large. Furthermore, if it is attempted to make the exit pupil
101
and the entrance pupil
102
coincide with each other, the degree of freedom in arrangement of the separator masks
113
and
114
is somewhat restricted.
In the focus detection optical system of a conventional multipoint focus detecting apparatus shown in
FIG. 5B
, a condenser lens is disposed for each focus detection zone, namely, two condenser lenses
121
and
122
are disposed for the two focus detection zones of the field mask
103
, respectively. In the focus detection optical system of this conventional multipoint focus detecting apparatus, two object light bundles which are passed through the two focus detection zones of the field mask
103
are converged and deflected by two condenser lenses
121
and
122
to two separator masks (the aforementioned exit-pupil dividing devices)
123
and
124
, respectively, so that the light distribution of each object light bundle (i.e., a object image) is formed on the corresponding line sensor (the aforementioned array type photoelectric conversion sensor)
127
or
128
via the corresponding pair of separator lenses (the corresponding pair of light distribution forming devices)
125
or
126
. In this conventional multipoint focus detecting apparatus shown in
FIG. 5B
, since a condenser lens (
121
or
122
) is disposed for each of the two focus detection zones of the field mask
103
, the exit pupil
101
and the entrance pupil
102
can be made to coincide with each other in both horizontal and vertical directions by the condenser lens
121
and
122
, and at the same time, the light distribution of the object light bundle formed on each of the two line sensors
127
and
128
and the distortion thereof can be corrected by the condenser lenses
121
and
122
. However, in this conventional multipoint focus detecting apparatus, more than one condenser lens is required, which extensively increases the number of lens surfaces that are to be formed on molded condenser lenses.
In the focus detection optical system of a conventional multipoint focus detecting apparatus shown in
FIG. 5C
, a condenser lens is disposed for each focus detection zone, namely, two condenser lenses
131
and
132
are disposed for the two focus detection zones of the field mask
103
, respectively. Furthermore, a prism is disposed for each condenser lens; namely, two prisms
133
and
134
are disposed for the two condenser lenses
131
and
132
, respectively. Each of the two prisms
133
and
134
deflects a bundle of rays which are passed through the corresponding condenser lens
131
or
132
so that the two light bun
Adams Russell
Asahi Kogaku Kogyo Kabushiki Kaisha
Greenblum & Bernstein P.L.C.
Smith Arthur A
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