Television – Camera – system and detail – Optics
Reexamination Certificate
1997-09-23
2003-06-10
Ho, Tuan (Department: 2612)
Television
Camera, system and detail
Optics
C396S121000
Reexamination Certificate
active
06577344
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a focus state detection apparatus used in an image sensing apparatus, such as a still camera and a video camera, and various kinds of observation apparatuses and, more particularly, to a focus state detection apparatus which performs focus state detection by using area sensors configured with two-dimensional solid-state image sensing devices, such as CCDs, capable of sensing an complete image.
FIG. 31
is a view illustrating a brief optical configuration of a camera including a conventional focus detection unit. In
FIG. 31
, reference numeral
101
denotes an object lens which introduces an image of an object (referred as “object image”, hereinafter) into the apparatus;
102
, a main mirror (half mirror) which is half transparent and reflects a part of light of the object image incoming through the object lens
101
;
103
, a reticle which is placed at a focal plane of the object lens
101
;
104
, a pentagonal prism which changes the traveling direction of light;
105
, an eyepiece;
106
, sub-mirror which operates when performing focus state detection;
107
, a film, such as a silver halide film; and
108
, a focus state detection unit.
Referring to
FIG. 31
, light from an object (not shown) passes through the object lens
101
, then a part of the light is reflected by the main mirror
102
upward, and the reflected light forms an image on the reticle
103
. The image formed on the reticle
103
is further reflected in the pentagonal prism
104
a plurality of times, and eventually reaches the eye of a user through the eyepiece
105
. Further, the light which passes through the main mirror
102
reaches the film
107
and exposes it with the object image thereby obtaining a desired image.
Meanwhile, a part of the flux of light which passed through the main mirror
102
is reflected by the sub-mirror
106
downward, and led to the focus state detection unit
108
.
FIG. 32
is a view for explaining the principle of focus state detection in relation to the object lens
101
and the focus state detection unit
108
shown in FIG.
31
.
In the focus state detection unit
108
shown in
FIG. 32
, reference numeral
109
denotes a field stop provided near the desired focal plane, i.e., a conjugate plane of a plane where the film
107
is supplied;
110
, a field lens arranged near the desired focal plane;
111
, a secondary lens system having two lenses
111
-
1
and
111
-
2
;
112
, a photoelectric conversion device including two line sensors
112
-
1
and
112
-
2
provided behind the lenses
111
-
1
and
111
-
2
, respectively;
113
, an iris diaphragm having two aperture openings
113
-
1
and
113
-
2
corresponding to the lenses
111
-
1
and
111
-
2
of the secondary lens system
111
, respectively; and
114
, an exit pupil of the object lens
101
. Note, the field lens
110
has power for forming an image of the aperture openings
113
-
1
and
113
-
2
of the iris diaphragm
113
in near areas
114
-
1
and
114
-
2
of the exit pupil
114
of the object lens
101
. In reverse, fluxes of light
115
-
1
and
115
-
2
which passed through the areas
114
-
1
and
114
-
2
further pass through the aperture openings
113
-
1
and
113
-
2
, respectively, and incident on the two line sensors
112
-
1
and
112
-
2
, thereby distributions of quantity of light are obtained by the two line sensors
112
-
1
and
112
-
2
.
The focus state detection unit
108
shown in
FIG. 32
adopts a so-called phase-difference detection method. When the focal point of the object lens
101
is in front of the desired focal plane, namely when an image is focused ahead of the desired focal plane, the images obtained by the two line sensors
112
-
1
and
112
-
2
approaches each other. In opposite, when the focal point of the object lens
101
is behind the desired focal plane, the images obtained by the two line sensors
112
-
1
and
112
-
2
recedes from each other. Since the shifted amount between the distributions of quantity of light of the two line sensors
112
-
1
and
112
-
2
has a predetermined functional relationship to a defocus amount of the object lens
101
, by calculating the shifted amount between the distributions in accordance with proper operation, it is possible to obtain defocus direction and amount. The object lens
101
is moved in accordance with the defocus direction and amount so that the defocus amount approaches 0. When the defocus amount becomes substantially 0, the focus state detection is finished.
In the camera including the conventional focus state detection unit
108
as shown in
FIG. 32
, an area used for the focus state detection (referred as “detection area”, hereinafter) is a strip and narrow as an area B with respect to an sensed image area A as shown in FIG.
33
. The size and shape of the detection area B is determined by the shape of the line sensors
112
-
1
and
112
-
2
, shown in
FIG. 32
, used in the focus state detection.
FIG. 34
is a block diagram showing a brief mechanism for charge control of the line sensors
112
-
1
and
112
-
2
. Referring to
FIG. 34
, an output VD, commonly used as a reference for the line sensors
112
-
1
and
112
-
2
, of a light-blocked pixel
120
(the pixel is referred as “dark pixel” and the output is referred as “dark voltage”, hereinafter), and an output VP from a maximum voltage detection circuit
121
connected to the line sensors
112
-
1
and
112
-
2
, namely the maximum voltage of the line sensors
112
-
1
and
112
-
2
, are inputted to a differential amplifier
122
. Then, the difference between the dark voltage VD and the maximum voltage VP is obtained and outputted. Charging of the line sensors
112
-
1
and
112
-
2
continues until the difference reaches a predetermined level VR, and when the difference reaches the predetermined level VR, charging of the line sensors
112
-
1
and
112
-
2
is terminated and a signal &phgr;R which is an end-charging signal for transferring the stored charges from pixels to charge capacitors is sent to the line sensors
112
-
1
and
112
-
2
. The reason for taking a difference between the maximum voltage VP and the dark voltage VD is that, by charging the line sensors
112
-
1
and
112
-
2
until the difference between the maximum voltage VP and the dark voltage VD reaches the predetermined level VR, it is possible to obtain the phase difference between the distributions of quantity of light for focus state detection in sufficient precision. Further, if charging is continued after the difference reaches the predetermined level, there is a possibility that the pixels of the line sensors
112
-
1
and
112
-
2
saturate, which may cause improper focus state detection. Therefore, when “VP−VD=VR” is satisfied, the end-charging signal &phgr;R is outputted to the line sensors
112
-
1
and
112
-
2
.
FIGS. 35A and 35B
are graphs showing image signals (distributions of quantity of light) from the line sensors
112
-
1
and
112
-
2
with reference to the dark voltage VD of the dark pixel
120
, and the maximum voltage VP of first and second images (in
FIGS. 35A and 35B
, the maximum voltage VP is in the first image), corresponding to the line sensors
112
-
1
and
112
-
2
, respectively, is the predetermined level VR. For using the signals from the line sensors
112
-
1
and
112
-
2
for focus state detection, when the difference between a voltage of any pixel of the line sensors
112
-
1
and
112
-
2
and the dark voltage VD reaches the predetermined level VR, charging is terminated and whether or not an image is focused is determined on the basis of output images.
FIG. 36
is a circuit diagram showing a brief configuration of the maximum voltage detection circuit
121
and its subsequent circuits, namely the differential amplifier
122
and a part of a charge controller
123
both shown in FIG.
34
. In
FIG. 36
, only two sets of circuits for outputs Vn and Vn−1 outputted from n-th and (n−1)-th pixels, respectively, are connected to a wire
136
, however, the same number of
Kadohara Terutake
Nagata Keiji
Ohtaka Keiji
Suda Yasuo
Yamashita Kenichiro
Canon Kabushiki Kaisha
Ho Tuan
Morgan & Finnegan L.L.P.
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