Television – Camera – system and detail – Optics
Reexamination Certificate
1997-03-04
2001-04-24
Ho, Tuan (Department: 2612)
Television
Camera, system and detail
Optics
Reexamination Certificate
active
06222588
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an automatic focus adjusting device.
2. Description of the Related Art
The advancement of technology related to various video apparatuses including video cameras, electronic cameras, etc., have been remarkable during recent years. As a result, it has become a standard practice to provide these apparatus with an automatic focus adjusting (AF) function for improvement in performance and operability.
According to a focusing method most popularly employed for the automatic focus adjusting (focusing) devices of these apparatuses, the sharpness of a picture is detected from a video signal obtained through photo-electric conversion by an image sensor or the like and then the position of a focusing lens is controlled and adjusted in such a way as to make the detected sharpness into a maximum degree.
The degree of sharpness is represented by a sharpness signal. The sharpness signal is evaluated in general either by detecting the intensity of a high frequency component extracted from a video signal through a band-pass filter thereinafter referred to as BPF) or by detecting the width of blur of the video signal (width of the edge part of an object image) through a differentiation circuit or the like.
In shooting an ordinary object of shooting, if the lens is out of focus, the level of the high frequency component of the video signal is low and the width of blur is wide. The level of the high frequency component increases and the width of blur decreases accordingly as the lens comes closer to an in-focus state. The level and the width respectively reach a maximum value and a minimum value when the lens reaches a completely in-focus state.
The focusing lens is controlled to drive it at a highest possible speed in the direction of increasing the sharpness if the sharpness is low and the driving speed is lowered accordingly as the sharpness increases in such a way as to bring the focusing lens to a stop just on the top of a hill-like curve representing the degrees of sharpness. This method of control is generally called a hill climbing automatic focusing method or a hill climbing AF method. The adoption of an automatic focusing device operating in accordance with this method has greatly enhanced the operability of an apparatus for taking moving images such as a video camera. This automatic focusing function has become indispensable to a video camera or the like.
FIG. 1
is a block diagram showing one example of the conventional automatic focus adjusting (focusing) device of the kind arranged to use a video signal in a video camera. The illustration includes lens groups
101
,
102
,
104
and
105
. The lens groups
101
and
104
are fixed lens groups. The lens group
102
is arranged to perform a magnifying power varying action (hereinafter referred to as a variator lens). Reference numeral
103
denotes a diaphragm. The lens group
105
is arranged to perform a focus adjusting action and to compensate a focal plane obtained after the magnifying power varying action (hereinafter referred to as a focusing lens).
Reference numeral
106
denotes an image sensor. An AF control microcomputer
107
is arranged to control a whole system including lens driving control, AF control, etc. An aperture encoder
108
is arranged to detect the aperture value of the diaphragm
103
. An amplifier
109
is arranged to amplify a signal outputted from the aperture encoder. A conversion circuit
110
is arranged to convert the signal of the aperture encoder
109
into a DC signal of a variable level. An A/D (analog-to-digital) converter
128
is arranged to A/D convert the output of the conversion circuit
110
into a digital signal and to supply the digital signal to the AF control microcomputer
107
.
A buffer amplifier
111
is arranged to amplify or impedance-convert the output of the image sensor
106
. A BPF
113
is arranged to take out a high frequency component of a video signal which is outputted from the image sensor
106
, the high frequency component being arranged to be used for AF control. An AF signal processing circuit
114
is arranged to form from the high frequency component a sharpness signal which is to be used in carrying out the AF control. An A/D converter
115
is arranged to A/D convert the output of the AF signal processing circuit
114
into a digital signal and to supply the digital signal to the AF control microcomputer
107
.
A variator lens driving motor
119
and a focusing lens driving motor
122
are respectively arranged to drive the variator lens
102
and the focusing lens
105
. Racks
120
and
123
are connected to the variator lens
102
and the focusing lens
105
, respectively, and constantly mesh with the rotation shafts of the variator lens driving motor
119
and the focusing lens driving motor
122
. Drivers
121
and
124
are arranged to drive the variator lens driving motor
119
and the focusing lens driving motor
122
in accordance with instructions received from the AF control microcomputer
107
. An integrator
125
is arranged to integrate a signal outputted from an AGC (automatic gain control) circuit
112
. A diaphragm control circuit
126
is arranged to control the aperture of the diaphragm
103
in such a way as to give an adequate amount of exposure in reference to a signal outputted from the integrator
125
. A driver
127
is arranged to drive the diaphragm
103
. The output signal of the A/D converter
115
to be inputted to the AF control microcomputer
107
has a value which varies with the magnitude of the high frequency component of the video signal. The amount of the high frequency component becomes a maximum amount when the lens is perfectly in focus and becomes smaller when it is out of focus.
In the arrangement described above, the output signal of the A/D converter
115
is called a focus voltage or a focus signal. The AF control microcomputer
107
is arranged to cause the focusing lens
105
to be moved in such a way as to make the value of the output signal of the A/D converter
115
(the focus signal) to become a maximum value. Further, depending on the state of a zoom switch which is not shown, the AF control microcomputer
107
outputs and gives a driving instruction to the drivers
121
and
124
to move the variator lens
102
toward its telephoto end position or toward its wide-angle end position.
A focusing action is performed in the following manner. In the case of an automatic focusing device of the kind arranged to monitor the increase or decrease of the amount of the high frequency component (focus voltage) as in the case of the arrangement shown in
FIG. 1
, the focusing lens is moved to cause the amount of the high frequency component to become a maximum amount as mentioned above. The amount of the high frequency component increases or decreases in relation to the position of the focusing lens, for example, as represented by a curve
201
in FIG.
2
.
FIG. 7
is a flow chart showing in outline a flow of processes of the automatic focusing action. Referring to
FIG. 7
, the focusing action is described as follows. Assuming that the focusing lens has been in repose with an in-focus state obtained for an object of shooting, in cases where the object changes and the focusing lens is moved by driving it again to maximize the focus voltage thereinafter, this process will be called “restarting the focusing lens”), the focusing action must be performed through the following processes.
(I) A check is made to find if the current position of the focusing lens deviates from an in-focus position (a step
706
of FIG.
7
).
(II) If so, a check is made to find whether a position where the focus voltage becomes a maximum value is located closer to a nearest distance position or closer to an infinity distance position than the current position of the focusing lens (a step
701
of FIG.
7
).
(III) The lens is moved toward the in-focus position in the hill-climbing manner and is brought to a stop at a point where the focus voltage comes to show its maximum
Tanaka Taeko
Yamazaki Tatsuya
Canon Kabushiki Kaisha
Ho Tuan
Robin Blecker & Daley
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