Photography – With exposure objective focusing means – focusing aid – or... – Reliability of focus/distance signal
Reexamination Certificate
1998-12-10
2001-01-09
Perkey, W. B. (Department: 2851)
Photography
With exposure objective focusing means, focusing aid, or...
Reliability of focus/distance signal
C396S106000
Reexamination Certificate
active
06173122
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a distance measuring apparatus and method for measuring the distance to an object to be measured and, for example, a distance measuring apparatus and method suitably applied to an automatic focusing mechanism of a camera.
Conventionally, a distance measuring device which performs trigonometrical measurement by projecting a light spot onto an object to be measured and receiving light reflected by the object using a position detection means such as a position sensitive detector (PSD) or the like is known. Further, another distance measuring device which circulates an accumulated charge using a ring-shaped charge transfer device, such as CCD, to integrate reflected light of ON/OFF-projected light spots and skims a predetermined amount of charges of external light components other than the light spot has been proposed by Japanese Patent Publication No. 5-22843 and Japanese Patent Application Laid-Open No. 8-233571. The distance measuring device of this type can keep accumulating charges while circulating the accumulated charge if the level of the accumulated charge is not high enough, thereby it is possible to obtain signals of good S/N ratio.
Further, a method for measuring a shift amount of two images of an object of interest received by two ring-shaped CCDs having the above configuration, and measuring a distance to the object on the basis of the measured shift amount is proposed in Japanese Patent Application Laid-Open No. 9-105623. The aforesaid distance measuring devices are often used in an automatic focusing mechanism of a camera.
First, the Japanese Patent Publication No. 5-22843 is explained below.
FIG. 21
is a diagram illustrating a configuration of a light-receiving unit used in a distance measuring apparatus.
Note, in
FIG. 21
, a photoelectric conversion (photo-receiving) device
520
of a light-receiving unit
500
is represented by three photoelectric conversion devices X, Y and Z, to simplify the explanation.
The light-receiving unit
500
operates in two different modes, namely, an active mode and a passive mode.
The active mode is to project light onto an object
515
to be measured, the distance to which is to be measured, by turning on and off a light emit element (here, infrared light-emitting diode; IRED)
514
to emit light pulses, receive light reflected by the object using the photoelectric conversion devices X, Y and Z, and store the charges. Whereas, the passive mode is to receive external light reflected by the object without turning on the IRED
514
using the photoelectric conversion devices X, Y and Z, and store the charges.
The distance measuring apparatus is of a hybrid-type capable of performing distance measuring operation both in the active mode and in the passive mode, and, when a reliable measurement result is not obtained in the active mode, then the distance is measured once again in the passive mode.
Further, the light-receiving unit
500
has a linear CCD
524
which includes ON-pixels
522
x
,
522
y
, and
522
z
and OFF-pixels
523
x
,
523
y
, and
523
z
, respectively corresponding to the photoelectric conversion devices X, Y and Z, and a ring-shaped CCD
521
which includes a plurality of ON-pixels and OFF-pixels.
Therefore, the charges obtained as a result of photoelectric conversion in the photoelectric conversion devices X, Y and Z are respectively transferred to the corresponding ON-pixels and OFF-pixels of the linear CCD
524
and stored, thereafter, transferred to the ring-shaped CCD
521
.
Next, timing of charge transfer operation in the light-receiving unit
500
is explained with reference to FIG.
22
.
Referring to
FIG. 22
, the IRED
514
turns on and off in synchronization with the ON/OFF (High/Low) of a charging signal in the active mode, and the IRED
514
is kept off independent of the ON/OFF of the charging signal in the passive mode.
First, charges obtained in the photoelectric conversion devices X, Y and Z while the charging signal is ON (i.e., High level) are transferred to the ON-pixels
522
x
,
522
y
, and
522
z
while an ON-pixel transfer signal is ON (i.e., High level).
Further, charges obtained in the photoelectric conversion devices X, Y and Z while the charging signal is OFF (i.e., Low level) are transferred to the OFF-pixels
523
x
,
523
y
, and
523
z
while an OFF-pixel transfer signal is ON (i.e., High level).
In this manner, charges due to projected light reflected by the object and external light are stored in the ON-pixels
522
x
,
522
y
, and
522
z
, while charges due to external light are stored in the OFF-pixels
523
x
,
523
y
, and
523
z
in the active mode.
After the charges obtained in the photoelectric conversion devices X, Y and Z are transferred to the ON-pixels
522
x
,
522
y
, and
522
z
and the OFF-pixels
523
x
,
523
y
, and
523
z
, the charges are transferred to the ring-shaped CCD
521
.
To transfer the charges to the ring-shaped CCD
521
, a ring transfer signal is used. The ring transfer signal becomes High so that charges from the same pixel of the linear CCD
524
are always transferred to the same pixel of the ring-shaped CCD. Accordingly, charges outputted from the ON-pixel
522
x
, corresponding to the photoelectric conversion element X obtained during the charging signal is ON, for example, are accumulated.
In
FIG. 22
, the numerals
1
,
2
,
3
, and so on, indicate the number of circulation. The number of circulation indicates the number of times charges are transferred to the ring-shaped CCD
521
.
More specifically, in the first circulation, charges are transferred to the ring-shaped CCD
521
once, as shown in
FIG. 23A
, and the charges obtained in one charging operation are stored. In the second circulation, charges obtained in two charging operations are accumulated, as shown in
FIG. 23B
, and in the third circulation, charges are transferred to the ring-shaped CCD
521
three times; in other words, three charging operations are performed and charges obtained in the three charging operations are accumulated in the respective pixels, as shown in FIG.
23
C.
When the charges accumulated in the ring-shaped CCD
521
do not reach a predetermined level (level in which distance measurement can be performed on the basis of the charges), i.e., incoming light to the photoelectric conversion devices X, Y and Z is low, the number of circulation, i.e., the number of charging operation, is increased, and the charges are sequentially transferred to the ring-shaped CCD
521
and accumulated until charges are accumulated to the necessary (predetermined) level. In this manner, it is possible to obtain charges of good S/N ratio.
Whereas, in a case where an amount of charge in the ring-shaped
521
succeeds a predetermined level within a predetermined times of circulation, i.e., in a case where incoming light to the photoelectric conversion devices X, Y and Z is high, it is necessary to adjust the amounts of charges to be stored in the pixels of the linear CCD
524
in one charging operation in order to prevent the pixels from being saturated.
As for adjusting the amounts of charges, there are a method of adjusting a charging period by controlling an electrical shutter function, and a method for controlling a frequency for operating the photoelectric conversion devices X, Y and Z, thereby controlling a charging period.
More specifically, in the method of adjusting the charge amounts by controlling the electrical shutter function, if a reference charging period is 100%, then the charging period is reduced to 70%, 50%, and so on, when the object
515
is bright.
Further, in the method of adjusting the charge amount by controlling the frequency for operating the photoelectric conversion devices X, Y and Z, if any of the ON-pixels
522
x
,
522
y
, and
522
z
and the OFF-pixels
523
x
,
523
y
, and
523
z
is saturated when the photoelectric conversion devices X, Y and Z are operated at 1 MHz, then by operating the photoelectric conversion devices X, Y and Z in the doubled frequency, namely at 2 MHz, it is possible
Harada Osamu
Matsumoto Yukihiro
Canon Kabushiki Kaisha
Morgan & Finnegan , LLP
Perkey W. B.
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