Optics: measuring and testing – By polarized light examination – With light attenuation
Reexamination Certificate
1999-07-08
2001-01-23
Pham, Hoa Q. (Department: 2877)
Optics: measuring and testing
By polarized light examination
With light attenuation
C250S201200, C396S123000, C358S474000
Reexamination Certificate
active
06177996
ABSTRACT:
This application is based on application No. H10-198293 filed in Japan on Jul. 14, 1998, the entire content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sensor unit in which a plurality of line sensors receiving light and generating photocharges are arranged, and a distance measurement apparatus having the sensor unit as the distance measurement sensor being used, for example, for automatic focusing of a camera.
2. Description of the Prior Art
A distance measurement apparatus measures the distance by applying the principle of the triangulation, and is used, for example, for an automatic focusing (AF) mechanism of a camera. As a distance measurement method for the distance measurement apparatus, a method which uses passive light is known. Hereinafter, this method will be called a passive correlation method. According to this method, the input image is used as it is without irradiating distance measurement light. The principle of this distance measurement method will be described.
FIG. 7A
shows an example of a distance measurement apparatus employing the passive correlation method.
FIG. 7B
shows an image signal obtained from an image sensor of this apparatus comprising a charge-coupled device (CCD). Incident light rays from lenses
100
disposed on the left and the right sides are aligned and imaged on the light receiving surface of a one-dimensional CCD
103
by use of mirrors
101
and a prism
102
. The image signal of the CCD
103
is, for example, as shown in FIG.
7
B. The longitudinal axis corresponds to the position on the CCD
103
, whereas the lateral axis represents the level of the image signal. The distance between the two images varies in correspondence with the distance to the subject. The distance between the two images is obtained by a correlation calculation of the image signal, and from the obtained distance, the distance to the subject can be determined. This is the principle of the passive correlation method.
Conventionally, many distance measurement apparatuses for cameras using the passive correlation method have performed distance measurement with one line of distance measurement area
61
horizontally to a photographic image plane
60
of a camera as shown in FIG.
1
. The distance measurement sensor provided in the conventional distance measurement apparatuses has a structure, for example, as shown in
FIG. 2
where a pair of left and right line sensors
75
and
76
are disposed with a control circuit
10
in between. The pair of line sensors
75
and
76
are situated substantially on the imaging surfaces of a pair of lenses disposed with a predetermined optical axis-to-optical axis distance therebetween. The line sensors
75
and
76
receive subject image light with light receiving element arrays
12
comprising a plurality of light receiving elements.
The photocharges generated by the light receiving element arrays
12
are transferred and outputted one by one for each pixel by a processing unit
11
in accordance with a clock supplied from the control circuit
10
. Based on the output of the distance measurement sensor, a microcomputer calculates the distance to the subject.
The distance measurement sensor shown in
FIG. 3
also has a pair of left and right line sensors
77
and
78
so as to have a function similar to that of the above-described distance measurement sensor (FIG.
2
). Processing units
31
are provided on both sides with the light receiving element arrays
12
in between for each pixel. Since the detection of one line of distance measurement area is performed with a pair of left and right line sensors, a pair of left and right line sensors will sometimes be referred to as one line sensor.
In the above-described conventional distance measurement apparatuses, however, since the distance measurement area
61
merely traverses the central part of the photographic image plane
60
as shown in
FIG. 1
, distance measurement is impossible when the subject
62
is situated in the lower part or the upper part of the image plane
60
.
To ensure the distance measurement of the subject
62
, a structure has been disclosed which enables distance measurement in a wide range, for example, by providing a plurality of lines of distance measurement areas
63
to
65
as shown in FIG.
4
. In this structure, the larger the distance D
1
between the distance measurement areas
63
and
65
at both ends is, the wider the range where subject detection and distance detection can be performed with a small number of lines is.
Examples of such distance measurement apparatuses having a plurality of lines of distance measurement areas include one having a distance measurement sensor structured as shown in FIG.
5
. The distance measurement sensor
85
shown in
FIG. 5
has two pairs of line sensors
81
to
84
and performs distance measurement with two lines.
The distance measurement sensor
85
has the control circuit
10
on the axis of symmetry. The two pairs of line sensors
81
to
84
are disposed in such a manner that the light receiving element arrays
12
and the accompanying processing unit arrays
11
are oriented in one direction.
When a plurality of distance measurement areas are provided as shown in
FIG. 4
, the larger the distance between the distance measurement areas (the range covered by the line sensors) is, the wider the range where subject detection and distance detection are possible is. It has been found that the distance measurement detection accuracy generally increases as the product of the optical axis-to-optical axis distance (base length) between a pair of lenses and the focal length of the lenses increases. When a high distance measurement detection accuracy is required (for example, when the focal length of the focal distance system of the taking system is long), it is necessary to increase the base length or the focal length.
When the focal length of the distance detecting system is increased, in order to increase the distance between the line sensors on the photographic image plane, it is necessary that the distance between the line sensors be larger (than that in the case where the focal length is short) in accordance therewith. This will be described with reference to
FIGS. 6A and 6B
. The focal length of the distance detecting system is shorter in
FIG. 6A
than in FIG.
6
B. In a case where the distance D
2
between the distance measurement areas at both ends is obtained with respect to a photographic image plane G, when the distance between both ends of line sensors
91
to
93
in
FIG. 6A
is d
8
and the distance between both ends of line sensors
94
to
96
is d
9
, d
9
>d
8
as is apparent from the figures.
As described above, when the focal length is increased, it is necessary to increase the distance between the line sensors. However, increase in the distance between the line sensors increases the size of the device (designated
85
in
FIG. 5
) constituting the line sensor. However, it is difficult to increase the size of the device constituting the line sensor because of yield and cost constraints.
For this reason, when the focal length of the distance detecting system is increased in order to increase the distance detection accuracy in a case where the focal length of the taking system is long, it is impossible to dispose the distance measurement areas with a sufficient distance therebetween within the image plane, so that it is impossible to improve the reliability of subject detection by detecting a wide area.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a sensor unit and a distance measurement apparatus with the sensor unit capable of solving the above-described problems.
Another object of the present invention is to provide a low-cost sensor unit where the line distance can be increased, and a distance measurement apparatus capable of subject detection in a wide range with a high distance detection accuracy by using such a sensor unit.
To achieve the above-mentioned object, a se
Burns Doane , Swecker, Mathis LLP
Minolta Co. , Ltd.
Pham Hoa Q.
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