Photography – With exposure objective focusing means – focusing aid – or... – Dual purpose photoelement
Reexamination Certificate
1999-09-30
2001-02-27
Perkey, W. B. (Department: 2851)
Photography
With exposure objective focusing means, focusing aid, or...
Dual purpose photoelement
C396S121000, C396S165000, C396S234000
Reexamination Certificate
active
06195509
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exposure control apparatus for a camera having a focus detection device in which an exposure can be precisely determined by detecting backlight.
2. Description of the Related Art
In a conventional camera having a multi-point object-distance measuring device, the focusing operation upon an object to be taken is carried out by employing, for example, the smallest object distance (closest object) selected from among object distances obtained by a plurality of distance measuring areas.
The brightness of the object is calculated based on an algorithm for a predetermined photometering system, such as an averaged overall photometering system, a center-weighted photometering system, or a spot photometering system, using the measurements of the object brightness obtained in a plurality of split photometering areas (the number of which is usually larger than the number of the distance measuring areas) which are partly overlapped on the distance measuring areas. To detect backlight, the difference in the measurement between the central photometering area and the remaining photometering area(s) is calculated, wherein the difference is checked to determine whether the difference is above a predetermined value in order to determine the presence of backlight. Namely, the focusing is carried out based on the measurement of the object distance in one distance measuring area selected from the plurality of distance measuring areas, and the detection of backlight is carried out based on the measurements of the plurality of photometering areas, made independently from the selected distance measuring area.
However, in such a known exposure control apparatus for a camera, a plurality of distance measuring areas are partly overlapped on a plurality of photometering areas. However, the detection of backlight for the object to be taken can be inaccurate since the judgment is carried out based on the plurality of photometering areas, independent of the distance measuring area selected for the focusing operation. Consequently, an accurate exposure value cannot be obtained. For instance, assuming that there are first to sixth photometering areas and first to third distance measuring areas which overlap the fourth, fifth and sixth photometering areas, respectively, the distance data from the first distance measuring area is selected to focus on the object. If photometering data from the sixth photometering area is used as the main measurement of the object brightness, and if the difference in the main measurement between the sixth photometering area and other photometering area (for example, the second photometering area) is above a predetermined value, it is judged that the object includes backlight. In this judgment, the photometering data of the fourth photometering area corresponding to the first distance measuring area whose distance data is utilized, is not used to detect backlight, and hence it is impossible to judge whether the main object within the first distance measuring area (i.e., the object located within the distance measuring area for which the focusing should be carried out) is actually subject to backlight.
SUMMARY OF THE INVENTION
It is an object of the present invention to eliminate the above-mentioned drawback by providing an exposure control apparatus for a camera in which backlight can be more precisely detected so as to obtain an accurate exposure value.
The basic concept of the present invention resides in acquisition of photometering data of the object, on which the focusing should be carried out, from a focus detection device in a passive focusing device in which object photometering data is employed.
In order to achieve the above mentioned object, there is provided an exposure control apparatus for a camera including: a focus detection device for receiving object light to measure the object distance; a photometering device for receiving object light within a plurality of photometering areas to measure the object brightness; and a backlight detection device for obtaining a main photometering value based on the object light received by the focus detection device, and for detecting the presence of backlight based on the main photometering value and a reference photometering value measured by the photometering device.
Preferably, the focus detection device includes a plurality of distance measuring areas, so that the object distance of an object in one of the distance measuring areas is selected and used for the focusing operation, and wherein the backlight detection device detects the main photometering value based on the object light in the selected distance measuring area.
Preferably, the photometering area which is used for the detection of backlight by the backlight detection device is located in a picture plane closer to the periphery of the picture plane than a central portion thereof.
Preferably, the photometering area which is used for the detection of backlight by the backlight detection device is not overlapped on the selected distance measuring area.
Preferably, the distance measuring device includes a passive distance measuring device which detects a distance between object images formed on a pair of line sensors by a pair of image forming lenses, based on integral values obtained from light receiving elements of the line sensors, so that the object distance can be determined in accordance with the detected distance between the object images. The distance measuring device includes a quantization device for detecting the brightness of the object images formed on the line sensors as an integral time in which the integral value of each light receiving element reaches a predetermined value, and a calculation device for producing output of the integral time of each light receiving element in terms of a relative integral time to a reference integral time which is defined by the integral time in which the integral value reaches first a predetermined value. The backlight detection device determines a real reference (fundamental) brightness which is represented by an actual object brightness corresponding to the reference integral time, so that the actual object brightness can be calculated based on each relative integral time corresponding to the selected distance measuring area, wherein a mean value of the calculated actual object brightness is calculated to define a main photometering value which is used for the detection of backlight.
Preferably, a strobe device is also included for emitting strobe light upon exposure when the backlight detection device detects backlight.
Preferably, an exposure calculation device is also included for calculating an optimal exposure based on the photometering value of the photometering device, wherein when the backlight detection device detects backlight, the exposure calculation device corrects the exposure value in the direction of under exposure based on the detection of backlight.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 10-279990 (filed on Oct. 1, 1998) which is expressly incorporated herein by reference in its entirety.
REFERENCES:
patent: 4664495 (1987-05-01), Alyfuku et al.
patent: 4878081 (1989-10-01), Kishida et al.
patent: 5923910 (1999-07-01), Nakahara et al.
patent: 440171 (1991-08-01), None
patent: 570968 (1993-11-01), None
patent: 5-68203 (1993-03-01), None
English language abstract of JP 5-68203.
Asahi Kogaku Kogyo Kabushiki Kaisha
Greenblum & Bernstein P.L.C.
Perkey W. B.
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