Photography – Flash system responsive to focal length or distance
Reexamination Certificate
1999-09-14
2001-05-29
Perkey, W. B. (Department: 2851)
Photography
Flash system responsive to focal length or distance
C396S123000, C396S130000, C396S159000
Reexamination Certificate
active
06240253
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an automatic focusing camera having a focus locking function for locking the focus when its taking lens focuses on a subject and having a plurality of distance-measurement areas from which to obtain information to be used for focus adjustment of the taking lens. The present invention relates also to a camera that performs light amount control in such a way that emission of light for illuminating the subject is stopped when the amount of light reflected from the subject reaches a predetermined level.
2. Description of the Prior Art
An automatic focusing camera is provided with a focus locking function for locking the focus of its taking lens when the taking lens focuses on a subject. This permits the user to change the composition of the picture to be shot freely after having focused the taking lens on the subject. On the other hand, in flash shooting, an automatic focusing camera performs light amount control by emitting illumination light while detecting the light reflected from the subject so that emission of the illumination light will be stopped when the detected amount of received light reaches a predetermined reference level.
In recent years, automatic focusing cameras have been proposed that are provided with a plurality of distance-measurement areas used to obtain information necessary for focus adjustment of the taking lens and a plurality of light-amount-control areas used to detect the amount of flash illumination light necessary for light amount control in flash shooting, with these distance-measurement and light-amount-control areas arranged so as to show correspondence between them.
FIGS. 28 and 29
schematically show configurations for achieving light amount control in such automatic focusing cameras.
These cameras have a multiple-point distance-measurement means having a plurality of distance-measurement areas and a multiple-area light-amount-control means having a plurality of light-amount-control areas including those which correspond to the distance-measurement areas. In the individual distance-measurement areas of the multiple-point distance-measurement means, acquisition and output of distance-measurement information are performed constantly to make such information available for detection of the focus condition of the taking lens with respect to the subject and for focus adjustment. When the distance-measurement information from any of the distance-measurement areas leads to a determination that the taking lens is focused on the subject, focus adjustment of the taking lens is stopped and thereby the focus is locked.
In flash shooting, the multiple-area light-amount-control means detects the reflection of emitted illumination light so that emission of the illumination light will be stopped when the sum of the amount of light received in the individual light-amount-control areas reaches a reference level. The contribution ratios of the individual light-amount-control areas used in calculating the sum of the amount of received light and the reference level are variable according to the position of the subject. The multiple-area light-amount-control means evaluates the position of the subject within the shooting range on the basis of the distance-measurement information of the individual distance-measurement areas output from the multiple-point distance-measurement means, and, in accordance therewith, determines the contribution ratios and the reference level. In this way, the subject is illuminated to appropriate brightness.
The camera shown in
FIG. 28
has an on-focusing information output means by which the distance-measurement information output from the multiple-point distance-measurement means when the focus is locked is fed to the multiple-area light-amount-control means. By contrast, the camera shown in
FIG. 29
has an on-shooting information output means by which the distance-measurement information output from the multiple-point distance-measurement means immediately before shooting is fed to the multiple-area light-amount-control means. Accordingly, the contribution ratios of the individual light-amount-control areas and the reference level are determined, in the camera shown in
FIG. 28
, when the focus is locked and, in the camera shown in
FIG. 29
, immediately before shooting.
There have also been proposed automatic focusing cameras that are provided with a plurality of photometry areas used to detect brightness necessary for exposure control, with some of those photometry areas corresponding to a plurality of distance-measurement areas.
FIGS. 30 and 31
schematically show configurations for achieving exposure control in such automatic focusing cameras. These cameras have a multiple-point distance-measurement means having a plurality of distance-measurement areas, a multiple-area photometry means having a plurality of photometry areas including those which correspond to the distance-measurement areas, and an exposure-control means for controlling exposure by adjusting the shutter speed and the diaphragm.
The exposure-control means, giving weights to the amount of light detected in the individual photometry areas of the multiple-area photometry means, calculates a weighted mean thereof, and performs exposure control on the basis of the resulting value. The weights given to the individual photometry areas are variable according to the position of the subject within the shooting range. The exposure-control means evaluates the position of the subject on the basis of the distance-measurement information of the individual distance-measurement areas output from the multiple-point distance-measurement means, and, in accordance therewith, determines the weights. In this way, exposure is controlled, with the brightness of the background taken into consideration, so that the subject will be shot with appropriate brightness.
The camera shown in
FIG. 31
has an on-focusing information output means by which the distance-measurement information output from the multiple-point distance-measurement means when the focus is locked is fed to the exposure-control means. Accordingly, the weights given to the individual photometry areas are determined when the focus is locked.
With any of these cameras, when the user changes the direction of the camera after the focus has been locked, or when the subject moves after the focus has been locked, the picture composition changes. However, with the camera shown in
FIG. 28
, where the contribution ratios of the light-amount-control areas and the reference level are determined when the focus is locked, changing the picture composition after locking the focus makes the already-determined contribution ratios and reference level inconsistent with the picture composition with which shooting is actually performed. Thus, it is impossible to achieve appropriate light amount control.
This problem does not occur with the camera shown in
FIG. 29
, where the contribution ratios of the light-amount-control areas and the reference level are determined immediately before shooting. However, there is no guarantee that the subject will invariably be caught in any of the distance-measurement areas immediately before shooting, and, even if the subject is caught in any of the distance-measurement areas, there is a possibility that low contrast will hamper acquisition of distance-measurement information sufficient to identify the subject. In such a case, it is impossible to determine the contribution ratios and the reference level in accordance with the position of the subject, and thus it is difficult to achieve appropriate light amount control.
There has also been proposed a method of preliminarily emitting illumination light immediately before shooting so that, on the basis of the reflection thereof, the reference value to be used to stop emission of the illumination light will be determined. However, this requires provision of an extra mechanism for controlling preliminary emission of illumination light, and thus requires a complicate camera design
Ichikawa Tsutomu
Nakamaru Akio
Ohmori Shigeto
Suzuki Tatsuya
Tsujimura Ichiro
Burns Doane , Swecker, Mathis LLP
Minolta Co. , Ltd.
Perkey W. B.
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