Photography – With object illumination for exposure
Reexamination Certificate
2000-06-23
2001-11-06
Adams, Russell (Department: 2851)
Photography
With object illumination for exposure
C396S168000, C396S187000
Reexamination Certificate
active
06314243
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to an electronic flash light-emission controlling apparatus and a camera with a built-in electronic flash. More particularly, this invention relates to technics that are applied to a camera that can perform a shooting with an appropriate exposure by utilizing the electronic flash.
2. Description of Related Art
U.S. Pat. No. 6,029,015 discloses a camera whose electronic flash is used even under conditions (external light brightness) in which an appropriate exposure can be obtained without the light of the electronic flash. U.S. Pat. No. 5,765,057 discloses a camera that prohibits an electronic flash from emitting a light when the brightness exceeds a predetermined brightness and the subject distance is longer than a predetermined distance.
In the case of a programmed shutter that adjusts an exposure by determining an aperture and a shutter speed from an opening shape of the shutter, an opening value of the shutter is determined according to an exposure value calculated from the brightness and the film speed and a range of the opening value within which the electronic flash can emit a light. In the camera disclosed in U.S. Pat. No. 5,765,057 that prohibits the electronic flash from emitting the light when the brightness exceeds the predetermined brightness and the subject distance is longer than the predetermined distance, however, the electronic flash may emit the light and may not emit the light even if an expected value of an exposure by the electronic flash is the same. Thus, the camera may waste energy. That problem occurs especially when the subject distance is long.
Even under conditions in which a shooting is possible by an AE control, for example, when the external light brightness is enough, the light of the electronic flash cancels a shade. But, if the electronic flash is used when the subject distance is short, the exposure by the electronic flash is excessive with respect to a control target value due to a restriction of an opening value of the shutter for a light-emission control of the electronic flash.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an electronic flash light-emission controlling method and apparatus and a camera that can save energy by estimating an exposure by an electronic flash and prohibiting an unnecessary light-emission of the electronic flash according to the estimated value and prevent an excessive overexposure when the subject distance is short.
The above subject can be accomplished by providing an electronic flash light-emission control method of adjusting a total exposure at a shooting by controlling a light-emission of an electronic flash with a programmed shutter in which an aperture of a lens and a shutter speed are determined on the basis of an exposure value determined from a subject brightness and a film speed, comprising the steps of: finding a control value for obtaining a target exposure according to at least a subject distance, a guide number of said electronic flash and the film speed; estimating an exposure by the electronic flash when said electronic flash emits a light according to the control value while an operation of said programmed shutter that is determined according to the exposure value determined from the subject brightness obtained by a photometry and the film speed is taken into consideration; and prohibiting the light-emission of the electronic flash when the estimated value of the exposure by the electronic flash is out of a predetermined permissible range with respect to the target exposure.
According to the present invention, the exposure by the electronic flash is estimated while an opening restriction of the shutter or a diaphragm by the programmed shutter is taken into consideration, and an unnecessary light-emission of the electronic flash is prohibited according to the estimated value. Therefore, energy can be saved and an excessive overexposure can be prevented.
A control target value of the exposure by the electronic flash according to the subject distance and the subject brightness may be previously prepared, and the control value may be determined according to the control target value. In this case, light-emission prohibition conditions for prohibiting the light-emission of the electronic flash may be found, and data of the control target value of the exposure by the electronic flash may be corrected with the light-emission prohibition conditions.
The above subject can be accomplished by providing an electronic flash light-emission control method of adjusting a total exposure at a shooting by controlling a light-emission timing of an electronic flash in association with an opening and closing control of a shutter that also works as a diaphragm and adjusts an aperture and a shutter speed by controlling an opening shape formed by said shutter, comprising: a first step of finding a first opening value for obtaining a target exposure according to at least a subject distance, a guide number of said electronic flash and the film speed; a second step of finding a range of a second opening value that can be controlled as a timing of the light-emission of the electronic flash according to an exposure value determined from the subject brightness obtained by a photometry and the film speed; and a third step of prohibiting the light-emission of the electronic flash when the subject brightness exceeds a predetermined reference value and the first opening value is more than a predetermined value, lower than a minimum value of the range of the second opening value.
The first opening value may be found according to a predetermined control target value of the exposure of the electronic flash as well as the subject distance, the guide number and the film speed, in the first step.
The electronic flash light-emission control method may comprise a step of prohibiting the light-emission of the electronic flash when the subject brightness exceeds a predetermined reference value and the first opening value is more than a predetermined value, higher than a maximum value of the range of the second opening value, instead of the third step or in addition to the third step. The predetermined value is preferably found according to a latitude of a photo film.
The above subject can be accomplished by providing an electronic flash light-emission control apparatus that has a shutter that also works as a diaphragm and adjusts an aperture and a shutter speed by controlling an opening shape formed by said shutter, an electronic flash part that emits a light in association with an opening and closing control of said shutter and a controlling device that adjusts a total exposure at a shooting by controlling a light-emission timing of said electronic flash part, comprising: a device that finds a first opening value for obtaining a target exposure according to at least a subject distance, a guide number of an electronic flash and the film speed; and a device that finds a range of a second opening value that can be controlled as a timing of the light-emission of the electronic flash according to an exposure value determined from the subject brightness obtained by a photometry and the film speed; wherein said controlling device prohibits the light-emission of the electronic flash when the subject brightness exceeds a predetermined reference value and the first opening value is more than a predetermined value, lower than a minimum value of the range of the second opening value.
Target value data of a control target value of the exposure by the electronic flash may be previously prepared, and the first opening value may be found according to the subject distance, the guide number of the electronic flash, the film speed and the control target value.
A controlling device, that prohibits the light-emission of the electronic flash when the subject brightness exceeds a predetermined reference value and the first opening value is more than a predetermined value, higher than a maximum value of the range of the second opening
Adams Russell
Fuji Photo Optical Co., Ltd.
Smith Arthur A
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