Photography – With object illumination for exposure – Having artificial illumination termination control
Reexamination Certificate
2001-05-31
2003-03-18
Adams, Russell (Department: 2851)
Photography
With object illumination for exposure
Having artificial illumination termination control
C396S161000
Reexamination Certificate
active
06535692
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a camera with a built-in electronic flash device and an electronic flash device provided with an automatic emission control circuit which emits a flash light, receives reflected light having been reflected by an photographic object by a light receiving element, and stops the emission of the flash light when the reflected light reaches a specified amount.
It has been heretofore known an automatic control electronic flash device which emits a flash light, receives reflected light having been reflected by a photographic object by a light receiving element provided in an electronic flash circuit, and stops the emission of the flash light when the reflected light reaches a specified amount; it has been proposed to build such an automatic control electronic flash device in a lens-fitted film unit or a simple camera. According to this, without providing a complex flash-automatic stop mechanism which varies the aperture stop in accordance with the photographing distance, a proper exposure can be always obtained regardless of the variation of the photographing distance, because the amount of flash light varies in accordance with the photographing distance with the aperture stop kept constant.
In the case where such an automatic control electronic flash device as mentioned in the above is built in a lens-fitted film unit or a simple camera, automatic emission control can be made from the shortest distance to the longest distance. In the above, the shortest distance implies the shortest photographing distance determined by the limit of exposure and focusing, and the longest distance implies the longest photographing distance determined by the guide number at full emission of flash light and the predetermined constant aperture stop value. To practice an automatic emission control at a distance falling within the above-mentioned range implies theoretically that a flash light is emitted in such a manner as to reach a light quantity suitable corresponding to the guide number, that is, the product of the constant aperture stop value multiplied by the photographing distance.
However, practically it is difficult to control the light quantity in such a manner as to reach the theoretical amount of light emission; a dispersion of the amount of light emission is produced owing to a dispersion of electrical parts etc. In order to make the amount of light emission having such a dispersion come close to the theoretical amount of light emission, it has been necessary to use high-priced electrical parts having very little dispersion or to make an adjustment for each device using a variable resistor or the like. As the result of this, an electronic flash device provided with an automatic emission control circuit became of high price, which made it difficult to build it in a lens-fitted film unit or a simple camera to which low price is essential.
In view of the above-mentioned problem, the inventors, after having carried out various photographing tests using a color negative film, found out an emission control level without practical problem even if there is a dispersion to some extent. It is an object of this invention to propose a camera with a built-in electronic flash device and an electronic flash device provided with an automatic emission control circuit having such an emission control level.
Further, another object of this invention will be explained below.
It has been heretofore known an electronic flash device which emits flash light, receives reflected light having been reflected by a photographic object by a light receiving element provided in an electronic flash circuit, and stops the emission of the flash light by actuating a thyristor when the reflected light reaches a specified amount; it has been proposed to build such an electronic flash device in a lens-fitted film unit or a simple camera. According to this, without providing a complex flash-automatic stop mechanism which varies the aperture stop in accordance with the photographing distance, a proper exposure can be always obtained regardless of the variation of the photographing distance, because the amount of flash light varies in accordance with the photographing distance with the aperture stop kept constant.
A switching device composed of a thyristor or the like has a characteristic such that the performance varies in accordance with the variation of environmental temperature. Accordingly, if a switching device is used in an electronic flash device provided with an automatic emission control circuit, the emission control capability varies with temperature variation. Further, if the emission control capability is varied too much by the temperature dependence of the switching device, a proper exposure cannot be made for a film, which makes it meaningless to build an automatic emission control circuit in the flash device. For this reason, it is necessary to use a switching device having a temperature characteristic regulated in a certain range; however, heretofore it has not been known how to regulate the temperature characteristic of a switching device for an automatic emission control circuit.
This invention has been made in view of the above-mentioned problem; it is another object of this invention to propose an electronic flash device provided with an automatic emission control circuit having the temperature characteristic of the switching device regulated within a proper range.
On the other hand, the less becomes the variation of the emission control capacity owing to the temperature characteristic of the switching device composed of a thyristor or the like, the more desirable it is for the automatic emission control circuit.
This invention has been made in view of the above-mentioned problem; it is still another object of this invention to propose an electronic flash device provided with an automatic emission control circuit which is less susceptible to the influence of the temperature characteristic of the switching device.
Further, it was large the size of a switching device composed of a thyristor or the like for use in an electronic flash device provided with a conventional automatic emission control circuit, and its unit price also was high. For this reason, it has been difficult to build an electronic flash device provided with an automatic emission control circuit in a lens-fitted film unit or a simple camera which is of small size and of low price.
This invention has been made in view of the above-mentioned problem; it is still another object of the invention to propose an electronic flash device provided with an automatic emission control circuit having a small-sized and low-priced switching device.
SUMMARY OF THE INVENTION
The above-mentioned objects can be accomplished by any one of structures described below.
Structure 1: A camera with a built-in electronic flash device comprising a photographing lens, an aperture stop, a flash emitting portion, a light receiving element for receiving reflected light by a photographic object which has been emitted by the flash emitting portion, and a flash circuit for making the flash emitting portion emit light having an automatic emission control circuit which stops the emission of the flash emitting portion when the amount of the reflected light received by the light receiving element reaches a specified value, wherein with respect to the automatic emission control circuit, A min satisfies the following conditional expression for a theoretical exposure value A,
(
A−
1)
EV≦A
min≦(
A+
0.5)
EV,
where A min is a minimum exposure value for a recording medium on which a specified photographic object is recorded when the photographic object located at a distance falling within a range from a specified shortest distance to a distance determined by the guide number of the flash emitting portion at full emission and the aperture stop is photographed.
Structure 2: A camera with a built-in electronic flash device as set forth in structure 1, wherein A max and the aforesaid minimum exposure value A min satisfy the followi
Hosaka Takao
Nakanishi Hiromi
Adams Russell
Konica Corporation
Muserlian Lucas and Mercanti
Smith Arthur A
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