Photography – Flash system responsive to focal length or distance
Reexamination Certificate
2003-08-18
2004-10-05
Adams, Russell (Department: 2851)
Photography
Flash system responsive to focal length or distance
C396S157000
Reexamination Certificate
active
06801716
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2002-246684, filed on Aug. 27, 2002, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electronic flash device for use with a camera, in particular, to a control device for use with an electronic flash device. In addition, the present invention relates to a photographing system having an electronic flash device and a camera.
2. Description of the Related Art
A discrete flash and an FP flash are known as flash systems of electronic flash devices for use with cameras. The discrete flash system flashes immediately after a shutter curtain is fully opened. On the other hand, the FP flash system repeatedly flashes, during the entire slit exposure with a shutter curtain not fully opened, at time intervals as the flashes are recognizable as flat light. The flash duration of the FP flash is longer than that of the discrete flash. Thus, the FP flash consumes much power than the discrete flash. As a result, the maximum flash intensity (referred to as 1/1 flash) of the FP flash is smaller than that of the discrete flash.
Japanese Unexamined Patent Publication Application No. HEI 5-45706 discloses a photographing system that performs the FP flash. A camera and a flash device of the photographing system share information of an object distance, an f-number of a lens, an exposure time (shutter speed), a film sensitivity, and so forth. The flash device is capable of selecting a flash duration that covers the exposure time. In addition, the flash device calculates a proper object distance at which an object is illuminated with a proper light amount based on data on a flash intensity, an f-number, a film sensitivity, and so forth that depend on a selected flash duration and displays the obtained proper object distance.
Also known is an electronic flash device that automatically switches a flash mode between the discrete flash mode and the FP flash mode depending on the exposure time and that allows the user to select one of flash intensities on display such as 1/1 flash, 1/2 flash, . . . , and 1/64 flash. Such an electronic flash device calculates a proper object distance for display in accordance with a selected flash intensity and a photographing condition such as an f-number.
In the foregoing photographing system, when a displayed proper object distance is different from an actual object distance, the user needs to adjust the system to reduce the difference for the purpose of taking a picture with a proper exposure amount. Specifically, the user needs to move or change a photographing condition such as an f-number to have the actual object distance closer to the displayed proper object distance. Thus, there has been demand for a photographing device that is able to set an appropriate photographing condition with less user's manipulation without changing the object distance.
In the foregoing electronic flash device, if the user does not want to change the object distance, he or she should select a flash intensity and then input several f-numbers until the displayed proper object distance is close to the actual object distance. For example, if the exposure time of the camera automatically increases because the luminance of an object has decreased, the flash mode is automatically switched from the FP flash mode to the discrete flash mode. In this case, even with the device in a photographing condition in which an object is illuminated with a proper exposure amount in the FP flash mode, the user should re-set an f-number in the discrete flash mode. Thus, the user should be familiar with the settings of both of the discrete flash mode and the FP flash mode. This is because even if the discrete flash and the FP flash are both the same 1/1 flash, the flash intensity of the discrete flash is different from that of the FP flash and the expression for obtaining the proper object distance in the discrete flash is different from that in the FP flash.
More specifically, the proper object distance in the discrete flash depends on the flash intensity, the f-number, and the film sensitivity. On the other hand, the proper object distance with the FP flash depends on the exposure time in addition to these parameters. In other words, obtaining a proper photographing condition in the FP flash is more complicated than that in the discrete flash because the FP flash requires one more parameters than the discrete flash. Meanwhile, there has been another demand for an electronic flash device that the user can easily set a photographing condition for setting a proper exposure amount in the same manner regardless of a type of flash mode.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a flash control device that automatically sets a photographing condition for setting a proper exposure amount and eliminates the necessity for the user to change an object distance as much as possible.
Another object of the present invention is to provide a flash control device that properly switches the flash mode between the discrete flash mode and the FP flash mode and sets a photographing condition for setting a proper exposure amount, thereby eliminating the user's trouble in caring about the setting of the flash mode.
Another object of the present invention is to provide an electronic flash device that has the foregoing flash control device.
Another object of the present invention is to provide a photographing system that has the foregoing electronic flash device.
The present invention is a flash control device for use with an electronic flash device which has switchable flash modes as a discrete flash mode for a discrete flash and an FP flash mode for an FP flash. The flash control device comprises: a distance input part for inputting an object distance; a calculating part; and an emission control part. When the electronic flash device is in the FP flash mode, the calculating part calculates a proper flash intensity in accordance with the object distance and an f-number, a sensitivity, and an exposure time of a camera. The proper flash intensity refers to a degree of intensity necessary for illuminating an object with a proper light amount. When the electronic flash device is in the discrete flash mode, the calculating part calculates the proper flash intensity in accordance with the object distance, the f-number, and the sensitivity. The emission control part instructs the electronic flash device to flash with the proper flash intensity. The flash control device controls the flashing so that the object is illuminated with a proper exposure amount. Thus, the flash control device according to the present invention may realize an effect that even beginner-level users who are not familiar with flash settings as the discrete flash, the FP-flash, and so forth can easily set a flash intensity for setting a proper exposure amount.
According to one of the aspects of the flash control device of the present invention, when the electronic flash device is in the discrete flash mode, the calculating part calculates the proper flash intensity which is proportional to the square of the object distance and the square of the f-number and is inversely proportional to the sensitivity. When the electronic flash device is in the FP flash mode, the calculating part calculates the proper flash intensity which is proportional to the square of the object distance and the square of the f-number and is inversely proportional to the sensitivity and the exposure time.
According to another aspect of the flash control device of the present invention, when the exposure time is shorter than an X-Sync shutter speed of a shutter of the camera, the emission control part switches the flash mode of the electronic flash device to the FP flash mode. When the flash mode is switched, the calculating part calculates a new proper flash intensity without changing the object distance.
Adams Russell
Nikon Corporation
Smith Arthur A
LandOfFree
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