Photography – With object illumination for exposure – With power supply detail
Reexamination Certificate
2001-06-07
2003-06-24
Adams, Russell (Department: 2851)
Photography
With object illumination for exposure
With power supply detail
Reexamination Certificate
active
06584286
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electronic flash apparatus and a camera having this electronic flash device.
2. Description of the Related Art
Many recent cameras have an electronic flash device. There are various types of cameras ranging from conventional fixed focus cameras to zoom cameras including a zoom lens. With the lenses of the recent cameras in the tele-side (long focus side of the lens), a distant object can be enlarged for photographing. Further, since the cameras having an electronic flash device have been reduced in size, users can carry these cameras with themselves more easily.
On the other hand, the electronic flash device requires a larger amount of charging energy to provide a proper quantity of light to a more distant object. Moreover, attempts are being made to reduce the size of the cameras and increase zoom magnification. As a result, the F No., which is indicative of the brightness of the lens on the tele-side, has increased (that is, the lens has become darker). This further increases the required amount of charging energy of the electronic flash device.
However, the reduced size of the cameras with the electronic flash device has led to several disadvantages such as a decrease in the total number of batteries (for example, lithium batteries) used as a power supply from two to one, thus reducing the power supply voltage. Further, such batteries have a high internal resistance. As a result, the amount of time required to charge the electronic flash disadvantageously increases.
Thus, there has been a demand for an electronic flash device which can reduce the charging time and a camera having such an electronic flash device.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an electronic flash device which reduces the charging time.
It is another object of the invention to provide an electronic flash device which is capable of performing charging operations suitable for manipulating and operating conditions of a camera.
It is a further object of the invention to provide an electronic flash device having a forward type booster circuit and a flyback type booster circuit and being capable of switching these two types of booster circuits to obtain proper charging time and charging efficiency.
To attain the above objects, a first aspect of the present invention provides an electronic flash device comprising a power supply, a main capacitor, a booster circuit for performing a boosting operation for increasing voltage from the power supply to thereby charge the main capacitor, the booster circuit having a forward type boosting section, and a flyback type boosting section, and a switching circuit for switching the boosting operation performed by the booster circuit from one performed by the forward type boosting section to one performed by the flyback type boosting section, during charging of the capacitor.
In a preferred form of the first aspect of the invention, the switching circuit switches the boosting operation performed by the forward type boosting section to the one performed by the flyback type boosting section after a charged voltage of the main capacitor has reached a predetermined value.
Alternatively, the switching circuit switches the boosting operation performed by the forward type boosting section to the one performed by the flyback type boosting section when a predetermined period of time has elapsed since charging of the capacitor was started.
In a preferred form of the first aspect of the invention, the forward type boosting section and the flyback type boosting section share an oscillation transformer connected in parallel to the main capacitor.
In a specific embodiment of the first aspect, the oscillation transformer has a primary coil and a secondary coil, and the forward type boosting section causes a current to flow through the primary coil of the oscillation transformer in a first direction to generate a current flowing from the secondary coil in a predetermined charging direction to thereby charge the main capacitor, and the flyback type boosting section causes a current to flow through the primary coil in a second direction opposite to the first direction to generate a current flowing from the secondary coil in the charging direction to thereby charge the main capacitor.
In a more specific form of this embodiment, the primary coil comprises a first coil, a second coil, and an intermediate terminal connecting between the first and second coils, the power supply having electrodes, the first and second coils being connected to one of the electrodes of the power supply, the intermediate terminal being connected to another one of the electrode of the power supply, and the forward type boosting section causing a current to flow through the first coil in the first direction to generate a current flowing from the secondary coil in the predetermined charging direction to thereby charge the main capacitor, while the flyback type boosting section causing a current to flow through the second coil in the second direction opposite to the first direction to generate a current flowing from the secondary coil in the charging direction to thereby charge the main capacitor.
Alternatively, the forward type boosting section and the flyback type boosting section each have an oscillation transformer connected in parallel to the main capacitor.
To attain the above objects, a second aspect of the present invention provides an electronic flash device incorporated in or mounted on a camera, comprising a power supply, a main capacitor, a booster circuit for performing a boosting operation for increasing voltage from the power supply to thereby charge the main capacitor, the booster circuit having a forward type boosting section, and a flyback type boosting section, and a selecting circuit for selecting the forward type boosting section or the flyback type boosting section depending on an operating status or an operative state of the camera.
In a specific form of the second aspect of the invention, the selecting circuit selects the forward type boosting section when the camera is in an operative state for preparing for photographing, and selects the flyback type boosting section before the camera is set in the operative state for preparing for photographing.
Specifically, for example, the selecting circuit selects the forward type boosting section or the flyback type boosting section depending on an operating state of a release operating member of the camera. For example, the camera is set into the operative state for preparing for photographing by a remote control operation.
To attain the above objects, a third aspect of the present invention provides an electronic flash device incorporated in or mounted on a body of a camera, comprising a main capacitor, a flyback type booster circuit for charging the main capacitor with a driving current which can be variably set, and a control circuit for causing the flyback type booster circuit to charge the main capacitor by setting the driving current from the flyback type booster circuit to a predetermined first value, when the camera is in an operative state for preparing for photographing, and by setting the driving current from the flyback type booster circuit to a predetermined second value which is smaller than the first predetermined value, before the camera is in the operative state for preparing for photographing.
To attain the above objects, a fourth aspect of the present invention provides an electronic flash device incorporated in or mounted on a body of a camera, comprising a main capacitor, a forward type booster circuit for charging the main capacitor, the forward type booster circuit having a first transformer, and a second transformer having a smaller turn ratio than the first transformer, and a control circuit for using the first transformer to charge the main capacitor when the camera is in an operative state for preparing for photographing, and for using the second transformer to charge the main capacitor before the camera is in
Ichimasa Shoji
Odaka Yukio
Adams Russell
Canon Kabushiki Kaisha
Robin Blecker & Daley
Smith Arthur A
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