An arrangement for controlling the flash duration in photographic cameras. A light-sensitive element within the apparatus responds to light originating from the source for flash bulbs and reflected by the object or scene to be photographed. The flash bulb is ignited by an ignition circuit which also generates the operating voltage for the light-sensitive device. Through the application of a discharge tube which has a considerably lower internal resistance, when ignited, than the flash bulb, the latter becomes extinguished when the quantity of light reflected by the object or scene and impinging upon the light-sensitive device, is of a predetermined magnitude quantity.
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14. An electronic flash arrangement for photographic process, comprising, in combination, flash generating means for generating a flash; ignition means connected to said flash generating means for igniting said flash generating means upon external activation, thereby initiating said flash, said ignition means comprising an ignition transformer connected to said flash generating means, an ignition capacitor connected to said ignition transformer and a charging capacitor connected to said ignition capacitor in response to said external activation in such a manner that a d.C. voltage is created across said charging capacitor resulting from discharge of said ignition capacitor; light measuring means operative only after application of an operating voltage thereto, for responding to light during an exposure and furnishing a terminating signal when said light has reached a predetermined light quantity; means for connecting said ignition means to said light measuring means in such a manner that said d.C. voltage across said charging capacitor constitutes said operating voltage; and means connected to said light measuring means and said flash generating means for terminating said flash upon receipt of said terminating signal.
12. An electronic flash arrangement for a photographic process, comprising in combination, flash generating means for generating a flash; ignition means connected to said flash generating means for igniting said flash generating means upon external activation, thereby initiating said flash, said external activation creating a current flow in said ignition means, said ignition means further comprising means for furnishing a d.C. voltage only after the start of said current flow; light measuring means operative only after application of an operating voltage thereto, for responding to light during an exposure and furnishing a terminating signal when said light has reached a predetermined light quantity; means connecting said ignition means to said light measuring means in such a manner that said d.C. voltage constitutes said operating voltage; and means connected to said light measuring means for terminating said flash upon receipt of said terminating signal. 13. An electronic flash arrangement for a photographic process, comprising in combination, flash generating means for generating a flash; ignition means connected to said flash generating means for igniting said flash generating means upon external activation, thereby initiating said flash, said external activation creating a current flow in said ignition means, said ignition means further comprising means for creating a d.C. voltage only after the start of said current flow; light measuring means operative only after application of an operating voltage thereto, for responding to light during an exposure and furnishing a terminating signal when said light has reached a predetermined light quantity; means connecting said ignition means to said light measuring means in such a manner that said d.C. voltage constitutes said operating voltage; and means connected to said light measuring means for terminating said flash upon receipt of said terminating signal.
1. An electronic flash arrangement for photographic cameras comprising, in combination, flash bulb means; ignition means connected to said flash bulb means for igniting said flash bulb means; light measuring means for responding to light from said flash bulb means and reflected by the object to be photographed; said ignition means connected to the light measuring means in a way as to deliver a d.C. operating voltage for the light measuring means, so that said d.C. operating voltage prevails only after the ignition of the flash bulb means, said flash bulb means becoming extinguished after ignition when the light reflected by said object and impinging upon said light measuring means is of a predetermined
magnitude. 2. The electronic flash arrangement for photographic cameras as defined in claim 1 12 wherein said ignition means comprises an ignition transformer connected to said flash bulb means; and an ignition capacitor connected to said ignition transformer means; and a charging capacitor connected in series with said ignition capacitor and said ignition transformer means when said flash bulb means is ignited, the voltage across the charging capacitor resulting from charging discharge of said ignition capacitor and being said d.C. operating voltage for operating said light measuring means. 3. The electronic flash arrangement for photographic cameras as defined in claim 2 14 wherein the capacitance of said charging capacitor is large compared to the capacitance of said ignition capacitor. 4. The electronic flash arrangement for photographic cameras as defined in large as the capacitance of said ignition capacitor. 5. The electronic flash arrangement for photographic cameras as defined in claim 1 12 wherein said light measuring means includes the series connection of a light sensitive element, an adjustable resistor, and an integrating capacitor. 6. The electronic flash arrangement for photographic cameras as defined in claim 5 wherein said light sensitive element is a photoresistor. 7. The electronic flash arrangement for photographic cameras as defined in claim 5 including controlled silicon rectifying means with cathode-control electrode path connected to said integrating capacitor means, discharge tube means connected in parallel with said flash bulb means and ignited by said controlled rectifier means, the internal resistance of said discharge tube means being substantially smaller when ignited than the resistance of said flash bulb means. 8. The electronic flash arrangement for photographic cameras as defined in claim 7 including protective resistor means between said integrating capacitor means and said controlledcontrol electrode-cathode path of said controlled rectifier means. 9. The electronic flash arrangement for photographic cameras as defined in claim 7 including an ignition transformer connected to said discharge tube means for igniting the same; ignition capacitor means connected between said ignition transformer means and said controlled rectifier means; and voltage divider means connected to said ignition capacitor means and said controlled rectifier means. 10. The electronic flash arrangement for photographic cameras as defined in claim 9 including resistor means connected between said voltage divider means and the junction of said ignition capacitor means and said controlled rectifier means. 11. The electronic flash arrangement for photographic cameras as defined in claim 10 wherein said resistor means has a resistance value substantially of in the order of megohms. |
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The present invention resides in an electronic flash apparatus for photographic applications which includes a light meter fed from a DC operating voltage supply. The electronic control circuitry containing the light meter extinguishes the flash bulb used in conjunction with the flash apparatus as soon as the scene to be photographed has reflected a predetermined amount of light onto the light-sensitive element of the light meter.
Heretofore, an electronic flash apparatus has been available for the purpose of omitting the requirement to set the diaphragm of a photographic camera prior to each exposure because of the different distances between the flash apparatus and the scene to be photographed. The flash apparatus serves under these conditions the purpose of illuminating the scene to be photographed. With such electronic flash apparatus, the flash bulb becomes automatically extinguished when the scene to be photographed is sufficiently illuminated. In this manner, the object or scene being photographed is correctly illuminated in view of the condition that the duration of the flash is controlled through the amount of light reflected by the scene upon a light sensitive element.
The light meter includes, for this purpose, an integrating arrangement which integrates the electrical current derived from the light-sensitive element and actuates in response thereto, a control arrangement, as soon as the integrated current attains a predetermined value. The conventional means for integration is in the form of a capacitor which integrates the current derived from the light-sensitive element. The capacitor becomes charged, and when the voltage across the capacitor attains a predetermined value, the control arrangement becomes actuated and the flash bulb becomes thereby extinguished. It is known in the art that for the purpose of extinguishing the flash bulb, a discharge tube is used in parallel with the flash bulb. The discharge tube has a considerably lower internal resistance than the flash bulb when it is ignited. The discharge tube becomes thus ignited through the control arrangement or circuitry when the capacitor has attained a predetermined voltage level. The lower internal resistance of the ignited discharge tube causes the discharge of the storage capacitor which provides electrical energy for the flash bulb, and as a result the flash bulb becomes extinguished.
An electronic arrangement provided with such a control circuit, however, has the disadvantage that the photographic process or operation can be interfered with through the prevailing ambient light, as well as through the photographic flash resulting from another camera in the neighboring vicinity. The ambient light causes current to be generated through the light-sensitive element before actuation of the flash apparatus, and this current is applied to the capacitor which performs its integrating function. As a result, the capacitor possesses unpredictable initial voltage prior to initiation of the flash. In view of this condition, the time interval during which the predetermined voltage across the capacitor is attained, is no longer well defined. Furthermore, a remote flash from another apparatus in the vicinity, can actuate the control arrangement or circuitry of the flash apparatus under consideration, at an undesired instant of time. The result of such action is that the storage capacitor becomes thereby discharged.
In order to avoid interference through the ambient light, it has been previously proposed to omit the integrating capacitor and to provide a single and sole photoresistor of predetermined characteristics. With such an arrangement, however, interference resulting from remote flashes can still not be avoided.
It is also known in the art, to connect the light meter into the circuit first at the beginning of the flash through a switch or shutter mechanism. With such design, disturbances or interferences can be avoided from either the ambient light or remote flashes. Such design, however, requires rather careful and meticalous mechanical construction which is considerably complex and thereby costly to manufacture. At the same time, such mechanism and design does not operate reliably.
In accordance with the present invention, on the other hand, an arrangement is provided in which the ambient light as well as remote flashes are taken into account through a very simple and reliable manner. The present invention provides that the operating DC voltage is realized through the ignition of the flash bulb by an ignition current from an ignition circuit for the flash bulb. The arrangement in accordance with the present invention is based on electrical structure rather than mechanical parts, and thereby the control circuitry is principally switched on only during the flash. In this manner, interferences from remote flashes and ambient light cannot be incurred.
The flash bulb of an electronic flash apparatus becomes ignited through the application of an ignition capacitor operating in conjunction with an ignition transformer. The ignition capacitor is connected to the primary winding of the ignition transformer, and when a synchronizing shutterherein referred to as terminating signal, than it does when the illumination intensity is of lower magnitudes. The adjustable resistor 7 must be set, as already indicated, in accordance with the sensitivity of the film material being used.
A control silicon diode 11 in the form of a thyristor receives its anode potential by way of a large resistor 12 which may be of the order of approximately 10 megohms. The resistor 12 is connected to the tap or junction 19 of a voltage divider comprised of resistors 13 and 14. This voltage divider is connected across the voltage supply of 500 volts for the flash bulb 2. The control or starting electrode of the thyristor is connected with the integrating capacitor 8, by way of a protective resistor 9. The cathode of this thyristor, on the other hand, is connected to ground potential. The anode-cathode path of the thyristor is not conducting when the voltage between the control electrode and the cathode is below a predetermined value. As long as the thyristor is nonconducting, the ignition capacitor 15 for a discharge tube 17, also remains charged. The ignition capacitor 15 is connected to the junction 18 leading to the anode of the thyristor, and leading also to the tap 19 of the voltage divider of resistors 13 and 14, by way of the large resistor 12. The other terminal of the capacitor 15 leads to ground potential by way of the primary winding of an ignition transformer 16.
When ignition of the flash bulb 2 is initiated through the short circuiting cable switch 20, the voltage across the charging capacitor 5 becomes available as a DC operating voltage. The integrating capacitor 8 thus acquires a voltage sufficient to fire the thyristor 11, this voltage being herein referred to as a terminating signal, as a result of the current flow from the charging capacitor 5 and through the photoresistor 6. When the thyristor is thus fired and the anode-cathode path of the thyristor is conducting, the ignition capacitor 15 for the discharge tube 17, discharges through the thyristor. As a result of this discharge, a current pulse is realized in the primary winding of the ignition transformer 16. The discharge tube 17 becomes ignited through the secondary winding of this transformer 16. This discharge tube 17, when ignited has a considerably lower resistance than the flash bulb 2, and therefore the latter is extinguished when the discharge tube becomes ignited. As a result of such action, the object or scene to be photographed is no longer illuminated. The discharge tube 17 is mounted within the interior of the electronic flash apparatus, and is covered against the exterior environment.
After the flash bulb 2 is extinguished through the discharge tube 17, a small residual voltage prevails across the storage capacitor 1 and also at the tap or junction 19 of the voltage divider comprised of resistors 13 and 14. In order that the voltage at the anode of the thyristor 11, and thereby the junction 18, acquires a small value for the purpose of again turning off the thyristor, a large ohmic value is selected for the resistor 12. Thus, this resistor is selected so that it has a value of the order of 10 megohms. The integrating capacitor 8 chargesdischarges, after control of the thyristor 11 has been exercised, through the protective resistor 9 and the cathode-control electrode path towards ground potential.
Through closing of a switch 10, the electronic control arrangement for automotic automatic extinguishing of the flash bulb 2, may be made inoperative.
The component values indicated in the circuit diagram of the drawing, have been designated only for the purpose of illustrating the basis for the selection of the components. It is quite possible to provide, in cases, different values for these components.
It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above.
While the invention has been illustrated and described as embodied in electronic flash apparatus for cameras, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.
What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:
| Patent | Priority | Assignee | Title |
| 4091398, | Jan 31 1975 | Nippon Kogaku K.K.; Sato Koki K.K. | Electronic photoflash unit having remote control device transmitter function |
| 4217523, | Nov 18 1976 | West Electric Co., Ltd. | Photographic flash device |
| 4377774, | Oct 15 1976 | Minolta Camera Kabushiki Kaisha | Electronic flash control device |
| 5438239, | Aug 14 1980 | Fluorescent lamp ballast with light output control |
| Patent | Priority | Assignee | Title |
| 3033988, | |||
| 3340426, | |||
| 3350603, | |||
| 3350604, | |||
| 3519879, | |||
| 3591829, |
| Executed on | Assignor | Assignee | Conveyance | Frame | Reel | Doc |
| May 01 1972 | Robert Bosch Elektronik GmbH | (assignment on the face of the patent) | / |
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