Electronic timing apparatus for controlling the duration of light emission of a flash unit

Claim 2

In combination with a flash device having a transconductive path and a trigger electrode and operable to emit a flash of light upon the application thereto of operating voltage through the transconductive path and the simultaneous application of an igniting pulse to the trigger electrode, an apparatus for automatically adjusting the operating duration of the flash device to obtain a controllable quantity of light energy therefrom, which comprises: normally disabled switching means interposed in the transconductive path for coupling the flash device to a source of operating voltage; detecting means for integrating a portion of the light energy contained in the emission from the flash device and for generating control signal that varies in proportion to the amount of light integrated; means for selectively applying an igniting pulse to the trigger electrode; and means coupled to the detecting means and to the applying means for enabling the switching means when an igniting pulse is applied to the trigger electrode and for subsequently disabling the switching means when the control signal has reached a predetermined value.

Claim 3

In an electronic timing apparatus wherein the duration of light energy emitted from a flash tube having a trigger electrode and a source of operating voltage is regulated to produce a predetermined quantity of emitted light energy: detecting means for integrating a portion of the emitted light to produce a control signal that varies in proportion to the amount of light integrated; a controllable gate serially connected with the main electrodes of the flash tube and the source of operating voltage and operative when open to apply operating voltage to the main electrodes, the gate having a control electrode responsive to signals of one polarity for opening the gate and responsive to signals of the opposite polarity for closing the gate; means for applying an igniting pulse to the trigger electrode of the flash tube; bipolar control means coupled to the applying means and to the detecting means for initially generating an output signal of the one polarity when an igniting pulse is applied to the trigger electrode and for subsequently terminating the last-mentioned signal and generating an output signal of the opposite polarity when the control signal has reached a predetermined value; and means for coupling the output signal of the bipolar control means to the control electrode of the gate.

Claim 4

In an electronic timing apparatus wherein the duration of light energy emitted from a flash tube having a trigger electrode and a source of operating voltage is regulated to produce a predetermined quantity of emitted light energy: detecting means for integrating a portion of the emitted light to produce a control signal that varies in proportion to the amount of light integrated; a controllable gate serially connected with the main electrodes of the flash tube and the source of operating voltage and operative when open to apply operating voltage to the main electrodes, the gate having a control electrode responsive to signals of one polarity for opening the gate and responsive to signals of the opposite polarity for closing the gate; means for applying an igniting pulse to the trigger electrode of the flash tube; bipolar control means coupled to the applying means and to the detecting means for initially generating an output signal of the one polarity when an igniting pulse is applied to the trigger electrode and for subsequently terminating the last-mentioned signal and generating an output signal of the opposite polarity when the control signal has reached a predetermined value; and means for coupling the output signal of the bipolar control means to the control electrode of the gate.

Claim 5

Apparatus as defined in claim 2 in; which the bipolar control means is a Schmitt trigger circuit.

Claim 6

Apparatus as defined in claim 2, in which the controllable gate is an interruptable thyristor having a transconductive path serially connected with the main electrodes of the flash tube, the transconductive path being rendered conductive upon the application of a voltage of the one polarity to its control electrode and rendered nonconductive upon the application of a voltage of the opposite polarity to its control electrode.

Claim 7

Apparatus as defined in claim 2, in which the detecting means comprises, in combination, a photosensitive element in operative association with the light emitted from the flash tube; a first capacitor; means for coupling the photosensitive element to the first capacitor and to the input of the bipolar means; and means for electrically exciting the photosensitive element when the gate is opened.

Claim 8

Apparatus as defined in claim 5, in which the applying means comprises, in combination, an ignition transformer having a primary winding coupled across the gate and the flash tube through a second capacitor; a secondary winding coupled to the trigger electrode of the flash tube; and means for momentarily short circuiting the primary winding and the second capacitor.

Claim 9

Apparatus as definEd in claim 6 in which the primary winding has an adjustable tap, and in which the apparatus further comprises means for coupling the adjustable tap to the input of the bipolar control means and to the first capacitor for establishing a reference voltage at the input of the bipolar control means.