Electronic flash system capable of automatic flash duration control

Claim 1

In an electronic flash system capable of automatically controlling the flash duration and comprising: a main discharge capacitor; a flash lamp for converting the energy stored in said main discharge capacitor into light; a photosensor circuit for providing an output signal in response to the light reflected back from a subject illuminated by the light emitted from said flash lamp; and a flash duration control circuit responsive to the output signal from said photosensor circuit for controlling the flash duration of said flash lamp, the improvement comprising: (a) a stored-voltage sensing circuit for sensing the voltage stored across said main discharge capacitor; (b) a first switching means which is controlled in response to the output from said storage-voltage sensing circuit; (c) an oscillator means which is controlled in response to the output from said first switching means; (d) a sound signal generating means coupled to said oscillator means for generating (i) a first sound signal of a first frequency in response to the output from said first switching means and (ii) a second sound signal, the frequency of which is different from said first frequency, in response to the output from a second switching means; (e) an operation mode sensing circuit for sensing the operation mode of said flash duration control circuit; and (f) a second switching means responsive to the output from said operation mode sensing circuit for controlling the mode of operation of said sound signal generating means.