Liquid crystal shutter control circuit for a video camera having a synchronized strobe flash

Claim 1

An electric shutter control apparatus for a video camera with an image pick-up device, for controlling the exposure time of light from an object onto said image pick-up device, said apparatus comprising: a lens system for said video camera arranged in front of said image pick-up device; first and second polarizing filter means with different respective polarizing angles arranged between said lens system and said image pick-up device; a liquid crystal device having a control terminal, arranged between said first and second polarized filter means; a synchronous circuit receiving an external synchronizing signal and producing therefrom a vertical synchronizing signal; first pulse generating means receiving said vertical synchronizing signal for generating a first pulse synchronized with said vertical synchronizing signal, said first pulse having a predetermined length of time; liquid crystal device control means receiving said first pulse for generating a signal for controlling an electrical field of said liquid crystal device to place said device in an ON state and allow the light from the object to be transmitted through said first and second polarizing filter means and said liquid crystal device for said predetermined length of time of said first pulse; second pulse generating means having an input connected to be triggered by said first pulse for generating a second pulse synchronized with said first pulse and with said vertical synchronizing signal; and external apparatus means receiving said second pulse for producing a light flash in response to said second pulse; wherein said first pulse generating means comprises: first multivibrator means for generating a shutter pulse in response to an operation of a shutter switch; and gate means for gating said vertical synchronizing signal during the time said shutter pulse is generated and producing said first pulse; and said liquid crystal device control means comprises: second multivibrator means for generating an output pulse having a predetermined length of time in response to said first pulse from said gate means; and third multivibrator means for generating said signal for controlling an electric field of said liquid crystal device in response to said output pulse from said second multivibrator means.