The optically isolated trigger input can accept a floating current source which is not referenced to the camera ground.  Alternatively, a ground referenced circuit can be made to source or sink current through the trigger input.  The optically isolated GPO is an open-collector current sink output.  If optical isolation is not required then the 3.3V HCMOS General Purpose outputs can be used instead.  For further information please refer to the pin assignment chart.

External circuit example 1 : HCMOS source trigger

External circuit example 2 : HCMOS sink  trigger

External circuit example 3 : Pushbutton switch trigger

External circuit example 4 : GPO to trigger other cameras