Abstract: A pyroelectric camera tube having a high resistivity target is operated by applying an increasing ramp voltage to the target so as to provide a pedestal potential which permits objects producing a negative change in temperature to be viewed and then pulsing the target to neutralise the resultant electric field established between the signal and electron beam scanned surfaces of the target. Thus during the rising ramp voltage the tube operates in a cathode potential stabilised mode and at the end of the ramp the target is pulsed to operate the tube in an anode potential stabilised mode. Since the pedestal voltage is provided by the ramp voltage the tube may be substantially evacuated.