Abstract: By rotating a diaphragm in front of a pickup device, for example a pyroelectric vidicon, eddy currents are generated in the diaphragm if the diaphragm is made of a metal. These eddy currents are generated as a result of the interaction between the moving diaphragm and the magnetic field of the deflection coils of the vidicon. If the diaphragm is instead made of an insulating material, separation of charges occurs on it as a result electrostatic generation, due to the interaction between the diaphragm and the electrostatic field of the vidicon. Compensation of the charge separation causes interference in the video signal. According to the invention a diaphragm of an insulating material is used which is covered with a pattern of electrically conductive tracks or a very high resistance layer. As a result of this no eddy currents and no noteworthy electrostatic charges can occur, so that an interference-free video signal is obtained.

Abstract: Infrared pick-up device comprising an infrared sensitive television pick-up tube and a diaphragm, which is alternately in the open and closed state, the amplitude of the available video signal being proportional to the speed at which the temperature changes, an additional, uniform radiation being superimposed on the scene radiation which can be changed so by a signal processing stage connected to the pick-up tube that the quantity of the average scene radiation plus the superimposed additional radiation is substantially equal to the radiation coming from the diaphragm in the closed state and acting on the target plate of the pick-up tube.