Circuit for stabilizing the black level in an output signal of a camera tube in a color television camera

A circuit for stabilizing a black level of an output signal of a camera tube in a color television camera in which said camera tube includes an optical filter means having an optically black part extending in parallel with a beam scanning direction of the camera tube, said stabilizing circuit comprising:

• a clamping circuit means for clamping an output signal of the camera tube during a horizontal beam blanking period and for restoring a DC component of the output signal;
• means responsive to a sampling pulse supplied every vertical scanning period for sampling and holding an output signal of the clamping circuit;
• and feedback circuit means for substantially negatively feeding back a holding voltage from said sampling and holding circuit to the clamping circuit, in which the optical filter means is mounted to the camera tube so that the optically black part of the optical filter means is nominally offset from the predetermined position by a specific distance which is determined by a maximum mounting error with respect to the center of the photoconductive surface.