Automatic diaphragm control device for use IWT CCTV camera

Claim 2

An automatic diaphragm control device for use with a CCTV camera in which a video signal applied from the CCTV camera is utilized for diaphragm control, said automatic diaphragm control device comprising: first means for continuous control of the video signal with respect to an absolute brightness of an object to be picked up; second means for continuous control of a proportion of the video signal corresponding to a bright portion in the whole picture when a ratio of the bright portion to a dark portion of this object is relatively high; and third means for stabilization of a control signal, which has been obtained by said first and second means and then rectified, with respect to a source voltage.

Claim 3

An automatic diaphragm control device for use with a CCTV camera in which a video signal applied from the CCTV camera is utilized for diaphragm control, said automatic diaphragm control device comprising: first means consisting of an inverting amplifier adapted for inverse amplification of the video signal applied from the CCTV camera with a variable degree of amplification and for continuous control of the video signal with respect to an absolute brightness of an object to be picked up; second means consisting of a limiter circuit connected to said inverting amplifier for continuous limitation of the video signal inversely amplified by said inverting amplifier and characterizing the bright portion in the whole picture; a voltage doubling rectifier adapted for rectification of the inverted signal obtained by said inverting amplifier and said limiter circuit; third means adapted to stabilize the rectified signal obtained in said voltage doubling rectifier at a level lowered by a predetermined voltage with respect to a middle point voltage intermediate the source voltage; and a comparator adapted to compare the rectified signal thus stabilized with said middle point voltage to produce a diaphragm control signal.

Claim 4

An automatic diaphragm control device for use with a CCTV camera in which a video signal applied from the CCTV camera is utilized for diaphragm control, said automatic diaphragm control device comprising: first means consisting of an inverting amplifier adapted for inverse amplification of the video signal applied from the CCTV camera with a variable degree of amplification and for continuous control of the video signal with respect to an absolute brightness of an object to be picked up; second means consisting of a limiter circuit connected to said inverting amplifier for continuous limitation of the video signal inversely amplified by said inverting amplifier and characterizing the bright portion in the whole picture; a voltage doubling rectifier adapted for rectification of the inverted signal obtained by said inverting amplifier and said limiter circuit; third means adapted to stabilize the rectified signal obtained in said voltage doubling rectifier at a level lowered by a predetermined voltage with respect to a middle point voltage intermediate the source voltage; and a comparator adapted to compare the rectified signal thus stabilized with said middle point voltage to produce a diaphragm control signal.

Claim 5

A device according to claim 2, wherein the inverting amplifier as the first means is so arranged to provide a low gain when the optimum video signal of the television camera is at a high level and to provide a high gain when the optimum video signal of the television camera is at a low level in order to maintain input/output characteristic uniform.

Claim 6

A device according to claim 2, wherein the second means comprises a switching transistor adapted to be continuously controlled at will adjacently to or remotely from the camera objective itself.

Claim 7

A device according to claim 2, wherein the third means is so arranged to stabilize the control signal at a level lowered by a predetermined voltage with the middle point voltage equal to a half of the source voltage and thereby to maintain the diaphragm value once adjusted under a given source voltage constant.