Imaging device capable of carrying out automatic focusing with stable detection accuracy and at a high response speed

An automatic focusing imaging device comprising:

• an imaging element for forming an image of an image pick-up light from an object through a lens system to apply photoelectric conversion to said image pick-up light at a photoelectric conversion surface provided on said imaging element to provide a video signal, said imaging element and said lens system defining the elements of an optical pair;
• a camera circuit for processing said video signal subjected to photoelectric conversion by said imaging element to generate a luminance signal, said camera circuit utilizing one of a plurality of processing techniques including filtering and blanking;
• filter means for extracting, as an analog signal, a high frequency band component of said video signal, said filter means comprising a high-pass filter for extracting an edge signal corresponding to said high frequency band component;
• a detector for detecting said edge signal extracted by said high-pass filter to output a detected signal;
• a logarithmic converter for applying logarithmic conversion to said detected signal from said detector to provide a focal point voltage having a predetermined characteristic;
• an analog/digital converter for converting said focal point voltage to data in the form of a digital signal;
• calculation means for calculating in advance an in-focus position for at least one of the elements from said optical pair which includes said lens system and said imaging element where said high frequency band component takes a maximum level to generate a control signal, said calculation means being responsive to said in-focus position to generate said control signal, said calculation means comprising a microcomputer having means for dividing a screen captured by said imaging element into a plurality of blocks to extract for each of said blocks a high frequency band component to determine high frequency component information corresponding to each of said blocks to calculate an in-focus value for each of said blocks to determine an in-focus value for the entire screen by using calculated results for each block to generate said control signal for carrying out focusing;
• a lens drive mechanism responsive to said control signal for carrying out focusing by moving said at least one element of said optical pair;
• non-linear conversion means provided at the preceding stage of said analog/digital converter, and for correcting in advance deterioration of the quantization resolution of said high frequency band component quantized at the time of calculation of the in-focus position of said at least one element from said optical pair;
• detection means for detecting focal depth information from said lens system to output said information;
• and wherein said microcomputer is responsive to said focal depth information detected by said detection means to calculate said in-focus value indicative of the state where said lens system is in focus.