| 摘要 |
PURPOSE:To attain automatic focus detection and adjustment from a video signal without using a special optical system and a photoelectric element by providing a gate signal generating circuit and a gate circuit outputting a chrominance signal from a video amplifier when the gate signal is inputted so as to input the chrominance signal through the gate circuit. CONSTITUTION:Only when the incident luminous intensity of the 3 primary colors is equal in a video signal, the gate circuit 6 is opened and a 3-primary color photoelectric output is fed to a comparison discrimination circuit 7. Then a green light signal output is large, red and blue signal outputs are small and equal nearly to each other at focusing, and when the focus is at front focus, the blue incident light is focused on the photoelectric plane, the blue output is large and the green and red lights are fogged, then the photoelectric output is small. In case of rear focus, the red incident light is focused on the photoelectric plane, the red output is large and the blue and green lights are fogged, then the photoelectric output is small. Thus, the focusing, front focus or rear focus is detected depending on the output ratio of the three primary colors from the comparison discriminating circuit 7, a driver 8 discriminates the focusing state from the detected outputs to move the lens in the focusing direction thereby applying focus adjustment automatically. |
