FOCUS CONTROLLER OF VIDEO CAMERA

摘要

PURPOSE:To control quickly the focus of a video camera without using any special parts by driving a photographing lens in order to maximize the changing factor of the luminance signal for an object existing a specific or plural horizontal scanning periods of a video signal. CONSTITUTION:A sampling device 29 samples only the luminance signal YN in a specific horizontal scanning period every vertical scanning period among luminance signals. A differentiation device 30 calculates the changing factor Y'N of the signal YN; while a maximum detector 31 detects the maximum value Y'N(max) of the factor Y'N. A capacitor 32 records the maximum voltage YC of the changing factor only when a switch 33 is closed. A differential amplifier 34 delivers the differential between the value Y'N(max) and the voltage YC showing the past focusing state which is used as a standard. Comparators 36 and 37 compare the differential output Y'out with reference voltage values V1 and V2 given from DC power supplies 38 and 39 respectively. In accordance with results of these comparisons, a discriminator 40 moves a photographing lens 41 back and forth for focusing by a lens driver 42.