Auto-focus regulating method for video cameras and device thereof

#The present invention relates to an auto-focus regulating method for video cameras and device thereof.

#Generally, the auto-focus regulating method for video cameras is classified roughly into an active method by infrared ray distance calculation or ultrasonic wave distance calculation and a passive method by image sensing or image detecting.

#According to the active method, infrared rays or ultrasonic waves illuminate an object to be photographed, and the reflected wave is received by a sensor installed in a camera so that the distance between the camera and the object can be measured, thereby driving the focus mechanism of lens so that the focus is regulated in accordance with the measured distance. The active method has advantages in that the focus can be adjusted at a close distance and the performance is high. However, it has a disadvantage in that it requires a separate distance calculator.

#The above objects and other advantages of the present invention will become more apparent by describing in detail a preferred embodiment thereof with reference to the attached drawings in which:

#FIG. 1 is a block diagram showing a conventional auto-focus regulating device:

#FIGS. 2A through 2C are graphical diagrams showing the operational characteristics of the device shown in FIG. 1:

#Now, referring to the attached drawings, a description will be given in detail of a preferred embodiment of an auto-focus regulating method for video cameras and device thereof according to the present invention.

#FIG. 1 shows a conventional auto-focus regulating device. in FIG. 1, a reference numeral 12 is a high frequency detector, 14 is an error detector, 16 is a focus driver and 18 is a clock generator.

#High frequency detector 12 comprises a high-pass filter 12a, an absolute value detector 12, an envelope detector 12c, analog-to-digital (A/D) converter 12d and an accumulator 12e.