A comprehensive focusing searching algorithm is designed.The traditional climbing search algorithm is improved by using upper and lower limits of focus range

pre-determining searching direction

and considering that the evaluation value go across the peak of focusing curve after second decline and setting the decline threshold.The traditional endless searching method is improved by using upper and lower limits of focusing range

pre-determining searching direction when the focusing lenses deviated from the focusing range.The scene is checked again to prevent it from errors due to interference after the focusing is completed.The search is disabled when the illumination is below the threshold.Focusing is quickly achieved by using image curve when the zoom lens are moving.Experiments show that using the comprehensive searching algorithm accurate and fast focusing can be achieved

prevents the searching from falling into the local peak

and have good anti-jamming and stability.