When using the monocular vision measurement model of lens imaging for displacement measurement,it is necessary to know the center coordinates of the clear imaging spot.When the object is displaced,in order to obtain clear imaging spots,the position of the lens needs to be adjusted so that it obeys the lens imaging law.However,due to lens manufacturing defects,the focus is not an ideal point,but a small area.When the image is close to clear,the lens clarity is basically unchanged by adjusting the position of the lens by fine movement.This is the insensitive area of the image,also known as dead zone,so it is very difficult to get clear lens imaging position.In order to solve this problem,a method to estimate the clear imaging position based on the speckle sequence image is proposed in this paper,that is,separately the speckle images at different positions of the lens is obtained,and the short path and center coordinates of the speckle image are obtained through image processing.According to the analyzing the model,two segments function are fitted by the ellipse radius data,and the intersection position is solved,which is the estimated clear image position.Finally,through experiments,the lens is adjusted to the estimated clear image position and the image is acquired.The clear lens imaging position is verified by the edge gradient detection and the pixel mean detection.