FOCUSING DEVICE

A focus adjustment apparatus which automatically focuses a camera or other optical equipment. The focus adjustment apparatus predicts complex fluctuations in the image plane position easily and accurately. The apparatus includes a focus detection device which detects a defocus amount, a lens position detection device which detects a lens position of the photographing optical system, and an image plane position computation device. The image plane position computation device computes the image plane position of the object image on the basis of the defocus amount and the lens position. The apparatus further includes an image plane speed computation device. The image plane speed computation device computes the image plane speed on the basis of a change over time in the image plane position. The apparatus also includes a statistical device. The statistical device performs statistical analysis on a sample interval composed of the image plane position and the image plane speed, and determines the undetermined coefficients in a preselected equation of motion. The equation of motion includes the image plane position and image plane speed. The apparatus also includes a predicting device which computes a predicted value of the image plane position on the basis of a solution of the equation of motion. The solution can be a time dependent function. The apparatus also includes a focus control device which controls focus based on the predicted value of the image plane position.