1. A method for automatically focusing every image point of an image of a sample formed by an optical objective, comprising, for each image point: deriving a representation of the autocorrelation function of the brightness distribution of the image of that image point; deriving a representation of the average of the auto correlation function of the brightness distribution of a plurality of image points in the region of that image point; deriving a representation constituting a function of the quotient formed by dividing the representation of said autocorrelation function for that image point by the representation of said average of the autocorrelation function; and varying the distance between the objective and the sample while iteratively performing said steps of deriving for determining the distance at which said function of the quotient has a maximum value.