Abstract: Process and apparatus for focussing of an optical display system in which the total of the light intensities for all the adjacent picture elements is added up and in passing through the focus area the maximum is determined from the total for a specific focussing which is then defined as focus plane, and in the adding up of each total by a preselection of the supplied signals only those brightness differences of adjacent picture elements are taken into account which make positive contributions to the adding up. The adding up and preselection is carried out by a computing device operating on an electronic basis for computing the total ##EQU1## in which x is the line position of a picture element, y the column position of the picture element, I.sub.x,y the intensity of the picture element, M the number of lines of the image and N the number of columns of the image.