Samples are taken of radiation throughput intensities while a radiation supplying, first element advances along a dithering displacement path, where the displacement path is spaced slightly away from but extends adjacent to an initial position of the first element and while a reference radiation signal is coupled radiatively between the first element and a counterpart, radiation receiving, second element. Those samples that are seen to be the greatest (I.sub.maxc) are identified. From this information, a determination is made of at least the approximate direction, if not the approximate length of an optimization vector which separates the initial position of the first element from a radiative coupling, new position having a greater coupling efficiency. The first element is automatically moved according to the optimization vector so as to be at or substantially close to the new radiative coupling position.