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.