  The luminosity variation of a stellar source due to the gravitational
microlensing effect can be considered also if the light rays are defocused
(instead of focused) toward the observer. In this case, we should detect a gap
instead of a peak in the light curve of the source. Actually, we describe how
the phenomenon depends on the relative position of source and lens with respect
to the observer: if the lens is between, we have focusing, if the lens is
behind, we have defocusing. It is shown that the number of events with
predicted gaps is equal to the number of events with peaks in the light curves.
