  We briefly tackle the following concepts in the Demkov-Ostrovsky (DO)
nodeless sector: (i) orbital impedance, (ii) orbital capacity, (iii) closeness
to reflectionlessness. Moreover, using previous supersymmetric results for the
DO problem, a strictly isospectral effect in the DO orbital impedances is
discussed and explicit plots are displayed for the Maxwell fisheye lens. This
effect, though rather small, is general, that is, it may apply to any focusing
structure.
