  The currently used linear and nonlinear lens inversion techniques are based
on distortion estimators whose complicated source redshift dependence makes the
influence of the redshift distribution of the sources difficult to take into
account and to analyze. However, the lens equations can be explicitly averaged
over the source redshift distribution by a suitable choice of the estimators.
Lens reconstruction procedures are outlined, which make use of all the
information and in which all the unknown quantities of the problem can be
recovered simultaneously in both the linear and nonlinear regime, for either
noncritical or critical lenses. These procedures require no prior knowledge of
the redshift distribution of the sources, but are possibly dependent on the
Cosmology in some instances. Possible methods of recovery of the source
redshift distribution itself are briefly discussed at the same time.

Astrophysics