  This paper investigates the possibilities offered by combining regularization
and preconditioning by the same symmetric positive semi-definite operator when
solving ill-posed problems. We study the question of the stopping criterion,
and the possibility offered by Ritz eigenelements for the a posteriori
filtering of the solution and the tuning of Tikhonov's weight. The method is
applied as the linear solver for an optical flow estimator and it is coupled
with a subspace recycling strategy.
