  We introduced the quasicentral modulus to study normed ideal perturbations of
operators. It is a limit of condenser quasicentral moduli in view of a recently
noticed analogy with capacity in nonlinear potential theory. We prove here some
basic properties of the condenser quasicentral modulus and compute a simple
example. We also discuss some associated variational problems. Part of the
results are in the more general setting of a semifinite von Neumann algebra.
