  Lensing in the context of rich clusters is normally quantified from small
image distortions, yielding a relative mass distribution in the limit of weak
lensing. Here we show the magnification effect of lensing can also be mapped
over a cluster, resulting in absolute mass determinations for the weak limit.
Furthermore, given both magnification and distortion measurements, the mass
distribution may be constrained in the strong regime. Methods for obtaining the
magnification using spectroscopic and/or photometric information are discussed,
for object detection within a fixed isophote or to a given flux limit.
  A map of the magnification around A1689 is constructed from the observed
depletion of background red galaxy counts.
