  We present the first measurement of individual cluster mass estimates using
weak lensing size and flux magnification. Using data from the HST-STAGES survey
of the A901/902 supercluster we detect the four known groups in the
supercluster at high significance using magnification alone. We discuss the
application of a fully Bayesian inference analysis, and investigate a broad
range of potential systematics in the application of the method. We compare our
results to a previous weak lensing shear analysis of the same field finding the
recovered signal-to-noise of our magnification-only analysis to range from 45%
to 110% of the signal-to-noise in the shear-only analysis. On a case-by-case
basis we find consistent magnification and shear constraints on cluster virial
radius, and finding that for the full sample, magnification constraints to be a
factor $0.77 \pm 0.18$ lower than the shear measurements.
