  Weak lensing of galaxies by large scale structure can potentially measure
cosmological quantities as accurately as the cosmic microwave background (CMB).
However, the relation between observables and fundamental parameters is more
complex and degenerate, especially in the full space of adiabatic cold dark
matter models considered here. We introduce a Fisher matrix analysis of the
information contained in weak lensing surveys to address these issues and
provide a simple means of estimating how survey properties and source redshift
uncertainties affect parameter measurement. We find that surveys on degree
scales and above can improve the accuracy on parameters that affect the growth
rate of structure by up to an order of magnitude compared to using the CMB
alone even if the characteristic redshift of the sources must be determined
from the data itself. Surprisingly, both sparse sampling and increasing the
source redshift can weaken the cosmological constraints.
