  We estimate the sensitivity of lensing observables to the parameters in the
lens model (isothermal sphere/Navarro-Frenk-White profile) parameters and to
cosmological parameters. We find that the observables are primarily dependent
on the lens model parameters, while the dependence on cosmological parameters
is minor (especially so for the dark energy parameters). We demonstrate the
lens model degeneracy by deriving both the projected mass density profile and
the circular velocity profile. We also identify a possible source of the
problem of fitting the averaged mass profile of CL 0024+1654 with the
Navarro-Frenk-White profile.
