  We present limits on the cosmological constant from the statistics of
gravitational lenses using newly completed quasar surveys, new lens data, and a
range of lens models. The formal limit is $\lambda_0 < 0.66$ at 95\% confidence
in flat cosmologies, including the statistical uncertainties in the number of
lenses, galaxies, quasars, and the parameters relating galaxy luminosities to
dynamical variables. The limit holds for either softened isothermal or de
Vaucouleurs models of the lens galaxies, suggesting that the radial mass
distribution in the lens galaxy is not a significant systematic uncertainty.
The cosmological limits are unaffected by adding a small core radius to the
isothermal lens models or by the luminosity of the lens galaxy. Inconsistent
models of the effects of a core radius make significant errors in the
cosmological constraints. Extinction in E/S0 galaxies can significantly reduce
the limits on the cosmological constant, but changing the expected number of
lenses by a factor of two requires a minimum of 100 times more dust than is
observed locally in E/S0 galaxies. Rapid evolution of the lenses is the most
promising means of evading these limits. However, a viable model must not only
reduce the expected number of lenses but do so without significantly altering
the average image separations, magnitudes, redshifts, and the relative
properties of optically and radio selected lenses.
