  We use three strong lensing clusters to constrain the cosmological parameters
Omega_m and Omega_lambda. Recent HST observations of galaxy clusters reveal a
large number of multiple images, which are predicted to be at different
redshifts. We showed in a previous work that if it is possible to measure
spectroscopically the redshift of many multiple images then one can constrain
(Omega_m,Omega_lambda) through ratios of angular diameter distances
independently of any external assumptions. Using three strong lensing clusters,
our combined results lead to tight constraints.
