The DAFT/FADA program is a combined US/France effort aiming at combining HST-archives with ground-based photometry, to produce the largest weak lensing and multiband survey of rich z = [0.4,0.9] clusters and photometric redshifts for the field and cluster galaxies. The two goals are to make a geometrical determination of the nature of Dark Energy, using weak lensing tomography, applied to the background galaxies around the clusters, and to investigate the cluster evolution with redshift.
By obtaining redshifts and shear measurements of about 20,000 galaxies, we will gain enough statistics to measure the equation of state of Dark Energy to a good enough accuracy to act as a training set for future Magnified Weak Lensing Tomography surveys. In addition, mass models plus spectroscopic and photometric redshifts will make the data base a treasure trove for cluster and galaxy evolution science. Some of the background galaxies will be magnified enough to lead to the discovery of galaxies at redshifts above 6.