TheDeep Lens Survey (DLS, short for "Deep Gravitational Lensing Survey") is an ultra-deepmulti-band optical survey of seven 4 squaredegree fields. MosaicCCD imagers at theNational Optical Astronomy Observatory'sBlanco (Cerro Tololo) andMayall telescopes (Kitt Peak) are being used. The deep fields took five years to complete (2001–2006), in four bands:B, V, R, and z', to 29/29/29/28mag per squarearcsecond surface brightness. Optical transient events (including moving objects such asminor planets andcomets) andsupernova candidates are released in real time.

The main goal of the survey is to produce unbiased maps of the large-scale structure of the mass distribution beyond the local universe, via very deep multicolor imaging of seven 2-degree fields and colour-redshifts. Theshear of distantgalaxies induced by themass of foreground structures will be measured. Theseweak-lensing observations are sensitive to all forms of clumped mass and will yield unbiased mass maps withresolution of onearcmin in the plane of the sky (about 120kpc/h atz = 0.2), in multiple redshift ranges. These maps will measure for the first time the change in large scale structure from z = 1 to the present epoch, and test the current theories of structure formation, which predict that mass in the low-redshift universe has a particular filamentary/sheetlike structure. These observations will directly constrain the clustering properties of matter, and, when compared with the results frommicrowave backgroundanisotropy missions, will test the basic theory of structure formation via gravitational instability.

While this is the main goal of the survey, a wide-field imaging survey has a myriad of other uses. In addition, the group is acquiring the data in a way which makes it possible to detect variable objects on scales of hours to months, by spreading observations of individual subfields over 4 runs over two years.

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