Observing Strategy

The individual exposures are 600-900s each, depending on the filter; taken in blocks consisting of five pointings dithered by up to 8 arcminutes to shift all low surface brightness features off themselves (to provide adequate sky-flatfielding) and cover 42'x42' in one "subfield" (9 subfields = one 2x2 degree field). This dither is repeated (with about a one arcminute offset) in each filter -- and then off to another sub-field within one of two fields.

In the first two survey runs, the survey team observed five sub-fields in the 0053+12 field and four sub-fields in 0919+30 to roughly half of the final depth in B,R and z'. The survey observations go deepest in R (to a surface brightness limit of 29 mag/sq.arcsec) and concentrate on R in good seeing in order to obtain the best lensing signal possible. The other bands are imaged less deep (approximately half of the exposure time of R, in order to provide photometric redshift estimates.)