  We describe the internal photometric calibration of the Deep Lens Survey,
which consists of five widely separated fields observed by two different
observatories. Adopting the global linear least-squares ("ubercal") approach
developed for the Sloan Digital Sky Survey (SDSS), we derive flatfield
corrections for all observing runs, which indicate that the original sky flats
were nonuniform by up to 0.13 mag peak to valley in $\z$ band, and by up to
half that amount in {\it BVR}. We show that application of these corrections
reduces spatial nonuniformities in corrected exposures to the 0.01-0.02 mag
level. We conclude with some lessons learned in applying ubercal to a survey
structured very differently from SDSS, with isolated fields, multiple
observatories, and shift-and-stare rather than drift-scan imaging. Although the
size of the error caused by using sky or dome flats is instrument- and
wavelength-dependent, users of wide-field cameras should not assume that it is
small. Pipeline developers should facilitate routine application of this
procedure, and surveys should include it in their plans from the outset.
