  Anisoplanatic effects can cause significant systematic photometric
uncertainty in the analysis of dense stellar fields observed with adaptive
optics. Program packages have been developed for a spatially variable PSF, but
they require that a sufficient number of bright, isolated stars in the image
are present to adequately sample the PSF. Imaging the Galactic center is
particularly challenging. We present two ways of dealing with spatially
variable PSFs when only one or very few suitable PSF reference stars are
present in the field. Local PSF fitting with the StarFinder algorithm is
applied to the data. Satisfying results can be found in two ways: (a) creating
local PSFs by merging locally extracted PSF cores with the PSF wings estimated
from the brightest star in the field; (b) Wiener deconvolution of the image
with the PSF estimated from the brightest star in the field and subsequent
estimation of local PSFs on the deconvolved image. The methodology is tested on
real, and on artificial images. The method involving Wiener deconvolution of
the image prior to local PSF extraction and fitting gives excellent results. It
limits systematic effects to ~2-5% in point source photometry and ~10% in
diffuse emission on fields-of-view as large as 28" x 28" and observed through
the H-band filter. Particular attention is given to how deconvolution changes
the noise properties of the image. It is shown that mean positions and fluxes
of the stars are conserved by the deconvolution. However, the estimated
uncertainties of the PSF fitting algorithm are too small if the presence of
covariances is ignored in the PSF fitting as has been done here. An appropriate
scaling factor can, however, be determined from simulated images or by
comparing measurements on independent data sets.
