In this paper we present the approach we have used to determine and account for the anisoplanatic point spread function ( PSF ) in deep adaptive optics ( AO ) images for the Survey of a Wide Area with NACO ( SWAN ) at the ESO VLT .
The survey comprises adaptive optics observations in the K _ { \mathrm { s } } band totaling \sim 30 \mathrm { arcmin } ^ { 2 } , assembled from 42 discrete fields centered on different bright stars suitable for AO guiding .
We develop a parametric model of the PSF variations across the field of view in order to build an accurate model PSF for every galaxy detected in each of the fields .
We show that this approach is particularly convenient , as it uses only easily available data and makes no uncertain assumptions about the stability of the isoplanatic angle during any given night .
The model was tested using simulated galaxy profiles to check its performance in terms of recovering the correct morphological parameters ; we find that the results are reliable up to K _ { \mathrm { s } } \sim 20.5 ( K _ { \mathrm { AB } } \sim 22.3 ) in a typical SWAN field .
Finally , the model obtained was used to derive the first results from five SWAN fields , and to obtain the AO morphology of 55 galaxies brighter than K _ { \mathrm { s } } = 20 .
These preliminary results demonstrate the unique power of AO observations to derive the details of faint galaxy morphologies and to study galaxy evolution .