Wavefront correctors acting in a single plane can only correct for phase distortion on a beam from a single direction. If the distortion arises in a distributed medium beams from other directions will be at best partially corrected. The region over which good correction occurs can be extended by using multiple correctors imaged at different locations in the medium. A procedure is derived here for locating the correctors to maximize the residual anisoplanatic error and this minimum error is evaluated for several atmospheric models. This procedure also applies to the simulation of distributed distortion by discrete phase screens.
Edward P. Wallner,
"Optimizing the locations of multiconjugate wavefront correctors", Proc. SPIE 2201, Adaptive Optics in Astronomy, (31 May 1994); doi: 10.1117/12.176121; https://doi.org/10.1117/12.176121