Postprocessing of imagery from active optics: some pitfalls

There may be pitfalls to watch for when recording imagery from active phase compensation devices located in the exit pupil of the system. At least three of these pitfalls are identified, and each is manifested as a degradation in the imagery. Both nearby and high altitude atmospheric disturbances contribute to the degradation. The first pitfall is identified as residual phase errors caused by measurement and hardware limitations. The second pitfall is identified as nonisoplanatism, and it occurs because wavefronts from different source points experience different high altitude disturbances. The third pitfall is identified as amplitude fluctuations in the exit pupil of the system, and it is also caused by the high altitude atmospheric disturbances. The two pitfalls caused by the high altitude disturbances are reduced by applying additional phase compensation in a plane that is the image of the high altitude disturbances. But even this may not be sufficient to eliminate the need for postprocessing of the image ry of extended sources.