Screen Shot 2019-02-13 at 9.09.27 AM Published February 13, 2019 at 528 × 476 in Screen Shot 2019-02-13 at 9.09.27 AM The perturbation model consists on simply dragging MSF phase errors along the nominal rays to the exit pupil. In this article we study the validity of this model. fig. 2(a) from the article.