I will close by mentioning two limitations of the technique which I associate with coarse- and fine-scale aberrations.

The underlying assumption of the technique is that the lenslets are small in diameter compared to the distoritons present in the optical wavefront. In other words, we assume that the wavefront is locally flat over the finite diameter of the lenslet.

This assumption begins to break down even for coarse, lower-order, aberrations when the magnitude of those aberrations is large. In this case, the wavefront is significantly curved over the lenslet aperture and the result is a blurry spot which is difficult to localize. If the aberrations are large enough, the spots can even overlap, which complicates the analysis considerably.