Notes:

One useful way to visualize the wavefront aberration function is to display it as an image that I call a "Pupil Map". Wherever the aberrated wavefront is lagging behind the reference plane wave we color the map dark, and wherever the wavefront is leading the reference we color the pupil map light. This visualization method takes advantage of a built-in mechanism of our visual systems that interprets bright areas as bulging forward and dark areas as a depression. Therefore, just by looking at the pupil map you can quickly gain insight into the shape of an aberrated wavefront.