ABSTRACT
The schematic of Figure 21.1 is highly simplified, assuming spherical and aligned surfaces. Nevertheless, it demonstrates two important facts regarding the optical errors of the human eye: that the blur increases with the off-axis angle to the object and that it depends on the size of the pupil. For instance, spherical aberration has a cubic dependence on pupil size and coma has a quadratic dependence, whereas TCA is independent. To exemplify, Figure 21.2 shows the variation in monochromatic image
quality over the visual field measured for one subject. The following paragraphs will briefly explain the origin of the four largest peripheral aberrations, namely, astigmatism, field curvature, coma, and TCA.
