Spherical aberration, coma, and the Abbe sine condition for physicists who don't design lenses.

Treatments of lens aberrations tend to be either short and descriptive surveys or detailed theoretical treatments. In this article, we take an intermediate approach, showing that the mechanism of spherical aberration can be easily understood on a qualitative level by comparing a sphere with the ideal lens shape prescribed by the Principle of Least Time, and by using a similar argument to understand coma aberration. We also use a simple argument from radiant flux conservation to explain why aberration-free imaging of finite-sized flat objects (as opposed to discrete points or curves) is impossible with just a single thin lens, and we provide a simple explanation of the Abbe Sine Condition as a figure of merit in aberration correction. [ABSTRACT FROM AUTHOR]