Once you learn how to model an optical system and analyze its optical errors, you can determine if the performance of the existing design is good enough, if it needs to be improved, or if you need to seek a new design form. In some cases, it's acceptable to change the specifications to improve the performance of a design (e.g., stopping down the lens). In other cases, the design can be modified to improve performance, a process called optimization. For example, the OSDsinglet design in Section 6.7 was modified by "bending" the lens to reduce its spherical aberration. If needed, lenses can be added (in Section 9.4, a lens with a different dispersion had to be added to a singlet to reduce the chromatic aberration), or a completely different design form can be sought. Up to this point, the optimization of lens performance (such as lens bending) has been done manually. This can be done automatically in CODE V using the automatic design mode (AUT) in CODE V (see the box, "CODE V's Automatic Design Process").
In this chapter, we will use AUT to reduce the third-order aberrations that we have discussed in Chapters 6 - 8. This is not a comprehensive approach to optimizing lens performance. In practice, just reducing third-order aberrations is not advised because real lenses can have large apertures and large fields that produce higher-order aberrations. Reducing the third-order aberrations may prevent them from balancing higher-order aberrations, and, typically, the final lens performance might be worse. However, this approach will provide you an introduction to AUT before we tackle full optimization of systems in the next chapter, while demonstrating some very important strategies for reducing third-order aberrations during optimization. It will show how different lens parameter variations can affect individual aberrations.