In optical systems, misalignment of components, quality imperfections of elements, or aberrations can internally reduce performance, while heat and atmosphere can externally reduce performance. Although design considerations and care during use of an optical system can reduce these problems, they may be too severe to solve with conventional methods. For example, in astrophotography, a field in which it is difficult to control external forces such as atmospheric disturbance, active methods are used for correcting performance. The key in both macro astronomy applications and micro optical applications is adaptive optics (AO).