This chapter discusses the integration of finite element derived response quantities such as displacements and stress into the model. These techniques allow mechanical design trades to be performed as a function of optical performance. Also discussed are methods to compute line-of-sight jitter and to evaluate the effects of mechanical obscuration on image quality.
4.1 Optical Surface Positional Errors
Mechanical loads acting on an optical system can significantly degrade optical performance by changing the position of the optical surfaces. Positional or rigid-body errors include translations and rotations of a surface in six degrees-of-freedom. Translation of the optic along the optical axis is called despace, changes in lateral position are called decenter, and tip and tilt refer to rotations about the lateral axes. These positional errors are shown in Fig. 4.1. For nonrotationally symmetric optics, rotation about the optical axis must also be considered. Common optical errors resulting from shifts in the position of an optical surface include focus, astigmatism, and coma. In addition, a boresight or a line-of-sight error may result as illustrated in Fig. 4.2.
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