SPECIFICATION OF SURFACE FIGURE AND FINISH IN TERMS OF SYSTEM PERFORMANCE

We describe methods of predicting the degradation of the performance o f a simple imaging system in terms of the statistics of the shape erro rs of the focusing element and, conversely, of specifying those statis tics in terms of requirements on image quality. Results are illustrate d for normal-incidence, x-ray mirrors with figure errors plus conventi onal and/or fractal finish errors. It is emphasized that the imaging p roperties of a surface with fractal errors are well behaved even thoug h fractal-power spectra diverge at low spatial frequencies.