This paper examines the role surface roughness plays in optical system performance, discusses the components of a surface roughness specification, and contrasts roughness with cosmetic defects.

1. SURFACE ROUGHNESS EFFECTS OPTICAL SYSTEM PERFORMANCE

In optical tolerancing, optical surfaces are often characterized in the spatial frequency domain1, events per some unit distance. In general, surface form error falls into one of three overlapping categories2, where each category represents a portion of the spatial frequency domain3. Figure, also known as irregularity in lens surfaces, represents an error at amacroscopic, full aperture, low spatial frequency level, while roughness looks at errors on a microscopic, sub-aperture, high spatial frequency level4. Figure 1 below illustrates the spatial frequency relationship between Figure and Roughness and the overlap in surface events. Midspatial errors occur between the Figure and Roughness categories...

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