Production tools for aspheric optics fabrication are getting more versatile, but the aspheric capabilities of current cost-effective metrology systems are less extensive. That means designers must constrain their solutions to fall within the capture range of particular metrology systems. But an appropriate characterization of the aspheric shapes during the design process can simplify design constraints, according to a presenter at Optifab 2009 in Rochester, NY. "Things need to evolve, and they always do," said Gregory W. Forbes of QED Technologies Inc., who worked with Chris Brophy of Optical Engineering Services on the description system. He said the conventional "monomial" representation of ashperic surfaces is difficult to handle, requiring the introduction of normalized variables and cancellation -- which he called "a hell of a painful thing" because it "wastes a lot of digits" to get the needed accuracy. Forbes and Brophy have come up with a "tailored" description option for mild aspheres that they say is cost-effective because it uses orthoginal polynomials, simplifying design constraints in applications where the testing is to be performed with stitched subaperture interferometry. Forbes compared the process to earlier results for more tightly constrained aspheres where the testing was done with full-aperture interferometry. He said that analogous ideas apply when, for even stronger aspheres, the metrology is to be performed with stitching in combination with a configurable near-nulling subsystem. "You gain a lot of efficiency and intuition just by changing the way you write things," said Forbes. Laura S. Marshall laura.marshall@laurin.com