Abstract

An accurate evaluation method is proposed for comprehensively characterizing ophthalmic freeform lenses (OFLs) by computing the curvatures of the freeform surface at an arbitrary direction in the transformed Cartesian coordinates based on space analytic geometry. The proposed method could especially produce the astigmatic axis, which is an indispensable characteristic of OFLs. An OFL designed with an analytical formula is characterized by our comprehensive method, not only with power and astigmatism contour plots that are consistent with the results from the conventional method, but also with the astigmatic axis, which can be analytically confirmed by combining a conventional quadratic equation with directional derivatives. Benefiting from the astigmatic axis, the comprehensive method could produce the combined astigmatism of both surfaces for double OFLs, which is not possible with the conventional method. The evaluation results of a double OFL are also presented and can be experimentally verified by fabrication and measurement. This might provide a new idea and a more comprehensive methodology for evaluatiing OFLs with high precision.

© 2014 Optical Society of America

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