Ronchigram simulations for free-form concave reflective surfaces

A new algorithm to simulate ronchigrams and bironchigrams for free-form reflective concave surfaces is reported. In order to know the surface saggita and its partial derivatives at any point within mirror domain a bicubic spline interpolation is done over a finite set of points where the free surface is defined. To simulate the ronchigram irradiances we used ruling with cosinusoidal transmittance instead of Ronchi ruling. Several examples of bironchigrams are shown for spherical surface affected by local and/or radial errors; and surfaces used in ophthalmic progressive lenses.