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Zemax senior optical engineer Zach Derocher will introduce TrueFreeForm, a grid-based surface optimisation of freeform surfaces in optical design, on Monday 24 June, at 11:00-11:20, in hall B2, booth number 356.

Some lens design applications use parametric functions for representing freeform surfaces. Most common perhaps is a linear combination of Zernike functions. There is a downside to parametric approaches, though, namely that optimisation of parameters typically forces the entire surface to change with each variable. In his talk, Derocher speaks about a grid-based surface where sag contributions are specified on a rectangular grid. Optimising on sag described in this fashion allows local influence on a specific region of the surface that is only as wide as twice the grid spacing.

Grid-based surface optimisation in OpticStudio lens design software allows flexibility in designing freeform optical components that is not possible with traditional surface types. The system Zemax focuses on is a corrector plate with the rear surface specified by a variable grid sag surface. The goal of the corrector plate is to correct for Wavefront error introduced by a Zernike phase surface. Derocher will describe the tests and report on findings, including the importance of constraints on the grid variables and techniques that improve the calculation efficiency.