Investigation of lens performance degradation by lens manufacturing error

Abstract

This report describes the development of two Mathcad programs and also discusses their functionality. Due to demand for optical system with high optical performance, there is increasing demand for aspherical lenses to be fabricated for use in such optical system. However, the fabrications of aspherical lenses are more complicated than spherical lenses; hence aspherical lenses are usually found to be the main source of error for faulty developed optical system. The first Mathcad program will allow optical engineers to make use of the “Grid Sag” surface type feature in ZEMAX to model the fabricated aspherical lens surface in any optical system and determined if the modelled optical system with the inputted measured sag error in the aspherical surface is consistent with the actual optical system performance. The objective is to use this model to gain a greater insight into the surface-error problem so that rectification in fabrication process could be implemented by the engineers. The second program converts the measured 2D surface sag error of the lens surface into a 3D model to allow the engineers to get a better visual of the surface sag error. The developed programs were shown to be functional and can be used successfully with ZEMAX. However, its capability is limited to the precision and accuracy of the form-tracer used to measure the sag errors on the lens surface. To overcome this, it is suggested that more intersecting scans are taken to give a better analysis of the errors on the lens surface. For better insight into surface errors for aspherical lens, it is paramount that a flexible 3D form testing equipment be used. Nevertheless, the developed programs to be used in conjunction with ZEMAX could prove to be a cost effective metrology solution for optical engineers who do not have the benefit of a flexible 3D form testing equipment.