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Radial and Linear Fresnel Lenses are finding application as light concentrators for Concentrated Photovoltaic and Concentrated Solar Thermal power applications. The efficiency of these diffractive lenses directly affects the yield of such systems. Peaks and valleys of the optical facets of the Fresnel lens must be sharp in order to prevent diffusion and transmission loss due to rounding. For diamond turned mould masters, optical facet tip sharpness is affected by machining accuracy, tool-path and tool wear/mileage. Strategies to optimise optical facet tip sharpness are presented which enable production of large lenses with minimal degradation of optical quality. Radial Fresnel produced with diameters over 500mm and Linear Fresnel over 1m long are discussed with data on structure fidelity and tool wear.