Today, there are different manufacturing methods available for the fabrication of aspherical surfaces. Among these methods, machining with CNC has as its biggest advantage a very high flexibility regarding geometry and material. No special form tools are necessary, and nearly all brittle materials are machinable. Additionally, the highest form accuracy of the lens surface can be reached with the subsequent ultraprecision finishing processes.
The typical process chain for the machining of aspherical surfaces with CNC consists of three steps: The zonal grinding process, which is described in this chapter, has the role of generating a highly precise but still microscopic rough surface, which achieves its optical quality in a subsequent polishing step.
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