Lens design for manufacture
The manufacture of complete optical systems can be broken down into three distinct stages; the optical and mechanical design, the production of both optical and mechanical components and finally their assembly and test. The three stages must not be taken in isolation if the system is to fulfil its required optical performance at reasonable cost. This report looks first at the optical design phase. There are a number of different optical design computer packages on the market that optimise an optical system for optical performance. These packages can be used to generate the maximum manufacturing errors, or tolerances, which are permissible if the system is to meets its design requirement. There is obviously a close relationship between the manufacturing tolerances and the cost of the system, and an analysis of this relationship is presented in this report. There is also an attempt made to optimise the design of a simple optical system for cost along with optical performance. Once the design is complete the production phase begins and this report then examines the current techniques employed in the manufacture, and testing of optical components. There are numerous methods available to measure the surface form generated on optical elements ranging from simple test plates through to complex interferometers. The majority of these methods require the element to be removed from the manufacturing environment and are therefore not in-process techniques that would be the most desirable. The difficulties surrounding the measurement of aspheric surfaces are also discussed. Another common theme for the non-contact test techniques is the requirement to have a test or null plate which can either limit the range of surfaces the designer may chose from or increase the cost of the optical system as the test surface will first have to be manufactured. The development of the synthetic aperture interferometer is presented in this report. This technique provides a non-contact method of surface form measurement of aspheric surfaces without needing null or test plates. The final area to be addressed is the assembly and test stage. The current assembly methods are presented, with the most common industry standard method being to fully assemble the optical system prior to examining its performance. Also, a number of active alignment techniques are discussed including whether the alignment of the individual optical elements is checked, and if need be adjusted, during the assembly phase. In general these techniques rely upon the accuracy of manufacture of the mechanical components to facilitate the optical alignment of the system. Finally a computer aided optical alignment technique is presented which allows the optical alignment of the system to be brought within tolerance prior to the cementing in place of an outer casing. This method circumvents the need for very tight manufacturing tolerances on the mechanical components and also removes the otherwise labour intensive task of assembling and disassembling an optical system until the required level of performance is achieved.