Research On MTF Testing Methods Of Optical Inspection Lenses

With the continuous improvement of the performance of optic-electrical testing instruments as well as the rapid development of the computer technology, optical lenses have been widely used in the automatic testing system in industry. As a demand for higher quality, it becomes more and more significant to choose an effective way to evaluate the image quality of the lenses.MTF(Modulation Transfer Function) is an accurate, objective and quantitative parameter of an optical lens, testing lens MTF is recognized as one of the most effective and comprehensive methods to evaluate the optical imaging systems. This paper discusses the limitations existed in the current MTF measurement system of the optical inspection lenses developed by our laboratory. Based on deeply insight into the optical transfer function theory and commonly used MTF measurement methods, some improvements are made on the process of image acquisition and contrast testing method. Meanwhile, Slit and Knife-edge testing methods are also adopted to measure the MTF of the lenses. A comparison among the above methods is used to judge the validity of the current contrast testing method for accurate and reliable MTF measurement for these optical inspection lenses.The first part of the thesis generally introduces the comparison of the commonly used image quality evaluating methods, as well as the actuality and development of the MTF measurement technology. The improving application of the optical inspection lenses in industry and the current testing methods for these lenses in our laboratory are also described.The second part of the thesis generally introduces theoretical foundation of the MTF testing technology, for example, the definition of optical transfer function, the relationship between PSF,LSF,ESF and MTF, and also introduces three commonly used MTF test methods: Slit testing method, Knife-edge testing method and contrast testing method.The third part of the thesis elaborates on hardware components of the whole MTF testing system platform.The fourth part of the thesis highlights on the software achievement of the MTF testing system. In this part, it describes not only the improvement design on the image acquisition module, but also the data processing arithmetic used in this paper. The experimental method to measure the MTF of CCD is also elaborated. At last, the software processes of the three testing methods are analyzed.The fifth part of the thesis mainly compares the experimental results both on axis and off axis through the three methods. And the systematic errors and the factors that influence the results are also analyzed.The end of the thesis summarizes the research finished by this thesis, and prospects for the further work.