Study Of MTF Measurement Technique Based On Pinhole Image Analysis

Image quality evaluation of an optical system is an important part in applied optics. Optical Transfer Function(OTF) is an objective, accurate, quantifiable image quality evaluation parameter, and it can directly measured, which has been more important in image quality evaluation and widely applied in optical designing, manufacturing, testing and information processing. In the OTF measuring technique on image analysis, OTF date of an optical system is calculated by analyzing images of a characteristic object. For the simple structure of its measuring system and without theory error, now it has been the trend of development of OTF measuring method. The main researched contents and their achievements are as follows:1. Research on OTF measurement technique based on pinhole image analysis. Pinhole, slit and knife-edge always be objects in measurement on image analysis because their objects spectrum are simple. Pinhole has two dimension character, and can be used as object in OTF measurement system for getting two dimension OTF data one time without changing scan angle or slit direction. The main disadvantage of OTF measurement based on pinhole image analyzing is low image-plane energy and liable to being polluted by noise. The OTF measurement technique based on image analysis of the pinhole is researched deeply. A set of OTF measurement equipment on the pinhole image analysis was analyzed. Each part was analyzed in constituent and characteristic in detail. The OTF measurement equipment consists of modules and can give OTF measurement results of varies system by replacing a certain module.2. Effects of measurement system parameter setting on measurement precision and corresponding correction method are researched. The system is composed of target maker, the system will be tested and image analysis. Auxiliary optical system, spatial frequency calibration and the performance parameter of CCD affect measurement precision. The effects of auxiliary optical system designed independently can be corrected by dividing out Geometry Aberration Modulation Transfer Function(GMMTF).The system parameters affecting the spatial frequency calibration are determined, and the measurement methods of these parameters are provided. Trough analysis of CCD imaging theory, the effect of CCD performance parameter on OTF measurement precision is researched and its error correction method is established.3. According to the practical index of the camera optical system, the OTF measurement equipment was calibrated by a 50mm focus plane-convex standard lens, and the noticeable problems in calibration process and their solving methods are given in detail. Compared experiments to national first class metrology station of China show that the measurement error of this OTF measurement equipment less than±3% within 100lp/mm spatial frequency.