Measurement Of Long Focal Length Of Lens Utilizing Talbot Effect And Morie Technique

Long focal-length lens are widely applied in various technical domains such as ICF driver, astronomical optical system, aerial remote-sensing camera, and so on. Accurate measurement of long focal-length lens is in favor of right employment of optical apparatus and sufficiently exerting tactical performance of martial optical devices. At present, some difficulties are encountered in measurement of long focal length of lens. Fortunately, amongst many methods of measurement of long focal length of lens presented in recent years, a method utilizing Talbot effect and Morie technique is valuable and promising. In the paper, the focal length of lens is determined respectively by the space between beat pattern of Morie fringes and the number of Morie fringes according to the principle of the method. We perform corresponding experimental research and analyze digital processing Morie fringes. The main work and obtained results is summarized as follows:1. Some common methods of measurement of focal-length optical system are depicted and classified. Applicability and limitation of them is indicated. Particularity of measurement of long focal-length system is concluded.2. We describe the principle of the method of measurement of long focal length of lens utilizing Talbot effect and Morie technique in detail, analyze thefeasibility of the method, validate it through a series of experiments. In the measurement, we rationally discuss the exact selection of the pitch and relative position of the two gratings and study the influence on experimental measurement introduced by the difference of Morie fringes between the integral and fractional times of Talbot distances.3. The space between parallel Morie fringes underlies the measurement of long focal length of lens. The abstraction of central lines of Morie fringes can optimize measurement of the space between parallel Morie fringes. Hence, it can improve the precision of measurement of long focal length of lens and loosen the requirement of precision of metrical equipments.4. The measurement of long focal length of lens can be realized through counting the number of Morie fringes. The full range of Morie fringes can be captured through transversely moving CCD, sequentially, the Tightness of counting is guaranteed.In conclusion, the detailed analysis of theory and experimental research are performed in the measurement of long focal length of lens utilizing Talbot effect and Morie technique. The results indicate that the improvements based on the space between parallel Morie fringes and the number of Morie fringes presented in the paper are feasible and valuable. The method utilizing Talbot effect and Morie technique can also be applicable in the measurement of short and immediate focal length of lens by appropriately adjusting experimental equipment.