Measurement System, Based On The Talbot Effect Of A Long Focal Length

In this dissertation, the principle of Talbot effect theory and moire fringe technology was studied. On the basis of Talbot effect and moire fringe technology, a novel method for the long focal length measurement of large aperture lens was presented.when a plane wave passed through a lens and illuminated on a Ronchi grating, Talbot images will appear at periodic Talbot distance behind the grating, the period of the Talbot image of the Ronchi grating had a relationship with the long focal length of the lens. If we put another Ronchi grating at the position of the Talbot image, then moire fringe will appear, according to the principle of moire fringe, the angle of the moire fringe also has a corresponding relationship with the focal length of the lens. By image capture system, the digital image of the moire fringe was captured and the angle of the moire fringe could be accurately calculated by computer, according to the relationship between the angle of moire fringe and the focal length, the focal length can be got. The feasibility of this method was analyzed; the accuracy of this method was discussed and also the factors that would affect the measurement accuracy was demonstrated. Improvement was made according to these factors, for example, iterative method was used in the frequency domain of the moire fringe image to accurately calculate the angle of the moire fringe. For large aperture lens, scanning method was developed to measure the focal length in different locations within the lens.A complete set of long focal length measurement system have been developed. We have finished the feasibility analysis of this method, hardware and software design of the system, including the mechanical structure designing, laser booming system designing, image capturing system designing and image arithmetic programming. Experiments data demonstrates that this system can work very well.