| The general measurement methods for focal length are introduced in this thesis. Combined with the application background of this project, theory analysis and formula derivation of Talbot effect and Moire fringes for Ronchi gratings are presented. Based on these, a novel method for long focal length measurement is presented, which is achieved by calculating the angle of Moire fringes formed by Talbot image of one Ronchi grating and another Ronchi grating. The angle of Moire fringes is obtained by processing on the Moire fringes image, which is captured into computers by CCD camera.Considering the features of large aperture long focal lenses, planar scanning structure and mirror reflecting structure are proposed to realize the measurement method for long focal length, and the feasibility for these mechanical designs is analyzed in detail. Meanwhile the software solutions for capturing Moire fringes image, controlling planar scanning system and calculating the angle value of Moire fringes are discussed, especially for the algorithms of Fast Fourier Transformation (FFT) and the acquisition of maximum position improved, which are used in the calculation of fringes' angle.In this thesis the details of operating the digital measurement instrumentation for long focal length are also introduced, such as environmental requirement, structural adjustment, system calibration and software operation. The data obtained by test shows the high precision of this measurement instrumentation. |
PDF Full Text Request