Research On Diopter Measurement Technology Of Progressive Multifocal Lenses Based On Phase-shifting Taber Interferometer

With the development of optometry technology and the improvement of people's requirements for the comfort of wearing glasses progressive multi-focus lenses account for an increasing proportion of the glasses market.The new glasses not only bring better wearing experience and vision correction effect,but also greatly improve the detection difficulty.The progressive multi-focus lens design makes it difficult to measure the diopter distribution of this kind of lens with the traditional single-point measurement method.Among the overall measurement methods,Talbot interferometer method has become one of the important diopter measurement methods for multi-focus lenses due to its high measurement accuracy,simple optical path and low environmental requirements.In this paper,the basic theory of measuring lens diopter based on Talbot interferometer is analyzed,the formula of measuring lens diopter is derived,and the formula is improved to facilitate the subsequent calibration of system parameters.Based on the moire fringe collected in practice and the theory of measurement,a method for solving the local fringe Angle based on the fringe phase field is studied.In order to avoid the influence of the fringe harmonics,a nine-step phase-shifting method is used to solve the fringe phase.The simulation results show that this method can avoid the influence of uneven distribution of ambient light and incident light source on the fringe Angle,and the accuracy reaches 0.2° in the full angle range.In order to meet the requirements of fringe quality and system range,the design idea of grating spacing with decimal Talbot spacing was adopted,and the main parameters of Talbot interferometer were set as follows: grating period was 0.2mm,grating included angle was 1.9°,and grating spacing was 6.5mm.Then the applicability of the parameter design is verified by simulation.In order to solve the matching problem between the reference raster coordinate system and the image coordinate system,a reference raster grating line calibration method based on Hough transform is proposed.The measurement system was built and calibrated according to the set parameters.Then,the single-focus lenses with dioptronic values of-7.5D,-5D,-3D,-1D,1D,3D,5D and 6D and the progressive multi-focus lenses with dioptronic values of 0.12 D in the far region and-1.28 D in the near region were measured.The measurement results show that the absolute measurement accuracy of the system is 0.12 D,which meets the requirements of national standards.And the system stability is excellent.