| To the measurement method of ultra-long focal length lens based on Talbot interferometry and Moire stripes, the inclined angle θ between Ronchi grating G2and G1, tilt angle a of moire stripes have greater impact on measurement accuracy. In order to solve this, On one hand, simulation analysis shows that how tilt angle a of moire stripes error caused by light path of imaging part, adjustment methods are proposed and also be tested and verified by experiments. On the other hand, in order to further improve measurement accuracy, a new way by moire stripes matching technique is proposed to measure long focal length. Both simulation and experiments are carried out to prove advantages of this method.As to minimize size of the measurement system of large size and ultra-long focal length lens, two mirrors are used to change light path. In this case, installation error of the two mirrors added may be a large obstacle to accurate measurement of ultra-long focal length lens. For the sake of analyzing how installation error of two mirrors infect the angle of moire stripes on receiver, moire stripes are understood as parallel lines which composed of point light source with certain light-path vector. This approach proposed uses the calculation formula from mirror deflection angle to the reflector unit normal vector, and the matrix form of the law of reflection, to calculate the relationship matrix from vector of incident light to vector of exit light. Based on unit normal vector of two mirrors, incident light-path vector, exit light-path vector, and analytic geometry, equation of line on which image of point light source place can be presented, so we can get the angle of moire stripes on receiver and so is the angle error caused by installation error of the two mirrors added into light path. In addition, the angle error of moire stripes is calculated theoretically in49different situations of small mirrors deflection smaller than1degree. The results indicate that the installation error of the two mirrors should be taken into consideration. A new method by using autocollimator to adjust the installation error of the two mirrors is proposed, installation error of the two mirrors can be controlled to lower than1 seconds through this method. Moire stripes angle error should be better than (10-4) order of magnitude in this situation. Experimental results show that Moire stripes angle measurement error is0.005degree, which fully illustrates the effect of mirrors adjustment when this system is used for the measurement of ultra-long focal length.In case of Measurement system of ultra-long focal length lens based on Talbot interferometry and Moire stripes, the major obstacle is caused by small relative errors of the inclined angle θ between Ronchi grating G2and G1, tilt angle a of moire stripes. As to improve measurement accuracy, a new way by moire stripes matching technique is proposed to measure long focal length. In this way, divergent light is used as light source. Before lens is put in light path, moving Ronchi grating G2until CCD catch a distinct moire stripes figure. Then put lens in light path, moving light source along the system optical-axis. The wavefront of divergent light pass through two Ronchi grating after refracted by lens, a new figure of moire stripes is catched by CCD. If two figure of moire stripes completely match, the focal length of lens can be calculated by combined focal length formula. In previous method, small relative errors of the inclined angle θ between Ronchi grating G2and G1, tilt angle a of moire stripes can cause large relative errors in the results. In comparison, the inclined angle θ and tilt angle a are not necessary by this method. The tilt angle a is the taken as basis to judge whether moire figure match or not. Both simulation and experiments have been carried out to prove the effectiveness and advantages. The experimental results show that relative error is about0.018%, therefore, The proposed method is very useful for measuring long focal length. |
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