利用Ronchi光栅的Talbot效应和Moiré条纹测量长焦透镜焦距,根据焦距与莫尔条纹斜率之间的定量关系可求得透镜焦距.分别采用Canny算子和形态学方法对光栅的栅线中心进行像素级定位,再用高斯曲线拟合对其进行亚像素定位.经过对标准条纹的标定,验证了该方法的条纹中心定位误差小于0.1个像素.采用光栅作为系统的自基准对CCD像素当量进行了亚像素标定,为条纹斜率和宽度的计算提供了可靠的测量基准,经过计算,采用这些数据计算的焦距误差为0.10%.

The focal length of measured lens can be figured out accurately according to its relation to the slope coefficient of Moiré fringes.An approach is presented to determine the location of grating centre at the level of pixel by Canny operator and detection based on mathematical morphology.The sub pixel localization is presented based on Gauss curve fitting.The localization accuracy is proved less than 0.1 pixel by calibrating the standard fringes.Then the grating is set as the reference to calibrate the equivalent length of CCD pixel to ensure the slope and width measuring of fringes accurate.The error of focal length is 0.10%.