Focal length measurement technique using talbot effect

A focal length measurement based on Talbot effect was presented, which could be used for long focal-length lens. The variation of Moiré fringes changed after the typical phase object of measured lens being added between two gratings. The images of Moiré fringes taken by CCD camera were processed with MATLAB. The focal length of measured lens was figured out accurately after calculating the slope coefficient of processed Moiré fringes, the separation angle between two gratings and measuring, and the distance between lens and the second grating. The experimental data indicate that, for a system with laser wavelength of 0.65 μm, measured lens focal length is 420 mm, and the measurement accuracy is 0.10%.