A low cost technique for automated measurement of focal length using Lau effect combined with Moiré readout

A low cost, accurate and relatively simple technique based on the Lau effect coupled with Moiré readout for measuring the focal length of collimating lenses is demonstrated. The method is based on defocusing the collimating lens and measuring the corresponding variation in the inclination angle of the Moiré fringes. Details of theoretical background, experimental arrangement and error analysis are presented. Experimental results of the measurements are in close agreement with the true values.