A method for determining the position of at least one edge of an object, in particular a strand, comprises illuminating the object using light from at least one coherent light source, wherein diffraction borders are generated on both geometric boundaries of the shadow caused by the object. The method also includes recording the spatial intensity profile of at least one diffraction border using at least one single or multi line optical sensor, differentiating the at least one recorded intensity profile with respect to location and plotting it using a squared location axis, and comparing the at least one recorded intensity profile, differentiated with respect to location and plotted using a squared location axis, to at least one periodic reference intensity profile. The position of at least one edge of the object is determined on the basis of the completed comparison.