Illustration of the sDIR method. The blue line represents the unweighted spectroscopic redshift distribution of the calibration sample. The red line is the DIR estimate of the redshift distribution of the full lensing catalogue, n_DIR, all(z). The black line in the upper panel shows a parametric fit to the red line and the lower panel shows the ratio of this fitted function to the blue line, which is a first guess of the smoothing weight.