Passband variations of the SDSS r filter. Top: measured variations of the SDSS r filters from Doi et al. (2010). Measurements have been performed for each of the six different CCD columns. The transmissions have renormalised so that the maximum of the transmission at Position index 1 is 1. The inset shows a zoom on the cut-off of the transmissions. The legend gives the position indices associated to each colour. Bottom: the first four moments of the six SDSS r passbands. Each transmission is identified with a specific colour, identical in the top and bottom panels.