Zoom of a DFOSC i filter image showing the four components of the lensed quasar and four nearby stars. The components are labeled following the notation of Wisotzki et al. (2002): “A” for the brighter component, “B”, “C” and“D” clockwise. The stars “R”, “S”, “T” and “U” were used to search for a suitable reference star. The “R” star was finally chosen. The contrast of the displayed image, on a negative scale, was selected to improve the visibility of the lensed components. The image is a median of the three CCD frames collected on 2008 August 8.