Part of the fields of view of RX J1131−1231 (top) and SDSS J1226−0006 (bottom) as seen by the Leonhard Euler 1.2 m Swiss telescope at La Silla Observatory. A total of 195 (388) frames with seeing < 1.25 (1.4) and PSF ellipticity < 0.15 (0.18) are stacked to produce the deep field image for RX J1131−1231 (SDSS J1226−0006). The insert shows a single exposure of 360 s in R band. The stars used for the PSF construction are labelled PSF_i, in red, and the reference stars used for flux normalisation are labelled in green, N_j. The field of view for the other lensed quasars are presented in Appendix A (Fig. A.1).