Field covered by the CHIP1 detector, through the NB filter and through the wide-band filter. Upper panel: total intensity image in redshifted Lyα band, obtained by coadding all images corresponding to all four polariser angles and to both ordinary and extraordinary beams, as recorded on the CHIP1 detector. The total equivalent exposure time is 13 h, 53 min, and 20 s. The five bands correspond to the positions of the ordinary beam; the bands where the extraordinary beam falls appear blank here, because the corresponding images have been aligned and stacked with those of the ordinary beam. This shows that only half of the field is accessible in the polarization mode. The red square indicates and surrounds the LAB image, which includes the overexposed QSO near its center. The black circles designate objects detected at each angle and beam, and for which the polarization was measured. The red segments are the polarization vectors for objects with a polarization fraction of P > 5 σ. Lower panel: total v_HIGH intensity image, corresponding to a total exposure time of 26 min, 40 s. The same red square as in the upper panel identifies the QSO. Both frames have the same scale.