slits to reduce the risk of contamination between slits. These two steps are purely practical, but make bookkeeping significantly easier.

*Flatfielding*
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In this processing step, we had to tackle three main issues:

The first one is an inherent complication in the FORS instruments. Due to the mechanical construction of the robotic slit masks and the location of the flat-field lamps, flat-field exposures show higher flux levels in a few rows at the upper or lower edge of the slit. To correct for this effect, there are two sets of flat-field lamps in the instrument. We took a sufficient number of flat-field exposures using both sets of lamps. We generated merged flats independently for each lamp set and generated the final flat-field frame by taking the smaller pixel value in the two frames. As the reflections from the two lamp sets do not overlap, this feature can be fully removed.

The second issue is a consequence of our unusual observing strategy. In some cases (due to geometric constraints imposed by the robotic slit masks) we could not target very faint objects with a particular slit, but we had several bright candidates available. In these cases, to maximize efficiency, we reconfigured 