Four different steps in the determination of transmittance curves shown for each of the 16 individual copies of the NB118 filter in VIRCAM. First row: collimated beam measurement at room temperature as provided by the manufacturer NDC. Second row: shift as expected due to the temperature difference. Third row: theoretical conversion to the convergent beam. Fourth row: response function including all theoretical filter transmittance, mirror reflectivity, detector QE, and atmospheric transmission (PWV = 1 mm, airmass = 1). In the plot, the 16 filters are separated into subsets of four filters corresponding to the four columns or stripes of the combined image (cf. Fig. 2d). In addition, the other 12 filters are shown in every panel in light gray. Positions and relative strengths of the sky emission lines are also included.