Filter geometry and measurement points. The filters have a diameter of 130 mm (black circle). The blue line shows the baffle, blocking light paths outside without causing vignetting. The nine-point original measurement apertures are shown by the black rectangles (to scale). Our refined 37-point measurements are marked by red dots instead of black rectangles, to avoid cluttering. The grey annulus displays the 90 mm obstructed beam footprint, that is, the part of the filter seen by a source at the centre of the FPA. The obstruction is off-centred due to the telescope’s off-axis design. The response curves made available online are integrated over this grey annulus. The light of a source mapped onto any of the four corners of the FPA intersects different parts of the filter; the centres of the correspondingly shifted footprints are shown by the blue squares.