Chromatic selection function of Euclid’s optical elements. Since the optical design minimises the number of refractive elements, mirror coatings and the dichroic element play a central role in preparing the passbands for the instruments. The VIS detectors have zero quantum efficiency for λ> 1.1 μm. The behaviour of the dichroic element above 2.2 μm is not specified; longer wavelengths could enter NISP and would be blocked by the filters. Figure adapted from Euclid Collaboration: Schirmer et al. (2022).