Left: 2k × 2k image of a single NISP detector showing the first-order dispersed image of a monochromatic PSF at 1800 nm taken with NISP RGS000. The corresponding zeroth order is not visible in this image because it falls into detector gaps about 800 pixels above the first-order PSF. Centre: zoom-in showing the surrounding area of the PSF in a region of 40 × 40 pixels. Right: zoom in on a region of 10 × 10 pixels centred on the PSF. Here, the colour scale has been adapted to not have the central core of the PSF saturated as in the left and central image. For a detailed description of image features, see the main text.