Ray tracing of the NISP Optical Assembly for three sources located at the centre and at two opposing edges of the focal plane. Light rays are shown, for each source, at wavelengths of 1250 nm (red), 1550 nm (green), and 1850 nm (blue), dispersed by grism RGS270. The dichroic element is located in the pupil plane of the telescope outside of NISP and is not part of the instrument.