Raytraces of spectral coma

This is a quick diagram which I produced in early 2020 for the purpose of comparing the optical performance of different grism configurations.

At the time, I was recording spectra using a slitless diffraction grating, and had the option of introducing prisms on either side of the grating to correct for spectral coma. I wasn’t sure whether it would be best to add the prism ahead of or behind the grating, or whether it might be better to use two prisms, so I ran some simulations, and the result is what you see below.

As an added bonus, here is an animated raytrace showing the effect of rotating a prism behind a slitless diffraction grating: