Sometimes it is useful to visualize an optical design and calculate the optical quality. A free program for doing that is BEAM4 from http://www.stellarsoftware.com/
I had used an earlier test version, but now it is available as a free version and more user friendly, so I gave it a try.
I chose the Czerny spectrograph example and modified it to calculate spot diagrams.
first result, optimized for resolutionquick spot diagram, only a few rays calculated, showing nicely the astigmatism of this design (focus optimized for spectral resolution)
Amateur Astronomer specialised in Meteors and Spectroscopy, FMA (Fachgruppe Meteorastronomie); AGG (Astronomische Gesellschaft Graubünden)
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Spectroscopy 