> Could you use this to rough out a Koehler illumination?

Please, ask extension dev via issues tracker.[0]

UPD: Dev is here now![1]

[0] https://github.com/damienBloch/inkscape-raytracing/issues

[1] https://news.ycombinator.com/user?id=damienbloch

I'd like to to add simple tools someday (like ABCD matrices along a beam). But at some point it's probably better to switch to more evolved softwares, like the ones mentioned in the thread

JFTR, A simple ray tracing showing the concept of Koehler illumination.[0]

[0] https://www.researchgate.net/figure/A-simple-ray-tracing-sho...