What optical design software exists for Linux?

I've been trying to find affordable optical or lens design software for Linux, but have been unsuccessful. Apparently there is a version of OSLO which will work, but that is waaaaaaay out of my price league and their educational version is Windows-only. Does anyone know of something suitable?

Have a look at Opus (optics for us) http://www.maxreason.com/software/optics/opus.html, which is under the GNU GPL. You can download it free of charge as well. I haven't found anything in Debian repositories.