Sunfish, there's a few optical raytrace programs out there that will handle a limited number of surfaces for free , but they are a great place to start to learn about optical design and evaluation if you use supporting texts .
I've just been having a look at Modas NG . You can download from the download page. I believe the full blown program is going open source soon and will be free .
Comes with a load of sample designs .
http://www.myoptics.at/modas/galleryng.html