This is a really great handout of Gauss' Ray Tracing Technique; it provides mathematical distinctions between positive and negative lenses: http://bolvan.ph.utexas.edu/~vadim/Classes/10f/rays.pdf
This is a really great handout of Gauss' Ray Tracing Technique; it provides mathematical distinctions between positive and negative lenses: http://bolvan.ph.utexas.edu/~vadim/Classes/10f/rays.pdf