Hello All, I would like to start learning how to ray trace but the tracing through a tube with a thickness of t has got me stumped. If I have an n1 (outside tube), n2 (Tube), and n3 (inside tube). n1≠n2≠n3. Knowing Θ1 (the angle of incidence in relation to the normal), I can calculate Θ2 from Snell's Law. The problem is that I am not sure as to how to calculate Θ3 (At the interface of the tube to the Inside of the tube). I am pretty sure I need to solve for Θ3 in relation to Θ2. I tried to approach the problem by trying to find the arclengths from the center of the tube, but I could not solve it from that method. Does anybody have some experience in this to point me in the right direction. I have attached a drawing since my explanation is not very clear. The drawing is not to scale. r2 refers to the radius of the outer circle and r1 refers to the radius of the inner circle. Thanks for any help!