This is the correct setup to get shadows from Rombo.material. It has a Shadow shader build-in however as of the beta you have to manually plug the Rombo.material to the Shadows slot.
A thick lens is a real lens system implementation. Actually is a raytraced lens system. However we don’t raytrace at render time over and over the lens system, we do it in a preparation step where we sample the iris and then save the values to work with that at render time. The more samples[…]