And I mean the angle with the normal vector. Suppose you shine a laser through a prism at a large angle of incidence, and the prism has index of refraction 1.7. You get the angle of incidence high enough, and you get total internal reflection. Then you put a 1/4 wavelength layer of MgF, index 1.38 on the face of the prism where the total internal reflection is occurring. Would the prism the let some light through, and then have the same total internal reflection angle that a pure MgF prism would have, allowing a higher angle with the normal? I'm designing an eyepiece and trying to figure out just how much bending I can get away with. What if some nanoparticles are added on top of the MgF, giving a second layer of index 1.18? Would that allow significantly higher angles? Would the nano particles likely be uneven and cause scattering? Nikon claims to have that technology.