@theluthier nice video, but unfortunately incorrect. He claims that towards a 90° viewing angle, every material has a perfectly mirror-like reflection (all of his curves end at 0). A rough material however, will never have a roughness of 0! No matter at which angle you look at it. I checked all of my matte-painted walls;)
There is also the issue, that in CG the Fresnel is calculated from the viewing angle, while in reality, the Fresnel is calculated from the light direction….But all of this is extremely complicated and I would suggest to not worry about this and just make amazing looking art! If it looks good, it is good;)
