I have created this thread to discuss and further develop the “micro roughness” effect - whereby the apparent roughness of a semi-glossy material falls off at grazing angles - thereby making reflections sharper.
I have already created a node group to simulate this effect and a BDRF solution to this effect has also been described in a siggraph paper - both linked below.
These two images show an arc vis scene from Blendswap both without (top image) and with (bottom image) the effect active. Credit for the scene goes to Blendswap user NewSee2l035 - but I had to adapt the materials for Cycles.
I have also created a video to show this effect based on real experiments done by MartinZ over in the Disney shader thread
One other advantage of this effect seems to be that it solves the Fresnel Halo effect at high roughness values without actually having to change the Fresnel parameters. The halo seems to disappear as a natural consequence of having angle dependent roughness.
I guess the aim is to try to come up with a node based solution that most accurately mimics this effect - with the hope that Cycles may one day incorporate this in it’s Glossy BDRF or Principled shader.