Blender Physically Based Shading: Fresnel
Why Blender Stack Exchange recommends it
Blender Stack Exchange answerers point people to it for an explanation of Fresnel reflection and a roughness-aware Fresnel node group for Cycles shaders.
Recommended by 3 people across 2 different months, 2016 to 2016.
What it is
A 12-minute tutorial by CynicatPro explaining how the Fresnel effect works and how to build a physically based dielectric shader in Blender, including a Fresnel node group that accounts for surface roughness. A downloadable shader accompanies the video.
What people said
Recommends JtheNinja · 2016-07 · Blender Stack Exchange · on “Is cycles fresnel node physically correct?”
Nothing is physically correct, it's all approximations. (raytracers don't even implement the wave nature of light...). But you're correct in that Cycles' fresnel node is not as close an approximation as it should be. I'll let Lukas Stockner, one of the Cycles' devs, explain: [LINK] tl:dr: the true fresnel result for a non-smooth surface requires you to calculate it with the direction the ray reflects from the microscopic imperfections of the surface. But this direction is not yet known when the mix shader is evaluated, so Cycles is forced to calculate fresnel for a smooth surface. There are various tricks to approximate the correct result that make things a little more accurate: [this video] It's
Recommends user13877 · 2016-12 · Blender Stack Exchange · on “How the Fresnel effect works and how to construct Physically-Based shaders in Blender?”
In this [this video] Cynicatpro explains how Fresnel works and builds a shader for dielectric materials. In explaining how roughness has an impact on the fresnel effect and how to simulate that in Blender he built this Fresnel node group: [LINK] When introducing the Geometry node he loses me. I think I understand why the "standard" Fresnel node has the Normal as an input (EDIT: I now think I don't). And I understand why roughness has an impact on Fresnel. But I don't understand why the Geometry - Incoming should be a "good" approach for simulating the effect of roughness on Fresnel. Who can explain ? BOUNTY QUESTION: The answers of @Leander and @lbalazscs were certainly helpful but I still don't
Recommends piegames · 2016-12 · Blender Stack Exchange · on “How the Fresnel effect works and how to construct Physically-Based shaders in Blender?”
B You can find a very good explanation of Cynicat's Fresnel node group about here [this video] . But you asked for it, so here my explanation: You can, simplifying a bit, categorize materials into two categories: metals, and dielectric. Almost every material is one of those or some mixture of them. The video refers primarily to dielectric materials. Dielectric materials have some base material (e. g. diffuse) and some reflection. The reflection is always white, and its amount is at a few percent when looking at it from straight above and increases up to almost 100% when looking at the surface with an angle of 90°. Two things influence the amount of specular reflection: the Index of refraction (IO
Cites Jaroslav Jerryno Novotny · 2016-09 · Blender Stack Exchange · on “Metal material with glass and gloss node?”
Glossy shader alone doesn't indicate metal - it indicates reflection. So it is very common in shader node groups because every material is reflective one way or another (except of some vantablack [LINK] , emissive materials, etc.) However the shader you presented is not physically correct - thus it is an example how not to construct shaders. You don't want to mix in glossy node through mix-node with constant mixing factor - you need to mix in glossy through fresnel: How do I create a reflective white material? [LINK] When you have a rough surface you need a specially constructed Fresnel node that accounts for the roughness (image borrowed from blenderguru [LINK] but original credit goes to c