Since Redshift 2.0 came out today, out of interest I clicked on the "what's new". Surprise, surprise :- ) It has TWO new PBR shaders, their own, and alSurface (so I presume you can almost directly render your Arnold scenes in Max).
This is first time I had it installed, looks like Vray 1.5 on steroids, so I just selected Bruteforce + Bruteforce for G.I (8 bounces), and 8 reflective bounces, progressive sampler and did some quick tests (I used my single Titan-X). I ignored samples and used universal sampling.
The bellow shaders are "Redshift material", which is rather super-extended PBR shader on anabolics with everything you can imagine. It offers multiple reflective models ( IOR-based, ComplexIOR based (n/K for metals), and Metalness workflow from Disney), roughness (and legacy glossiness), full-range, perfect self-shadowing (no grazing, rim lighting or halo effects) in all BSDFs (GGX, Ashikmin and Cook-Torrance). If I count correctly, it has 50 texture inputs ? Overkill is understatement, but most settings can be ignored and you can enjoy true, well functioning shader experience.
So let's get testing: Simple shaders with single map in ROUGHNESS (inverted glossiness with flat interpolation between 0-1, full-range) slot. I adjust the smudgy map output to drive value instead of using number to get some variation here. Specular is left
untouched, and is 255/255/255 White, so 100perc. For physically plausible materials, the specularity doesn't clamp. There is no such thing as 0.5 specularity. The specular maps slot, is meant as 'mask', no driving parameter for value. The only thing with need to work with in PBR renderer, is adjust roughness based on look that we want.
GGX BSDF
Cook-Torrance BSDF
Ashikmin-Shirley BSDF (this is what Corona used formerly, but look how different roughness and fresnel behaves)
Simple gold material done using color (from DontNod chart) in color and metalness set to 1. Simple, and functions as expected. Roughness behaves nice for metals also. I used GGX BSDF.
Here is comparison of fresnel behavior. (I chose Cook-Torrance although GGX gives rougher/dustier look, I preferred the look of this one for plastic ball)
And here is absolutely rough with GGX BSDF. I roughened the Diffuse also (for flater, dustier look).
In short, looks better than Vray and much more better than Corona. What gives.. ? Send legacy materials into history and don't look back.
Here is metalness workflow. 1.0 = Metallic IOR, DiffuseColor automatically becomes SpecularColor, just like in Disney PBR convention. Artist-friendly as it can gets.
Simple IOR workflow. When you need that exact IOR for specific material (like water=1.333) or just like the old-style. You can alternatively switch to ComplexIOR and input both n and K for metallic materials. No plugin needed.
Here is how the full shader looks with all parameters exposed. The first 3 are artistic features (ignore samples), the last panel is for technical(bias) tweaking. But even the artistic features are bit complicated in certain part like SSS. On other hand, those who use SSS for photorealistic characters, would presume prefer this version opposed to Disney's. Everyone else can ignore this, you don't have to touch anything you don't need.
From my quick testing, I give it 9/10, but only because I am simple person and lack direct access to artist-features like Sheen. Shader works fantastically and really lets you create material of your choice. Will do some full-scene conversion to see how the correct specular fare.
