Question about fresnel IOR

[SHoutzager]

Hey I am trying to wrap my head around this Fresnel IOR settings in Reflection part of BRDF (see attached image). Isn't index of refraction only for clear items, or does this IOR mean index of reflection? Is it the same principle?

Also, changing the number doesn't really change the reflectivity of the edges and the center. It all looks uniformly reflective. Thanks!

https://www.dropbox.com/s/jq87yxadz5gx7hl/ior.PNG?dl=0

[fooprobe]

Well it's the same basic variable as that for the fresnel IOR in the reflection layer of the old standard material. It does change the amount of reflection, so if you're not seeing that, maybe post some pics? Higher values will tend to reduce the fresnel effect and make the reflection appear more uniform. You also are using a refraction color other than white, which will also affect the amount of perceived reflection.

My understanding is that IOR does still refer to index of refraction. The IOR affects both the amount that light bends (what we usually call refraction) but also the amount that light is transmitted (dimmed) or reflected. So a material can have an IOR even though it's opaque.

Post some pics.

[mnewberg]

Wikipedia is always a good resource as well:

http://en.wikipedia.org/wiki/Refract...x#Reflectivity

[SHoutzager]

Good point Matt. It clears things up and opens up some issues. Index of Refraction is for all materials and gases as well. Starts at 1 and ends at 2.42 for diamonds. Plastics are normally 1.3 to 1.7 with an exception.

So why does VRay let you set the IOR up as far as you want? Wait it is there own term "fresnel IOR".

As far as pictures, my metallic renderings are "uniformly" metallic in the preview sphere and in renderings. There is no fresnel effect that I can control.

[fooprobe]

the "fresnel IOR" is just the refractive index of the material as used in the fresnel equations, n in the wikipedia entry. Metals are uniformly reflective, they do not exhibit fresnel reflections (the wikipedia entry on fresnel reflections notes an exception for conductive materials in general). That said, I have always been confused by the reflections IOR option in the standard material fresnel map. maybe it lets you have a different IOR for light transmission ("refraction") and for reflection - which again doesn't exist in the real world.

vray lets you do all kinds of things that don't exist in the physical world. like having a different "highlight glossiness" and "reflection glossiness". Maybe someday some materials scientist will invent a material that does have really high IOR.

So increasing the "fresnel IOR" beyond numbers that actual materials actually exhibit just plugs that number into fresnel's equations, and it approximates a metal and you get a more uniform reflection.

if you want a more fresnel-like effect on a metallic reflection (that is, very reflective), try using the falloff map in the reflection color map, or use an angle-blend material with a more-reflective and less-reflective material.

[fpedrogo]

We are not using the full complex IOR algorithm for the reflection. We are using a simple version one. Therefore, you will have to use values like 10, 16, 20, etc for metals.

[SHoutzager]

OK, getting a better idea of these settings. thanks.

[gzray]

You might find this interesting: http://www.manufato.com/?p=902
It is not about numbers but it explains how reflections work and how to use these in rendering. An eye opener to me being a rookie.

regards,
Gerard

[fooprobe]

That's a good article, but in vray there's no need to tint the specular (reflection) with the inverse of the diffuse in order to get a "white" specular effect on dielectric materials.