View Full Version : reflect and refract IOR misunderstanding in vray

08 August 2012, 09:16 PM
Hello everyone!

I have a little misunderstanding issue about fresnel IOR (reflection) et the IOR (refraction). I know what they do and how to use it, this isn't the problem.

Anyways in a Viscorbel's tutorial he gives us those numbers for the fresnel IOR:
water 1.33
plastic 1.45
glass 1.5-1.8
diamond 2.4
compound materials like wood, stone, concrete etc 3-6
metals 20-100

Up till there everything seems OK, but you gotta know something: the fresnel IOR and IOR are actually linked in V-ray (i read the manual) because this is how the materials work in real life. It means that if a material has an IOR of 3 then so is its fresnel IOR as well. This is why those 2 numbers are linked in the material slot by the L button.

So what's the matter? Well a bit further in the tutorial he gives a list of IOR (refraction this time), and look what we got:
Steel 2.50
Chrome Green 2.4
Chrome Red 2.42
Chrome Yellow 2.31
Chromium 2.97

How is this possible? Fresnel IOR and IOR have to have the same number, so in this case, those metals must have had an IOR more than 20 and less than 100 according to his fresnel IOR explanation .. :surprised

Can anyone help me out? This is really disturbing!
Thank you very much!
Have a nice day :)

08 August 2012, 07:27 PM
Anyone? Help! :)

08 August 2012, 02:36 AM
There's a check box you can tick/untick right around reflection IOR settings to link/unlink it to refraction IOR. I'm not sure if you can create separate IOR or different light colours however.

The IOR above 20 I believe it's a trick to get very reflective surface to look better.

08 August 2012, 02:24 PM
The thing is that those IOR numebrs aren't really for metals. The fresnel equation in vray (and most other renderers) is a simplified version of the full equation which basically only works correctly for non-metals.

The full equation uses two material variables instead of one. In the list where the lower numbers are given likely only that first number is listed, making it somewhat pointless.

When you can't calculate the full equation you'll have to approximate the reflection curve. You could do that by drawing it in a falloff curve, or use really high IOR numbers so it looks somewhat similar to the metal reflection curve. Which are the high numbers for metals in the first list you mentioned.

Don't confuse the two variables of the fresnel equation with the two different IOR values in vray. Like you mentioned those two should be linked unless you want to do some different things with the material for some reason.

So for vray forget about the lower IOR numbers for metals and use the higher ones to get a very rough approximation of the reflection curve.

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08 August 2012, 02:24 PM
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