Odd IOR Issue

[Aldaryn]

Since 1.5 final, we are experiencing some really strange IOR behavior. Look at this example rendered with sun+sky to illustrate the problem:



The on on the left has an IOR of 1.6, the middle is 1.3, and the right one is 1.1. I think the reflection falloff is wrong here.

Below is a shader swatch from a current project,:



This shader has an IOR value of 1.53, it is an almost exact IOR of the coating on the flooring tiles used in our project, and I can tell you, the real one doesn't looks like this.

In the scene shaders with IOR lover than 1.6 render really odd. Hard edged bands appear on the surface, and the shaders are useless in this form. We usually work with real world IOR values, and many of our shaders have a value below 1.6. To be honest, almost all of our shaders have the fresnel ticked.

Vlado, please comment on this!

best regards,

A.

[Codi]

We had similar problems with other reflective materials.
I think it's due the cuttof value in your material options, you can try to reduce it to 0.001 to get correct reflections for the materials with lower IOR values.

[bardo]

I confirm it's a cutoff value problem.
Lower you value until reflection is ok.
For my experience low IOR with low reflection value need low cutoff value.

my workflow is diffuse pure black, set fresnel ON (if i need it) and reflection value.
Set IOR and check result.
If wrong i modify cutoff value until reflection OK.

If you set this before setup your desider material (diffuse color or bitmap, bump, glossiness,refraction)you avoid future rendering problems.

BYe

[Aldaryn]

Thanks for the info! I thought that the fresnel function was altered in some way, and even thought that this one is the correct one, but never thought to change the cutoff value, since I never had to before when working with dark shaders and dull reflectance properties like low IOR.

I think I posted this a bit too hasty, please excuse me, some bad deadlines are onto us here, and in the minute, I was clueless., so didn't even tried to do some testing.

Tested, solved it. Thanks again!

best regards,

A .

[vlado]

It is not really a 1.5 final issue; this has been so in all versions of V-Ray so far; like the others suggested, lowering the cut-off should solve it.

Best regards,
Vlado

[Aldaryn]

Thank you!

Works as it should now!

Only thing I can't undestand, is why this never came up here. I'm a black glossy sahader maniac, and worked with such shaders many times before, and never did it happened.

best regards,

A.

[vlado]

I guess it's more obvious with the sun&sky, since they are quite bright.

Best regards,
Vlado

[bardo]

aldaryn..i'm not technical as vlado (as obvious) but i noted that with gamma 2.2 this problem is more visible then gamma 1.0

after switched to 2.2 gamma setup i supposed that vray can't consider reflection with float number but in a integer 255 scale value. So i supposed was a bug.

But after some tests and comparisons i was "illuminated" by light cutoff (same behaviuor)that drive me to solve this "problem".

Probably you don't use gamma 2.2 in past.

bye

[sharpcube]

Man i have that same problem a long time, thx for the solution
jiiiaaaa thx thx

[tricky]

We never have really used IORs and Fresnel with our shaders, but am interested in testing them out. Where are you getting these 'real world' IORs from? Is there a good place where I can find them for concrete/timber boards/paint etc? Also, when using IORs and Fresnel, do you just bung 100% white in the reflection and the Fresnel button will sort out the actual reflectance levels? I mean, concrete for instance isn't that reflective at all (except at extremely accute viewing angles in certain lighting conditions.

[BELCORP_SAC]

We never have really used IORs and Fresnel with our shaders, but am interested in testing them out. Where are you getting these 'real world' IORs from? Is there a good place where I can find them for concrete/timber boards/paint etc? Also, when using IORs and Fresnel, do you just bung 100% white in the reflection and the Fresnel button will sort out the actual reflectance levels? I mean, concrete for instance isn't that reflective at all (except at extremely accute viewing angles in certain lighting conditions.

X2 some body knows where i can find a nice IOR chart to use? and maybe a nice tutorial of how to use correctly de ior´s values?

That would be nice!

Thx !!

[sharpcube]

Vacuum 1 (exactly)
Air @ STP 1.0002926
Gases @ 0 °C and 1 atm
Air 1.000293
Helium 1.000036
Hydrogen 1.000132
Carbon dioxide 1.00045

Liquids @ 20 °C
Benzene 1.501 Water 1.333
Ethyl alcohol (ethanol) 1.361
Carbon tetrachloride 1.461
Carbon disulfide 1.628

Solids at room temperature
Diamond 2.419
Strontium titanate 2.41
Amber 1.55
Fused silica 1.458
Sodium chloride 1.50

Other materials
Pyrex (a borosilicate glass) 1.470
Ruby 1.760
Water ice 1.31
Cryolite 1.338
Acetone 1.36
Ethanol 1.36
Teflon 1.35 - 1.38
Glycerol 1.4729
Acrylic glass 1.490 - 1.492
Rock salt 1.516
Crown glass (pure) 1.50 - 1.54
Salt (NaCl) 1.544
Polycarbonate 1.584 - 1.586
PMMA 1.4893 - 1.4899
PETg 1.57
PET 1.5750
Flint glass (pure) 1.60 - 1.62
Crown glass (impure) 1.485 - 1.755
Fused Quartz 1.46
Bromine 1.661
Flint glass (impure) 1.523 - 1.925
Cubic zirconia 2.15 - 2.18
Diamond 2.419
Moissanite 2.65 - 2.69
Cinnabar (Mercury sulfide) 3.02
Gallium(III) phosphide 3.5
Gallium(III) arsenide 3.927
Silicon 4.01

Acetone 1.36
Agate 1.54
Air 1.00
Alcohol 1.33
Aluminum 1.44
Amber 1.55
Amethyst 1.54
Aquamarine 1.58
Azurite 1.73
Bronze 1.18
Calcite 1.49
Carbon Tetrachloride 1.46
Chlorine, liquid 1.39
Crystal 2.00
Emerald 1.58
Ethyl Alcohol 1.36
Fluoride 1.56
Glass 1.52
Gold 0.47
Hydrogen, liquid 1.10
Ice 1.31
Jade 1.61
Mercury, liquid 1.62
Nitrogen, liquid 1.22
Obsidian 1.49
Onyx 1.49
Opal 1.450
Oxygen, liquid 1.22
Pearl 1.54
Plastic 1.46
Plexiglas 1.50
Pyrite 1.82
Quartz 1.54
Ruby 1.76
Silicon 4.24
Silver 0.18
Teflon 1.35
Topaz 1.62
Topaz, Blue 1.61
Turquoise 1.62
Water at room temperature 1.33
Zirconia, Cubic 2.17

[m_hinks]

Thanks a lot. I pressume those numbers are for the IOR for both refraction and reflection?

[BELCORP_SAC]

Thanks a lot. I pressume those numbers are for the IOR for both refraction and reflection?

I have that doubt to , the ior value is for reflection and refraction at the same time ? obvious if the material is transparent.

Thx a lot

Onz

[Sawyer]

I am kind of confused by this stuff. I understand the IOR for refractions but what is and index of reflection? (and could we possible change letters? maybe iof i don't know something different.)

Now the color swatch for reflections is how much it reflects. The Fresnel aspect is the reflection is adjusted for viewing angle (right? Snells law and all that) then is the IOReflection a multiplier on top of that? That is how I have been using it but I only eyeball it.

I see lists of indexed refractions:

http://en.wikipedia.org/wiki/List_of_refractive_indices

but nothing for reflections.