fresnell IOR vs refraction IOR

[flipside]

I seems like the fresnell IOR is only independant of the refraction IOR when refraction color is set to black.

This material should render very reflective because of the high reflection IOR, but it renders like if the refl IOR is set to 1.55 (taken from the refraction IOR).




Using different ior for fresnell and refraction in refractive materials is very handy when you wanna make glass a bit more reflective, without changing the refraction look.

Or in my case, if you want to make a refractive material with IOR=1.0, to be able to render any reflections at all
(refr ior=1.0 in combination with fog color creates some kind off translucency look).

[Jean-Paul Paloux_cg]

fresnell IOR vs refraction IOR

you have any pics of all this experimentations ?
Jp

[dalomar_cg]

fresnell IOR vs refraction IOR

I'm not sure exactly what the effect of what your trying to get is, but I asked Joe and the IOR values aren't linked. If you want to see the reflections on an object with fog and a refraction IOR of 1.0 you might need to set the fresnel IOR significantly higher than what you would normally (maybe 5 or higher) depending on how much reflection you want. Hope that helps? a pic and some settings would be helpful because I'm not 100% sure of what your trying to achieve.

[Micha_cg]

fresnell IOR vs refraction IOR

I'm not sure exactly what the effect of what your trying to get is, but I asked Joe and the IOR values aren't linked. ....

But if an user set refraction IOR 1 and reflection IOR 1.55, than the reflections are looking like IOR 1 too - invisible.

http://www.asgvis.com/phpBB2/viewtopic.php?t=891

[dalomar_cg]

fresnell IOR vs refraction IOR

In this case for some reason it causes the effect of the reflections "disappearing", however with other cases the IOR act independently. The case of having an IOR of 1 propabably causes some anomilies within the math (similar to dividing a number by 0). It also may be because the falloff is going from a pure white(100% reflective) to a pure black(0% reflective). If you change the pure black color to a dark grey the reflections should show up again. Both changing the color or increasing the IOR will create reflections on an object with an IOR of 1.

[Micha_cg]

fresnell IOR vs refraction IOR

Thank you for the trick. A little workaround.


... in a previous beta release it was working well ...

[Gijs]

fresnell IOR vs refraction IOR

well, there is definately an issue with the fresnell thing. See image below. When there is no refraction layer at all, the fresnell reflection looks OK, when a refractive layer with IOR 1 is added, there is no reflection at all, and when the IOR in refractive layer AND the refractive ior in the fresnel map is set both to 1, a slight reflection reappears...

[joe_b]

fresnell IOR vs refraction IOR

if you crank up the fresnel IOR you will get your reflections back. Damian had to get it up to around 10 - 20 to get reflections visible again. I can't say that this is physically accurate or not though. In 3dsmax do you get different results than this?

[Gijs]

fresnell IOR vs refraction IOR

In 3dsmax, you can't make such material, since there is no transparency setting for the diffuse part, so I can't really tell. What I find logical is that the material would show identical results with or without a refractive layer when the refractive layer is 100% white and IOR=1.
What I find the most strange, is the fact that when both fresnel and refract IOR are 1.55 in the fresnel map, the reflections are gone(second example) while in the last example (when the refract IOR in the fresnel map is 1) reflections are showing up (though very thin)

[joe_b]

fresnell IOR vs refraction IOR

Perhaps there is some mistake on my part or a miscalculation with the V-Ray plugins. When I have a few minutes I will do some tests to see if I can finally put this issue to bed - as it has been brought up before a few times by Micha and others.