# Water fresnel ?

what is the correct fresnel for water ? I havent foulnd it ont he web so i wonder if anny one knows what it is?

glitchglitch

1.5

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and 10 characters

:eek::eek::eek: Fligh, wrong?! Amazing!

1.5? That’s IOR, and it’s for plain glass, not water… clean water’s IOR around 20°C is 1.3333.

From the manual:

“Please note that in order to get a physically accurate Fresnel effect with the current algorithm, you have to set Fresnel to 5.0 and Fac to 1.25. Nevertheless, you can play with these values for the sake of artistic freedom, if you feel the need to.”

True fresnel would depend on the material the light is passing from and into… water transitioning to air, the index of refraction is all you need to set (water = 1.3333) for realism, unless you want something artistic.

In case you want to read up on it, check out:

(here’s a single page to explain it, with animations:
Reflection and Refraction of Light

Fligh, wrong?!

Chuckle… hey, I don’t think I’m right as often as you seem to think.

The glitch post was supposed to be a link to Jeremy Blinns discussion on the subject (which no longer works) and another link I can’t find now about how it’s calculated for PovRay. Fact is, Fresnel is not a Factor but a Coefficient of two or more factors, depending on how complex you want to get; relative everything for the following: density, temperature, turbulance and impurity, besides reflectivity, angle of light incidence, intensity, color and a whole mess of other things, most of which can be set seperately in Blender. Clear glass in a vacuum with direct light is somewhere around .3. Turbid (waves), muddy water in a humid (hazy) atmosphere with a low light angle is somewhere around 7. I took a lazy guess at 1.5 (since he didn’t mention what shaders he’s using or what IOR, etc I thought it safe) but I’ll remember in future that you’re watching me!

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Not to get too off-topic, but yea - your hit-to-miss ratio pretty much makes me take your replies as gospel. I’ve learned more in your replies to others than months of fumbling around in a drunken haze…

re: fresnel, aye, without teaching calculus or getting into physics debates, would coding the response against actual critical angles be better than a 0.0-5.0 range, maybe? One day when Ton looks bored someone might want to mention this…