Fresnel, fac and IOR

I’ve been messing around with the Fresnel and IOR settings to get a better understanding of how they work. I don’t know if this is of any use to people but I thought I’d share the results of my experiments.

basic set up was a camera, large smoothed UVSphere and a cube positioned behind the UVSphere

  1. Changing only the Fresnel setting:

http://homepage.mac.com/garagecat/.Pictures/Photo%20Album%20Pictures/2004-08-08%2003.25.48%20-0700/Image-3A298B10E92511D8.jpg

  1. Changing the fac setting, with Fresnel set at 3 different values:

http://homepage.mac.com/garagecat/.Pictures/Photo%20Album%20Pictures/2004-08-08%2003.25.48%20-0700/Image-3A29A0C4E92511D8.jpg

  1. Changing IOR values (with Fresnel set at 3, fac at 2)

http://homepage.mac.com/garagecat/.Pictures/Photo%20Album%20Pictures/2004-08-08%2003.25.48%20-0700/Image-3A29AD3EE92511D8.jpg

  1. Changing the camera angle so it is no longer in line with sphere and cube. (Fresnel 3, fac 2)

http://homepage.mac.com/garagecat/.Pictures/Photo%20Album%20Pictures/2004-08-08%2003.25.48%20-0700/Image-3A29BB28E92511D8.jpg

As a footnote: I assume the Fresnel shader is named after Augustin Jean Fresnel (1788-1827) who is famous for his work with lighthouses, the Fresnel lens and working on the wave theory of light.

He published his first paper in October 1815 on his wave theory of light and made a first attempt to explain the phenomenon of diffraction

very good tests although the color choice wasnt that grand. you should have used a white background, red sphere, and yellow or blue cube. The settings are very interesting and i’d love to see a reflections version! nice work! :wink:

Thanks Prince. Still not sure if its of any use to anyone. However, I often find that after a setting change here and a tweak there, I’m completely lost in Blender space and have no idea how to re-create the effect I just got.

Here’s a couple of slightly different versions. I tried to be fairly systematic, so hopefully it shouldn’t have too many errors. [EDIT] I lied. On the first one the first Fac value is 1.25, and not 1. hmmm [/EDIT][edit]corrected[/edit]

  1. Fresnel and Fac

http://homepage.mac.com/garagecat/.Pictures/Photo%20Album%20Pictures/2004-08-08%2014.21.27%20-0700/Image-CA1CBABAE98011D8.jpg

  1. IOR

http://homepage.mac.com/garagecat/.Pictures/Photo%20Album%20Pictures/2004-08-08%2010.41.25%20-0700/Image-01FB03A1E96211D8.jpg

Very small changes in the IOR settings have a big impact on the image.

Hey …stuff like this is very useful.

that’s good to know JDA. I’ve just corrected the mini-mistake. feel free to take a copy

aye, i’ll take a copy too! :wink:

Very useful. Using blenders own render I have trouble with getting say a glass to look like it has been made with a red glass, that is, it transmits just red light. Anyone know what factors should be set for this.

FYI here are some approximate refractive indices of some common materials. Approximate in that the refractive index of most materials depends on the wavelength of light.

air 1.00
water 1.33
glass 1.5-1.6
crystal glass (also called lead or flint glass) 1.6-1.9
diamond 2.42
quartz 1.65
corundum (ruby, sapphire) 1.77
alcohol 1.36
chloroform 1.45

You have trouble for a good reason, alpha in blender does not do filtering.

You have trouble for a good reason, alpha in blender does not do filtering.[/quote]

really? what do you mean by filtering then?

do you mean this? ->

http://myfilelocker.comcast.net/donkim/psuedoglass.jpg

I just whipped up a simple scene here in about 5 min, model and material both suck, but it does show what i think you mean by filtering.
Is this it or am I missing something here?

Yes that looks ok to me. What are your settings?

well, once you have your glass looking how you want it, just activate the transparent shadow (in the shaders box) button in the material of any object (ex: the floor plane) that you want to receive the colored shadow. AFAIK this only works with ray shadows, doesn’t seem to work with z-buffered lamps.

hope that helped.

Few months ago I was experimenting with fresnel alot … I looked it up through google and found alot of mathmetics… Then finally I came across an easy explanation… I’ll post the link here when I find it again …

If I remember correctly fresnel is the angle at wich light bounces back from a reflective surface, wich means that viewing it from certain angles increases or decreases the reflection wich you see… Very handy now where’s that darn link…

really? what do you mean by filtering then?

do you mean this? ->
[/quote]

NO.

the shadow are colored, but the transmitted light is unchanged.

look at a raytracer like POV, you have 2 parameters, transmit and filter.

In the second case, the light which pass through the object is filtered by its color and for example, if the color of object is Red only, only red component of light will pass.

So if you have, say a red plane with filter 0.5 then a blue plane with filter 0.5, no light will be able to pass and the result color is Red, the shadow will be black.

try it in blender, you get a yellow result and a colored shadow, like transmit.

Hence Blender don’t do filtering.

note that usually, a mix of the both is used.

Hi,
I just wanted to say thanks for posting your investigation. As a new user it has helped me a lot and gave me the idea to make a “lens” to put in front of the camera. I’m sure people have done that before, but like I said, I’m new.
Thanks.
Tim

thanks corsica S, thats useful feedback. I might try some more experiments soon

Excellent idea, something I’ve been meaning to do for ages.

Most helpful, printing now. :smiley:

Thanks for the hard work,

Sonix.