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View Full Version : can someone explain brewster's angle to me?



IRML
09-05-2009, 06:01 PM
...more specifically how I can use it in relation to surfacing

I know the definition of it, what it does to the polarisation of light etc... but that just doesn't help me comprehend what the visible effects of it are

what I do know is you can do the ArcTan of the refraction index and get an angle that you can use with fast fresnel, but that's way too old school for my liking, and I don't know how to translate that into something that'll work with nodes

I'd just love for someone to explain in layman's terms what this S and P polarisation is; what it means for reflection and refraction, fresnel curves and gradients; if I need to think about it on transparent surfaces, or if it'll help with non transparent surfaces too........ you get the idea

thanks

SplineGod
09-05-2009, 08:38 PM
Basically that relection, refraction, transparency etc are a function of the viewing angle thru a reflective or transparent material.
For example, if y ou are staring into a window straight on. It wont be as reflective if you look into the window from a more extreme angle.
Look at the body of a nice shiney ar. Its s less reflective looking straight at the surface and more reflective towards the more curved areas.
Mirages are also created due to this effect.
When you adjust the rearview mirror in your car to reduce the reflection its becuase youre changing the angle to do the same thing.
I generally dont use fast fresnal etc but use gradients intead so I can control the final look.

Also a mirage is caused by the sky reflecting off the road at brewsters angle. Also the light we see coming off the road at that angle is polarized. The vertically polarized light is absorbed by the road and the horizontally polarized lighti is reflected. This is why polaroid sunglasses reduce road glare because they are vertically poloarized which allows them to absorb the horizontally polarized light and pass whats left of the vertically poloarized light.

IRML
09-06-2009, 03:25 AM
what you've said just sounds like fresnel curves

SplineGod
09-06-2009, 04:16 AM
Exactly! Theyre both related. :)

IRML
09-06-2009, 05:47 AM
this I already understand, but it doesn't help me put it into practise

say I have a list of refractive indices for several metals, and I wanted to recreate their surfaces in lightwave, how do I use the refractive indices to do this? I don't think it's as simple as just putting that into a fresnel node and plugging it into reflection

SplineGod
09-06-2009, 06:27 AM
IOR for a transparent material works a bit differently then IOR for a reflective material which is more complex. Im pretty sure that in LW IOR is used to effect refraction and not reflection.
Another thing is that alot of this depends upon other factors like how rough or polished the surface is etc.
I tend to use gradients based on incidenet angle to get the surface to look like what I want rather then what a real fresnal shader might impose. Most people I know tend to work that way as well.

IRML
09-06-2009, 11:56 AM
IOR for a transparent material works a bit differently then IOR for a reflective material which is more complex.can you explain more about this?