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Fresnel in Vray
show user profile  3joez
Is there a formula to balance Fresnel reflections?
I explain.
Looking around in the web you will find values of reflection in percentages. That simply means a table of indexes of reflection for a given material.
Say glass is around 20% so that means that when I make a glass material I will calculate 256*20 and that divided by 100. It gives 51.
You try, and that gives you a nice starting point (then affect shadows, IOR at 1.6, refract almost at maximum, blah, blah).
Now, a lot of materials (like dielectric ones) have fresnel reflections. When I turn it on, I notice that the reflection value looks like it has
been turned down. So I've got to compensate bumping it up to say, more than 100. How does that compensation work? I mean, why Fresnel looks like
it dims reflection? Is there a formula to understand that?
read 829 times
7/30/2012 7:32:31 PM (last edit: 7/30/2012 7:32:31 PM)
show user profile  Nik Clark
I can't help with your problem, but the equation is quite a simple one:


Hope this helps :)



read 826 times
7/30/2012 7:37:58 PM (last edit: 7/30/2012 7:39:07 PM)
show user profile  Bolteon
the majority of materials on earth have some level of falloff to their glossiness.

the reason why that falloff seems to dim is that the reflection is naturally dimmer when looking at it straight on (where light is bouncing directly back at you) as you progress towards the edges or incidence angle (fully perpendicular) you're actually receiving the bend/bounce of a lot more light (ie refraction/reflection on a surface level) and thus the edges become "hotter" than those parallel in respect to your viewing angle.

-Marko Mandaric



read 798 times
7/30/2012 9:05:21 PM (last edit: 7/30/2012 9:05:21 PM)
show user profile  3joez
Thx.
@Nik What do the "s" and "p" stand for?
@Bolts - " as you progress towards the edges or incidence angle (fully perpendicular)you're actually receiving the bend/bounce of a lot more light" - this I can't figure out. How is that? In fact, when you receive more light the reflection should be dimmer.
read 779 times
7/31/2012 7:36:15 AM (last edit: 7/31/2012 7:36:15 AM)
show user profile  Error404
I'm not sure if this is a good analogy or not,

Think about if you had a large metal immovable sphere and you threw a small rock at it. If you hit the center of the sphere straight on, the little rock is going to pretty much just fall straight to the ground, or maybe bounce back a little. If you hit the sphere towards the edge at a glancing angle, the little rock is going to skip/ricochet off and still keep a lot of it's velocity. The farther towards the edge of the sphere you hit, the less change in angle the rock makes when it hits and skips off (it keeps more of it's momentum).

Light doesn't really have momentum per say, but the analogy kind of works if you think about the angles and how much of the reflected light is bounced off.

www.DanielBuck.net - www.DNSFail.com

read 761 times
7/31/2012 7:16:24 PM (last edit: 7/31/2012 7:34:21 PM)
show user profile  Bolteon
to add what dan is saying above and answer your question...


technically yes; as you progress towards ithe incidence angle; a single light ray will get dimmer but the amount of light bouncing back to you (imagine the reversal of dan's analogy; rocks skipping back towards you) is exponentially larger in volume and thus while being dimmer in a singular sense; is much brighter in a quantitative sense.

it's the same reason why a (perfect) chrome ball technically captures full 360 reflections towards it's edges (even though it's only shot from the front).

-Marko Mandaric



read 747 times
7/31/2012 7:50:34 PM (last edit: 7/31/2012 7:50:34 PM)
show user profile  killerbee2
or to go further on abstracting error404s explenation, make a sphere in max and add hair to it without gravity. When you render you'll notice the sides have a nice thick fur while looking straight at it you'll notice the spacing between the hairs.




read 732 times
7/31/2012 11:29:57 PM (last edit: 7/31/2012 11:29:57 PM)
show user profile  3joez
Thanks guys. Bolts, perfect explanation.
read 712 times
8/1/2012 9:10:01 PM (last edit: 8/1/2012 9:10:01 PM)
show user profile  Bolteon
you're welcome. we try...

-Marko Mandaric



read 707 times
8/1/2012 10:20:37 PM (last edit: 8/1/2012 10:20:37 PM)
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