Re: Fresnel effects -- plugin tool 2004-01-20 - By Eric Winemiller
Back
However it is in real life, Carrara does not do it as a consequence of
refraction, thus in Carrara a plug-in is required.
You can easly do a simple test. Drop two infinite planes in a scene. Make
one checkered, the other transparent with an index of refraction for water
(but no reflection), and make it a little higher than the first. Add the sky
atmosphere (so you have something to reflect). Render. No matter where you
place the camera, that plane of water will never reflect the sky. All you
see is the checkered plane underneath. In the real world, you would see the
sky reflected in the water.
Now maybe it should provided that functionality in the box, but you could
argue that about lots of features that the 3rd party plug-in developers
provide.
Regards,
Eric Winemiller
Digital Carvers Guild
3D plug-ins for Carrara
http://digitalcarversguild.com
-- -- Original Message -- --
From: "nospam2" <nospam2@(protected)>
To: "m3d242" <Carrara@(protected)>
Sent: Tuesday, January 20, 2004 3:34 PM
Subject: Re: [Carrara] Re: Fresnel effects -- plugin tool
> Hello m3d242,
>
> >> What's called the Fresnel effect is in fact nothing but another way to
> m> describe the refraction indice of the material.
>
> m> That's incorrect. The Fresnel effect and the index of refraction are
not the
> m> same thing.
>
> See my just previous post.
> The Fresnel effect is not the same thing than refraction, true : it is a
consequence of refraction.
> It is the result that sinus being bounded by -1 and +1, at low angle the
ray cannot enter the material having an higher refraction indice and then is
totaly reflected instead of being partly reflected and partly refracted.
> SInce Carrara takes refraction into account, how is it that it cannot
produce the Fresnel effect ?
>
> What I mean is : to calculate the Fresnel effect, one only need the light
ray angle of incidence and the refraction indice of both material (air and
water for example).
> Since Carrara already knwos all that, I don't see the point for an extra
plug-ins.
>
> >> Since refraction is one of the shaders channels in Carrara, I do'nt see
why
> m> the effect would not be rendered by the rendering engine.
>
> m> The Fresnel effect is the roll off of transparency to
> m> reflectivity (or reflectivity to
> m> transparency) on the surface of an object depending on the viewing
angle.
> m> The index of refraction takes into account how light bends (or
refracts) when
> m> passing through and object. The index of refraction has noting to do
with how
> m> reflecive an object is.
>
>
> What you call the roll off of transparency to reflectivity is not a
property per se. It is just a consequence of the refraction law.
> In the absolute, a transparent object could have a zero reflectivity
indice and still produce the Fresnel effect.
> If you look at this imaginary object straight from the top, you see
through it. Then as the angle of vision get smaller (= tangential to the
object surface), at some point you would stop seeing through it (this
property is used in the optical fiber).
> That is the Fresnel effect.
>
> Of course, in the reality, all objects have some reflection property. SO,
obviously, at the angle when there is no more refraction, all the light is
reflected.
> that is why the Fresnel effect is associated with reflection in people
minds. But it is a consequence of the refraction law, not the reflection
law.
>
>
> --
> Best regards,
> nospam2 mailto:nospam2@(protected)
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