When to Fresnel and when Not to.

[WWX]

I have asked this question before from a element point of view and the feedback i got, if i recall correctly was that one can select the Fresnel option for basical all elements except for metalic ones.

The part i am struggeling with is how to create the material when the Fresnal option is selected as the control of the reflectivity of the material playing with the grey scales from 0 to 255 seems to make very little if no difference in how much the material reflects, until the colour is basically white and then it becomes very reflective. So there is no gradual adjustment (or I sould say I don't know how)

So please how should I think when starting to create a Vray material, when to use Fresnel and when not to an if using it how do one fine tune/control the reflectivity of the material.

Thanks

[Kyle_Grace]

You unlock the IOR and adjust that value.

[miraldo]

I usually start by setting the reflection color as bright as I want the reflection on the rim of the objects to be.
Considering that fresnel sets a reflection falloff, where its most reflective area will be the rim of the objects (i.e. where the normals of the object reach for a perpendicular angle towards the camera), the reflection color sets the maximum amount of reflection.

After this, i find easier to control the fresnel amount by raising its value from a low value like 1.3 (where reflection on the center of the objects will be very dim). If I want the fresnel falloff to be minimum I just keep raising the fresnel value.

Like Kyle_Grace said, in order to change the fresnel amount you either need to unlock its value (fresnel IOR) from the refraction IOR value below, or simply change the refraction IOR value leaving both values locked.

Also, Egz has a great article on reflection behaviour on Vray.info:
http://www.vray.info/topics/t0039.asp

[samuel_bubat]

If you want to have full control over the reflections, I would suggest using a falloff map in the reflection slot. It acts similar to fresnel with standard settings perpendicular/parallel
(reflection intensity by angle of the surface, relative to the camera). But unlike fresnel
you have precise control.