The Fresnel effect is that reflections are brighter when they strike a surface at a shallow angle. The devil is in the details. You can use an Edge_Blend node to modulate reflection value (amount of reflection) but while it may be directionally correct, it won't be accurate.

To get a completely accurate effect, you need quite a bit of math for the effect, and if you don't have Poser Pro, you need shader gamma correction. This is quite an ordeal to do by hand, but matmatic can take care of that for you pretty easily.

The main parameter of interest in this effect is called the Index of Refraction, or IOR. It may seem odd that refraction has something to say about reflection, but they go hand in hand. Even for opaque materials that do not pass light through, there is still an IOR involved that will determine how the reflections change with viewing angle.

The IOR of air is so close to 1 that we can safely assume it is one.

Reflection happens when light passes from one medium (usually air) to another medium in which the IOR is not 1, or vice versa. When the IOR of a material is 1, there is no reflection at all. When IOR is more or less than 1, there is reflection. How much and how it modulates depends on what the ratio of the material IOR is to air. Some materials have a thin coating that alters the effective IOR of the material. This is why a clear-coat finish on car paint makes it shiny - it has a higher IOR than the paint alone would.

Most materials have an IOR somewhere between 1 and 2. Water is IOR 1.33. Glass or glass-like materials are around 1.5.

So let's see how to do this with matmatic. 

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