User manual
© Next Limit Technologies 2010
Maxwell Render 2.5 User Manual
Chapter 10. Maxwell Materials | 65
F.01 Nd=30 F.02 Nd=30 with Force Fresnel
F.03 Nd=30 F.04 Nd=30 with Force Fresnel
You should turn on Force Fresnel when you are working with untextured re. 0°
and re.90° channels to create more realistic metals or other shiny materials. Force
Fresnel will then ensure a correct reectance across the entire surface, even if you
set a very dark re. 0° color.
K
From a physical point of view, the index of refraction is not just a plain number. In fact
it is a number derived from a complex calculation to dene the refractive index at one
particular wavelength. This is the calculation:
Refraction at a particular wavelenght = Nd + K
.
i
The Nd represents the refractive index, which is the well-know concept of Index of
Refraction we often use.
The K is the extinction coefcient: the amount of absorption loss when an electromagnetic
wave propagates through a material. This is usually confused with the Abbe, but it is not
related to this. K is related to the extinction of the wave.
The use of the K value is optional. In most situations it is enough to just use the Nd value.
Only in specic situations where the extinction effect is important, is it necessary to use
the K parameter to get a more precise result.
The values of the extinction coefcients are obtained from measurements in laboratory,
and are also included in the IOR les.