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With a
transparent material such as glass there will be both reflection and
refraction of light depending on the relative angle and position of
both glazing and light. To create a focusng effect the glazing index
of refraction for transmitting photons should be greater than 1.0.
In reality the Refraction index value for glass surrounded
by air is generally taken to be 1.44. or a value between 1.50 and
1.89. The average estimate of daylight transmittance through clear
6mm sheet glass is around 0.8 and through clear double glazing with
average dirt is aorund 0.5. Refractive objects with different shapes
will refract diffrerently and the refraction will vary according to
how concave or convex the shape is.
The default for this
control is a value of 1. Increasing the refraction value above 1
(usually to values between 1.33 and 1.50) focuses the caustics
whilst decrasing the value to less than one diffuses the effect. A
value of 0 for the refractive index produces no caustics as no
refraction through the glass is occuring and takes a long time to
render whilst mental ray is searching for
photons.
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