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Cycles: Expand thin film documentation #104861

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Aaron Carlisle merged 1 commits from LukasStockner/blender-manual:thinfilm into blender-v4.2-release 2024-07-20 23:44:44 +02:00
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manual/render/shader_nodes/shader/principled.rst
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@ -347,21 +347,33 @@ Strength
Strength from 0.0 to 10.0
Thin Film
---------
Thin Film :guilabel:`Cycles Only`
---------------------------------
Thin Film simulates the effect of iridescence which is the
phenomenon of a surface changing color as the view angle changes.
Thin Film simulates the effect of interference in a thin film sitting on top of the material.
This causes the specular reflection to be colored in a way which strongly depends on the view
angle as well as the film thickness and the index of refraction (:term:`IOR`) of the film and
the material itself.
This effect is commonly seen on e.g. oil films, soap bubbles or glass coatings. While its
influence is more obvious in specular highlights, it also affects transmission.
.. note::
Thin-film interference is currently only applied to dielectric materials. Support for
thin films on top of Metallic is planned in the future.
Thickness
The thickness of the film, in nanometers a value of 0 disables the simulation.
For reference the thickness of a colorful looking bubble is about 200 to 500 nanometers.
The thickness of the film in nanometers. A value of 0 disables the simulation.
The interference effect is strongest between roughly 100 and 1000 nanometers, since this is
near the wavelengths of visible light.
IOR
Index of refraction (:term:`IOR`) for rays transmitting through the thin film
For most materials, the IOR is between 1.0 (vacuum and air) and 4.0 (germanium).
Index of refraction (:term:`IOR`) of the thin film.
The common range for this value is between 1.0 (vacuum and air) and roughly 2.0,
though some materials can reach higher values.
The default value of 1.33 is a good approximation for water.
For reference soap has an IOR of 1.5, so the IOR for a soap bubble should be between 1.33 and 1.5.
Note that when the value is set to 1.0 or to the main IOR of the material, the thin film
effect disappears since the film optically blends into the air or the material.
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