Transmittance
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Transmittance must be a color other than black for transparency to appear. Setting a brighter transmittance color results in clearer transparency, but you should remember that this parameter is also tied to the Attenuation Distance. |
Attenuation
Glass, water, or even air are transparent when thin, but become opaque when a specific thickness is reached (different for each material). As light travels through a material, it loses energy. The Attenuation distance parameter allows you to specify how far light can move through an object before losing half its energy. For example, if you have a 2cm thick glass window and you set the attenuation distance to 2cm, the light shining through the glass on the other side will be half as bright.
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To better understand the concept of Attenuation, consider sea water. When the water layer is very thin (like water in the palm of your hand) you do not see attenuation: the water looks transparent. When you have more water thickness, you see a typical sea color (grey, dark-blue or light blue-green, depending on deep or shallow waters). The Transmittance color represents the color that you want to get approximately at the Attenuation distance. Beyond this distance, the light is more and more attenuated, it loses more and more energy, and the view eventually turns opaque if the volume is thick enough.
Abbe
Different wavelengths of light can be refracted at slightly different angles as they pass through a material, and this is what causes dispersion, the effect seen when a beam of light passes through a prism and is split up into the different wavelengths of light.
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Dispersion must be enabled in the global Material Properties panel; otherwise the Abbe parameter in the BSDF will be grayed-out. Because dispersion generally takes longer to render, it is disabled by default. See the Global Material Properties section. |
