One of the features artists have asked for is the ability to do dispersion inside mental ray without needing a custom shader.
Unexposed in the main UI is an option for “weight tint” that is a luminance you can control inside a mila_mix or mila_layer node to get the effect. Slightly offsetting the ior of the transmission nodes is what controls the spread of the dispersion effect.
I will update this post again when I have a useful phenomenon to provide to make this simpler, but in the meantime you might come up with your own experiments. Updated below.
You can find the three band (color) phenomenon here. (Copy and paste if your browser doesn’t download the file. Place in your “include” folder for mental ray shaders)
The phenomenon exposes the following controls for the user as a transmission-only component. You can layer this with other components manually by connecting it through the hypershade. The incarnation of MILA in Maya right now isn’t setup to use custom phenomenon flexibly just yet. By altering the phenomenon you can include other controls. For example you can add a tint control instead of having only colorless transmission. Or for nicer looking dispersion you can create six bands instead of the three in this version (Think ROYGBIV).
You can see the power here of Phenomenon and MILA. You can create and store constructs and expose the controls you want for yourself or others. Using the conventions outlined in the MILA documents you can continue to build complex materials with all the benefits of importance sampling and light sharing.
*hint: if you find the result is a little “green” (assuming you have connected this as RGB) then you can reduce the ray cutoff to solve it. It’s not always necessary and is based on the model. The link to the string options for MILA are HERE. Eventually such controls will be exposed in the UI natively.