I just want to share an aproach to Realistically "FAKE" dispersion in a refractive material.
Since Corona A5 does not have a dispersion setting and i needed to have a diamond, came up with this idea.
The post render tab in corona allows to save green, red or blue channel of a render, so in order to fake diamond refraction one just need to find the refrection index of diamond for determined color.
This page shows the index of refraction as a curve and can show you the IOR for determined wavelength.
http://refractiveindex.info/?shelf=3d&book=crystals&page=diamondI use diamond specs but it could be applied to any refractive material.
So we need to find the aprox equivalence between wavelength and RGB color... (remember this is a fake, but a very informed one... XD). This place has something one could use
http://academo.org/demos/wavelength-to-colour-relationship/For red (255,0,0) = 658nm that gives us a IOR of: 2.40975
For green (0,255,0) = 510nm that gives us a IOR of: 2.43024
For blue (0,0,255) = 440nm that gives us a IOR of: 2.44856
So we create 3 materials each with diferent IOR as stated, then render just saving the channel for that IOR color.For example, apply the first material with IOR 2.40975 and save the image but just the red channel (set appropiate numbers in post tab of corona red:1 green:0 blue:0).
Do that for each Material saving the correspondent color channel for that ior.
The next step is open the 3 images in photoshop as layers and set the layer as Linear dodge (ADD) to get the composite of the 3 wavelengths.
And there you have it. A really convincent fake dispersion for a diamond render or any refractive material.
Here can have the test scene used in max 2014 and corona A5 and the composite in photoshop, and the final image as shown.
By the way the scene is illuminated just with CoronaSun and sky only. But i Guess works with hdrs or custom illumination as well.