The mia_lens_bokeh shader.

Todays mental ray experiment focuses on lens artifacts
such as chromatic aberration, scratches and blooming/glare.

First of: chromatic aberration.
Chromatic aberration is an artifact often seen when using
low end or wide angle lenses. Due to the colors different wavelengths
and the differing index of refraction on the lens, the color spectra
gets separated, mostly on high contrast parts of the image.
( for a more correct explanation take a look at this wikipedia page )

One way to produce this effect is to use the new
bokeh shader shipped with Maya 2008 (mia_lens_bokeh).
The result produced this way will not be at all physically correct
but will give a similar look to the rendering.

Ok, lets see some example.

Top image image taken with a higher quality lens producing no chromatic aberration.
Bottom image taken with a wide angle lens producing substantional chromatic aberration.

Next let's look at the result we get from our bokeh shader

Notice that we only get the effect on the out of focus regions.
This is due to the use of the bokeh shader which is a depth of field shader.

The setup to get this result is really quite simple.
What you need to edit on the shader is the following:

• Check the "Use bokeh" check box
  
• higher the bokeh samples (or the image will render black)
• load a color map texture in the "Bokeh" slot

The texture used in the rendering above is a really crude RGB map
that look like this.


Thats all on chromatic aberration for now.