This is a very simple stereo lens shader for mental ray, which I created to 
experiment with rendering both the left and right frame IN THE SAME FILE.
The proposed benefits would be:
 - no camera rig required. 
 - simpler compositing, especially of multi-pass renderings. 

It works but was never used, so I have no idea if the stereo effect is correct for any uses. 

I should add - it was created for XSI, probably version 5, on intel, and this repo contains the SPDL files as well. 
enjoy - 
anthor@mesmer.com