Here you go. Sorry it came out to 20 minutes. It seems everything I record comes out to 20 minutes lately no matter how hard I try to make it shorter. Hopefully this will give you some useful information on how to use the mental ray approximation editor to dynamically control tessellation at render time.

Mental ray approximation nodes are very powerful for nurbs as well as polygons and subds and is one reason I like to use the mental ray renderer over the maya software renderer.

Here is a link to the video...

https://youtu.be/on7PezD6ND4