Transparency behind object

[MULTIAD]

Greetings, how can i knock out the background and object so that it's 100% transparent behind my subject being rendered. I'd like to save it as a PNG with alpha transparency so that we don't have to clippath in Photoshop post-pro. I've tried this before and haven't had any success. I'd appreciate any help!

Cheers,
Chris

[Yannick]

The Vray Mtl wrapper should be what you need.
http://www.spot3d.com/vray/help/maya...per_params.htm