Invisible object with an alpha


I’m wondering how to set my material so that an object is invisible, but still has an alpha channel that knocks out objects behind it. Basically, I need to object to exist in the Alpha Channel only and not in RG&B Channels.

Any help is much appreciated.


In the “Options” section of your objects’s materials, check the “Sky” box. Should do what you need it to. (This is for 2.5X)


That seems to knock out things in front of the object as well. Essentially I’m trying to make smoke look like it’s coming out of a doorway and around the doorway. I want collision objects to disturb the smoke, but I don’t want to render those collisions objects because they represent the doorway that was filmed in the backplate.

Hope this is making sense.