Material that shows up as alpha channel on render, but shows up in reflections Another way to put it is that I want to create a material that will do the cropping for me.

If I apply this shader to a cube in the middle of the shot, then my render will have a cube-shaped block of transparency in the middle of the shot, even if there are objects behind the cube.

Can anyone provide me a pointer on this? I'm new to nodes.

Thank you thank you!

EDIT: I'm using Cycles.

EDIT EDIT: Thank you for your answer, Denis. I realized today that there's one thing missing from the solution you provided. I also need the object to cast shadows and show up in reflections. I can't quite get my head around to make that happen. Any help out there?

EDIT EDIT EDIT: Figured it out!
Cycles Render

All you have to do is to add a Holdout node to the material output on the masking object.



Blender Render

Enable Transparency on the material of the masking object, set transparency method to Mask and change Alpha to 0