Alpha channel
 

How can one turn the alpha channel on when rendering with mental ray, is it even possible?

I dont think it is, I've been having this same problem and I can't find a way of doing it. It's always greyed out and unselectable in my versino of maya.

Alan

The reason it is grayed out is because the alpha channel is always on for Mental ray.

but it isnt rendered properly and programs like shake can't read it as normal. It's really frustrating cause that means I have to manually add in bloody photoshop (which for a 200 frame sequence is a mind numbing experience even using the automate feature!)

Alan

Pure: that must be a maya 6 issue since i haven't had any problems with MR alphas in maya 5. Yes, it's greyed off but it still renders it properly. Haven't had any trouble in Digital Fusion. However After Effects doesn't want to import MR rendered iffs at all for some reason...

Alpha with mental ray in Maya 7
 

I can click on the alpha only button in the render view, the thing is, there is no alpha rendering, everything is black.

In the mental ray render settings, I have the alpha channel (mask) selected. Still nothing. Is is a mental ray texture issue?

Does anyone know how to solve this issue? I need an alpha channel!

Figured it out.

make sure you check Pass Custom Alpha in Mental Ray Render Globals>Custom Entities

im supreise Pure or KB didnt know this. :p
hehe