Tips

Preview RGB, Alpha and Depth in the render window

To preview RGB, Alpha and Depth in the render window, you have to enable "Save Preview Image" in the Render/Output Tab.
Now if you right-click in the external render window after rendering has finished, the preview cycles through RGB -> Alpha -> Depth -> RGB :-)
This is for messiah:studio 2.0

Render:

Preview RGB, Alpha and Depth in the render window