Using the Cycles Render Engine How can I make an object invisible when I render?
These are some of the options to make an object not render in Cycles.
To make the object invisible/unrenderable
Disable the object for rendering (turn off the camera icon)
Move the object you don't want to a layer that is not renderable
Give it a transparent shader:
To make the object invisible to camera but keep the shadows and interaction with other objects (reflections, etc)
Restrict the visibility for camera:
Using Nodes: use a light path so the object is invisible to the camera only:
To make the object transparent as alpha channel:
use a holdout shader so it renders as transparent
Place the object on a different layer and use that layer as mask:
Use a Pass index for the object and use that on the compositor to subtract the object from the final render:
Similarly, you can assign a pass index to the material and use that as alpha on the compositor:
For the last three options the Transparent Background option has to be enabled: