Render a surface transparent only if directly visible I want to render some glass, in order to actually see something it requires a background. However I want the glass object to have a transparent surrounding. How do I make a background which is considered by the refraction of the glass but is transparent when it is seen directly by the camera?
Using blender internal, for the material of the objects you want to disappear, turn on transparency and choose mask with an alpha of 0.0.



The transparent objects will still show in reflections but not be seen in the camera.