Stop objects hidden by other objects from showing up in render....

OK, this is simplified from my real project, but shows the problem I have.

I have a cube on top of a plane. The plane receives shadows from the cube. Below the plane is a 2nd cube, colored red for clarification. Next to the first cube is a sphere with a reflective material. The sphere is reflecting the first cube as it should, and it’s also reflecting the 2nd cube, which I don’t want to happen, as seen here:

Now I know to stop the 2nd cube (the red one) from showing up in the sphere’s reflection I could un-check traceable in it’s material. However in my real project during the animation the 2nd cube will move above the plane that’s hiding it and at that point I will want it to be reflected in the sphere.

I’m thinking I need to use a mask layer to accomplish this, but the manual lacks information (mentions images that aren’t included), and I’ve googled around for this subject, found this page:
which I assume are the images missing from the manual, but the .blend files are missing from this page.

I’ve attached the .blend file that produces the above image. If anyone could point me in the right direction, I’d be really thankful!!!



example.blend (545 KB)


What about animating 2nd cube alpha channel instead of its traceability? I mean set transparency alpha to 0.0, when it is below the plane and gradually increase alpha´s value as the cube appears.

Thanks LuisEDB, but in my real project that won’t work. In the real thing, the red box is actually a black box that forms sort of a ‘bottomless pit’ in a table that several objects rise up thru the hole. Where the camera is positioned you can see partially down thru the ‘bottomless pit’ so it needs to be rendered, but it’s reflection shouldn’t be rendered.

Perhaps I should update the example to show this more clearly…

Thanks anyway,