mia_portal_light makes invisible object behind it visible

[rchr]

Hey All, I'm trying to figure out this mental ray puzzle on the relationship of reflections and objects in Maya 2011 hotfix 2 Windows 7.

As you all know, Area light in Maya has a very harsh rectangular shape when it is visible and this also creates a fairly boring looking reflection on to an object, so my aim is to create a different shaped object or texture to reflect on to the object and I want any reflectors in the scene to be Invisible to the eye, but still visible in reflections.

Note: FG is used and Mia_exposure_photographic is used for linear workflow.

So I created a poly "reflector" object with cast/receive shadow and cast/receive FG turned off. Also, Primary Visibility is turned off

Then created Maya Area Light -> Converted to MR Area Light -> mia_portal_light plugged into light_shader and photon emitter slot. Added mib_blackbody in the custom environment. Visible is unticked.

Put reflector object slightly behind the Area Light. Notice that even though the primary visibility is turned off, it is still visible if it's behind the Area Light. According to Maya manual, there is a section on troubleshooting Mental Ray on how "Object still renders when primary visibility is turned off" its solution is to disable the Visible in Transparency flag. With this method, now the reflector object is invisible when rendered. However the reflection has also disappeared.

Is there a way to get around this? Is there a better method to do what I'm after?

It's best that you look at the scene file to analyze. Scene file attached is a Maya 2011 version but you can open it on any version. Go File-> Open scene "option box"-> tick Ignore Version.