Hello guys,
I will like to render a coulple of passes to make a post pro. The only problem I have is using the mia exposure for tone mapping + ambient occlusion.
My scene will render black if the mia exposure is connected to the camera.
How do I need to render the Ambient Occlusion without disconnecting my mia exposure to the camera?
Is there a way? Or I should render separately?
Any help I will truly appreciate.
Cheers!
I would make a traditional AO render layer and disconnect the camera lens through a layer overide.
-C
Hi Dangertaz,
I dindt really understand 100% what you meant, but you gave me the idea an new I get it work.
Thank you for your help!! 
I would like to add that you should be using the mib_amb_occlussion material for this pass.
It offers a lot more control than the built in ambient occlusion feature in rendersettings.
Expanding a little bit on the other replies, the ideal case for the AO pass is to create it on an additional render layer, using the built-in preset. This way, maya automatically creates a surface shader connected to a mib_amb_occlusion, giving you total control over the samples, max. distance, spread, etc.
Regarding overrides, when you have your AO layer selected, go to the render globals > features, and expand “extra feaures”. Right click on lens shaders and then select “create layer override”. Simply uncheck it and you will have an AO pass without lens shaders affecting it.
It seems everyone’s answer is to discard the AO pass in favor of an AO layer? Doesn’t this defeat the purpose of the pass system itself, and create additional rendering overhead?
I suppose it depends on the needs of the OP, though, but I always prefer a render pass to a render layer, when possible. I haven’t had this problem with disconnecting lens shaders for my AO passes before, but I’m still using Maya 2012.
In terms of speed, there wont be much difference between the layer or pass methods. It’s still adding an extra bit of compute time for the AO whether you go the passes route or the layer route. Unlike things like reflection/refraction/spec/diffuse which are components of the mia_x_passes and get calculated automatically, it will always add compute time including AO in the mix. It will still add translation time to mentalray going the layer route instead of passes, but for simple scenes the time is negligible and much faster going the layer route imo.