New to AO- I'm doing something wrong here

[Jozvex]

You didn't say which program or renderer you're using, but I can see it's Max from the screenshot. Are you using Mental Ray?

Make sure all your objects have their "able to be seen in reflections" option turned on (sorry I forget what they call it in Max) and that their normals are facing the right way.

Maybe on the AO shader/feature there's a 'distance' type of parametre that you could increase? The render is mostly white meaning nothing is finding a surface which occludes it. The 'distance' setting on occlusion shaders specifies how far the renderer will look for an occluding surface, from the point that it's currently rendering.

The only other thing that springs to mind is, are you using some sort of gamma/exposure/tonemapping settings that might look fine in your main beauty pass but are screwing up this pass?

[Munumunup]

You didn't say which program or renderer you're using, but I can see it's Max from the screenshot. Are you using Mental Ray?

Oh Man. (kicks self)

Yes it is in 3ds Max and I'm using Mental Ray shader.

Thanks for the tips. I cranked up the distance parameter and that fixed it.
Also, the main thing was that I had to move the camera. The camera was sitting outside the tank, looking in through the inverted normals of the tank wall. This worked fine for the beauty render, but not with AO.
Once I'd moved the camera inside the tank wall, I could see the AO render of my intended shot.

[Ransom]

Try turning off all the lights (except for the default). A_O is usually used in passes, so save the a/o as one file than, combine in photoshop or after effects.

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