Nulls, animating POI and cameras...

Hi again.

I find it really tricky to get my feeble brain around this.

I have a camera parented to a Null. The camera is set -500 in the z (this null is used to easily animate and control the camera). The null is set at [0,0,0], and rotates around another 3D layer also set at [0,0,0], so we 'fly around' the object. Fine. Problem occurs when I try to animate the camera's POI to another object. I want to look at something else as we fly around - in fact I want to be able to animate the camera's POI as the camera flys around.

Simply setting the camera's POI with an expression like:

thisComp.layer("POInull").position;

...fails - and I know it's to do with Layer Space transforms (because camera is child of Null), so I try this is in the POI expression box for the camera:

toWorld(thisComp.layer("POInull").anchorPoint);

...and this fails too.

I just want to attach the camera's POI to a Null, but also have the camera be a child of another Null. I'm sorry for being so lame but it's just doing my head in. Any help most welcome. Also - any good pointers to info on this type of thing? I wish I was more confident about layer space transforms in AE expressions - always seems to come up in the studio.

Thanks.

Regards, Paul.