I don't understand your problem. The first sentence makes it sound like you want to move a camera through a layer by animating a null that is the parent of the camera and as the camera gets closer to the window the opacity of the window is reduced. The second sentence sounds like you already have an expression tied to the null or the camera that is lowering the opacity of the layer's as the distance to the camera decreases. The second sentence makes it seem like the first sentence is already answered. I don't know what you want to do or what you are asking.
Please explain further or give us a screenshot that shows all of the modified properties of at least one of the layers that is giving you problems revealed. Do that by selecting the layer or layers in question and pressing the U key twice. Please don't scale the screenshot way down. We need to be able to see what's going on.
sorry I confused myself haha, but Im looking to pan in to a window of a shop but everything else seems to be fading as if the opacity is being lowered, so before i can even get close to where i want to be in on the window all the layers have faded out as in dissapeared. I hope that makes a little more sense
I have fixed it now!