Linking 3D rotation to opacity

[jemron]

I have a composition that is set up similar to the video here:

http://www.laurenroundy.com/null_3D.mov

Basically the individual images are all spaced evenly around a null object in the center of the comp, and then they are all parented to that null object so that as the null object is rotated in 3D space, the individual images rotate around with it.

What I want is for the images to only be full opaque when they are perfectly facing the camera. To make this easier, I will only be rotating this images on the Y axis, and I won't be messing with the null's x or z axis.

How can I set it up so that as the images are facing the camera (so, for example, the null is set it 0 degrees on the y axis, and image 1 is facing the camera) that they are fully opaque, but then, as the null rotates to say -35 degrees, image one fades down and the next image (image 2) is now facing the camera and fully opaque?

Does that make sense. I would like them to fade and even blur if possible when they aren't directly facing the camera. If the null rotates to +35 degrees, I would want the same thing to happen (image 1 fades away and the next image in the sequence fades in)

Please help! Thanks!

[Mylenium]

http://www.aenhancers.com/viewtopic.php?f=2&t=854

Mylenium