constant distance between camera and a layer

I've found a few answers that come close to my problem, but I'm not good enough with expressions to adapt them to my needs...

I have about 20 layers randomly distributed in 3d space. I used a variation of Dan's "how to build a better camera man" code from the pan, tilt, focus, zoom composition. In addition, I put a one liner on the camera's Position that links it to the Point of Interest, adding 200 to the z. My intent was to always have the camera a set distance from the layer on interest.

This works fine when all the photos are on the orientation (namely "0" rotation). However, it falls apart when I want to introduce some random orientation to the photos. When the camera points to a photo, I want it to be facing straight on to it, not at an angle.

I think I need to do something with the target.toWorld opeation, but I'm not sure. Everything I've found seems to deal with a camera that is sitting still and the layers are moving in front of it.

Any thoughts or comments of ridicule?

Mike