Depth-Based Opacity Fade
Fades objects as they move away from camera (parallax helpers).
Code
var cam = thisComp.layer("Camera");
var d = length(toWorld(anchorPoint) - cam.position);
linear(d, 500, 2000, 100, 0);
3dopacitydepth
How to Use
Paste on Opacity. Tweak near/far distances 500–2000 to suit your scene scale.