Camera Zoom from rotation.

I need to get the camera to zoom in when looking up or down, but come back to the default distance when looking straight.

The following code only works for looking down:

 private var PrevX;
 private var CurX;
 
 function Start() { 
     PrevX = transform.parent.transform.eulerAngles.x;
 }
 
 function Update () {
     CurX = transform.parent.transform.eulerAngles.x;
     //Looking Up
     if (CurX > 180) { 
         transform.Translate( 0, 0, (PrevX - CurX) / 20);
     //Looking Down
     } else if (CurX < 180)  {
         transform.Translate( 0, 0, (CurX - PrevX) / 20);
     }
     PrevX = transform.parent.transform.eulerAngles.x;
 }

Have any ideas, or suggestions?