How do I limit a smooth look rotation?

I've spent all day so far on t$$anonymous$$s and I'm getting nowhere.

I have a camera that is pointing at an object w$$anonymous$$ch is positioned at the mouse cursor using ScreenToWorldPoint, however, I want to constrain the left /right motion of the smooth follow. Part of my script (w$$anonymous$$ch works) prevents any further movement when the mouse cursor leaves the screen but I am trying to stop any further rotation when either the cursor object (target) reaches a certain position OR the camera $$anonymous$$ts a certain angle. I have tried both methods but neither work...I just get a flickering as the camera moves beyond the bounds that I input.

Here is the code.... function Update () {

     //limit to the edges
     if(Input.mousePosition.x>=Screen.width||Input.mousePosition.x<=0)
     {
         return;
     }
     
     if(Input.mousePosition.y>=Screen.height||Input.mousePosition.y<=0)
     {
         return;
     }
     
     //Limit..None of t$$anonymous$$s works. I've triend constraining the object AND the rotation of the camere
     if(transform.position.z>-3)
     {
         transform.position.z=-3;
         transform.position=transform.position;
         return;
     }
 
     //smooth look here
     rotation = Quaternion.LookRotation(transform.position - Camera.main.transform.position);
     Camera.main.transform.rotation = Quaternion.Slerp(Camera.main.transform.rotation, rotation, Time.deltaTime * damping);
 
     //move target at mouse
     transform.localPosition = Camera.main.ScreenToWorldPoint(Vector3 (Input.mousePosition.x,Input.mousePosition.y,10));
 
 }