Movement of camera over time

Im using the code below to try and move the camera from one location to another however it also changes the x and z values, what is best way to change a camera say from y 10 to 0.5 over 2 seconds, thanks! update: It works as expected when the camera has no parent, when its the child of a player controller, the x and z are changed.

 public class CameraZoom : MonoBehaviour {
 
     public float startY=10f;
     public float speedSecs=12f;
     public float ynow=0;
     private Vector3 updatePos;
     private Vector3 startPos;
 
     void awake() {
 
     }
 
     // Use this for initialization
     void Start () {
         startPos = (Vector3.up * startY);
         updatePos =(Vector3.up * 0.5f);
     }
     
     // Update is called once per frame
     void Update () {
 
     }
 
     void FixedUpdate() {
         if ( ynow<speedSecs) {
             Debug.Log ("camera update! " + Mathf.Lerp(startY,  0.5f, ynow));
             ynow += Time.deltaTime;
 
             transform.position = ( Vector3.Lerp(startPos , updatePos, ynow/speedSecs));
         }
     }
 }