2d camera movement with Lerp problem

Hi guys, I'm having difficulties using the Lerp function to do as I wish. Perhaps anyone knows what to do. It should be a somple task, I'm doing a 2d platform game and the camera starts centered at the player position. As soon as the player moves a little further than the camera center (the value of the extra is stored in "vikelsepos") I want the camera to smoothly position itself a little bit in front of the player and then follow the player from this in-front position until something else happens. This is where I run into trouble. No matter how I manipulate the in parameters for Lerp the camera still lags behind the player or at best centeres around the player but never in front of the player like I want it to. I guess it has something to do with that the interpolation that the Lerp function computes won't let the values of "targetpos" get large enough, but I'm not sure. Or should I try something other than Lerp for this to happen?

 using UnityEngine;
 using System.Collections;
 
 public class Kameraflytt : MonoBehaviour
 {
     GameObject Spelaren;
     float vikelseposx = 1f;
     float targetposx;
 
         // Use this for initialization
         void Start ()
         {
         Spelaren = GameObject.Find ("Spelaren");
         }
     
         // Update is called once per frame
         void FixedUpdate ()
         {
         if (Spelaren.transform.position.x - transform.position.x > vikelseposx) {
             targetposx = Mathf.Lerp (transform.position.x, Spelaren.transform.position.x, 0.5f);
             transform.position = new Vector3 (targetposx, 4f, -1);
 
     }
     
     }
 }