DollyZoom

DollyZoom.cs

using UnityEngine;
using System.Collections;

// http://en.wikipedia.org/wiki/Dolly_zoom

public class DollyZoom : MonoBehaviour
{

    public Transform target;

    Camera cam;
    float distance = 0f;
    float fov = 60;

    float viewWidth = 10f;

    void Start()
    {
        cam = Camera.main;
    }

    void Update()
    {
        Vector3 pos = target.transform.position;

        fov = cam.fieldOfView;
        distance = viewWidth / (2f * Mathf.Tan(0.5f * fov * Mathf.Deg2Rad));

        pos.z = -Mathf.Abs(distance);
        cam.transform.position = pos;


        Debug.Log(distance);
    }
}