unity制作瞄准镜效果

using UnityEngine;
using System.Collections;

public class bj : MonoBehaviour
{
    public GameObject obj;//声明一个可以外部拖拽赋值的游戏物体
 // Use this for initialization
 void Start () {
 
 }
 
 // Update is called once per frame
 void Update ()
    {
        if (Input.GetMouseButtonDown(0))//获取鼠标按键按下，“0”为鼠标左键
        {
            obj.SetActive(true);
            Camera.main.fieldOfView = 20;
        }
        if (Input.GetMouseButtonDown(1))//获取鼠标按键按下，“1”为鼠标右键
        {
            obj.SetActive(false);
            Camera.main.fieldOfView = 60;
        }
    }
}