Opacity CheckBox(VisualStudio) don't work

There's no code problem, the debug doesn't have any problem but when I test, when I checked the checkbox the opacity doesn't change. Nothing happen. I'm using VisualStudio 2013 Express. Here's the code:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace TP3
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void textBox1_TextChanged(object sender, EventArgs e)
        {

            int carac = textBox1.Text.Length;
            label2.Text = carac.ToString();

        }

        private void label2_Click(object sender, EventArgs e)
        {




        }

        private void checkBox1_CheckedChanged(object sender, EventArgs e)
        {
            Form Form1;
            Form1 = new Form1();
            if(checkBox1.Checked == true)
            {
             Form1.Opacity = 1;
            }


        }
    }
}