pictureBox1 = new System.Windows.Forms.PictureBox();
                ((System.ComponentModel.ISupportInitialize)(pictureBox1)).BeginInit();
                pictureBox1.Location = new System.Drawing.Point(40, 27);
                pictureBox1.Name = "pictureBox1";
                pictureBox1.Size = new System.Drawing.Size(650, 750);
                pictureBox1.SizeMode = PictureBoxSizeMode.AutoSize;
                pictureBox1.TabIndex = 3;
                pictureBox1.TabStop = false;
                pictureBox1.Click += new System.EventHandler(this.pictureBox1_Click);
                pictureBox1.MouseWheel += new System.MouseEventHandler(pictureBox1_MouseWheel);
                this.Controls.Add(pictureBox1);
                ((System.ComponentModel.ISupportInitialize)(pictureBox1)).EndInit();
                pictureBox1.Image = Image.FromFile(Fname);

........

        void pictureBox1_MouseWheel(object sender, MouseEventArgs e)
        {
            pictureBox1.SizeMode = PictureBoxSizeMode.Zoom;
            MessageBox.Show("MouseWheel");
        }