Public Class frmLupe
 
    Dim fc As Double = 4
 
    Dim pb As New PictureBox With {.Parent = Me, .Dock = DockStyle.Fill,
        .BackColor = Color.White, .SizeMode = PictureBoxSizeMode.Zoom}
    Dim bmp As Bitmap
    Dim WithEvents timCopy As New Timer With {.Interval = 500, .Enabled = True}
 
    Private Sub timCopy_Tick(sender As Object, e As EventArgs) Handles _
      timCopy.Tick
 
        'Aktuelle Größe der Lupe
        Dim w As Integer = pb.Width
        Dim h As Integer = pb.Height
 
        'Größe des darstellbaren Bildschirmabschnitts
        Dim sw As Integer = w / fc
        Dim sh As Integer = h / fc
 
        'Position des Bildschirmabschnitts gemäß Mausposition 
        Dim mt As Integer = Me.MousePosition.Y
        Dim ml As Integer = Me.MousePosition.X
        mt = Math.Max(0, mt - sh \ 2)
        ml = Math.Max(0, ml - sw \ 2)
 
        If bmp IsNot Nothing Then
            bmp.Dispose()
            bmp = Nothing
        End If
 
        bmp = New Bitmap(sw, sh)
        Using g As Graphics = Graphics.FromImage(bmp)
            'Kopieren des Bildschirmabschnitts in die Bitmap
            g.CopyFromScreen(New Point(ml, mt), New Point(0, 0), New _
              Drawing.Size(sw, sh))
            'Anzeigen
            pb.Image = bmp
        End Using
 
    End Sub
End Class