This simple type of reflecting telescope was invented by Sir Isaac Newton. The primary paraboloidal mirror at the closed end of the telescope tube focuses incoming light toward a flat diagonal secondary mirror. The focal length is determined by the curvature of the paraboloid. The secondary mirror directs the focused beam toward the eyepiece. The thin "spider" supporting the secondary mirror is not shown. The telescope happens to be directed toward the planet Saturn and the observed image is shown as an inset.