Lens having extended depth of focus, method for designing the same, and optical system having the same

The lens includes a plurality of lens layers, each lens layer being axi-symmetric and having an extended depth of focus to focus light in a corresponding section of a focal curve in the form of a straight line located on an optical axis. In the optical system, light is focused on an optical axis to obtain a clear image in a wide distance range between a camera and an object. The optical system has a point spread function that is simpler and more symmetric. That is, the optical system provides improved continuity of a lens surface and easiness and flexibility in optical designing.