Conical in shape Fresnel zone (CFZ) lens of flat dielectric rings is introduced and studied in this research. It is contrasted to a plane Fresnel zone (PFZ) lens, a CFZ lens of conical rings and a refractive plane-hyperbolic (PH) lens. For the same aperture diameter of about 25mm and focal length of 30 mm, a 229-GHz CFZ lens of flat rings with a 30-degree opening semi-angle significantly surpasses the PFZ and PH lenses in focusing gain and efficiency. Also, it exhibits a subwavelength transverse resolution and much higher axial resolution. The cited 30-degree flat-ring CFZ lens has 4.5 times smaller weight than the PH lens, and is easy to manufacture as a plane multilayer package by means of precise machining or modern photolithographic and other microelectronic technologies. Nevertheless, the CFZ lens benefits over the corresponding PH refractive lens are attained on account of smaller frequency bandwidth and bigger lens thickness. The new flat-ring CFZ lens design can be applied in accurate imaging systems or for a creation of light and efficient microwave, terahertz and optical lens antennas.