The possibility of using the lenses with an aspherical surface for terahertz/sub-terahertz (THz/sub-THz) imaging systems has been considered. Diffraction-limited optical system of four identical plano-convex aspheric lenses has been obtained. Tests of the lenses have been performed on the specially made stand. These calculated and experimental data have similar values, which confirms the use of such lenses in the THz/sub-THz imaging systems.