In Fig. 3 and Fig. 4 above, we can directly see how are the focal length, the full width at half maximum (FWHM), and the transmittance of silver nanoslit lenses and gold nanoslit lenses varying with the thickness of the lenses. By reducing the thickness from 2*λ to 1/2*λ, we have shortened the focal length of the silver lens by 13.0% percents and improved the transmittance by 27.3% percents. Admittedly, the FWHM becomes wider, but it is still in the good range comparing to that of the normal lens. Similarly, for the gold nanoslit lens, the focal length is shortened by 7.7% percents while the transmittance is increased by 40.6% percents. These improvements are really noticeable, because with such high transmittances the lenses are actually suitable for real world applications such as shortening the eyepieces of telescopes.