Superlens as matching device
  The question is considered about possibility of overcoming diffraction limit at device, named superlens. This device is a flat slab, executed from material with index of refraction n,equal n=-1. It is shown, what this device really can focus the radiation to the spot, smaller than wavelength, but herewith superlens works not as optical instrument, based on the laws of geometric optics, but as certain matching device, for which does not exist diffraction limit. This is possible if thickness of superlens is comparable with wavelength, and distances from superlense to the wave source and to its image are also in order of wavelength. 
V.G.Veselago