A theory of diffraction in the system consisting of the left-handed
and the right-handed materials is proposed. The theory is based upon
the Huygens's principle and the Kirchhoff's integral and it is valid
if the wavelength is smaller than any relevant length of the
system. The theory is applied to the calculation of the smearing of
the foci of the Veselago lens due to the finite wavelength. We show
that the Veselago lens is a unique optical instrument for the 3D
imaging, but it is not a ``superlens'' as it has been claimed
recently.