We systematically investigate lensing of electromagnetic waves by a negative refractive-index material slab constructed from a two-dimensional photonic crystal with properly designed equifrequency-surface configuration [Luo et al., Phys. Rev. B 65, 201104 (2002)]. We find that a point source placed in the vicinity of the slab can form a good-quality image in the opposite side of the slab. However, the image is strongly confined in the near-field region of the slab and gradually degrades and disa