  We analyze the performance of a planar lens based on realistic negative index
material in a generalized geometry. We demonstrate that the conventional
superlens design (where the lens is centered between the object and the image)
is not optimal from the resolution point-of-view, develop an analytical
expression for the resolution limit of a generalized lens, use it to find the
optimum lens configuration, and calculate the maximum absorption practical
nearfield superlenses may have. We demonstrate that in contrast to the
conventional superlens picture, planar imaging is typically accompanied by
excitation of surface waves at both interfaces of the lens.
