We analyse the resolution of Maxwell's fisheye in terms of the efficiency with which a pulse emitted from one point (source) can be absorbed at another point (drain) that is slightly displaced from the position of the image of the source. The drain is active and is designed to absorb the maximum possible amount of energy emitted by the source. Based on the size of the area where the energy can be absorbed efficiently, we address the question of whether such an active drain can provide subwavelength resolution and show that the answer is negative because this area is diffraction limited. We support our theoretical results with numerical simulations.