Abstract: An imaging proportional counter which significantly reduces parallax errors when imaging point sources of radiation located at variable distances from the detector entrance window. The imaging proportional counter includes a gas filled enclosure with a concave shallowly curved radiation permeable entrance window allowing radiation from the source to enter the enclosure. A multi-wire grid assembly is spaced behind the entrance window within the enclosure. When a potential difference is applied between the grid assembly and concave entrance window an electrostatic field is generated such that near the interior surface of the window the field lines form a spherically focussed region. The concave entrance window also allows increased fill gas pressures such that radiation entering the detector will interact with the fill gas very near the entrance window while still in the spherically focussed region.