Image sharpening of time-tagged counts from a photon counting detector: Application of a modified Wiener filter

A method of using a modified Wiener filter on time-tagged single photon data has been developed, which can pre-process the data for use by a wide range of image sharpening algorithms, making optimum use of the available information. Application of the method, with the simplest possible centroiding algorithm (using a bright, unresolved reference object within the image field), to data from a 50-cm telescope at the Roque de los Muchachos Observatory, is shown to result in near diffraction limited images of the bright triple-star system ADS6650, with high dynamic range, at extremely low counting rates. The method is shown to be applicable, with a 1.5-m telescope, to fields containing reference stars as faint as 16^.m75. The use of the Wiener filter with single photon events is shown to be of advantage compared with methods which use data binned into TV frames, even under excellent seeing conditions.