Wide-Field Resolution in Radiography

Multiple star test objects were placed so as to record the entire field covered on a 35 × 43-cm (14 × 17-in.) film and radiographed to determine the apparent shape of the focal spot and the directions in which degradation is maximum and minimum. It was found that geometric unsharpness decreases along lines radiating outward from the center of the anode shadow. The small focal spots used in magnification may be anticipated to behave in a similar fashion. It was also shown experimentally that truly lateral resolution is approximately constant over the field. A theoretical explanation for this finding is offered.