The source size is obtained by referencing manufacturers specifications for a given Xray or gamma ray source. Industrial X-ray tubes often have focal spot sizes of 1.5 mm
squared but microfocus systems have spot sizes in the 30 micron range. As the source
size decreases, the geometric unsharpness also decreases. For a given size source, the
unsharpness can also be decreased by increasing the source to object distance, but this
comes with a reduction in radiation intensity. The object to detector distance is usually
kept as small as possible to help minimize unsharpness. However, there are situations,
such as when using geometric enlargement, when the object is separated from the
detector, which will reduce the definition.