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.

What affects geometric unsharpness?

Geometric unsharpness is caused by aspects of the geometry of the X-ray beam. Two principal factors play simultaneously: the apparent focal spot size and the ratio between object-film distance (OFD) and focus-film distance (FFD).

What is the formula for geometric unsharpness?

Ug = F (t / d)