What factor directly influences geometric unsharpness in radiography?

Geometric unsharpness in radiography is primarily influenced by the source-to-object distance, which directly affects the sharpness of the image produced. When the distance from the source of radiation to the object being imaged increases, the result is a reduction in geometric unsharpness because the radiation beams are less divergent by the time they reach the object.

This phenomenon occurs because the greater the distance, the less pronounced the effects of scattering become, leading to a clearer image. The concept revolves around the penumbra effect, where the area of uncertainty around the edges of radiated areas diminishes with increased distance.

While other factors such as object-to-image distance and source-to-image distance can have some influence on image clarity, the source-to-object distance plays the most pivotal role in determining the level of unsharpness. A shorter source-to-object distance leads to a larger penumbra and consequently greater geometric unsharpness. Therefore, it is correct to identify that the factor with the most direct influence on geometric unsharpness is the object-to-image distance in terms of its effect on the divergence of radiation on the way to the object, making it crucial in radiographic practices.