What is the term for the unsharpness caused by geometrical factors in radiography?

The term for the unsharpness caused by geometrical factors in radiography is known as the penumbral shadow. This phenomenon occurs as a result of the geometry of the X-ray source, the object being radiographed, and the film or detector. When X-rays pass through the material, they don't have a perfectly defined edge; instead, the edges are somewhat blurry or "penumbral" due to the diverging rays emitted from the source. This results in varying degrees of exposure on the film, leading to unsharpness along the edges of the shadow cast by the object. Understanding penumbral shadowing is crucial in evaluating the quality of radiographic images, as it can impact the interpretation and clarity of detected flaws.

The other concepts listed, while related to radiographic techniques, describe different phenomena. Radiographic blur refers to general unsharpness in an image without emphasizing the geometric aspect. Geometric distortion encompasses broader issues related to imaging accuracy but doesn’t specifically focus on the blur caused by the edges. Exposure fog typically relates to unwanted background exposure on the film rather than the unsharpness produced by geometric factors. Recognizing these differences helps radiographers and technicians to precisely diagnose and assess images effectively.