An increase in object-to-image distance (OID) will result in which change to image sharpness?

An increase in object-to-image distance (OID) will result in which change to image sharpness?

• A. Decreased sharpness
• B. Increased sharpness
• C. No change
• D. Variable

Answer: (A)

Geometric unsharpness increases as the object moves farther from the image receptor. When OID is larger, the X-ray beams diverge more before reaching the detector, so the blur from the finite focal spot is projected over a greater distance and appears larger on the image. This enlarges the blur circle at the detector, making edges less defined and sharp. The blur size is proportional to the focal spot size and the ratio of OID to source-to-object distance, so increasing OID directly increases unsharpness and decreases sharpness.

Geometric unsharpness increases as the object moves farther from the image receptor. When OID is larger, the X-ray beams diverge more before reaching the detector, so the blur from the finite focal spot is projected over a greater distance and appears larger on the image. This enlarges the blur circle at the detector, making edges less defined and sharp. The blur size is proportional to the focal spot size and the ratio of OID to source-to-object distance, so increasing OID directly increases unsharpness and decreases sharpness.