Reducing the object-to-image distance (OID) will have what effect on spatial resolution?

Reducing the object-to-image distance (OID) will have what effect on spatial resolution?

• A. Increase magnification and blur
• B. Decrease magnification and blur
• C. Increase magnification only
• D. Decrease blur only

Answer: (B)

Reducing the distance between the object and the image receptor changes the imaging geometry so the image is less enlarged and edges are sharper. When the object sits closer to the receptor, magnification decreases because the rays haven’t spread as much before they hit the receptor. At the same time, geometric unsharpness (blur) from the finite focal spot size also decreases because the divergent beams have less distance to blur as they reach the receptor. The combined effect is a sharper image with less blur, i.e., improved spatial resolution. So reducing the object-to-image distance decreases both magnification and blur.

Reducing the distance between the object and the image receptor changes the imaging geometry so the image is less enlarged and edges are sharper. When the object sits closer to the receptor, magnification decreases because the rays haven’t spread as much before they hit the receptor. At the same time, geometric unsharpness (blur) from the finite focal spot size also decreases because the divergent beams have less distance to blur as they reach the receptor. The combined effect is a sharper image with less blur, i.e., improved spatial resolution. So reducing the object-to-image distance decreases both magnification and blur.