Which change to exposure setup will increase magnification and potentially reduce spatial resolution?

• A. Increase SID
• B. Increase OID
• C. Use a small focal spot
• D. Shorten exposure time

Answer: (B)

Geometric magnification in radiography depends on how far the object is from the image receptor. If you increase the object-to-image distance (OID) while keeping the source-to-image distance (SID) the same, the image on the receptor becomes larger—that's magnification. This larger image also amplifies blur from the focal spot (geometric unsharpness), which lowers spatial resolution. So increasing OID will increase magnification and can reduce sharpness. Increasing SID would do the opposite and reduce magnification; using a smaller focal spot improves sharpness without increasing magnification; shortening exposure time doesn’t change magnification (it mainly affects motion blur).