If you keep SID constant but reduce OID significantly, what happens to magnification?

If you keep SID constant but reduce OID significantly, what happens to magnification?

• A. Magnification increases
• B. Magnification remains unchanged
• C. Magnification decreases
• D. Magnification becomes unpredictable

Answer: (C)

Magnification in this setup depends on the distances between the source, the object, and the image receptor. The magnification M equals SID divided by the source-to-object distance (SOD), and SOD equals SID minus OID. If you hold SID constant and reduce OID, the distance from the source to the object (SOD) increases. A larger SOD means the projection on the receptor is smaller, so magnification decreases. Mathematically, M = SID / (SID − OID); as OID gets smaller, SID − OID gets larger, and M drops. For example, with SID fixed at 100 cm, shrinking OID from 20 cm to 5 cm increases SOD from 80 cm to 95 cm, and magnification goes from 100/80 = 1.25 to about 100/95 ≈ 1.05. Intuitively, when the object is closer to the receptor (smaller OID), the image shrinks on the receptor. So the magnification decreases.

Magnification in this setup depends on the distances between the source, the object, and the image receptor. The magnification M equals SID divided by the source-to-object distance (SOD), and SOD equals SID minus OID.

If you hold SID constant and reduce OID, the distance from the source to the object (SOD) increases. A larger SOD means the projection on the receptor is smaller, so magnification decreases. Mathematically, M = SID / (SID − OID); as OID gets smaller, SID − OID gets larger, and M drops.

For example, with SID fixed at 100 cm, shrinking OID from 20 cm to 5 cm increases SOD from 80 cm to 95 cm, and magnification goes from 100/80 = 1.25 to about 100/95 ≈ 1.05. Intuitively, when the object is closer to the receptor (smaller OID), the image shrinks on the receptor.

So the magnification decreases.