Which statement about how SID affects size distortion is correct?

Which statement about how SID affects size distortion is correct?

• A. Size distortion increases with a shorter SID
• B. Size distortion is minimized at very long SID
• C. SID has no effect on magnification
• D. Size distortion decreases with a longer SID

Answer: (D)

As SID increases, the image magnification and therefore size distortion decrease. The magnification factor is M = SID / (SID − OID). With the object fixed at a certain distance from the source (constant OID), increasing SID raises both the numerator and the denominator, but the ratio moves closer to 1. That means the image size more closely matches the true object size, reducing distortion. For example, with a fixed OID of 5 cm, magnification at 100 cm SID is about 1.053, while at 200 cm SID it’s about 1.026—the larger SID produces less magnification. Conversely, a shorter SID increases magnification and the distortion. So the statement that size distortion decreases with a longer SID is the correct one.

As SID increases, the image magnification and therefore size distortion decrease. The magnification factor is M = SID / (SID − OID). With the object fixed at a certain distance from the source (constant OID), increasing SID raises both the numerator and the denominator, but the ratio moves closer to 1. That means the image size more closely matches the true object size, reducing distortion. For example, with a fixed OID of 5 cm, magnification at 100 cm SID is about 1.053, while at 200 cm SID it’s about 1.026—the larger SID produces less magnification. Conversely, a shorter SID increases magnification and the distortion. So the statement that size distortion decreases with a longer SID is the correct one.