What is the magnification factor with a 42-inch SID and a 10-inch OID?

To determine the magnification factor, the formula used is:

[ \text{Magnification Factor} = \frac{\text{SID}}{\text{SID} - \text{OID}} ]

where SID is the Source-to-Image Distance and OID is the Object-to-Image Distance.

In this case, the given values are 42 inches for the SID and 10 inches for the OID. Plugging these numbers into the formula gives:

[ \text{Magnification Factor} = \frac{42}{42 - 10} = \frac{42}{32} ]

Calculating this yields:

[ \text{Magnification Factor} = \frac{42}{32} = 1.3125 ]

When rounded, this value is approximately 1.3. Therefore, the correct answer reflects the calculation based on the provided SID and OID values.

Understanding the relationship in this formula is critical. The magnification factor shows how objects appear larger due to their distance from the imaging device. A smaller OID relative to the SID results in less magnification, which is precisely what the calculation reveals in this scenario.