The light field must correspond to the actual exposure field within a tolerance of:

The light field must correspond to the actual exposure field within a tolerance of:

• A. +/- 1% of the SID
• B. +/- 2% of the SID
• C. +/- 5% of the SID
• D. +/- 10% of the SID

Answer: (B)

The key idea is that the visual light field used to guide exposure must match the actual X-ray exposure field with very small, distance-accurate tolerance. This keeps the area irradiated exactly where intended, protecting patient tissues outside the target anatomy and ensuring the image shows the correct region across different distances. The accepted tolerance is plus or minus 2% of the source-to-image distance. That means the light field edges should align with the exposure field within about 2% of how far away the x-ray source is. For example, at a SID of 100 cm, the alignment should be within roughly 2 cm; at 120 cm, about 2.4 cm. This level balances precision with practicality in everyday equipment checks. Smaller tolerances (like 1%) would be more demanding and harder to maintain consistently, while larger tolerances (5% or 10%) would allow noticeable misalignment, potentially exposing non-target areas or cropping out part of the anatomy of interest.

The key idea is that the visual light field used to guide exposure must match the actual X-ray exposure field with very small, distance-accurate tolerance. This keeps the area irradiated exactly where intended, protecting patient tissues outside the target anatomy and ensuring the image shows the correct region across different distances.

The accepted tolerance is plus or minus 2% of the source-to-image distance. That means the light field edges should align with the exposure field within about 2% of how far away the x-ray source is. For example, at a SID of 100 cm, the alignment should be within roughly 2 cm; at 120 cm, about 2.4 cm. This level balances precision with practicality in everyday equipment checks.

Smaller tolerances (like 1%) would be more demanding and harder to maintain consistently, while larger tolerances (5% or 10%) would allow noticeable misalignment, potentially exposing non-target areas or cropping out part of the anatomy of interest.