Which statement about focus and temperature measurement accuracy is true?

• A. Focus does not affect measurement
• B. A focused image generally yields more accurate temperature readings
• C. Out-of-focus images yield more accurate readings
• D. Temperature readings are independent of focus when imaging small hotspots

Answer: (B)

In infrared temperature measurement, image sharpness directly affects how accurately we can read temperature, especially for small hotspots. When the image is focused, the hotspot’s radiant energy is concentrated into a few pixels, producing a clear, higher peak value that more closely matches the actual temperature at that location. This sharpness preserves spatial detail and prevents the true temperature from being diluted across many pixels.

If the image is out of focus, the hotspot blurs over a larger area, so the hottest region is spread out and its peak value is smeared downward. That smoothing blends temperatures from surrounding areas and underestimates the maximum temperature, reducing both the accuracy of the reading and the ability to pinpoint the hotspot correctly. This effect is more pronounced with small targets, where even a slight defocus can significantly distort the measurement.

So, a focused image generally yields more accurate temperature readings, especially for small hotspots.