Spot size describes what aspect of infrared measurement?

• A. The size of the area on the object that is being measured
• B. The distance from the camera to the object
• C. The lens focal length
• D. The number of pixels in the image

Answer: (A)

Spot size is the area on the object's surface that contributes to a single infrared reading. It reflects how much of the scene a single pixel’s temperature value represents, set by the camera’s instantaneous field of view and how far away you are. A smaller spot means you’re sampling a smaller patch, giving finer spatial detail but potentially more sensitivity to small temperature variations; a larger spot averages temperature over a bigger area, which can smooth out details but produce a more stable reading. Distance to the target and the optical setup determine the spot size— moving closer or using a magnified view reduces it, while increasing distance or using a wider field of view increases it. The other factors—how far the camera is from the target, the lens design, or how many pixels the image has—affect measurement and image formation in different ways but do not define the area that a single measurement covers.