Principle of distance measurement by thermal imaging cameras

The most common query among thermal photographers is, “How far can I really measure with a thermal imaging camera?”

It's a bit more complicated to explain, but fundamentally measuring distance depends on the resolution and field of view (FOV) of the thermal imaging camera, as follows:

A thermal imaging camera with a higher resolution allows you to get more pixels on your measurement target, which improves accuracy even when measuring from a distance. A narrow field of view (e.g. 6°) magnifies objects at a distance, again allowing more pixels to be obtained from a distant target.

When using an infrared camera to measure temperature, your target to be measured needs to get at least 3 x 3 pixels to ensure an accurate measurement. It is common practice to ensure that the area to be measured completely covers the small circular hole in the center of the cross of the camera's spot temperature measurement tool or center temperature measurement point. This is because if the area to be measured does not completely cover the small round hole, even if you can see the measurement target in the viewfinder, it does not mean that you will be able to measure it accurately.

The target to be measured should be at least 3 x 3 pixels and cover the spot size of the measuring tool.