While an infrared camera’s standard lens is likely fine for most circumstances, the option to add a telephoto or wide-angle lens can prove useful in certain building inspection situations. First, if you are new to infrared and think you might have the need for an optional lens, know that not all camera models are designed for one, so be sure to check this before you buy. These are also optional accessories so be sure it fits within your budget.
A wide-angle lens can allow you to work more quickly and efficiently in tight spaces or where your perspective does not provide a wide enough Field of View (FOV). This would include a scenario on the interior where you cannot view enough of an exterior wall in a small bedroom or perhaps an office without standing out in the hallway.
The above shots from an upstairs bedroom inside a 200-year-old cape show a lath and plaster wall with missing insulation in cold-weather conditions. It demonstrates a fairly common situation that we encounter with houses of this vintage in Vermont that have 1½ floors. Likely a former attic, the space was converted to a few small bedrooms many years ago by a previous owner. The result may be a cozy living space for the homeowners but can prove quite challenging for the building thermographer to image, and analyze, in only a few shots with just a standard lens. Both images were taken from the doorway, first with the standard lens (left) and then with a wide-angle (right) showing the more expansive field of view.
Another example of where a wide-angle lens might be useful is outside in a high-density residential neighborhood where yards are small or the spacing between buildings is tight. A wide-angle lens can help provide a larger FOV in spite of the limited viewing distance, allowing you to see more of the building in one shot.
If you are primarily inspecting larger structures including multi-family units, high-rise apartments, or office buildings, a telephoto lens is certainly worth considering. These two images (shown below) of a small commercial office building demonstrate the differences seen between a standard (left) and telephoto lens (right). Standing at the same spot we can clearly see the changes to the field of view. The telephoto lens increases your resolution from this point, allowing you to see smaller areas of detail on the building at a greater distance.
One quick final note about lenses, concerning your imager and its digital zoom capability (available on some models). Know that using the zoom feature does not increase resolution and is not a replacement for an optional lens. It may work to some degree on higher resolution imagers such as a 640 x 480 if you zoom in to a 2x power setting, but in our experience, it seems to pixelate images significantly on lower resolution systems, especially when using the maximum zoom.
It is important to note that the standard lens on an infrared camera sold for building applications is going to provide you with a sufficient and workable field of view to do your job in most situations, especially with residential applications. If, however, you feel you have the need (and the budget) an optional lens is definitely something to consider.