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 aspects of building inspections. 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 to support that feature. This is an important consideration when budgeting for the purchase of a new infrared camera. Know what camera models provide that option and know how much to budget for this added feature. Also, worth noting is what is considered a typical field of view values for infrared cameras. For this article we will consider the following:
- Standard FOV: 24ºx 18º
- Wide-Angle FOV: 48º x 36º
- Telephoto FOV: 12º x 9º
Many infrared cameras designed for building applications come with a standard lens that many would consider to be a wide-angle lens. Another important consideration when reviewing infrared camera specifications. 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 several wall cavities in the expanded field of view. This allows for a comparison of the thermal performance of several wall cavities giving the thermographer the information he needs to analyze the situation.
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. Again, the benefit here includes more coverage but more importantly the opportunity for improved qualitative analysis looking for issues or exceptions of the buildings' thermal performance.
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 a telephoto lens. It may help to some degree on higher resolution imagers such as a 640 x 480 if you zoom in to a 2x zoom setting, but in our experience, it seems to pixelate images significantly on lower resolution systems, especially when using the maximum zoom. Remember the zoom feature is electronic, not optical.
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.