Lens Choice for Looking Through IR Windows

More and more organizations are installing IR windows or sight glasses in their electrical equipment so inspections can be made with an infrared camera.

The advantages are obvious: worker safety is improved as  thermographers and electricians don't have to open live electrical cabinets, and inspection times can be reduced.

However, what lens choice is the best to use with your infrared camera to provide adequate resolution, and yet see as much of the electrical equipment as possible?

Here are three images that were taken at a power plant looking at an ISO phase buss. The buss is only about a foot away and is taken looking through an infrared window (crystal type).

25 deg.

45 deg.

90 deg.

Images courtesy - John Fricot, FLIR Systems

As you can plainly see, the 90° lens is clearly the way to go.  It provides enough detail for analysis, yet extends your field of view by a huge amount.