Notes & Caveats
Near-IR focus will be different according to the wavelength of the source, potentially resulting in split or haloed focus. For best results you must either filter at the front of the lens with IR glass to choose the part of the spectrum you want to work in, or control the wavelength of your IR sources carefully. Mixed sources of light can also show up the same focus issue.
Not all lenses perform equally in IR. Some will exhibit hotspots, some will have internal reflection and flare issues, and some very modern lenses may appear darker than expected in IR due to their sophisticated coatings.