Hotspots on Infrared Images
Hotspots on IR images are central overexposed areas. They seem to occur more on unconverted cameras than converted ones and only with some lenses.
I’ve been working on a theory for some time that at least part of this issue is caused by light leaking through the viewfinder during the usually long exposures with unconverted cameras. I have found this when testing some cameras myself and it has been confirmed now by several other people that ensuring the viewfinder is covered solved the problem.
While I don’t believe it is the complete answer, I do believe it is a part answer, at least for some people.
I’ll be doing more testing on this and will report the results in full shortly.