I found similar problems with floppy disks. Although I found it more useful that exposed film, I also found that different floppy disks were more or less transparent to visible light and IR. I ripped apart old old ones and new ones, and eventually found an old one that seemed just right. I don’t know whether the fact that they have been exposed to light and/or have data on them might make a difference? Even the best one I found was nowhere near as good as a thorlabs filter though (but of course they are expensive)
I did consider buying one of the many lenses on ebay used for nightshot cameras, but wasn’t sure I’d get what I was looking for. Anybody else have any experience with them?
